Note: Descriptions are shown in the official language in which they were submitted.
SYSTEM, METHOD, AND APPARATUS FOR APPLYING
TRANSCUTANEOUS ELECTRICAL STIMULATION
Related Applications
[0001] This application is a continuation-in-part of U.S. Patent
Application
Serial No. 16/295,086, filed on March 7, 2019, which claims the benefit of
U.S. Provisional Application Serial Number 62/725,755, filed on August 31,
2018, and also claims the benefit of U.S. Provisional Application Serial
Number 62/751,173, filed on October 26, 2018.
[0002] This application is also a continuation-in-part of U.S. Patent
Application Serial No. 16/295,145, filed on March 7,2019, which claims the
benefit of U.S. Provisional Application Serial Number 62/725,755, filed on
August 31, 2018, and also claims the benefit of U.S. Provisional Application
Serial Number 62/751,173, filed on October 26, 2018.
[0003] This application is also a continuation-in-part of U.S. Patent
Application Serial No. 16/295,253, filed on March 7, 2019, which claims the
benefit of U.S. Provisional Application Serial Number 62/725,755, filed on
August 31, 2018, and also claims the benefit of U.S. Provisional Application
Serial Number 62/751,173, filed on October 26, 2018.
[0004/6] This application also claims the benefit of U.S. Provisional
Application Serial Number 62/931,342, filed on November 6, 2019. This
application also claims the benefit of U.S. Provisional Application Serial
Number 62/931,351, filed on November 6, 2019. This application also claims
the benefit of U.S. Provisional Application Serial Number 62/931,421, filed on
November 6, 2019. This application also claims the benefit of U.S. Provisional
Application Serial Number 62/931,426, filed on November 6, 2019. This
application also claims the benefit of U.S. Provisional Application Serial
Number 62/931,885, filed on November 7, 2019. This application also claims
the benefit of U.S. Provisional Application Serial Number 62/932,172, filed on
November 7, 2019. This application also claims the benefit of U.S. Provisional
Application Serial Number 62/932,529, filed on November 8, 2019.
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Technical Field
[0006] The invention relates to a wearable electronic medical device for
transcutaneous electrical stimulation of peripheral nerves for the purpose of
treating one or more medical conditions.
Background
[0007] There are many known technologies that use electrical stimulation
of peripheral nerves to treat medical conditions. Implantable stimulation
technologies require surgical implantation of stimulation leads, with a pulse
generator that is either surgically implanted or connected externally to wire
leads. Percutaneous stimulation technologies are less invasive, but still
require the stimulation electrodes to pierce the skin. While these
technologies
can be effective in treating certain conditions, they are less desirable due
to
their invasiveness and because they can require the continued or routine
attention of specialists, requiring doctor's office visits, phone calls, etc.
Summary
[0008] A system for applying transcutaneous electrical stimulation includes
a wearable, such as a garment, sock, sleeve, brace, strap, etc. The wearable
includes an electronic stimulator device that provides transcutaneous
electrical stimulation to peripheral nerves for treatment of medical
conditions.
Advantageously, the wearable allows the subject to use the system at a time
and place that is convenient. The subject may choose to use the device while
they are at work or at home, or while walking, relaxing, or sleeping, as long
as
certain environments and/or activities (e.g., wet environments/activities) are
avoided. Since there are no implantable or percutaneous components, the
risk of infection, battery fault burns, and transcutaneous power transfer
discomfort and/or bleeding, are greatly reduced or eliminated.
[0009] The wearable includes electrodes that are arranged in a
predetermined pattern or array, and that engage the subject's skin at desired
locations when the wearable is worn. These skin surface mounted electrodes
can, for example, be similar to those of other transcutaneous electrical nerve
stimulation ("TENS") units to implement high voltage skin surface electrical
stimulation. The electrodes include stimulating electrodes and recording
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electrodes, which the wearable can position at the same location or at
different locations on the subject's skin. In fact, the identities of
individual
electrodes, i.e., stimulating or recording, can change depending on the
application/treatment for which the system is being used. The stimulating
electrodes apply the transcutaneous electrical stimulation to the subject's
skin, and the recording electrodes record the electromyogram (EMG)
responses elicited by the stimulation.
[0010] The wearable also includes a control unit that is electrically
connected to the electrodes and that is operable to control electrical
stimulation applied by the stimulating electrodes and to control the recording
of EMG responses by the recording electrodes. The control unit executes
closed-loop control algorithms, which adjust stimulation patterns,
periodically
or constantly, based on the elicited EMG response from the recruited nerves
as feedback. Alternatively, instead of the EMG response providing the closed-
loop feedback, or as a supplement to the EMG response, the system can
include alternative devices, such as mechanomyogram (MMG) devices (e.g.,
an accelerometer), or can implement electronic measurements, such as
electrode impedance, to implement the closed-loop control.
[0011] This closed-loop control eliminates the need for "programming
sessions" commonly required for neurostimulation systems. The day-to-day
variability that arises due to electrode placement and skin impedance
necessitates these sessions to make sure that the electrodes are positioned
to provide adequate stimulation treatment. With the present system, instead of
physically adjusting the electrode positions on the subject in order to find
the
arrangement that produces the desired response, the system itself can select
which electrodes to use, and can adjust the number and pattern of electrodes
until an acceptable response (EMG and/or MMG) is achieved. Once the
appropriate electrodes pattern is identified, the order, intensity, timing,
etc. of
the stimulation can be further tuned or adjusted to optimize the EMG and/or
MMG response. The system can tailor the electrical stimulation applied by
each individually controllable electrode in the array so that the stimulation
characteristics of each electrode (e.g., frequency, amplitude, pattern,
duration,
etc.) is configured to deliver the desired stimulation effect. This tailoring
can
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be implemented automatically through the algorithm, which incrementally
adjusts these characteristics, monitoring the and/or response at each
increment until optimal settings are identified. Stimulation therapy can then
be
applied with these settings, according to the algorithm, which can be dictated
by the requirements of the treating physician.
[0012] Throughout the electrical stimulation treatment process, the system
can implement periodic or continuous measurement of system integrity. One
such measurement is that of electrode impedance to remove the risks that
can arise when electrodes lift away from the skin or certain properties of the
electrodes deteriorate. The impedance measurement capability could also
potentially be used to provide an indication of the optimal electrode location
for nerve stimulation. This may be the case, for example, in areas where the
skin is thin and where the stimulated nerves are most superficial. Thus,
impedance values may be used as an input to the closed-loop stimulation
algorithm to adjust stimulation patterns. By way of example, when stimulating
the tibial nerve, the posterior area of the medial malleolus typically has
comparatively thin skin and is the site where tibial nerve is most
superficial,
which leads to its being a good candidate for measuring electrode impedance.
[0013] The control unit and the architecture of the system may be
designed to constantly optimize stimulation by monitoring the quality of nerve
recruitment periodically or on a pulse-by-pulse basis, with the goal of
keeping
recruitment strength to a minimum (which can reduce muscle twitching) and to
minimize the stimulation energy being delivered through the skin. The EMG
recording feature is capable of detecting both M-wave and F-wave responses,
which can be used as feedback inputs (together or independently) to the
closed-loop stimulation algorithm to determine the level of activation of the
stimulated peripheral nerve. A significant aspect of the F-wave is that it
provides an indication that the stimulation-evoked peripheral nerve action
potential has activated motor neurons in the associated spinal cord
nerves/nerve plexus. For example, an F-wave response to tibial nerve
stimulation indicates that the tibial nerve action potential has activated
motor
neurons in the sacral spinal cord/sacral plexus.
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[0014] The wearable transcutaneous electrical stimulation device can be
used to stimulate various peripheral nerves in order to treat medical
conditions associated with those nerves. For example, the system can be
used to apply electrical stimulation to the tibial nerve to treat pelvic floor
dysfunction, e.g., overactive bladder (OAB) medical conditions. As another
example, the system can be used to apply electrical stimulation to the tibial
nerve to treat sexual dysfunction. In this manner, it is believed that tibial
nerve
stimulation could be used to treat genital arousal aspects of female sexual
interest/arousal disorder by improving pelvic blood flow. In yet another
example, the system can be used to apply electrical stimulation to the tibial
nerve to treat plantar fasciitis.
[0015] As another example, the system can be applied to the wrist area to
provide stimulation to the ulnar nerve and/or median nerve. The stimulation
electrode array can, for example, be placed on the inside of the lower arm
anywhere 0 to 20 cm from the wrist line. EMG recording electrodes can be
placed on the base of thumb to record signal from abductor/flexor pollicis
brevis. EMG recording electrodes alternatively or additionally can be placed
on the base of pinky to record signal from abductor/flexor digiti minimi
brevis.
The nerve activation could be confirmed by recording M-wave and F-wave
EMG signals from the relevant muscles. The EMG signal can also be used as
a control signal to adjust the stimulation parameters or stimulation electrode
patterns. This technology can be applied to median nerve activation for pain
management in carpal tunnel syndrome, hypertension management, and
nerve conduction study/nerve injury diagnosis for medianlulnar nerve
neuropathy, etc.
[0016] As a further example, the system can be used to apply
transcutaneous electrical stimulation to provide neurostimulation to
peripheral
nerves in order to enhance nerve regeneration after peripheral nerve injury.
[0017] Implementing closed-loop control, the system can utilize measured
EMG responses to detect and obtain data related to the electrical activity of
muscles in response to the applied stimulation. This data can be used as
feedback to tailor the application of the electrical stimulation. Additionally
or
alternatively, the system can also implement MMG sensors, such as
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accelerometers, to measure the physical response of the muscles. Other
feedback, such as impedance measurements between electrodes and other
biopotential recording, can also be utilized. Through this closed-loop
implementation, the system can utilize techniques such as current steering
and nerve localization to provide peripheral nerve stimulation therapy for
treating various medical conditions.
[0018] The system, method, and apparatus for applying transcutaneous
electrical stimulation disclosed herein has many aspects, which can be
included or utilized in various combinations.
[0019] According to one aspect, a method treats a medical condition by
applying transcutaneous electrical stimulation to a target peripheral nerve of
a
subject.
[0020] According to another aspect, alone or in combination with any other
aspect, the method can include positioning a plurality of stimulation
electrodes
on a skin surface proximate the targeted peripheral nerve, the stimulation
electrodes being spaced from each other in a predetermined configuration.
The method also can include positioning one or more recording electrodes on
a skin surface remote from the stimulation electrodes at a location where
electromyogram (EMG) responses to electrical stimulation of the targeted
peripheral nerve can be detected. The method also can include stimulating
the peripheral nerve by applying electrical stimulation pulses via a
stimulation
electrode pattern selected from the plurality of stimulation electrodes
according to stimulation parameters under closed-loop control in which EMG
responses to the electrical stimulation pulses are monitored via the recording
electrodes and the stimulation parameters are adjusted in response to the
monitored EMG responses. The method further can include, in response to
detecting an unacceptable condition of the recording electrodes, applying
electrical stimulation pulses via the stimulation electrode pattern according
to
the stimulation parameters under open-loop control in which the stimulation
parameters are maintained without adjustment.
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[0021] According to another aspect, alone or in combination with any other
aspect, the unacceptable condition of the recording electrodes can include
unacceptable impedance measurements.
[0022] According to another aspect, alone or in combination with any other
aspect, the step of applying electrical stimulation pulses further can include
monitoring for mechanomyogram (MMG) responses to the electrical
stimulation pulses and applying the electrical stimulation pulses under closed-
loop control in which the stimulation parameters are adjusted in response to
the monitored MMG responses.
[0023] According to another aspect, alone or in combination with any other
aspect, the step of applying electrical stimulation pulses can include
detecting
impedances of the recording electrodes and, in response to detecting
acceptable impedances of the recording electrodes, applying the electrical
stimulation pulses.
[0024] According to another aspect, alone or in combination with any other
aspect, the method can include: obtaining sample measurements via the
recording electrodes, checking the sample measurements for noise, checking
the sample measurements for voluntary EMG responses, applying the
electrical stimulation pulses under closed-loop control in response to
determining an acceptable level of noise and the absence of voluntary EMG
responses, and applying the electrical stimulation pulses under open-loop
control in response to determining an unacceptable level of noise or the
presence of voluntary EMG responses.
[0025] According to another aspect, alone or in combination with any other
aspect, each application of an electrical stimulation pulse under closed-loop
control can include: applying the electrical stimulation pulse, executing a
time
delay, recording EMG responses via the recording electrodes after the time
delay is executed, and adjusting the stimulation parameters in response to the
recorded EMG responses. The duration of the time delay can be about 5 ms
or less.
[0026] According to another aspect, alone or in combination with any other
aspect, adjusting the stimulation parameters in response to the recorded EMG
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responses under closed loop control can include: increasing the amplitude of
subsequent stimulation pulses in response to the recorded EMG responses
being below a predetermined EMG window, decreasing the amplitude of
subsequent stimulation pulses in response to the recorded EMG responses
being above the predetermined EMG window, and maintaining the amplitude
of subsequent stimulation pulses in response to the recorded EMG responses
being within the predetermined EMG window.
[0027] According to another aspect, alone or in combination with any other
aspect, each application of an electrical stimulation pulse under open-loop
control can include: applying the electrical stimulation pulse, and executing
a
time delay having a duration sufficient to maintain a constant stimulation
period. The duration of the time delay can be about 75 ms.
[0028] According to another aspect, alone or in combination with any other
aspect, the stimulation electrode pattern can be selected from a pattern list,
wherein the method further can further include generating the pattern list by:
a) identifying a set of predetermined stimulation electrode patterns, each
stimulation electrode pattern identifying which of the plurality of
stimulation electrodes will apply the electrical stimulation pulses, and
each stimulation electrode pattern having associated with it the
stimulation parameters according to which it applies stimulation pulses;
b) selecting a stimulation electrode pattern from the set of predetermined
stimulation electrode patterns;
c) generating a stimulation pulse using the selected stimulation electrode
pattern according to its associated stimulation parameters;
d) determining via the recording electrodes whether the stimulation pulse
using the selected stimulation electrode pattern elicited an EMG
response;
e) adding the selected stimulation electrode pattern to the pattern list in
response to detecting an EMG response;
f) omitting the selected stimulation electrode pattern from the pattern list
in
response to not detecting an EMG response; and
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repeating steps b) through f) for each stimulation electrode pattern in the
set of predetermined stimulation electrode patterns to complete the
pattern list.
[0029] According to another aspect, alone or in combination with any other
aspect, the method can include optimizing the stimulation electrode patterns
in the pattern list by:
g) adjusting the stimulation parameters for each stimulation electrode
pattern in the pattern list to attempt to elicit an improved EMG
response;
h) selecting a stimulation electrode pattern from the set of predetermined
stimulation electrode patterns;
i) generating a stimulation pulse using the selected stimulation electrode
pattern according to its associated stimulation parameters;
j) determining via the recording electrodes whether the stimulation pulse
using the selected stimulation electrode pattern elicited an EMG
response;
k) adding the selected stimulation electrode pattern to the pattern list in
response to detecting an EMG response;
I) omitting the selected stimulation electrode pattern from the pattern list
in
response to not detecting an EMG response; and
repeating steps h) through I) for each stimulation electrode pattern in the
set of predetermined stimulation electrode patterns to complete the
pattern list. Steps h) through I) can be repeated until each electrode
pattern in the pattern list is optimized.
[0030] According to another aspect, alone or in combination with any other
aspect, the method can also include ordering the stimulation electrode
patterns in the pattern list according to their elicited EMG and/or MMG
responses.
[0031] According to another aspect, alone or in combination with any other
aspect, stimulating the peripheral nerve can include stimulating the tibial
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nerve. Stimulating the peripheral nerve can include stimulating the tibial
nerve
at a location between the medial malleolus and the Achilles tendon.
[0032] According to another aspect, alone or in combination with any other
aspect, monitoring EMG responses can include recording EMG signals that
result from recruitment of the tibial nerve's motor fibers. This can include
positioning the recording electrodes on the bottom of the subject's foot near
the abductor hallucis and the flexor hallucis brevis to record the EMG
signals.
[0033] According to another aspect, alone or in combination with any other
aspect, stimulating the peripheral nerve can treat overactive bladder, sexual
dysfunction, or plantar fasciitis.
[0034] According to another aspect, alone or in combination with any other
aspect, stimulating the peripheral nerve can include stimulating the ulnar
nerve and/or median nerve for pain management in carpal tunnel syndrome,
hypertension management, and nerve conduction study/nerve injury diagnosis
for median/ulnar nerve neuropathy, etc. Stimulating the ulnar nerve and/or
median nerve can treat carpal tunnel syndrome or hypertension. Stimulating
the ulnar nerve and/or median nerve to perform a nerve conduction study or
nerve injury diagnosis.
[0035] According to another aspect, alone or in combination with any other
aspect, stimulating the ulnar nerve and/or median nerve can include
positioning the stimulating electrodes on the inside of the lower arm 0 to 20
cm from the wrist line, and recording EMG responses can include positioning
the recording electrodes on the base of thumb to record signal from
abductor/flexor pollicis brevis, and/or positioning the recording electrodes
on
the base of pinky to record signal from abductor/flexor digiti minimi brevis.
[0036] According to another aspect, alone or in combination with any other
aspect, stimulating the peripheral nerve can include applying the electrical
stimulation pulses to the peripheral nerve to enhance nerve regeneration after
peripheral nerve injury.
[0037] According to another aspect, alone or in combination with any other
aspect, a system for treating overactive bladder by applying transcutaneous
electrical stimulation to the tibial nerve of a subject can include a
plurality of
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electrical stimulation electrodes, the stimulation electrodes being spaced
from
each other in a predetermined configuration, one or more recording
electrodes, a structure for supporting the stimulation electrodes and the
recording electrodes spaced apart from each other, and a control unit for
controlling the operation of the stimulation electrodes and the recording
electrodes. The control unit can be configured to perform the method
according to any of the aspects disclosed herein, alone or in combination with
any other aspect.
[0038] According to another aspect, alone or in combination with any other
aspect, an apparatus for applying electrical stimulation includes a plurality
of
electrical stimulation electrodes spaced from each other in a predetermined
configuration, one or more recording electrodes, a structure for supporting
the
stimulation electrodes and the recording electrodes spaced apart from each
other, and a control unit for controlling the operation of the stimulation
electrodes and the recording electrodes. The control unit is configured to
energize the stimulation electrodes under closed-loop control using the
recording electrodes to measure feedback, energize the stimulation
electrodes under open-loop without measuring feedback, and determine
whether to energize the stimulation electrodes under closed-loop control or
open-loop control based on determining whether the feedback measured by
the recording electrodes is reliable.
[0039] According to another aspect, alone or in combination with any other
aspect, the structure can include a wearable structure configured to position
the stimulation electrodes in the proximity of a peripheral nerve and to
position
the recording electrodes in the proximity of a muscle activated by the
peripheral nerve.
[0040] According to another aspect, alone or in combination with any other
aspect, the wearable structure can position the stimulation electrodes
proximate the peripheral nerve and the recording electrodes proximate a
location where EMG signals that result from recruitment of the peripheral
nerve's motor fibers can be detected.
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[0041] According to another aspect, alone or in combination with any other
aspect, the wearable structure can include a strap, wherein the stimulation
electrodes and recording electrodes are positioned at different locations
along
the length of the strap. The strap can be configured to have a portion wrapped
around the subject's ankle to position the stimulating electrodes proximate
the
tibial nerve between the medial malleolus and the Achilles tendon. The strap
can also be configured to have a portion wrapped around the subject's foot to
position the recording electrodes on the bottom of the subject's foot near the
abductor hallucis and the flexor hallucis brevis.
[0042] According to another aspect, alone or in combination with any other
aspect, the wearable structure can include a brace comprising an upper
portion upon which the stimulation electrodes are positioned and a lower
portion upon which the recording electrodes are positioned. The upper portion
of the brace can be configured to be wrapped around the subject's ankle to
position the stimulating electrodes proximate the tibial nerve between the
medial malleolus and the Achilles tendon. The lower portion of the brace can
be configured to be wrapped around the subject's foot to position the
recording electrodes on the bottom of the subject's foot near the abductor
hallucis and the flexor hallucis brevis.
[0043] According to another aspect, alone or in combination with any other
aspect, the apparatus can also include an accelerometer supported by the
support structure adjacent or near the recording electrodes, wherein the
control unit can be configured to determine whether to energize the
stimulation electrodes under closed-loop control or open-loop control based
on acceleration values determined by the accelerometer.
[0044] According to another aspect, alone or in combination with any other
aspect, the control unit can include a microcontroller, a stimulator output
stage
controlled by the microcontroller, and at least one analog output switch
operatively connected to the stimulator output stage and controlled by the
microcontroller. The stimulator output stage can include a plurality of
channels
for providing electrical current to the stimulating electrodes via the output
switch, wherein each channel of the output stage includes a current source
and current sink, and wherein the microcontroller is configured to actuate the
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output switch to selectively identify which stimulation electrodes are active
and to assign a channel of the output stage with each active stimulation
electrode, wherein the output stage associated with each stimulating
electrode determines whether the stimulating electrode operates as an anode
or a cathode.
[0045] According to another aspect, alone or in combination with any other
aspect, the microcontroller can be configured to determine amplitude and
timing values for the current source and current sink for each channel of the
output stage and their associated active stimulation electrodes.
[0046] According to another aspect, alone or in combination with any other
aspect, the apparatus can include an impedance measurement circuit that is
operatively connected to the stimulator output stage and is configured to
measure electrode impedances.
[0047] According to another aspect, alone or in combination with any other
aspect, the apparatus can include at least one analog input switch that is
operatively connected to the microcontroller, wherein the microcontroller is
configured to operate the analog input switch to determine which of the
recording electrodes are used to measure feedback.
[0048] According to another aspect, alone or in combination with any other
aspect, the apparatus can include an analog front end circuit that is
operatively connected to the analog input switch, wherein the analog front end
is configured to facilitate sampling the recording electrodes at a
predetermined sample rate in order to determine whether the feedback
measured by the recording electrodes is reliable. The sample rate can be
1,000 ¨ 8,000 samples per second.
[0049] According to another aspect, alone or in combination with any other
aspect, the microcontroller can be configured to initiate via the analog front
end a sampling window after energizing the stimulation electrodes, wherein
during the sampling window the recording electrodes are used to measure
feedback signals to determine whether EMG data is present.
[0050] According to another aspect, alone or in combination with any other
aspect, the apparatus can include a radio for communicating wirelessly with
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an external device for programming the microcontroller,
uploading/downloading data, and remotely monitoring and/or controlling
operation of the control unit.
[0051] According to another aspect, alone or in combination with any other
aspect, a method for treating overactive bladder can include applying
transcutaneous electrical stimulation to the tibial nerve of a subject. The
method can include positioning a plurality of stimulation electrodes on a skin
surface at a location between the medial malleolus and the Achilles tendon
proximate the tibial nerve, the stimulation electrodes being spaced from each
other in a predetermined configuration. The method also can include
positioning one or more recording electrodes on a skin surface remote from
the stimulation electrodes at a location on the bottom of the subject's foot
near
the abductor hallucis and the flexor hallucis brevis muscles to record
electromyogram (EMG) responses that result from recruitment of the tibial
nerve's motor fibers. The method also can include stimulating the tibial nerve
by applying electrical stimulation pulses via a stimulation electrode pattern
selected from the plurality of stimulation electrodes according to stimulation
parameters under closed-loop control in which EMG responses to the
electrical stimulation pulses are monitored via the recording electrodes and
the stimulation parameters are adjusted in response to the monitored EMG
responses. The method further can include, in response to detecting an
unacceptable condition of the recording electrodes, applying electrical
stimulation pulses via the stimulation electrode pattern according to the
stimulation parameters under open-loop control in which the stimulation
parameters are maintained without adjustment.
[0052] According to another aspect, alone or in combination with any other
aspect, a system for treating overactive bladder by applying transcutaneous
electrical stimulation to the tibial nerve of a subject can include a
plurality of
electrical stimulation electrodes, the stimulation electrodes being spaced
from
each other in a predetermined configuration, one or more recording
electrodes, a structure for supporting the stimulation electrodes and the
recording electrodes spaced apart from each other, and a control unit for
controlling the operation of the stimulation electrodes and the recording
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electrodes. The control unit can be configured to perform the method
according to any of the aspects disclosed herein, alone or in combination with
any other aspect.
[0053] According to another aspect, an apparatus for applying electrical
stimulation includes a plurality of electrical stimulation electrodes, the
stimulation electrodes being spaced from each other in a predetermined
configuration. The apparatus also includes one or more recording electrodes.
The apparatus also includes a wearable structure for supporting the
stimulation electrodes and the recording electrodes spaced apart from each
other. The apparatus further includes a control unit for controlling the
operation of the stimulation electrodes and the recording electrodes. The
control unit is configured to energize the stimulation electrodes to apply
stimulation to a tibial nerve and record physiological response using the
recording electrodes. The control unit is further configured to automatically
detect the foot, right or left, upon which the apparatus is worn by monitoring
a
phase relationship or time delay between applying stimulation to the tibial
nerve and recording the physiological response.
[0054] According to another aspect, alone or in combination with any other
aspect, the phase relationship or time delay can be indicative of the foot,
right
or left, upon which the apparatus is worn.
[0055] According to another aspect, alone or in combination with any other
aspect, the control unit can be configured to measure and store right-foot and
left-foot reference values for the phase relationship or time delay during
calibration of the apparatus. The control unit can also be configured to
determine the foot upon which the apparatus is worn by comparing a
measured value of the phase relationship or time delay to the recorded
values.
[0056] According to another aspect, alone or in combination with any other
aspect, the wearable garment can include an ankle brace and the stimulating
electrodes can include left-side stimulating electrodes and right-side
stimulating electrodes configured so that the left-side electrodes are
positioned adjacent the tibial nerve near the medial malleolus when worn on
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the right foot, and so that the right-side electrodes are positioned adjacent
the
tibial nerve near the medial malleolus when worn on the left foot.
[0057] According to another aspect, alone or in combination with any other
aspect, the control unit can be configured to select whether to use the left-
side
electrodes or right-side electrodes in response to determining the foot upon
which the apparatus is worn.
[0058] According to another aspect, alone or in combination with any other
aspect, the left-side electrodes can be spaced differently than the right-side
electrodes so that the differences in the phase shift and/or timing of
feedback
signals is enhanced.
[0059] According to another aspect, alone or in combination with any other
aspect, the wearable garment can include a strap and the stimulating
electrodes can include a singular set of stimulating electrodes. The strap can
be flipped to position the stimulating electrodes on the ankle adjacent the
tibial
nerve near the medial malleolus for either the left or right foot.
[0060] According to another aspect, alone or in combination with any other
aspect, the polarity of the stimulation electrodes changes depending on which
foot the apparatus is worn. The control unit can be configured to adjust the
polarity of the stimulation electrodes in response to determining the foot
upon
which the apparatus is worn.
[0061] According to another aspect, alone or in combination with any other
aspect, the apparatus can include a plurality of stimulation electrodes, and
the
control unit can be configured to select which of the stimulation electrodes
to
utilize. The control unit can also be configured to select stimulation
electrode
pairs and measure the impedance between the selected pairs. The control
unit can be further configured to determine the foot upon which the apparatus
is worn in response to the measured impedance.
[0062] According to another aspect, alone or in combination with any other
aspect, an apparatus for applying electrical stimulation includes a plurality
of
electrical stimulation electrodes, the stimulation electrodes being spaced
from
each other in a predetermined configuration. The apparatus also includes one
or more recording electrodes. The apparatus also includes a wearable
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structure for supporting the stimulation electrodes and the recording
electrodes spaced apart from each other. The apparatus further includes a
control unit for controlling the operation of the stimulation electrodes and
the
recording electrodes. The control unit is configured to energize the
stimulation
electrodes to apply stimulation to a tibial nerve and record physiological
response using the recording electrodes. The recording electrodes have an
elongated configuration and are positioned on the garment to extend laterally
across the width of the bottom of the subject's foot at spaced locations along
the length of the foot so as to extend across the longitudinal muscle groups
of
the foot from which an elicited response is to be recorded. According to this
aspect, the apparatus can also include a compliant member that facilitates
forming the electrodes to the contour of the foot bottom, the compliant
member comprising an elastic structure positioned underneath the recording
electrodes and is deformable so as to conform to the bottom of the foot so
that the recording electrodes are maintained in continuous contact with the
foot.
[0063] According to another aspect, alone or in combination with any other
aspect, an apparatus for applying electrical stimulation includes a plurality
of
electrical stimulation electrodes, the stimulation electrodes being spaced
from
each other in a predetermined configuration. The apparatus also includes one
or more recording electrodes. The apparatus also includes a wearable
structure for supporting the stimulation electrodes and the recording
electrodes spaced apart from each other. The apparatus further includes a
control unit for controlling the operation of the stimulation electrodes and
the
recording electrodes. The control unit is configured to energize the
stimulation
electrodes to apply stimulation to a tibial nerve and record physiological
response using the recording electrodes. The electrodes and electrical traces
that electrically connect the stimulation and recording electrodes to the
control
unit are embedded in the wearable structure.
[0064] According to another aspect, alone or in combination with any other
aspect, an apparatus for applying electrical stimulation includes a plurality
of
electrical stimulation electrodes, the stimulation electrodes being spaced
from
each other in a predetermined configuration. The apparatus also includes one
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or more recording electrodes. The apparatus also includes a wearable
structure for supporting the stimulation electrodes and the recording
electrodes spaced apart from each other. The apparatus further includes a
control unit for controlling the operation of the stimulation electrodes and
the
recording electrodes. The control unit is configured to energize the
stimulation
electrodes to apply stimulation to a tibial nerve and record physiological
response using the recording electrodes. The stimulation electrodes,
recording electrodes, and electrical traces that electrically connect the
stimulation and recording electrodes to the control unit comprise a single
component in which the electrodes and traces are formed as one or more
layers of electrically conductive material that are supported on a flexible
substrate attached to the garment.
[0065] According to another aspect, alone or in combination with any other
aspect, an apparatus for applying electrical stimulation includes a plurality
of
electrical stimulation electrodes, the stimulation electrodes being spaced
from
each other in a predetermined configuration. The apparatus also includes one
or more recording electrodes. The apparatus also includes a wearable
structure for supporting the stimulation electrodes and the recording
electrodes spaced apart from each other. The apparatus further includes a
control unit for controlling the operation of the stimulation electrodes and
the
recording electrodes. The control unit is configured to energize the
stimulation
electrodes to apply stimulation to a tibial nerve and record physiological
response using the recording electrodes. The stimulation electrodes,
recording electrodes, and electrical traces that electrically connect the
stimulation and recording electrodes to the control unit are directly applied
to
the wearable structure by spraying or deposition. According to this aspect,
the
traces can be configured to have a curved/bent/waved appearance so as to
be deformable in response to the wearable structure being stretched, twisted,
folded, or otherwise deformed during use.
[0066] According to another aspect, alone or in combination with any other
aspect, an apparatus for applying electrical stimulation includes a plurality
of
electrical stimulation electrodes, the stimulation electrodes being spaced
from
each other in a predetermined configuration. The apparatus also includes one
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or more recording electrodes. The apparatus also includes a wearable
structure for supporting the stimulation electrodes and the recording
electrodes spaced apart from each other. The apparatus further includes a
control unit for controlling the operation of the stimulation electrodes and
the
recording electrodes. The control unit is configured to energize the
stimulation
electrodes to apply stimulation to a tibial nerve and record physiological
response using the recording electrodes. The controller is configured to
determine an optimal charge for applying stimulation by applying stimulation
within a range of pulse widths defined at an upper bound defined by a subject
tolerance limit and at a lower bound by a threshold for an evoked response.
The controller is configured to modulate the pulse width of applied
stimulation
within the range of pulse widths. According to this aspect, the control unit
can
be configured to apply a patient-specific target therapy by linearly
interpolating
the stimulation parameters between the upper and lower bounds.
[0067] According to another aspect, alone or in combination with any other
aspect, an apparatus for applying electrical stimulation includes a plurality
of
electrical stimulation electrodes, the stimulation electrodes being spaced
from
each other in a predetermined configuration. The apparatus also includes one
or more recording electrodes. The apparatus also includes a wearable
structure for supporting the stimulation electrodes and the recording
electrodes spaced apart from each other. The apparatus further includes a
control unit for controlling the operation of the stimulation electrodes and
the
recording electrodes. The control unit is configured to energize the
stimulation
electrodes to apply stimulation to a tibial nerve and record physiological
response using the recording electrodes. The control unit is configured to
detect via the recording electrodes the presence of an EMG response to
stimulation therapy. The control unit is also configured to, in response to
detecting no EMG response, deliver stimulation therapy under open-loop
control without EMG feedback. The control unit is also configured to, in
response to detecting an EMG response, determine a detection rate for the
EMG response and, in response to the detection rate, select a closed-loop
control regime comprising one of a response appearance control regime, a
response strength control regime, or an appearance + strength control
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regime. The appearance control regime comprises determining a response
detection rate setpoint as a percentage of the determined detection rate, and
modulating stimulation parameters in closed-loop to maintain the response
detection rate at the response detection rate setpoint. The response strength
control regime comprises determining a response strength setpoint as a
percentage of the EMG response strength of the feedback used to determine
the detection rate, and modulating stimulation parameters to maintain the
response strength at the response strength setpoint. The appearance +
strength control regime comprises determining a minimum detection rate
threshold as a percentage of the response detection rate, modulating
stimulation parameters to maintain the detection rate at or above the minimum
detection rate, and determining a response strength setpoint as a percentage
of the EMG response strength of the feedback used to determine the
detection rate, and modulating stimulation parameters to maintain the
response strength at the response strength setpoint.
[0068] According to another aspect, alone or in combination with any other
aspect, an apparatus for applying electrical stimulation includes a plurality
of
electrical stimulation electrodes, the stimulation electrodes being spaced
from
each other in a predetermined configuration. The apparatus also includes one
or more recording electrodes. The apparatus also includes a wearable
structure for supporting the stimulation electrodes and the recording
electrodes spaced apart from each other. The apparatus further includes a
control unit for controlling the operation of the stimulation electrodes and
the
recording electrodes. The control unit is configured to energize the
stimulation
electrodes to apply stimulation to a tibial nerve and record physiological
response using the recording electrodes. The controller is configured to
record information related to the application of stimulation therapy and
transmit the information to a patient controller. The patient controller is
configured to transmit the information to a server wherein optimized therapy
is
determined by compiling a quantitative summary of stimulation including
stimulation history/schedule, stimulation parameters, elicited muscle
responses, and the effect the stimulation had on the patient as recorded in
patient diary entries. The optimized therapy is further determined by
implementing informatics to correlate the stimulation profile (current
amplitudes, voltages, pulse profiles), the feedback history (EMG data), and
the patient diary entries so that, over time, the stimulation profile can be
used
to optimize therapy for each individual patient, thus improving patient
outcomes.
[0068a] According to another aspect, alone or in combination with any other
aspect, an apparatus for applying transcutaneous electrical stimulation to a
peripheral nerve of a subject, comprises: a plurality of electrical
stimulation
electrodes; one or more recording electrodes; a wearable structure for
supporting the stimulation electrodes and the recording electrodes in a
predetermined arrangement; and a control unit for controlling the operation of
the stimulation electrodes and the recording electrodes, wherein the control
unit is configured to energize the stimulation electrodes according to
stimulation parameters to apply stimulation to the peripheral nerve, and to
detect physiological responses to the applied stimulation using the recording
electrodes, wherein the stimulation parameters comprise a pulse parameter
and an associated current amplitude parameter, the control unit being
configured to execute a stimulation control algorithm to select the pulse
parameter from a range of pulse parameters and to select the associated
current amplitude parameter from a range of current amplitude parameters,
the range of pulse parameters being defined at an upper bound by a subject
tolerance limit for the associated current amplitude parameter and at a lower
bound by an evoked response threshold for the associated current amplitude
parameter, and wherein the range of pulse parameters and the range of
current amplitude parameters are interpolated from one or more calibrated
range of pulse parameters for a predetermined current amplitude.
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Drawings
[0069] Fig. 1A illustrates a left-foot implementation of an electronic
medical
device for delivering transcutaneous electrical stimulation of peripheral
nerves, according to a first example configuration.
[0070] Fig. 1B illustrates a right-foot implementation of the electronic
medical device for delivering transcutaneous electrical stimulation of
peripheral nerves, according to the first example configuration.
[0071] Fig. 2A is an inner surface plan view of the electronic medical
device of Figs. 1A and 1B.
[0072] Fig. 2B is an outer surface plan view of the electronic medical
device of Figs. 1A and 1B.
[0073] Figs. 2C-E are outer surface plan views of the electronic medical
device of Figs. 1A and 1B illustrating sequential steps in preparing the
device
for use.
[0074] Fig. 3A illustrates a left-foot implementation of an electronic
medical
device for delivering transcutaneous electrical stimulation of peripheral
nerves, according to a second example configuration.
[0075] Fig. 3B illustrates a right-foot implementation of the electronic
medical device for delivering transcutaneous electrical stimulation of
peripheral nerves, according to the second example configuration.
[0076] Fig. 4A is an inner surface plan view of components of the
electronic medical device of Figs. 3A and 3B.
[0077] Fig. 4B is an outer surface plan view of the components of the
electronic medical device of Figs. 3A and 3B.
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[0078] Fig. 4C is an outer surface plan view, taken from a first side,
illustrating the components of Figs. 4A and 4B assembled to form the
electronic medical device of Figs. 3A and 3B.
[0079] Fig. 4D is an outer surface plan view, taken from a second side,
opposite the first side, illustrating the components of Figs. 4A and 4B
assembled to form the electronic medical device of Figs. 3A and 3B.
[0080] Fig. 5 is a schematic block diagram of a control unit portion of
the
electronic medical device.
[0081] Fig. 6 is a diagram illustrating example electrode arrangements for
portions of the electronic medical device.
[0082] Fig. 7 is a flow chart illustrating an example nerve localization
process implemented by the electronic medical device.
[0083] Fig. 8 is a series of charts illustrating examples of recorded EMG
responses to electrical nerve stimulation.
[0084] Fig. 9 is a flow chart illustrating an example open-loop and closed-
loop electrical nerve stimulation processes implemented by the electronic
medical device.
[0085] Fig. 10 illustrates the anatomy of a human foot.
[0086] Fig. 11 illustrates an electronic medical device for delivering
transcutaneous electrical stimulation of peripheral nerves, according to
another example configuration.
[0087] Fig. 12 illustrates an electronic medical device for delivering
transcutaneous electrical stimulation of peripheral nerves, according to
another example configuration.
[0088] Fig. 13 illustrates recording electrode placements for the
electronic
medical devices of Figs. 11 and 12.
[0089] Fig. 14 is a graph that illustrates the effect of the size of
recording
electrodes of the electronic medical device.
[0090] Fig. 15 is a graph that illustrates the effect of switching the
electronic medical device between the feet of a subject.
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[0091] Fig. 16 is a graph that illustrates a method for determining
optimal
charge for neurostimulation.
[0092] Fig. 17 is a graph that illustrates adjusting the optimal charge in
response to adjusting the applied current amplitude for neurostimulation.
[0093] Fig. 18 is a graph that illustrated an operating zone within which
neurostimulation can be executed.
[0094] Figs. 19A-19C are examples of interpolated target therapy ranges.
[0095] Figs. 20 and 21 are flow chards that illustrate two different
methods
for determining target stimulation.
[0096] Fig. 22 is a flow chart that illustrates a method by which to
control
the application of stimulation therapy.
[0097] Fig. 23 is a flow chart that illustrates another method by which to
control the application of stimulation therapy.
Description
[0098] An electronic medical device, a system including the medical
device, and a method for using the medical device, is configured to apply
transcutaneous electrical stimulation to peripheral nerves to treat various
medical conditions.
[0099] For example, the system can be used to stimulate the tibial nerve
(transcutaneous tibial nerve stimulation "TTNS") to treat medical conditions
associated with pelvic floor dysfunction, e.g., over-active bladder (0AB). In
a
TTNS implementation, the electronic medical device applies electrical
stimulation near the medial malleolus, which activates both sensory and motor
fibers in the nerve. The activation of the sensory fibers of the tibial nerve
helps
to treat the urge-related symptoms of OAB. The activation of the motor fibers
can, however, cause unwanted side effects, such as toe twitch or spasm.
[00100] As another example, the system can be used to apply electrical
stimulation to the tibial nerve to treat sexual dysfunction. In this manner,
it is
believed that tibial nerve stimulation could be used to treat genital arousal
aspects of female sexual interest/arousal disorder by improving pelvic blood
flow.
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[00101] As another example, the system can be applied to the wrist area to
provide stimulation to the ulnar nerve and/or median nerve for pain
management in carpal tunnel syndrome, hypertension management, and
nerve conduction study/nerve injury diagnosis for medianiulnar nerve
neuropathy, etc.
[00102] The system and/or the device employed by the system can have a
variety of implementations. According to one implementation, the electronic
medical device (i.e., the electrodes, control unit, wiring, etc.) can be fixed
to a
garment that is worn by the subject. The garment can be tight or snug-fitting
so as to maintain sufficient contact between the subject's skin and can be
configured to position the electrodes at locations specific to the peripheral
nerves being stimulated. For example, to stimulate peripheral nerves in the
area of the foot or ankle, such as the tibial nerve near the medial malleolus
as
described above, the garment can be in the form of a sock, ankle brace, strap,
sleeve, or other like structure. For stimulating peripheral nerves on the leg,
the
garment can be a brace, strap, or sleeve sized appropriately for lower leg,
knee, or upper leg positioning. For knee or ankle positioning, the garment can
be configured, e.g., with openings, slots, or interconnected sections, to
allow
for bending with the joint while maintaining electrode positioning and
contact.
[00103] Similarly, for stimulating peripheral nerves on the hand, the garment
can be in the form of a glove, mitten, hand brace, or sleeve. For stimulating
peripheral nerves on the arm, the garment can be a tight/snug fitting brace,
strap, or sleeve (e.g., neoprene) that is sized appropriately for lower arm
(forearm/wrist), elbow, or upper arm positioning. For wrist and/or elbow
positioning, the sleeve can be configured, e.g., via openings, slots, or
interconnected sections, to allow for bending with the joint while maintaining
electrode positioning and contact.
[00104] In keeping with the above, it will be appreciated that the manner in
which the electronic medical device can be secured or supported on the
subject can vary. It will also be appreciated that the manner in which the
electronic medical device is supported is not critical, as long as contact
between the electrodes and the subject's skin is maintained, the positions of
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the electrode on the subject are maintained, and that the aforementioned are
achieved in a manner that is comfortable to the subject.
Strap Implementation
[00105] Figs. 1A-B illustrate a system comprising an example configuration
of the electronic medical device 10 for providing transcutaneous electrical
nerve stimulation, referred to herein as a neurostimulator, supported on a
subject 12. The neurostimulator 10 of Figs. 1A-B includes a garment in the
form of a strap 20 that supports the neurostimulator and its components on
the subject 12. In the example configuration of Figs. 1A-B, the strap 20
connects the neurostimulator 10 to the subjects foot 14, with Fig. lA
illustrating a left foot implementation, and Fig. 1B illustrating a right foot
implementation. In both instances, the strap 20 is wrapped figure-eight style,
with one loop extending around the foot and one loop extending around the
lower leg/ankle. Opposite end portions of the strap 20 can be interconnected,
e.g., via a buckle or loop 22 and an end portion 24 of the strap that extends
through the loop, is folded over, and connected to itself with a hook and loop
fastener. The hook and loop fastener is shown in Fig. 2B and includes a hook
portion 26 and loop portion 28.
[00106] The strap 20 implementation of the neurostimulator 10 is
advantageous in that it is versatile and can be adapted to secure the
neurostimulator to a wide variety of locations on the subject 12. The strap 20
can easily be wrapped around the foot 14 and/or ankle 16, as shown, and can
also be wrapped around and secured to any location along the length of the
subject's leg 18, either in a single loop or more than one loop, as the length
of
the strap permits. At the knee, the strap 20 can be wrapped, for example, in a
figure-eight style in a manner similar to that illustrated in Figs. 1A and 1B.
[00107] Referring to Figs. 2A-B, the neurostimulator 10 includes a several of
components that are secured or otherwise supported on the strap 20. The
securement of these components can be achieved in a variety of manners,
such as by adhesives, stitching, mechanical fastening, hook and loop
fasteners, or a combination thereof.
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[00108] The neurostimulator 10 includes stimulation electrodes 50 that are
arranged in one or more arrays 52 and positioned on an inner surface 36 of
the strap 20 at a widened end portion 30 of the strap. The number of
stimulation electrodes 50, the area covered by the array 52, the electrode
density (i.e., number of electrodes per unit area) in the array, and the
distribution or pattern of electrodes within the array all can vary depending
on
the intended application of the neurostimulator 10. Additionally, the
neurostimulator 10 can include more than one stimulation electrode array 52
again, depending on the application. In the example configuration of Fig. 2A,
the stimulation electrode array 52 includes six stimulation electrodes 50
arranged in a generally elongated kidney-shaped manner. The number and
arrangement of the stimulation electrodes 50, and the location/position of the
electrode array 52 on the strap 20 are by way of example only and are by no
means limiting.
[00109] In the example configuration of Fig. 2A, the stimulation electrodes
50 can be dry electrodes, in which case the neurostimulator 10 can include a
removable/replaceable stimulation gel pad 54 shaped and sized to coincide
with and cover the stimulation electrode array 52. In use, the gel pad 54
facilitates a strong, reliable electrical connection between the stimulation
electrodes 50 and the subject's skin.
[00110] The neurostimulator 10 also includes dedicated recording
electrodes 60 that are arranged in one or more arrays 62 and positioned on
the inner surface 36 of the strap 20 spaced from the stimulation electrode
array 52. The spacing between the stimulation electrodes 50 and the
recording electrodes 60 can be important, as it can be necessary to provide
adequate distance between the electrodes so that electrical stimulation
signals can be separated or distinguished from responses (e.g., neurological,
muscular, neuromuscular, etc.) to those electrical stimulation signals. This
facilitates utilizing responses to stimulation sensed by the recording
electrodes 60 as feedback in a closed-loop stimulation control scheme, which
is described in detail below.
[00111] The number of recording electrodes 60, the area covered by the
array 62, the electrode density (Le., number of electrodes per unit area) in
the
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array, and the distribution or pattern of electrodes within the array all can
vary
depending on the intended application of the neurostimulator 10. Additionally,
the neurostimulator 10 can include more than one recording electrode array
62 again, depending on the application. In the example configuration of Fig.
2A, the recording electrode array 62 includes four electrodes 60 arranged
linearly in two parallel rows of two electrodes. The number and arrangement
of the recording electrodes 60, and the location/position of the electrode
array
62 on the strap 20 are by way of example only and are by no means limiting.
[00112] In the example configuration of Fig. 2A, like the stimulation
electrodes 50, the recording electrodes 60 can also be dry electrodes.
Because of this, the neurostimulator 10 can also include a
removable/replaceable gel pad 64 shaped and sized to coincide with and
cover the recording electrode array 62. In use, the gel pad 54 facilitates a
strong, reliable electrical connection between the recording electrodes 60 and
the subject's skin.
[00113] Referring to Fig. 2B, the neurostimulator 10 also includes an
electronic control unit 70 that is operative to control the application of
transcutaneous electrical nerve stimulation via the stimulating electrodes 50
and to receive stimulation feedback gathered by the recording electrodes 60.
The control unit 70 is located at the widened end 30 of the strap 20 on an
outer surface 38, opposite the inner surface 36, of the strap 20. The buckle
22
can be a portion of the control unit 70 or can be connected to the control
unit.
In the example configuration of Fig. 2B, the control unit 70 has a generally
elongated kidney-shaped configuration similar to that of the stimulating
electrode array 52 and is positioned on the outer surface 38 generally
opposite the stimulating electrode array. This is by no means necessary to the
design of the neurostimulator 10, as the shape and location of the control
unit
70 can vary.
[00114] In the example configuration of Fig. 2B, however, the shape and the
positioning of the control unit 70 is convenient. The control unit 70 is
detachably connected to the remainder of the neurostimulator 10 via a plug-in
or snap-in connector 72 (see Fig. 2B), which receives a mating connector 74
(see Fig. 20) on the control unit 70. Fig. 2B shows the control unit 70
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connected to the neurostimulator 20 via the connector 72, and Fig. 2C shows
the neurostimulator 20 with the control unit detached from the connector and
removed. Configuring the control unit 70 to be detachable/removable allows
the control unit to be utilized with other neurostimulator configurations and
also allows the strap 20 and the components remaining on the strap (e.g., the
electrodes, etc.) to be replaced when worn out, expired, or otherwise due for
replacement.
[00115] Advantageously, the stimulating electrode array 52 can be part of
an assembly in which the stimulating electrodes 50 can be mounted on a
substrate or housing 56 constructed, for example of plastic. This
substrate/housing 56 can itself be secured to the strap 20 (e.g., via
adhesives,
stitching, or mechanical fastening) to thereby secure the stimulation
electrode
array 52 to be strap. Forming the stimulating electrode array 52 in this
manner
facilitates a precise arrangement and spacing of the stimulation electrodes 50
and makes it easy to secure them to the strap 20.
[00116] The connector 72 can also be formed as a portion of the housing
56. The connector 72 can be configured to protrude from a side of the housing
56 opposite the stimulation electrodes 50. The connector 72 can, for example,
extend through a hole in the strap 20 to position the connector on or
extending from the outer surface 38. When the control unit 70 is connected to
the connector 72, the strap 20 can be positioned between the control unit and
the portion of the housing 56 supporting the stimulator electrode array 52.
[00117] The connector 72 can support a plurality of terminals for electrically
connecting the control unit 70 to the stimulation electrodes 50 and the
recording electrodes 60. Certain terminals in the connector 72 can be
electrically connected to the stimulation electrodes 50 by wires or leads that
are embedded within the plastic housing material (e.g., via insert molding).
Embedding the leads in this manner helps maintain adequate spacing
between the conductors, which avoids the potential for shorts in the
circuitry.
[00118] Other terminals in the connector can be electrically connected to
the recording electrodes 60 by wires or leads 66 that are partially embedded
within the plastic housing material (e.g., via insert molding) and pass
through
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the housing 56, extending to the feedback electrode arrays 62. Through this
configuration, all of the necessary electrical connections to the stimulation
and
recording electrodes 50, 60 are made when the control unit 70 is installed on
the connector 72.
[00119] The neurostimulator 10 also includes electrode backing 80 that
facilitates safe storage and portability of the system. Fold lines 82, 84
shown
in Fig. 2A indicate lines along which the neurostimulator 10/strap 20 can be
folded to place the device in the stored condition. The steps involved in
placing the neurostimulator 10 in the stored condition are illustrated in
Figs.
2C-2E.
[00120] As shown in Fig. 2C, the control unit 70 is detached from the
housing 56. The control unit 70 is secured to the end portion 24 of the strap
20 by the hook and loop fastener 26, 28. Next, as shown in Fig. 2D, with the
inner surface 36 facing up, the widened end portion 38 is folded over along
the fold line 82, which places the stimulating electrode array 52 on a
corresponding portion of the electrode backing 80. Next, as shown in Fig. 2E,
the strap 20 is folded over along the fold line 84, which places the recording
electrode array 62 on a corresponding portion of the electrode backing 80.
This leaves the neurostimulator 10 in the stored condition of Fig. 2E.
[00121] To use the neurostimulator 10, the strap 20 is simply unfolded and
the control unit 70 is connected to the housing 56 via their respective
connectors 72, 74. The hook and loop fastener 26, 28 can be disconnected,
the strap 20 wrapped around the appropriate anatomy of the subject, and the
fastener re-connected to attach neurostimulator 10 to the subject.
Conveniently, where the neurostimulator 10 is configured for stimulating the
tibial nerve in the position illustrated in Figs. 1A-B, the widened end 30 of
the
strap 20 can include a visual alignment cue 90, such as a hole in the strap,
that becomes aligned with the medial malleolus of the ankle when the
stimulating electrodes are properly positioned.
Brace Implementation
[00122] Figs. 3A-B illustrate a system comprising another example
configuration of an electronic medical device 110 for providing transcutaneous
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electrical nerve stimulation, referred to herein as a neurostimulator,
supported
on a subject 112. The neurostimulator 110 of Figs. 3A-1B includes a garment
in the form of a brace 120 that supports the neurostimulator and its
components on the subject 112. In the example configuration of Figs. 3A-B,
the brace 120 connects the neurostimulator 110 to the subject's foot 114, with
Fig. 3A illustrating a left foot implementation, and Fig. 38 illustrating a
right
foot implementation. In both instances, the brace 120 has an upper portion
130 wrapped around the lower leg/ankle and a lower portion 150 portion
wrapped around the foot/ankle. Each of these portions are secured to the
subject via a connection such as a hook and loop fastener.
[00123] The brace 120 implementation of the neurostimulator 10 is
advantageous in that it is versatile in its ability to position the
stimulating
electrodes and recording electrodes at different locations on the subject. For
example, stimulating electrodes can be positioned on the upper portion 130 of
the brace 120 wrapped around the ankle, and recording electrodes can be
positioned on the lower portion 150 of the brace wrapped around the foot.
This can be especially advantageous for closed-loop neurostimulation of the
tibial nerve. In this implementation, stimulating electrodes on the upper
portion
130 can be located between the medial malleolus and the Achilles tendon to
provide electrical stimulation to the tibial nerve. Recording electrodes on
the
lower portion 150 can be located on the bottom of the subject's foot, near the
flexor muscles (abductor hallucis and the flexor hallucis brevis) for the big
toe
and can record the EMG signals that result from recruitment of the tibial
nerve's motor fibers.
[00124] As another advantage, the brace 120 is configured for placement at
or about a subject's joint and provides for movement of that joint. While the
brace 120 is illustrated as being applied at the subject's ankle joint, it
will be
appreciated that the brace 120 can also be applied at the knee joint or elbow
joint. Additionally, positioning the brace 120 at a joint is not critical, as
it can
be seen that the brace can be applied at any location along the subject's arms
or legs, size permitting.
[00125] The construction of the neurostimulator 110 is illustrated in Figs.
4A-D. For the example configuration of Figs. 4A-D the upper portion 130 and
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lower portion 150 of the strap 120 are separate components that are
interconnected by adjustment bands 122. The adjustment bands 122 can
allow for adjusting the spacing between the upper and lower portions 130,
150, e.g., via a buckle or hook and loop fastener, or the bands can be of a
fixed size amongst a range of sizes, e.g., x-small, small, medium, large, x-
large, etc. The respective sizes of the upper and lower portions 130, 150 can
be similarly sized. In fact, the upper portion 130 can itself be composed of
first
and second portions 132, 134 connected by a band 136 that allows for
adjusting the spacing between the upper and lower portions 130, 150, e.g.,
via a buckle or hook and loop fastener.
[00126] The upper portion 130 of the brace 120 includes a hook and loop
fastener composed of a hook portion 140 and a loop portion 142, which are
positioned opposite each other along an upper extent of the upper portion.
The upper portion 130 also includes opposite tab portions 144 to which the
adjustment tabs 122 (see, Figs. 4C-D) are connected, e.g., via stitching.
Similarly, the lower portion 130 of the brace includes a hook and loop
fastener
composed of a hook portion 152 and a loop portion 154, which are positioned
opposite each other along a lower extent of the lower portion. The lower
portion 150 also includes opposite tab portions 156 to which the adjustment
tabs 122 (see, Figs. 4C-D) are connected, e.g., via stitching.
[00127] The neurostimulator 110 includes a several of components that are
secured or otherwise supported on the brace 120. The securement of these
components can be achieved in a variety of manners, such as by adhesives,
stitching, mechanical fastening, hook and loop fasteners, or a combination
thereof. Figs. 4A and 4B illustrate the neurostimulator 110 in a partially
assembled condition, with the electronic components of the neurostimulator
mounted on the brace 120 prior to the first and second portions 132, 134
being interconnected by the adjustment bands 122. This construction is
advantageous because it allows the electronic components of the
neurostimulator 110 to be assembled onto brace 120 while the upper and
lower portions 130, 150 lie flat. The lying flat illustration of Figs. 4A-B is
for
purposes of simplicity as it allows the upper and lower portions 130, 150 to
be
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illustrated lying flat. Fig. 4A illustrates an inner surface 124 of the brace
120.
Fig. 4B illustrates an outer surface 126 of the brace 120.
[00128] The neurostimulator 110 includes stimulation electrodes 170 that
are arranged in one or more arrays 172 and positioned on the inner surface
124 of the upper portion 130 of the brace 120. In the example configuration
illustrated in Fig. 4A, the stimulation electrode arrays 172 are positioned on
opposite sides of the adjustment band 136 connecting the first and second
portions 132, 134 of the upper portion 130. This arrangement can, for
example, allow the brace 130 implementation of the neurostimulator 110 to be
ambidextrous.
[00129] The number of stimulation electrodes 170, the area covered by the
stimulation electrode arrays 172, the electrode density (i.e., number of
electrodes per unit area) in the arrays, and the distribution or pattern of
electrodes within the array all can vary depending on the intended application
of the neurostimulator 110. In the example configuration of Fig. 4A, each
stimulation electrode array 172 includes six stimulation electrodes 170
arranged in a generally rectangular manner in two rows of three electrodes.
The number and arrangement of the stimulation electrodes 170, and the
location/position of the electrode array 172 on the brace 120 are by way of
example only and are by no means limiting.
[00130] In the example configuration of Fig. 4A, the stimulation electrodes
170 can be dry electrodes, in which case the neurostimulator 110 can include
one or more removable/replaceable stimulation gel pads 174 shaped and
sized to coincide with and cover the stimulation electrode array 172. In use,
the gel pads 174 facilitate a strong, reliable electrical connection between
the
stimulation electrodes 170 and the subject's skin.
[00131] The neurostimulator 110 also includes recording electrodes 180
that are arranged in one or more arrays 182 and positioned on the inner
surface 124 of the lower portion 150 of the brace 120 at a location spaced
from the stimulation electrode arrays 172. The spacing between the
stimulation electrodes 170 and the recording electrodes 180 can be important,
as it can be necessary to provide adequate distance between the electrodes
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so that electrical stimulation signals can be separated or distinguished from
responses (e.g., neurological, muscular, neuromuscular, etc.) to those
electrical stimulation signals. This facilitates utilizing responses to
stimulation
sensed by the recording electrodes 180 as feedback in a closed-loop
stimulation control scheme which, again, is described in detail below.
[00132] The number of recording electrodes 180, the area covered by the
array 182, the electrode density (i.e., number of electrodes per unit area) in
the array, and the distribution or pattern of electrodes within the array all
can
vary depending on the intended application of the neurostimulator 110. In the
example configuration of Fig. 4A, there are two recording electrode arrays
182, each of which includes two recording electrodes 180 arranged linearly.
The number and arrangement of the recording electrodes 180, and the
location/position of the electrode arrays 182 on the brace 120 are by way of
example only and are by no means limiting.
[00133] In another implementation, the neurostimulator 110 can be
configured to include MMG sensors (e.g., accelerometers) for sensing muscle
movement as opposed to electrical activity. The optional MMG sensors are
illustrated in dashed lines at 186 in Fig. 4A. In this implementation, the MMG
sensors 186 can be implemented in addition to or in place of, the EMG
electrodes 180. Implementing the MMG 186 sensors along with the EMG
sensors 180 can prove beneficial in that the combination can provide
additional functionality. For example, the MMG sensor 186 can be used to
confirm the validity of an EMG measured feedback response. Additionally, the
MMG sensors 186 (or any other accelerometer for that matter) can be used to
verify that the subject in a resting, i.e., not moving, condition prior to
initiating
a therapy session.
[00134] In the example configuration of Fig. 4A, like the stimulation
electrodes 170, the recording electrodes 180 can also be dry electrodes.
Because of this, the neurostimulator 110 can also include a
removable/replaceable recording gel pad 184 shaped and sized to coincide
with and cover the recording electrode arrays 182. In use, the gel pad 184
facilitates a strong, reliable electrical connection between the recording
electrodes 180 and the subject's skin.
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[00135] Referring to Fig. 4B, the neurostimulator 110 also includes an
electronic control unit 200 that is operative to control the application of
transcutaneous electrical nerve stimulation via the stimulating electrodes 170
and to receive stimulation feedback gathered by the recording electrodes 180.
The control unit 200 is located on the outer surface 126 of the upper portion
130 adjacent the adjustment band 136 and opposite one of the stimulating
electrode arrays 172 on the inner surface 124 of the upper portion. In the
example configuration of Fig. 4B, the control unit 200 has a generally
elongated racetrack-shaped configuration similar, to that of the stimulating
electrode arrays 172, although narrower. This is by no means necessary to
the design of the neurostimulator 110, as the shape and location of the
control
unit 200 can vary.
[00136] In the example configuration of Fig. 4B, however, the shape and the
positioning of the control unit 200 is convenient. The control unit 200 can be
detachably connected to the remainder of the neurostimulator 110 via a plug-
in or snap-in connector, such as by a connector (not shown) that is similar or
identical to the connector associated with the control unit of the example
configuration of Figs. 2A-D. Configuring the control unit 200 to be
detachable/removable allows the control unit to be utilized with other
neurostimulator configurations and also allows the brace 120 and the
components remaining on the brace (e.g., the electrodes, etc.) to be replaced
when worn out, expired, or otherwise due for replacement.
[00137] Advantageously, each stimulating electrode array 172 can be part
of an assembly in which the stimulating electrodes 170 can be mounted on a
substrate or housing 176 constructed, for example of plastic. This
substrate/housing 176 can itself be secured to the brace 120 (e.g., via
adhesives, stitching, or mechanical fastening) to thereby secure the
stimulation electrode array 172 to be brace. Forming the stimulating electrode
array 172 in this manner facilitates a precise arrangement and spacing of the
stimulation electrodes 170 and makes it easy to secure them to the brace
120.
[00138] In a manner similar or identical to that of the example configuration
of Figs. 2A-D, the connector of each stimulating electrode array 172 can also
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be formed as a portion of the housing 176. The connector can be configured
to protrude from a side of the housing 176 opposite the stimulation electrodes
170. The connector can, for example, extend through a hole in the brace 120
to position the connector on or extending from the outer surface 126. When
the control unit 200 is connected to the connector, the brace 120 can be
positioned between the control unit and the portion of the housing 176
supporting the stimulator electrode array 172.
[00139] Again, in a manner similar or identical to that of the example
configuration of Figs. 2A-D, the connector can support a plurality of
terminals
for electrically connecting the control unit 200 to the stimulation electrodes
170 and the recording electrodes 180. Certain terminals in the connector can
be electrically connected to the stimulation electrodes 170 by wires or leads
that are embedded within the plastic housing material (e.g., via insert
molding). Embedding the leads in this manner helps maintain adequate
spacing between the conductors, which avoids the potential for shorts in the
circuitry.
[00140] Other terminals in the connector can be electrically connected to
the recording electrodes 180 by wires or leads 184 that are partially
embedded within the plastic housing material (e.g., via insert molding) and
pass through the housing 176, extending to the recording electrode arrays
182. Through this configuration, all of the necessary electrical connections
to
the stimulation and recording electrodes 170, 180 are made when the control
unit 200 is installed on the neurostimulator 110.
[00141] Referring to Figs. 4C-D, the neurostimulator 110 is assembled by
connecting the first and second portions 132, 134 of the upper portion 130
with the adjustment band 136. The upper and lower portions 130, 150 are
interconnected by two adjustment bands 122 that interconnect their respective
tab portions 144, 156. This completes the assembly of the neurostimulator
110, placing it in a condition to be worn by the subject in the manner
illustrated in Figs. 3A-B.
[00142] To use the neurostimulator 110, the brace 120 is simply unfolded
and the control unit 200 is connected to the housing 176 via the connectors.
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The hook and loop fasteners 140, 142 and 152, 154 are disconnected, the
brace 120 wrapped around the appropriate anatomy of the subject. In Figs.
3A-B, the upper portion 130 is wrapped around the lower leg/ankle 112 of the
subject, and the lower portion 150 is wrapped around the foot 114 of the
subject. The hook and loop fasteners 140, 142 and 152, 154 are re-connected
to attach neurostimulator 110 to the subject. Conveniently, where the
neurostimulator 110 is configured for stimulating the tibial nerve in the
position
illustrated in Figs. 3A-B, the upper portion 130 of the brace 120 can include
visual alignment cues 210, such as holes in the brace, that become aligned
with the medial malleolus of the ankle when the stimulating electrodes 170 are
properly positioned.
Control Unit Configuration
[00143] The control units 70, 200 of the example configurations of the
neurostimulator 10, 110 of Figs. 1A-4D can have a variety of configurations.
An example configuration for the control units 70, 110 is shown in Fig. 5.
Referring to Fig. 5, the control unit 70, 200 includes a microcontroller 220
powered by a primary or rechargeable battery 222 via a battery protection and
charging circuit 224. The circuit 224 offers battery protection typical for a
medical device, such as over-current and over-voltage protection, under-
voltage protection, and a charging controller. An external cable or charging
cradle 226 charges the battery 222 via the circuit 224. Alternatively, the
battery 222 can be charged wirelessly, e.g., via a wireless charging cradle. A
pushbutton 228 cycles on/off power to the control unit 70, 200.
[00144] The battery protection and charging circuit 224 also marshals power
to a high voltage power supply circuit 230, a digital power supply circuit
232,
and an analog power supply circuit 234. The high-voltage power supply circuit
230 is used to provide a stimulation compliance voltage to the output stage's
current sources and sinks. Since this device is a transcutaneous stimulator,
it
can require a compliance voltage in the range of about 40 ¨ 200 V or more in
order to provide the necessary current to stimulate the tibial nerve. For this
embodiment, a compliance voltage of 120 volts is used for the compliance
voltage.
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[00145] A radio controller 240, such as a Bluetooth or Zigbeee radio
controller, provides a communication input to the microcontroller 220 for
functions such as programming the control unit 70, 200,
uploading/downloading data, and monitoring/controlling the neurostimulator
10, 110 during use. The radio controller 240 could, for example, pair the
microcontroller to an enabled device, such as a smartphone, tablet, or
computer, executing software that enables the user to monitor or otherwise
control the operation of the neurostimulator 10, 110. The microcontroller 220
controls the operation of indicators 242, such as LEDs, that indicate the
state
or condition of the control unit 70, 210. The microcontroller 220 can control
an
accelerometer 244, which can provide input to determine whether the
neurostimulator 10, 110, and thus the subject, is moving or at rest.
[00146] The microcontroller 220 is responsible for controlling the stimulation
output, measuring the electrode impedance, and processing the EMG
response. The microcontroller 220 runs software for performing these
functions, including decision-making algorithms to allow the device to provide
the desired therapy. The microcontroller 220 controls the operation of an
amplitude control circuit 250, a timing control circuit 252, and a digital-to-
analog converter (DAC) 254. By "circuit," it is meant that these functions can
be implemented in any desired manner, e.g., through discrete components,
integrated circuits, or a combination thereof. The amplitude control circuit
250,
timing control circuit 252, and DAC 254 drive a stimulator output stage 260,
which provides stimulator output signals (e.g., pulse-width-modulated "PWM"
output signals) to one or more analog output switches 262. The output
switch(es) 262 are operatively connected to a port 280 comprising a plurality
of terminals (E1-E8 in Fig. 5) that facilitates connecting the control unit
70,
200 to the stimulator and recording electrodes, for example, via the leads 66,
184 (see, Figs. 2A and 4B, respectively). Through this connection via the
leads 66, 184, the stimulator output stage 260 can be operatively connected
to the stimulator electrodes 50, 170.
[00147] The microcontroller 220 receives electrode impedance values via
an impedance measurement circuit 264 that is operatively connected to the
stimulator output stage 260. The microcontroller 220 also receives electrode
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feedback values (e.g.. F-wave and M-wave values) via an analog front end
270 that is operatively connected to one or more analog input switches 272.
The input switch(es) 272 are also operatively connected to the terminals/port
280 and can thereby receive feedback from the recording electrodes 60, 180
that facilitates connecting the control unit 70, 200 to the stimulator and
recording electrodes, for example, via the leads 66 (see, Fig. 2A) or 184
(see,
Fig. 4B).
[00148] The impedance measurement circuit 264 allows for measuring the
impedance of the electrodes. It is important to measure the impedance often,
in case one or more of the electrodes begins to lift from the skin. There are
two potential hazards related to electrode lifting that should be mitigated.
First,
if an electrode is partially lifted from the skin, the surface area of the
electrode
that is in contact with the skin is reduced and the current density of the
stimulation current is increased, which can be unsafe. Second, if an active
electrode is completely lifted from the skin, a brief but large amount of
energy
can be delivered to the tissue when the electrode makes contact with the skin,
which can result in pain.
[00149] Electrode impedances measured via the impedance measurement
circuit 264 can also be used as an additional input for a closed-loop
stimulation optimization algorithm.
[00150] The stimulator output stage 260 provides the current to the
stimulating electrodes via the output switch 262. Each channel of the output
stage includes a current source and current sink, which allows each channel
to provide either a positive or negative current to the tissue through the
corresponding stimulation electrode(s) 50, 170. In this configuration, each
current source and sink can have independently programmable amplitude
control 250 and timing control 252, which provides the capability to "steer"
the
current applied via the stimulation electrodes 50, 170, as described below.
The programmable range can vary depending on the application, and is
selected to be capable of achieving the desired nerve recruitment. In an
example configuration, the current sources can have a programmable range
from zero to +20 milliamperes (rnA), and the current sinks can have a
programmable range from zero to -20 mA.
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[00151] As shown in Fig. 5, the analog output switches 262 and input
switches 272 can both be operatively connected to each of the terminals El -
E8. Through operation of the switches 262, 272 as commanded by the
microcontroller 220, the identity or role of the terminals, i.e., output
terminal or
input/feedback terminal, can be actively identified. This allows the
microcontroller 220 to selectively identify, activate, and deactivate
electrodes
in a desired pattern, order, combination, etc., according to the particular
therapy regimen being applied. This also allows the therapy to be tailored,
for
example, in response to signals received from the recording electrodes.
Control Overview
[00152] According to one example implementation, the neurostimulator 10,
100 described above can control the application of stimulation therapy
according to two general phases: nerve localization and stimulation delivery.
These two phases work synergistically to provide the functionality set forth
in
the following paragraphs.
[00153] During the nerve localization phase, the target peripheral nerve
structure, e.g., the tibial nerve, is localized when the neurostimulator 10,
100
is donned and activated. In the nerve localization phase, the neurostimulator
10, 100 implements a process in which the following functions are performed:
= Ramping up stimulation energy across various electrode
patterns.
= Monitoring EMG response after each stimulation pulse.
= Determining the electrode pattern and stimulation
parameters that optimally activate the target peripheral
nerve.
[00154] During the stimulation delivery phase, electrical stimulation is
delivered to the target peripheral nerve structure using the electrode
pattern(s) and stimulation parameters determined during the nerve
localization phase. In the stimulation delivery phase, the neurostimulator 10,
100 implements a process in which the following functions are performed:
= Deliver stimulation pulses to the target peripheral nerve.
= Continuously optimize the delivery of stimulation pulses,
which includes:
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= Monitoring EMG response after each stimulation
pulse.
= Monitoring electrode impedance.
= Adjusting either the electrode pattern (current-
steering) or stimulation energy to optimize recruitment
of the tibial nerve.
= Automatically stopping stimulation at the end of the therapy
session.
[00155] The nerve localization and stimulation delivery phases are
described in more detail in the following sections.
Nerve Localization
[00156] In practice, the control unit 110 can be programmed with a set of
electrode patterns that identify which stimulation electrode 50, 170 in an
electrode array 52, 172 are active, and also the polarity or type, i.e., anode
(+)
or cathode (-) assigned to the electrode. Fig. 6 illustrates an example
configuration for an electrode array 52, 172 and a chart illustrating an
example set of electrode patterns. In the example illustrated in Fig. 6, the
electrode array 52, 172 has eight electrodes 50, 170, identified at El -E8,
and
the chart identifies ten different electrode patterns (patterns 1-10) for the
electrode array. For each electrode pattern, each electrode is identified as
being a cathode (C), anode (A), or inactive (blank). Thus, for example, in
pattern 3, electrodes El and E2 are cathodes, electrodes E5 and E6 are
anodes, and electrodes E3, E4, E7, and E8 are inactive. While there are a
large number of patterns that are possible with an eight-electrode array, the
patterns can effectively be narrowed down to a shorter list, such as the
illustrated 10 patterns or more, depending on the nerve under recruitment.
[00157] The neurostimulator 10, 110 can be configured to perform a nerve
localization routine to determine which of the electrode patterns should be
utilized on a subject. In the example configuration of Fig. 6, the electrode
array 52, 172 can be specifically designed, i.e., shaped and electrodes
positioned, to stimulate the tibial nerve in the region between the medial
malleolus and the Achilles tendon. The electrode array 52, 172 can be
configured to perform stimulation on this or other regions where peripheral
nerve stimulation is desired.
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[00158] In the example configuration of Fig. 6, the electrode array 52, 172 is
curved to allow the medial malleolus to be used as a placement guide. Also,
the array can be symmetrical so that it can be placed on either ankle. The
electrode arrangement within the array must be configured to capture the
tibial nerve, meaning that the nerve must pass below or between at least one
pair of electrodes. If the tibial nerve passes outside the extents of the
array,
activation of the tibial nerve requires much higher stimulation energies, or
it
may not be possible to activate the tibial nerve at all.
[00159] The purpose of using an array for stimulation (as opposed to a
single pair of electrodes) is to create an optimized stimulation field for
recruiting the target (e.g., tibial) nerve. If the stimulation field is too
small, the
nerve will not be recruited and therapy will not be delivered. If the
stimulation
field is too large, too many motor neurons will be recruited resulting in
undesired effects, such as pain, twitching, or muscle spasm. In order to
optimize the stimulation field, the ability to steer current using multiple
electrodes if preferred. For example, electrode pattern 8 assigns electrodes
E3 and E4 as anodes and electrodes E7 and E8 as cathodes. Viewing the
arrangement of these electrodes 50, 170 on the array 52, 172, it can be seen
that the use of this electrode pattern could be effective on a nerve path that
passes directly adjacent or between these electrode pairs.
[00160] By selecting the appropriate stimulation electrodes 50, 170 from the
stimulation electrode arrays 52, 172, and varying the amplitude and polarity
of
the current applied via the selected electrodes, the electric field applied to
the
subject can be shaped so that the current is steered to the target nerves. By
shaping the field, the neurostimulator 10, 100 can automatically adjust to day-
to-day donning and placement variability for a given subject. Current steering
also allows the neurostimulator 10, 100 to work across a subject population
with wide anatomical variation, for example providing a shallow field for
subjects with nerves that are superficial to the skin, or a penetrating field
for
subjects with nerves that are deep. In the illustrated example configurations,
the stimulation electrode arrays 52, 152 include six electrodes. Any number of
stimulation electrodes greater than one can be used. In general, the "field
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steering" capability of the neurostimulator 10, 100 increases with the number
of stimulating electrodes 50, 170 that are included.
[00161] Because there will be session-to-session variability in the location
of
the stimulating electrode array 52, 172 due to the don/doff process, as well
as
variability in skin/tissue impedance, providing open-loop stimulation applying
rigid pre-programmed stimulation parameters could be disadvantageous,
often providing too little or too much stimulation energy to recruit the
nerve.
Advantageously, the nerve localization algorithm is executed at the beginning
of each therapy session to determine which of the preprogrammed electrode
patterns will be most effective.
[00162] Fig. 7 illustrates a flowchart showing the method or process 300
implemented by the nerve localization algorithm. The steps in the process 300
are not meant to be exclusive, i.e., other steps can be included. Nor is the
process 300 intended to be strictly followed in terms of the order shown in
Fig.
7 or described herein. The process 300 illustrates steps, perhaps a minimum,
necessary to localize the peripheral nerve that is to be stimulated.
[00163] It should be noted here that, the process 300 is a closed-loop
algorithm that utilizes feedback recorded via the recording electrodes 60, 180
to make determinations and/or adjust settings. As such, the process 300
relies on utilization of the feedback to determine which of the electrode
patterns effectively achieves nerve recruitment. Specifically, the process 300
relies on feedback from the recording electrodes 60, 180 to provide indication
of EMG response feedback. Alternatively, the process 300 can rely on
accelerometers to provide MMG response feedback.
[00164] Referring to Fig. 7, the process 300 begins at step 302, where an
impedance measurement is performed in order to determine which, if any, of
the electrodes E1-E8 have open or prohibitively high impedance. This step
302 can be considered an integrity check for the electrodes 50, 170 in the
array 52, 172 to determine if any of the electrodes in the array are not
sufficiently contacted with the skin. If any of the electrodes in the array
are
determined to be performing in a substandard manner, indicated by displaying
an open (infinitely high) or sufficiently high impedance, those electrodes and
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the electrode patterns that utilize those electrodes can be eliminated from
use.
[00165] For example, in the example of Fig. 6, it can be seen from row 2
that electrode E6 has high impedance. In this instance, electrode patterns 3,
6, 7, and 9 are eliminated form use in the current therapy session.
Alternatively, the algorithm could instruct the control unit to provide some
indication to the user, such as an alarm or display, to re-position or adjust
the
electrodes to see if contact can be improved.
[00166] To avoid interfering with stimulation and EMG measurement, the
integrity check at step 302 can be completed in a short amount of time, such
as 25 milliseconds or less. Also, the impedance measurement can be
conducted so as to cause little or no sensation in the subject's skin.
Therefore, the excitation current for perfoming the integrity check should be
low-amplitude, such as 1 mA or less. For the integrity check 302, the
impedance value at each electrode is not critical. Instead, determining
whether the impedance is below a certain threshold is adequate.
[00167] Additionally, conditions other than high or low impedance can be
determined in this integrity check. For example, indicators such as dry/wet
contact checks, whole/brittle/fractured contact checks, contact surface area
checks, and contact reflectance checks can be made during the connectivity
evaluation. Sensors, such as don/doff, stretch, strain, bending or contact
sensors (via electrical, optical or mechanical means) can also be used for
conducting the connectivity evaluation. These sensors could also be
incorporated into a buckle, clasp, snap, hook/eye or zipper feature.
[00168] Once the integrity check is performed, the process 300 proceeds to
step 304 where the first electrode pattern (that hasn't been eliminated by the
integrity check) is loaded. The process 300 then proceeds to step 306 where
the neurostimulator 10, 110 generates stimulation pulse(s) using the electrode
pattern loaded in step 304. The process 300 proceeds next to step 310,
where a determination is made as to whether the stimulation pulses
generated at step 306 elicited an EMG response, i.e., feedback measured via
the recording electrodes. Step 310 can additionally or alternatively determine
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whether there is a MMG response where the feedback devices include
accelerometer(s).
[00169] If, at step 310, EMG (or MMG) is not detected, the process 300
reverts to step 314, where a new electrode pattern is loaded. The process 300
then proceeds to step 306, as described above. If, at step 310, EMG (or
MMG) is detected, the process 300 proceeds to step 312, where the electrode
pattern is added according to pattern selection rules. The process 300 then
proceeds to step 316, where a determination is made as to whether the
current electrode pattern is the last electrode pattern in the list.
[00170] The pattern selection rules at step 312 for adding an electrode
pattern can be defined to prioritize electrode patterns identified as being
the
best suited to recruit the target nerves. These pattern selection rules may be
implemented as follows:
= If one pattern is significantly better than the others (e.g., as
determined from the EMG data, see below), that pattern
should be used as the primary pattern moving forward.
= If two or three patterns are roughly equivalent, any one of the
patterns can be used as the primary pattern. Moving forward,
this pattern can be switched to other ones if the nerve
recruitment displayed by the current primary pattern begins
to diminish.
= If the nerve recruitment for a particular pattern begins to
diminish and increasing the stimulation parameters does not
fix the problem, similar patterns can be re-introduced to the
algorithm.
[00171] If, at step 316, it is determined that the current electrode pattern
is
not the last pattern in the list, the process 300 reverts to step 314, where a
new electrode pattern is loaded. The process 300 then proceeds to step 306,
as described above. If, at step 316, it is determined that the current
electrode
pattern is the last pattern in the list, this indicates that the pattern list
is
complete. The process 300 proceeds to step 320 where the stimulation
parameters for the electrode patterns in the pattern list are optimized. At
step
320, the stimulation parameters (e.g., frequency, amplitude, pattern,
duration,
etc.) are updated to optimize the nerve recruitment for each pattern. The
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process 300 then reverts back to the initial step at 302 and proceeds as
described above. If the recruitment for a given electrode pattern improves,
the
stimulation parameters are kept. If not, they revert back to previous values.
This process repeats itself until the pattern list is filled with electrode
patterns
optimized for nerve recruitment.
[00172] From the above, it will be appreciated that the nerve localization
process 300 determines which of the electrode patterns to utilize and which to
discard for any given stimulation therapy session, and then optimizes the
stimulation parameters for the utilized patterns. The execution of this
process
300 is fast. During execution, the neurostimulator 10, 110 applies stimulation
therapy pulses via the stimulating electrodes 50, 170 and monitors for EMG
responses via the recording electrodes 60, 180 after each pulse.
[00173] The analog front end circuit 270 can replace traditional EMG
measurement circuitry such as a filter, amplifier, rectifier, and/or
integrator.
The control unit 110 utilizes the analog front-end circuit 270 to sample the
recording electrodes at a predetermined sample rate, such as 1,000 ¨ 8,000
samples per second. The EMG sampling window will begin after the
stimulation pulse is finished, and the window will last for a predetermined
brief
period, such as 8-90 milliseconds. The resulting EMG data, comprised of M-
wave or F-wave or both, will be analyzed using a Fast Fourier Transform
(FFT) technique that clearly shows if EMG is present.
[00174] To execute the process 300 of Fig. 7, the neurostimulator 10, 110
monitors for electromyogram (EMG) signals via the recording electrodes 60,
180 in response to stimulation applied via the stimulation electrodes 50, 170.
Fig. 8 illustrates examples of the EMG responses that can be recorded, which
include: No EMG Response, F-wave Response, M-wave Response, and M
and F-wave Response. In the example where no EMG response is recorded,
the stimulation pulse artifact can be seen on the left, with no response
following. In the example where an M-wave response is recorded, the
stimulation pulse artifact can be seen on the left, followed by the M-wave at
about 6 to 10 ms post-stimulation. In the example where an F-wave response
is recorded, the stimulation pulse artifact can be seen on the left, followed
by
the F-wave responses at about 50 to 55 ms post-stimulation. In the example
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where both an M-wave and F-wave responses are recorded, the stimulation
pulse artifact can be seen on the left, followed by the M-wave and F-wave at 6
to 10 ms and about 50 to 55 ms post-stimulation, respectively. These
response times could change slightly, depending on a variety of factors, such
as the hydration and/or salinity of the subject tissue, the arrangement and
spacing of the electrodes, and the characteristics of the stimulation signals.
[00175] For each of the four recorded response scenarios, Fig. 8 also
illustrates a corresponding Fast Fourier Transform (FFT) results for the raw
post-artifact signal. The FFT results are calculated by the microcontroller
220
and are used in the process 300 to determine whether an EMG response is
present (see, step 310 in Fig. 7).
Stimulation Delivery
[00176] The neurostimulator 10, 110 can apply stimulation therapy using an
open-loop control scheme, a closed-loop control scheme, or a combination of
open-loop and closed-loop control schemes, depending on the control
algorithm programmed into the microcontroller 220. For open-loop control, the
control units 70, 200 can apply electrical stimulation via the stimulation
electrodes 50, 170 according to settings (frequency, amplitude, pattern,
duration, etc.) without regard to any feedback measured via the recording
electrodes 60, 180. This is not to say that feedback is not measured, just
that,
in an open-loop control scheme, the feedback is not used to inform or control
the algorithm executed by the microcontroller 220 to control the application
of
stimulation therapy. In a closed-loop control scheme, the neurostimulator 10,
110 implements a control algorithm in which feedback from the recording
electrodes 60, 180 informs and helps control the application of stimulation
therapy.
[00177] Fig. 9 illustrates by way of example a process 400 by which the
neurostimulator 10, 110 controls the application of electrical nerve
stimulation
using the electrode pattern(s) identified by the nerve localization process
300
of Fig. 7. The stimulation control process 400 can employ both open-loop and
closed-loop control, with closed-loop steps or portions of the process being
illustrated in solid lines and open-loop steps or portions being illustrated
in
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dashed lines. Ideally, the process 400 will proceed with closed-loop control,
as it is able to utilize feedback to optimize the application of stimulation
therapy.
[00178] The process 400 begins at step 402, where the impedances of the
recording electrodes 60, 180 are checked. If, at step 404, it is determined
that
the recording electrode impedances are too high (e.g., resulting in
unavailable
or unreliable feedback), the process 400 then shifts to open-loop mode (see
dashed lines) and proceeds to step 412, where a delay is implemented. The
purpose of delay 412 is to assist in maintaining a constant stimulation
period,
meaning that the duration of delay 412 should be equal to the duration of
closed-loop step 406. After completing delay 412, the process 400 proceeds
to step 414, where the stimulation electrode impedances are checked.
[00179] At step 404, if the impedances of the recording electrodes are
acceptable, the process 400 remains in closed-loop mode and proceeds to
step 406, where samples are obtained via the recording electrodes to check
for significant noise or voluntary EMG responses. At step 410, if noise or EMG
are present, the feedback is considered unreliable and the process 400 shifts
to open-loop mode and proceeds to step 414. At step 410, if significant noise
or voluntary EMG is not present, the feedback is considered reliable and the
process 400 remains in closed-loop mode and proceeds to step 414.
[00180] At step 414, regardless of whether the process is in open-loop
mode or closed-loop mode, the impedances of the stimulation electrodes 50,
170 are checked. At step 416, if the stimulation electrode impedances are
acceptable, the process 400 proceeds to step 420 and the neurostimulator 10,
110 generates stimulation pulses, which are applied via the stimulation
electrodes using the optimal electrode pattern, as determined by the nerve
localization process 300 (see Fig. 7). If, at step 416, the stimulation
electrode
impedances are too high, the process 400 proceeds to step 420 and the
neurostimulator 10, 110 generates stimulation pulses that are applied via the
stimulation electrodes using an alternative electrode pattern selected from
the
pattern list determined by the nerve localization process 300. In either case,
after generating the stimulation pulse using the optimal pattern (step 420) or
the alternative pattern (step 422), the process 400 proceeds to step 424.
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[00181] At step 424, the process 400 implements a pre-recording delay to
allow time for the electrical stimulation applied at step 420 or 422 to elicit
an
EMG response. As discussed above, these delays can be relatively short, so
the delay at step 424 can, likewise, be short, e.g., 5 ms or less. If the
process
400 is in open loop mode, it proceeds to step 432, where a further delay is
implemented. This delay 432 should match the duration of closed-loop steps
426 and 430 so that a constant stimulation period is maintained. If the
process
400 is in closed-loop mode, it proceeds to step 426 and checks for feedback
via the recording electrodes 60, 180. The process 400 then proceeds to step
430, where any detected EMG feedback signals are recorded and analyzed.
[00182] At this point, regardless of whether the process 400 is in open-loop
mode (step 432) or closed-loop mode (step 430), the process proceeds to
step 434, where a determination of whether the number of stimulation pulses
applied in the current therapy session has reached a predetermined number
(N). If the predetermined number (N) of pulses have not yet been applied, the
process proceeds to step 436, the stimulation amplitude is maintained at the
current level, and the process 400 reverts back to step 402, where the
impedance of the recording electrodes is checked and the process 400
repeats. If, at step 434, the predetermined number (N) of pulses has been
reached, the process 400 proceeds to step 440.
[00183] At step 440, if the process 400 in open-loop mode, the process
proceeds to step 442, the stimulation amplitude is maintained at the current
level, and the process 400 reverts back to step 402, where the impedance of
the recording electrodes is checked and the process 400 repeats. At step 440,
if the process 400 is not in open-loop mode (i.e., is in closed-loop mode),
the
process proceeds to step 444, where a determination is made as to whether
the EMG recorded at step 430 is below a predetermined window, i.e., below a
predetermined range of acceptable EMG values. If the EMG is below the
predetermined window, the process 400 proceeds to step 446, where the
stimulation amplitude is increased for the next pulse, if permitted. The
process
400 then reverts back to step 402, where the impedance of the recording
electrodes is checked and the process 400 repeats with the increased
stimulation amplitude.
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[00184] If, at step 444, the EMG is not below the window, the process 400
proceeds to step 450 where a determination is made as to whether the EMG
is above the predetermined window. If the EMG is above the predetermined
window, the process 400 proceeds to step 452, where the stimulation
amplitude is decreased for the next pulse. The process 400 then reverts back
to step 402, where the impedance of the recording electrodes is checked and
the process 400 repeats with the decreased stimulation amplitude. If, at step
450, the EMG is not above the predetermined window, the EMG is
determined to be within the predetermined window and the process 400
proceeds to step 454, where the stimulation amplitude is maintained at the
current level for the next pulse. The process 400 then reverts back to step
402, where the impedance of the recording electrodes is checked and the
process 400 repeats.
Elongated Electrodes for Monitoring of EMG by Simultaneous Recruitment of
Multiple Muscles
[00185] Fig. 10 illustrates the primary innervation of the human foot 500.
The tibial nerve 502 travels inside the foot 500 via the tarsal tunnel 504,
posterior towards the medial malleolus 506. The tibial nerve 502 lies lateral
towards the posterior tibial artery inside the tarsal tunnel 504 and also
produces medial calcaneal branches, in order to innervate the heel while
penetrating the flexor retinaculum. The tibial nerve 502 bifurcates with the
posterior tibial artery, in the middle of the medial malleolus and the heel,
into a
large medial plantar nerve 508 and a smaller lateral plantar nerve 510. The
plantar nerves 508, 510 branch into the common plantar digital nerves 512
and the proper plantar digital nerves 514.
[00186] As discussed previously, stimulation of nerves, such as the tibial
nerve 502, can provide therapeutic benefits to multiple conditions, with one
example being overactive bladder (0AB). For consistent therapy, monitoring
muscle activity induced by the activation of neuromuscular junction is
important. For example, the neurostimulator 10, 110 described above with
reference to Figs. 1-9 includes electrodes 60, 180 for monitoring
Electromyography (EMG) from the post-synaptic muscle, which allows to
confirm pre-synaptic nerve recruitment, as well as adjust stimulation
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parameters to provide optimized therapy levels. These electrodes can be built
into a wearable garment, thus precluding the need for manually placement of
the electrodes as a separate part of the system for each therapy session.
[00187] Figs. 11 and 12 illustrate example configurations of neurostimulator
designs that can implement recording electrodes that provide a robust and
reliable signal under a broad variety of conditions, such as anatomical
differences between the subject wearing the device, differences in placement
of the electrodes on the subject, variability in the position of the
stimulator
garment on the subject, relative movement or shifting of the recording
electrodes relative to the target muscle groups, physical bodily movement
during use, and undulations in the foot profile. The improved recording
electrodes can facilitate therapy that is uninterrupted during normal daily
activities, which can significantly improve the usability and compliance of
the
system.
[00188] Fig. 11 illustrates a neurostimulator 520 that is generally similar in
design and operation to the neurostimulator 110 of Figs. 3A-4C, with the
exceptions described below. The neurostimulator 520 has a brace
configuration including a brace 522 upon which the neurostimulator
components are supported. The configuration of the neurostimulator 520 is
similar in some respects, and identical in others, to the braced configuration
shown in Figs. 3A-4C. The neurostimulator 520 can thus be worn as a
garment in the manner shown in Figs. 3A-B.
[00189] Fig. 12 illustrates a neurostimulator 550 that is generally similar in
design and operation to the neurostimulator 10 of Figs. 1A-2E, again with the
exceptions described below. The neurostimulator 550 has a strap
configuration including a strap 552 upon which the neurostimulator
components are supported. The configuration of the neurostimulator 550 is
similar in some respects, and identical in others, to the strap configuration
shown in Figs. 3A-4C. The neurostimulator 550 can thus be worn in the
manner shown in Figs. 1A-B.
[00190] The manner in which the neurostimulators 520, 550 are supported
on the subject, Le., worn, can vary. For example, the neurostimulators could
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be configured in the form of a sock that fits over the subject's foot and
ankle,
or in the form of a sleeve that slides over the foot/ankle, leaving the toes
exposed. The support structure for positioning the neurostimulator
components on the subject can have any configuration suited to place the
components at the desired location on the subject.
[00191] The neurostimulators 520, 550 include recording electrodes 524,
554, respectively, that have an elongated profile configured to extend
laterally
across the longitudinal muscle groups of the foot (see, Fig. 10). This
relieves
the need to focus the monitoring of EMG feedback on a specific post-synaptic
muscle being activated. The recording electrodes 524, 554 cover a large
anatomical area of the foot so as to record activation of muscle tissue that
is
located adjacent or near the electrodes. This helps minimize the likelihood of
a total loss of electrical evoked muscle signals, compared to recording
electrodes that rely on a more precise placement.
[00192] The neurostimulators 520, 550 can be configured so that the
elongated recording electrodes 524, 554 span over the whole width of the
bottom of the foot 500. This is shown in Fig. 13. The recording electrodes
524,
554 can alternatively be configured to have lengths to provide different
coverage of the foot 500, and can also be configured to be positioned in
alignment with each other, or staggered relative to each other, so that at
least
one of the electrodes covers the entirety of the target muscle bundles. The
spacing between the recording electrodes 524, 554 can, for example, be
between 6 cm and 12 cm, measured from the longitudinal centerlines of the
electrodes, as indicated generally at dimension X in Fig. 13.
[00193] Fig. 14 illustrates the effect that the size, i.e., width of the
recording
electrodes 524, 554 has on the voltage recorded in response to stimulation
applied in an identical manner. As shown in Fig. 14, all three size - 3 cm, 6
cm, and 10 cm, recorded a response, and the response had a similar
waveform. The amplitudes of the recorded responses varied inversely with the
size of the recording electrodes. This shows that the large electrodes 524,
554 are capable of recording EMG responses to tibial nerve stimulation.
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[00194] When more than one muscle is recruited, it has been confirmed that
there is no adverse impact on the integrity of the combined feedback signal
received by the elongated electrodes 524, 554 due to their simultaneous
recruitment. This feedback signal is further analyzed using particular signal
processing and noise reduction techniques. The elongated electrodes 524,
554 can therefore advantageously improve the recording function of the
neurostimulators 520, 550.
[00195] To promote good, reliable contact between the electrodes and the
subject's foot, the neurostimulators can include a compliant member that
facilitates forming the electrodes to the contour of the foot. This is shown
by
way of example in the magnified section view detailed in Fig. 11. In one
embodiment of the system, a compliant member is added underneath the
recording electrodes, to accommodate different foot profiles and potential
undulations. Such a compliant member could be a part of the garment, such
as a sheath of foam or silicone embedded in the fabric, or it could be an
external wearable system, such as a band, that essentially provide a similar
and uniform pressure on the recording electrodes. The form and stiffness of
this compliant member may be customized based on individual size or the
arch of the foot.
Integrated wearable device with built-in stimulating and recording
[00196] The neurostimulators described herein, including the
neurostimulators 520, 550 of Figs. 11 and 12, can have an integrated
construction in which the stimulating and recording elements, e.g.,
electrodes,
traces, etc., are integrated into a single wearable garment. This construction
ensures the positioning of the elements on the garment which, in turn,
ensures the automatic placement of all the electrodes when the garment is
worn by the subject.
[00197] Figs. 11 and 12 illustrate examples of components that can be
integrated with the neurostimulator garments. Referring to Fig. 11, the
stimulating electrodes 530, 532 and recording electrodes 524 electrically
connected to conductive traces 534, which provide the electrical connectivity
to the controller (not shown) via connector 536 (shown schematically).
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Similarly, referring to Fig. 12, the stimulating electrodes 556 and recording
electrodes 554 electrically connected to conductive traces 556, which provide
the electrical connectivity to the controller (not shown) via connector 560
(shown schematically). Figs. 11 and 12 are, of course, examples of the types
of neurostimulators into which this integrated construction can be
implemented. It will be appreciated that the integrated construction can be
implemented in various alternative neurostimulator configurations, including
any of the configurations disclosed herein.
[00198] The neurostimulators 520, 550 have integrated constructions in
which the electrodes and traces are embedded into their respective garments
522, 552, thus eliminating a need for external wiring, adhesive or other such
mechanisms that can limit the usability or reliability of the garment.
According
to one implementation, the stimulation electrodes, recording electrodes and
traces are all fabricated as a single part in which the electrically
conductive
and insulating components are formed as one or more layers of electrically
conductive materials, such as a flexible printed circuit, that is supported on
a
flexible substrate.
[00199] This prefabricated part may than be attached to the garment using
a multiplicity of processes, one such example being thermal pressing. In this
construction, the substrate supporting the electrical components can comprise
a thermal adhesive that facilitates the thermally pressed attachment.
Alternatively, the conductive and insulative layers can be directly imparted
on
the garment using processes such as spraying or deposition.
[00200] The electrodes have conductive material exposed to ensure good
contact with patient body. The traces may be made from a conductive
material printed on a non-conductive sheet and then adhered to the garment.
However, an electrical contact between the traces and human body is
undesirable, and prevented by means of insulation, which could be the non-
conductive sheet, or may include an additional layer of insulation material.
The garment may be made of a material that provides sufficient flexibility, is
compatible with human body and allows for electrode printing. An example of
such garment material may be neoprene. Thus, a system having all
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electrodes and traces within a single component minimizes any connectivity
losses, compatibility or dimensional tolerancing challenges.
[00201] Advantageously, these constructions have the ability to flex during
normal use of the garment when the fabric is stretched. To facilitate
stretching, the traces can be configured to have a curved/bent/waved
appearance, as shown with the traces 558 in the example configuration of the
neurostimulator 550 of Fig. 12. When the garment 552 is stretched, the
curved traces 558 can un-curve/un-bend so that the electrical continuity of
the
traces is maintained. This curved/bent/waved configuration of the electrical
traces can be implemented in any of the neurostimulators disclosed herein.
Method of automatic detection of sidedness of qarment on a human subject
[00202] According to another aspect of the invention, the neurostimulators
described herein can be configured to automatically detect the foot, i.e.,
right
or left, upon which the neurostimulator is worn. The neurostimulator is
configured to be worn on either foot. Regardless of the foot upon which the
neurostimulator is worn, the recording electrodes are positioned across the
foot in the manner shown in Fig. 13. The stimulating electrodes, however,
positioned on the ankle at the tibial nerve near the medial malleolus, are
positioned differently depending upon which foot, right or left, the
neurostimulator is worn.
[00203] Advantageously, since the recording electrodes 524, 554 extend
across the foot (see Fig. 13), there is no need to have recording electrodes
520, 550 that are specific to a left or right foot implementation. For the two
primary garment types disclosed herein (H-brace 520 - Fig. 11 and strap 550 -
Fig. 12), the stimulation electrode arrangements are mirror imaged so that the
neurostimulators can be worn on either foot. Specifically, the H-brace
neurostimulator 520 (Fig. 11) includes left stimulating electrodes 530 and
right
stimulating electrodes 532. When worn on the left foot, the left stimulating
electrodes 530 are positioned on the left ankle at the tibial nerve near the
medial malleolus. When worn on the right foot, the right stimulating
electrodes 532 are positioned on the right ankle at the tibial nerve near the
medial malleolus.
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[00204] The strap neurostimulator 550 (Fig. 12) can include a singular set of
stimulating electrodes 556. This is because the strap 552 is symmetrical and
can be flipped too position the stimulating electrodes 556 on the ankle at the
tibial nerve near the medial malleolus for the left or right foot. In this
scenario,
however, since the neurostimulator 550 is flipped, both the recording
electrodes 554 and the stimulation electrodes 556 are also flipped from front
to back and vice versa. Because of this, depending on the foot upon which the
foot is worn, the electrodes 554, 556 will be located on the front on one
foot,
and on the rear on the other foot. Similarly the stimulation electrodes 556
reverse polarity, such that the electrode that was cathode on one foot
becomes the anode on the other foot.
[00205] The neurostimulators 520, 550 are configured to record the evoked
muscle response to the activation of tibial nerve as a phase relationship (or
time delay) between the stimulation signal and the EMG response. When the
garment is moved from one foot to the other, this phase relationship is
altered,
thus providing a unique differentiator between the two feet. The phase
relationship is shown in Fig. 15. In Fig. 15, the average evoked response 3 ms
after a stimulation pulse is shown for two types of stimulation identified as
Type 1 and Type 2. Types 1 and 2 are simply the same stimulation pulse
applied on a different foot of the same subject. As shown in Fig. 15, the
evoked response from the stimulation pulse differs depending on the foot
upon which it is applied. Through clinical calibration, this phase
relationship
can be correlated with each foot, thus providing a unique identification of
which foot the garment is worn on. By programming the controller of the
neurostimulators 520, 550 with these unique identifications, the foot onto
which the neurostimulator is fitted can be determined automatically without
input from the user. This determination can be used to select the polarity of
the stimulating electrodes in the strap configuration of the neurostimulator
550, or can be used to select which set of stimulating electrodes - left 530
or
right 532 - to use.
[00206] In another configuration of the neurostimulator 520, 550, the need
to switch electrode polarity in response to the foot onto which the device is
fitted can be avoided. In this configuration, the neurostimulator 520, 550 can
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be configured to include redundancy in stimulation electrodes. For the H-
brace neurostimulator 520, the redundancy is shown in the left/right
electrodes 530, 532. For the strap neurostimulator 550, the redundancy can
be implemented by altering the pin configuration to selectively chose a pair
(or
group) of electrodes. To make this determination, the controller is configured
to alter the pin configuration of the neurostimulator to alter the measured
impedance between the stimulation electrodes. The left/right foot
determination is made by finding the impedance between the electrodes that
is indicative of the foot location. In one implementation, the expected
impedance can be about 5k-ohm.
[00207] In a further configuration, the spacing between the cathode and
anode may be deliberately made unequal between Left and Right side of the
garment. This will result in two differences. First, the overall feedback
signal,
including phase and amplitude, will be different because the response is
dependent on stimulation electrode configuration and spacing. Second, this
will cause the impedance between the two electrodes to be different. Either of
these values can be measured during the therapy session, and thus can then
be used to determine which foot of the subject.
A System of Providing Optimal Charge for Neurostimulation
[00208] As discussed previously, the neurostimulators 520, 550 have wide
therapeutic applications, such as pain management and bladder control.
According to these treatment methods, a known amount of charge is applied
through either a pair or multiplicity of electrodes attached to the subject's
body. Most systems determine the amount of charge using the amplitude of
the voltage or current applied, or through the duration of the pulse, or pulse
width, of the voltage of current applied. All these methods have limitations
in
terms of therapy range, energy usage and in accounting for different patient
sensation or anatomical response.
[00209] According to another feature, the neurostimulators 520, 550 can be
configured to control the application of stimulation therapy in a manner that
compare the amplitude of the stimulation signal to the pulse width, to provide
a optimal combination of therapy, energy use, patient sensation and ease of
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use. This can be implemented in both closed-loop, with where stimulation is
modulated based on an evoked electrical response, or in open-loop where no
response is recorded. Also, the neurostimulators 520, 550 can be configured
for current-control or voltage-control. Because of this, it should be
understood
that, when the term 'stimulation signal' is used herein, it can be associated
with electric current or voltage.
[00210] In one example configuration, a method for determining optimal
charge for neurostimulation involves applying stimulation within a range of
pulse widths that are defined by both the subject's tolerance as well as the
threshold for evoking a response. This is shown in Fig. 16. In this example, a
closed-loop current-controlled system adjusts the pulse width up or down
based on the EMG response feedback signal measured via the recording
electrodes. The upper bound of the pulse width can be defined at or near the
patient's tolerance limit, as shown by the solid dicsonnfort line shown in
Fig.
16. The lower bound of the pulse width can be defined at or near the
threshold for evoked response. In the example of Fig. 16, the target therapy
is
determined at a certain point, between these two parameters, such as the
midpoint, and the therapeutic range is determined to be a fraction of the
target
therapy level, as indicated generally by the bracket in Fig. 16.
[00211] After the initiation of therapy and over the course of time, a need to
change the therapeutic regime can arise, this can result, for example, from a
patient's tolerance changing over time, device characteristics changing over
time, or the body's response changing as a result of therapy. Accordingly, the
applied current amplitude can be adjusted and a new corresponding range of
pulse width defined. This is shown in the example of Fig. 17. As shown in Fig.
17, as an example, patient discomfort and detection thresholds may define an
initial current of 20 nnA (shown at A) with a corresponding range of pulse
widths. Over time, however, for one or more of the reasons set forth above, a
higher stimulation charge may be desired. Accordingly, for example, the
current amplitude can be manually increased to 30 mA (shown at B), defining
a correspondingly new operating range for the pulse width. The difference
between the curves in Fig. 17 define between them a region that defines a
range of stimulation strength-duration curve for a sample subject.
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[00212] As another example configuration, stimulation can be executed
within an operating zone defined by a range of pulse widths and range of
current amplitudes. This is shown in Fig. 18. As shown in Fig. 18, these
ranges are illustrated by the shaded region R, which defines the operating
parameters, pulse width and current amplitude, according to which stimulation
therapy is executed. Operating within the defined range allows the controller
to adjust both the current amplitude and pulse width individually or
simultaneously. The controller can operate in closed-loop mode using EMG
feedback to modulate the current and pulse width, as described previously.
Alternatively, the controller can operate in closed-loop mode using
stimulation
energy as the feedback, with the tolerance limits of the subject being used to
help determine setpoints for the energy, and the stimulation output is
modulated to maintain that energy level setpoint. These parameters, Le.,
tolerance limits and corresponding energy setpoints, can be defined during
the initial calibration, and they system makes the decisions on the current
amplitude and pulse width based on this calibration, while delivering the
desired stimulation charge.
Providing optimal therapeutic control parameters for neurostimulation, based
on patient's motor and neural response.
[00213] Stimulation of nerves has wide therapeutic applications, such as
pain management or bladder control. For best possible patient outcomes, it is
important to determine the optimal stimulation parameters that provide
therapeutic benefits, while ensuring no patient discomfort that could lead to
non-compliance. Accordingly, a method for determining these optimal
stimulation parameters utilizes multiple factors, including patients' muscle
and
sensory responses. According to the method, the therapy target is based on
the individual patient's response induced by the stimulation, therapeutic
needs
and tolerance threshold, while at the same time ensuring the therapeutic
window never extends beyond any of these limits.
[00214] According to this method, the closed-loop system is employed that
detects and quantifies the stimulation evoked response, such as EMG or
nerve response, when a stimulation is applied. The lower threshold of
therapeutic window is defined at the level at which the evoked response is
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detected. This is based on two factors, one being a physical confirmation of
recruitment of the corresponding nerve to ensure system operates as
intended, and second being the ability to continuously adjust the stim based
on the evoked response. The upper threshold is defined by the sensory
feedback, or at a level that a patient can comfortably tolerate for a duration
of
a typical therapy session.
[00215] The upper (discomfort) and lower (detection) thresholds define the
operating range and also define the optimal stimulation therapy that is
targeted for a specific patient. This patient-specific target therapy is
linearly
interpolated between the upper and lower thresholds in a manner that is
determined by the clinical need for a certain indication. Examples of these
interpolated target therapy ranges are illustrated in Figs. 19A-19C. Referring
to Figs. 19A and 19B, stimulation current is constant at 20 mA with the pulse
width being modulated to apply therapy between the discomfort and detection
thresholds. In this example, the linear interpolation can be at the midpoint,
such that low end of the stimulation pulse width range is at 50% of the range
and the upper end is at 75% of the range. Comparing Figs. 19A and 19B, it
can be seen that the detection and discomfort thresholds, which are patient-
specific, determine the upper and lower limits of the 50-75% pulse width
range. While this example illustrates a 25% range, alternative ranges, higher
or lower, can be implemented.
[00216] Alternative ranges can be selected, for example, to increase the
system output. To achieve this, the lower limit can, be defined at a higher
percentage of the range, such as 75% of the range. In this example, the upper
range can be set accordingly, such as at 85-90%. As shown in Fig. 19C, it can
be seen that the stimulation current also can affect the upper and lower
limits
of the 50-75% pulse width range. Increasing the current moves the range to
the right, as shown in Fig. 19C, where the threshold curves have reduced
pulse widths. The pulse width range is therefore reduced accordingly at this
higher stimulation current.
[00217] The examples of Figs. 19A-19C utilize variable pulse width at a
fixed current amplitude. Alternatively, a range determination may be made for
systems that use a fixed pulse width and variable current amplitude.
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Furthermore, a system can comprise of a combination of variable current and
pulse width, for example to optimize power consumption, and a target may
similarly be obtained based on the amount of charge applied through
stimulation.
[00218] Figs. 20 and 21 illustrate two different methods by which the target
stimulation is determined. According to the method 600 of Fig. 20, at step
602, stimulation is ramped up, Le., the pulse width is increased at a constant
current amplitude. At step 604, the detection stimulation level (Le., where a
response, such as EMG, is detected) is determined. At step 606, the
discomfort stimulation level (Le., where the subject experiences discomfort)
is
determined. Next, at step 608, the stimulation output is determined via
interpolation. At step 610, the evoked response (EMG) for the stimulation
output determined at step 608 is measured to determine the target evoked
response that is implemented when applying therapy with closed-loop control.
[00219] According to the method 620 of Fig. 21, the evoked response itself
may be computed at the two threshold values, and the target evoked
response is interpolated based on the two thresholds of evoked response. At
step 622, stimulation is ramped up, i.e., the pulse width is increased at a
constant current amplitude. At step 624, the evoked response (e.g., EMG) is
measured at the detection threshold. At step 626, the evoked response (e.g.,
EMG) is measured at the comfort threshold. At step 628, the target therapy is
determined by interpolating between the evoked responses determined at
steps 624 and 626.
System and method for real-time biological responses feedback based neural
stimulation control.
[00220] Fig. 22 illustrates a process or method 660 by which to control the
application of stimulation therapy. The method 660 can, for example, be
implemented with any of the neurostimulator configurations disclosed herein,
and can be used to treat any condition or disorder treatable with neural
stimulation, such as overactive bladder disorder. While neural stimulation can
elicit useful biological responses, some of the evoked biological responses do
not share a linear relationship with the provided stimulus. Accordingly, the
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method 660 implements an algorithm for utilizing the presence and strength of
the evoked biological responses, respectively, to control the input stimulus
during delivery of therapy.
[00221] The method 660 addresses the nonlinearity of the evoked biological
responses makes it difficult to use as feedback for controlling for a neural
stimulation device. Implementing the method 660, the neurostimulator is
adapted to provide effective feedback control during neural stimulation with
or
without a presence of a biological response. This helps maximize the therapy
during application of neural stimulation. The methods 660 utilizes the
presence of an evoked biological response, the strength of the evoked
response, and voluntary input from the user/subject/patient to modulate the
control signal in a closed-loop stimulation application.
[00222] Biological responses are not always linear with provided
stimulation: higher stimulation doesn't always generate higher biological
responses. "Biological responses," as used herein, refers to any stimulation
evoked biological change, i.e., physiological signals, biochemical responses
in
the body, biomechanical responses, etc. Accordingly, the algorithms
implemented by the method 660 should treat the presence of the biological
responses, and the strength of the biological responses separately, and
according to the general guidelines:
= No biological response - Open loop stimulation control within
the tolerable stimulation range.
= Biological response evoked - Use the frequency of response
appearance within a predefined time window as the therapy
level, i.e., within a 1 second time window. The appearance of
the evoked biological responses should be at least 50%
among all the stimulus delivered.
= Biological response evoked - Identify the presence of the
response, calculate the strength of the response, set x%
(include 0%) higher of this strength level as the default
therapy level. Patient or physician can set new strength level
as the therapy level as needed.
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= Combine multiple types of biological responses.
[00223] Based on the user/subject/patient subjective feelings, voluntary
input to control the delivery of neural stimulation can be given, i.e.:
= Intentional voluntary input:
- User input commands through a device hardware interface
or software application, i.e. a physical button pressing on the
device, or command input from the app.
- a voice command.
= Unintentional voluntary input:
- User voluntarily generate artifact, noise or voluntary
biological response (e.g. from wincing in pain) that manifests
in the recording sensors.
- User voluntary verbal response (e.g., shout, scream) of the
unpleasant stimulation. The device recognize its using its
built-in microphone and voice recognition technology.
[00224] Fig. 22 illustrates a high level flow chart to show that illustrates
the
method 660, which functions according to the principles described above. The
algorithm implemented by the method 660 is based on the appearance and/or
strength of the biological response to the application of stimulation signals.
The method 660 uses the appearance and strength of these biological
responses as control features in applying closed-loop neurostimulation.
[00225] The method 660 can be implemented by a neurostimulator, which
applies stimulation therapy via one or more stimulation electrodes, and
monitors a biological response, such as an EMG response, via one or more
receiving electrodes. The method 660 can, for example, be implemented in
any of the neurostimulators disclosed herein.
[00226] At step 664, stimulation therapy is delivered via a neurostimulator.
At step 666, a determination is made as to whether a response, such as an
EMG response, is detected. If no response is detected, the method 660
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proceeds to step 662, where the neurostimulation is delivered in open-loop
control, i.e., without feedback. The method 660 reverts back to step 664,
where stimulation therapy is delivered, and continues to step 666 to determine
whether a response is detected. As long as there is no detected response to
the stimulation, the method 660 continues to deliver stimulation therapy under
open-loop control.
[00227] At step 666, if a response, such as an EMG response, to the
stimulation is detected, the method 660 proceeds to step 668, where the
response detection rate is calculated, then to step 670 where the control
regime is determined based on the detection rate. The control regime can be
response appearance control, response strength control, or response
appearance + strength control. Under response appearance control, the
method 660 proceeds from step 670 to step 672 where a determination is
made as to the response detection rate that will be the setpoint for closed-
loop control. The method 660 proceeds to step 674 where closed-loop control
of the stimulation is performed to maintain the X% of the detection rate
determined in step 672, where X can be 100 or less. Stimulation parameters,
i.e., current amplitude and/or pulse width, are modulated to maintain the
detection rate identified in step 672.
[00228] Under response strength control, the method 660 proceeds from
step 670 to step 680, where a response strength setpoint is calculated. This
setpoint is used for closed-loop control. The method 660 proceeds to step 682
where closed-loop control of the stimulation is performed to maintain the
response strength at a certain level, Z% greater than the response strength
setpoint calculated in step 672, where Z can be zero or greater. Stimulation
parameters, i.e., current amplitude and/or pulse width, are modulated to
maintain the response strength at the setpoint.
[00229] Under response appearance + strength control, the method 660
proceeds from step 670 to step 676, where Y% of the response detection rate
is determined as the minimum detection threshold, where y can be 100 or
less. At step 678, the minimum detection threshold is used as a setpoint to
maintain Y% of the response detection rate under closed-loop stimulation
control. The method 660 proceeds to step 680, where a response strength
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setpoint is calculated. This setpoint is implemented in closed-loop
stimulation
control at step 682, where the control is performed to maintain the response
strength at the certain level, Z% greater than the response strength setpoint
calculated in step 672, where Z can be zero or greater. Thus, under the
response appearance + strength control scheme, stimulation is modulated
under closed-loop control to maintain both a response detection rate and a
response strength.
Use of informatics for improvina stimulation therapy and patient outcomes
[00230] Referring to Fig. 23, the system can implement a method 640 by
which the neurostimulator can be used to provide information that is used to
improve stimulation therapy and patient outcomes. According to the method
640, the neurostimulator records information at step 642 and provides this
information wirelessly, e.g., via Bluetooth 644, to a patient controller, such
as
a smartphone or tablet. The information/data is then transmitted via Wi-Fi 648
(local and/or cellular/LTE) and stored on the cloud/server 650. From there,
data analysis and informatics are used to determine optimized therapy 652.
[00231] The data used at step 652 can be recorded stimulation history, the
elicited muscle responses, and the effect the stimulation had on the patient.
For example, an overactive bladder patient can use the controller to record a
bladder diary that forms a portion of the information/data at step 646. As
such,
the data transmitted to the cloud/server 650 can include a real-time
stimulation history or a quantitative summary of each therapy session.
[00232] Once this information is uploaded and available, a portal uses
informatics to correlate the three main characteristics: the stimulation
profile
(e.g., current amplitudes, voltages, pulse profiles), the feedback history
(e.g.,
EMG data), and the patient diaries. The algorithms implemented at the
informatics stage 652 use this data to assess the effect of stimulation on the
feedback signal and system efficiency. As this data is collected over a larger
period of time and over a larger population of patients, it can be used for
monitoring patient compliance, usability and efficacy. This information can be
used to optimize therapy for each individual patient and thus improving
patient
outcomes.
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[00233] While aspects of this disclosure have been particularly shown and
described with reference to the example aspects above, it will be understood
by those of ordinary skill in the art that various additional aspects may be
contemplated. A device or method incorporating any of the features described
herein should be understood to fall under the scope of this disclosure as
determined based upon the claims below and any equivalents thereof. Other
aspects, objects, and advantages can be obtained from a study of the
drawings, the disclosure, and the appended claims.
