Note: Descriptions are shown in the official language in which they were submitted.
-~92~093~ PCT~US90~
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STr~L~TOR FOR SURFACE STn~ATION IN P~LY~ PATI~
Technical Fi~ld
This invention relates to functional electrical
stimulation (FES) of paraplegics and more particularly
to an improved microcomputer controlled apparatus and
methodology.
Back~round Art
Work on functional electrical stimulation of
paraplegics is based on the discovery of the Italian
physiologist Luigi Galvani in the late 18th century
that a muscle will contract when in contact with an
electrical charge. This has been first applied
systematically to paralyzed patients by W. Liberson in
1960 (in W. Liberson et al., Arch. Phys. Med. Rehab.,
Vol. 42, p. 101, 1961). Since then considerable work
has been devoted to that topic, as reviewed by Graupe
et al. (J. Biomed Eng. Vol. 5, pp. 220-226, July
1983), by Graupe et al. (Critical Reviews in
Biomedical Engineering, CRC Press, Vol. 15, pp. 187-
210, 1988) and in a recent text by A. Kralj and T.
Bajd ("Functional Electrical Stimulation: Standing
and Walking after Spinal Cord Injury", CRC Press, Boca
Raton, FL, 1989).
It was thus shown that the application of trains
of pulses of adequate amplitude, pulse-width and
pulse-repetition-frequency at appropriate locations
above the region of certain key muscle, enables
paraplegic patients with complete or near-complete
upper-motor-neuron lesions to stand up and to take
steps with the support of parallel bars or a walker.
The merits of such standing and of the primitive
walking accomplished by these steps is both
psychological and physiological in the exercise
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W092/~3~ PCT/US90/OU~
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provided to the patient which enhances circulation,
cardiac output and movement of joints to prevent or
slow down ossification and contractures (Kralj and
Bajd, "Functional Electrical Stimulation: Standing
and Wal~ing after Spinal Cord Injury," CRC Press, Boca
Raton, FL, 1989, pp. 33, 68, 130-131). Furthermore,
there are indications (not yet fully proven due to the
limited application of FES which is presently
available only in research labs and research clinics),
that FES is beneficial in prevention or reduction of
incidence of pressure sores and of osteoporosis (~rajl
and Bajd, same as above, pp. 8, 33, 49, 69, 131 and
135) and in the reduction of severity of spasticity
(Krajl and Bajd, same as above, pp. 3, 8, 37-47). FES
is limited to upper-motor neuron lesions since in that
case the peripheral nerves (at the lower extremities,
in our case) are intact though they cannot communicate
with the central nervous system due to the spinal-
cord lesion. However, since the peripheral nerves are
healthy and intact, they respond to FES even after
many years of paralysis without stimùlation. In two
patients, after 35 years of paralysis and with no
stimulation over that whole time, the peripheral
nerves responded to FES fully satisfactorily.
Disolosure Of Invention
In accordance with one aspect of the present
invention, the present system provides non-invasive
electrical stimulation for paralyzed patients with
upper-motor-neuron lesions so as to provide
capabilities for unbraced standing and walking. In a
preferred embodiment, only a single pulse power and
amplitude amplifier of stimulation pulses is utilized,
in contrast to the multiple pulse amplifiers that are
presently used ~usually one per stimulation channel),
noting that systems using multiple pulse-amplifiers
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require relatively heavy and cumbersome hardware,
since, for patient walking purposes, a multitude of
output-stimulus pulse channels (four at least) are
required.
The use of a single pulse-amplifier for multiple
channel stimulation is achieved in the present
invention by the use of a microprocessor
(microcomputer) controller system that provides output
channel multiplexing and which also generates stimuli
pulses and controls pulse-width, pulse-amplitude,
pulse-repetition-frequency and which provides warning
(preferably audible) to the patient when the system
saturates. As an example, the system provides warning
when muscle fatigue is such that no further increase
in pulse-amplitude is possible to combat the fatigue
(i.e. to recruit further muscle fibers not reached by
the present electrical fields produced by the
stimuli), due to reaching maximal predetermined pulse
levels.
In accordance with another aspect of the present
invention, the system provides the combination of
multiplexing and of complete microprocessor -
(microcomputer) control including microprocessor
controlled warning and microprocessor-controlled
provisions of fail-save features. The warning aspect
is of major importance since the patient, ~eing
paralyzed, cannot feel muscle fatigue. The warning is
determined responsive to computerized sensing of the
appropriate control input levels, which the patient
sends, such as through activating manual finger-
switches attached to the walker, as control inputs to
the microprocessor controller, to increase the level
of the stimuli when he senses, via pressure in his
arms (which hold the support of the walker,) that he
needs higher such levels. Alternatively, the control
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inputs can be automatically generated from feedback
signals derived from the patient (such as via sensing
electrodes).
The significance of the provision of fail-save
features for situations where certain major system
failures occur is important, since the system is
designated for use by paralyzed persons who have no
sensation at their lower extremities. These persons
depend on these stimulator~s safety features, and the
above failures without fail-safe features, may cause
them to fall, noting that it is of utmost importance
to prevent falls.
In accordance with another aspect of the present
invention, directed to the safety feature of
preventing falls, the system provides an increased
level of stimulus to the standing remaining quad for
the duration of a step by the other leg during each
step, by a predetermined increase level value. This
provides a safety mechanism to prevent possible falls
of a patient while taking a step. When taking a step,
all of the patient's weight is on the leg not
stepping, the stepping leg being in the air (being
moved to produce a step). The computing portion of
the system determines both when to take the step, and
at the appropriate time of taking the step, increases
the stimulus to the remaining guad by between ten and
twenty percent above the ten steady state level.
-In accordance with another aspect of the present
invention, solid state cascaded voltage-doublers are
used, instead of the heavier pulse-transformers, for
the purpose of stimuli pulse-generation. Another
innovative aspect of the présent invention is the
employment of a telemetry link between the walker-
mounted patient-operated switches and the stimulator
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itself, to avoid the employment of wires between
walker and the usually patient-borne stimulator.
In accordance with yet another aspect of this
invention, in order to avoid high voltage at channel
outputs under no-load conditions, the output of the
- pulse-amplifier circuit may be connected to a voltage-
sensitive load, such as a fast ZNR transient surge
resistor (e.g. a zinc-oxide nonlinear resistor device)
in series with an appropriate load resistor, such that
the output channels to the stimulation electrodes,
that are attached to the patient, will be loaded by a
resistance of no more than a few thousand ohms if the
output of the pulse-generator circuit (e.g. pulse-
transformer) exceeds some predetermined voltage (such
as in the range of 50 to 130 volts).
In accordance with another aspect of this
invention, opto-isolators are coupled from the output
of the channel outputs and to the electrodes, so as to
provide isolation of the various output channels, so
as to avoid back current from feeding back into the
microprocessor and other circuitry, and so as to
isolate the various output channels to prevent cross-
talk.
In accordance with another aspect of this
invention, any command to activate a "sit-down" mode
(in order to stop stimulation when the patient wishes
to sit-down), may be overridden by pressing of any
command switch, to avoid that the patient may fall if
inadvertently activating the "sit-down" co~mand.
Also, when the "sit-down" command switch is pressed,
the sit-down function which under the present
invention implies gradual cessation of stimulation to
the patient's quadriceps muscles, will be delayed
under an aspect of this invention in its execution of
this gradual reduction of stimuli to zero by a
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predetermined number of seconds, (e.g. 5 to 12
seconds). Furthermore, under again another aspect of
this invention, the activation of the sit-down command
will immediately give the patient a warning signal
which may be a flashing light on the walker to
indicate to the patient that the "sit-down" function
has been initiated.
Additional safety features are also associated
with the "sit-down" mode. First, since the computer
is determining when to take steps, it can time events
precisely. As one additional safety feature, when
going to a sit-down mode, the system increases
stimulus level to both the right and left quadriceps
muscles via the electrodes for attachment thereto,
thus giving extra support to the quads for sitting,
since the person may already be fatigued at this point
where they are ready to sit-down. The increase in
level is in the range of ten to 20%.
In accordance with another aspect of the present
invention, the system measures its own output current
between the multiplexer and the electrodes (or
alternatively it can measure the voltage drop over a
fixed impedance at that location) and couples the
measurement value back to its input for determination
of whe~ther the output current (or voltage) drop is
below a predefined threshold. The predefined
threshold, in a preferred embodiment, is approximately
50% of the lowest output level to any electrode.
Alternatively, by trial and error, other thresholds
can be chosen. If there is a drop below this
predefined threshold, this implies that enough current
is not being output to some channel (or channels),
i.e. such as an electrode is loose or disconnected.
The computing unit of the apparatus then provides an
audible sound alarm and/or visual alarm for the
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user/patient, and disallows any step, but maintains
the patient in a standing mode (at least on one leg
since during a step one leg is in the air). If the
other leg happens to be the one disconnected (the one
being stood on is the one where the electrode
disconnects), the patient will fall, except as self-
supported by his/her arms on a walker unit.
In describing use of this system for upper-
motor-neuron paraplegics, noting that this invention -
is concerned with standing and walking by such
paraplegics implies limitation of the system to
patients whose spinal cord lesion is virtually at the
thoracic T12 level or higher ~approximately above the
belt level). The functions and features as discussed
above and their combination in the manners discussed
above are essential and unique for applications to
standing and walking by paralyzed patients. This
constitutes a major and essential difference from any
stimulator for pain relief or for exercise of muscle
where no walking is intended to be stimulated and
controlled.
~rief Description Of Drawinas
The present invention may be better understood by
reference to the written specification in conjunction
with the drawings, wherein:
Fig. 1 is an electronic schematic block diagram
of one embodiment of an FES Stimulation System in
accordance with the present invention; `
Fig. 2A shows the complete system with walker,
patient and FES stimulator box;
Fig. 2B shows a side view of Fig. 2A;
Fig. 2C shows a top view of the walker of Figs.
2A-B;
Fig. 2D shows a perspective view of the walker of
Figs. 2A-C;
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Fig. 3 illustrates one embodiment of the walker
mounted switch control unit;
Fig. 4 illustrates the voltage pulse waveform for
a typical FES system pulse output;
Figs. 5A-D provide voltage vs. time waveforms
illustrating the envelope of pulses as distributed to
four channels during FES activated walking;
Fig. 6 illustrates an electrical block diagram
for a specific alternate embodiment of a FES
stimulator box;
Fig. 7A shows the stimulus level plotted
vertically versus time plotted horizontally for the
right quadriceps muscle;
Fig. 7B illustrates the stimulus level versus
time for the left quadriceps;
Fig. 8A and 8B illustrate stimulus level versus
time waveforms for the right quadriceps (Fig. 8) and
left quadriceps (Fig. 8B);
Figs. 8C and 8D illustrate step occurrence versus
time waveforms for step right (Fig. 8C) and step left
(Fig. 8D); and,
Fig. 9 is an electrical schematic block diagram
illustrating the output level detect safety subsystem
of the present invention.
Mod- For Carrving Out The Invention
The FES stimulation device under this invention
is a system as in Fig. 1, that comprises of an FES
stimulation box 100 that is battery-operated 111,
using AA or AAA 1.5 volt batteries or similar
batteries, and which includes a stimuli pulse-
generator 103, a microprocessor-control circuit 104
and related interface and which has a control panel
107 of pressure switches on its cover.
The same stimulator box 100 also houses the
telemetry (ultrasound or radio frequency, or infra-
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red) receiver in realizations of the invention where
telemetry is employed. Alternatively, connector
interface circuitry can be provided for non-telemetry
applications. It may also house the audible warning
element 108, and may house a low-battery voltage
indicator 109 and/or a low-battery visual 110 or
audible warning 108 and a display of stimuli levels
that is activated to show the level of a given channel
when the appropriate control switch is activated by
the user. The stimulation box 100 is connected on its
input side 121 to walker-mounted hand (finger)
switches (switching unit) 101 and on its output side
124 to the stimulation surface electrodes 102 attached
to the patient. The complete system with a patient is
shown in Fig. 2A.
Referring to Fig. 2A, paraplegic user 99 is shown
supporting himself with his arms, and by use of the
present FES system, with a walker 98 having finger
switches control unit 101 mounted thereto, and the FES
stimulator box 100 affixed to his belt.
Fig. 2~ illustrates a side view of Fig. 2A.
Fig. 2C illustrates a top view of the walker 98,
while Fig. 2D provides a perspective view of the
walker 98 and finger switches control unit 101. The
walker 98 is preferably constructed of aluminum pipe,
of from 1/2" to 1-1/2" diameter, ergonomically
determined, but typically 1/2" or 3/4".
The switching unit 101 that is mounted on the
handles of the walker 98 as illustrated in Fig. 2A, is
divided into two sub-units, interconnected by wire,
one on the right hand side hand-bar and one on the
left-hand side hand-bar. The walker should preferably
be a reciprocating walker, using aluminum tubing of
approximately 1 inch diameter.
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As illustrated in Fig. 3, the right hand-side
walker-mounted switching sub-unit consists of an
"ontoff" switch 131 for stand-up and sit-down, and of
a switch 132 for activating a right step and of a
switch 133 for increasing the stimulation level for
both the stimulus to the right region of the
quadriceps muscles (for strengthening right quadriceps
muscle contractions in standing) and for the stimulus
to the right peroneal nerve (for the right step), and
where a short duration pressing of that switch
increases the stimuli level to the quadriceps and a
substantially longer such duration increases it for
the right step. The left hand-side switching sub-
unit includes a "sit-down~ switch 134, such that the
sit-down function is activated only when both the left
"on/off" switch 131 and the right "off", (namely "sit
down") switch 134 are simultaneously pressed, whereas
standing reguires pressing the right "on/off" switch
131 alone, and where one must start pressing the left
"off" switch 134 before pressing the right "on/off"
switch 13i and continue pressing it until after
releasing the right switch 131. The left hand-side
sub-unit also includes a left step switch 135 and a
level increase switch 136 that again serves to both
increase level of left quadriceps and of left step
stimuli. Thus, there are 3 switches on each sub unit
as illustrated in Fig. 3.
As illustrated in Figs. 1-3, the switching unit
101 is connected for use with an ultrasound
transmitter which via a coding circuit, both mounted
on the walker, transmit the appropriate codes to the
stimulator box. The codes as illustrated herein are:
(i) stand-up : press switch 131.
(ii) right step : press 132.
(iii) left step : press 135.
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(iv) sit-down : press 131 and 134 simultaneously.
(v) increase stimulation to right quads
(quadriceps) : press 133 (short duration).
(vi) increase stimulation to left quads
(quadriceps) : press 136 (short duration).
(vii) increase stimulation for right step : press
133 (long duration).
(viii) increase stimulation for left step : press
136 (long duration).
This ultra-sound communication link coding
circuit and transmitter, together with the appropriate
receiver 140 mounted in the stimulation box 100
constitute the communications link of 121 of Fig. 1.
The receiver 140 couples the received coded signal for
input to the microprocessor circuit 104 where this
input is decoded to determine which command is being
sent from the input commands (i) to (viii) above. In
an alternate embodiment, a wire link substitutes this
coded ultrasound link as link 121 above. Switch 131
can be omitted in some realizations or could serve
only for stand-up purposes. In these cases, sit-down
is activated by a long duration activation of switch
134 alone, which could be located at the right or left
sub-unit with the "stand-up" switch, if employed,
being located at the opposite sub-unit.
In addition, in either realization, inputs (i) to
(viii) can alternatively be inputted from the
stimulator-mounted switching control panel 107 where,
additionally, four further inputs can be generated.
These inputs are as follows:
(ix) decrease stimulation to right quads
(x) decrease stimulation to left quads
(xi) decrease stimulation to right step
(xii) decrease stimulation to left step.
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However, on this panel 107 each function (i) to
(xii) may have its own switch. In a realization where
the region of the gluteus maximus muscles are
stimulated, then any of the above functions relating
to a step should be considered as functions relating
to the gluteus maximus of the same side (right or
left), since it is considered that persons with a
relatively unstable trunk who require stimulation of
the gluteus maximus are not supposed to walk with the
present system. In cases of minor trunk instability,
a corsette may be worn by the patient, and walking may
be executed without stimulating the gluteus maximus if ~-
approved by a medical practitioner.
The microprocessor control circuit of 104 has
further inputs 123 via internal adjustment circuit 112
which includes a set of pins where applied voltages
are input as (4) commands to adjust pulse rate, pulse
duration (width), maximal stimuli levels, and can ~-
additionally be used to adjust duration of ramp-like
envelopes of stimuli amplitudes that are employed at
the initialization of stand-up and/or at the end of
sit-down, these ramps being a gradual initial-
increase/final decrease of stimuli amplitudes, to
avoid a too sudden start/cessation of contraction in
stand-up/sit-down. For stand-up, a certain overshoot-
at the end of the ramps is possible, to provide
contraction force for standing-up that is above the
force required otherwise for standing, noting the
energy required to stand-up from a sitting position.
The microprocessor 104 generates pulse trains and
controls at its output 124 the pulse characteristics
according to the inputs from 112 and from the switch-
inputted functions concerned with stimuli level which - ;
may either modify pulse duration or pulse amplitude.
All these are outputted through 125 to the pulse and
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amplitude amplifier 103 whose output is multiplexed in
response to the control as determined by
microprocessor 104, and which serves to provide
stimuli for all functions (stand, right step, left
- step). The pulse amplifier 103 is controlled
responsive to the microprocessor via link 126 to
output these pulses through the distribution interface
circuit 105 as determined by the processor 104
according to the input switches of 101 or of 107. The
circuit 105 thus couples the stimuli to the various
skin surface electrodes (2) that are attached with
tape to the skin at the appropriate stimulation
locations as discussed above. Note that components
103, 104, 105, 107 and 117 are all mounted on the
stimulator box 100.
In accordance with another aspect of this
invention, opto-isolators are coupled from the output
of the channel outputs and to the electrodes, so as to
provide isolation of the various output channels, so
as to avoid back current from feeding back into the
microprocessor and other circuitry, and so as to
isolate the various output channels to prevent cross-
talk.
Opto-isolators as available from many of the
co~mercial manufacturers of opto-isolators can be
utilized, including those from Texas Instruments,
Hewlett-Packard, and many, many others.
Opto-isolators 205 are illustrated in both Figs.
1 and 6. ~he optoisolators 205 are shown in dashed
form in both Figs. 1 and 6, since they may optionally
be included or not included depending upon design
criteria. In the preferred embodiment, the opto-
isolators 20S are included, having inputs coupled from
the channel distribution and multiplexing circuitry
105, and optically isolating, amplifying and coupling
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to the surface electrode array 102, being adapted for
coupling to connectors which are coupled to cables
coupled to the electrodes. Similarly, for Fig. 6, the
opto-isolators 205 are shown as coupling between the
electrode multiple interface unit 105C outputs and
providing opto-isolation to and from the skin
electrodes on the patient.
The stimuli levels are computed by counting the
number of times the appropriate switches are pressed,
so that each time an appropriate switch is pressed,
the stimuli level at the corresponding channel is
increased by a predetermined increment.
The pulse amplifier 103 can consist of a single
pulse transformer or, alternatively, of a single solid
state cascade of voltage doublers to output a train of
pulses which may all be positive or all negative, or
may have a positive component followed immediately by
a negative component (or vice versa) as illustrated in
Fig. 4. When quads and steps are stimulated then the
pulse-rate is set by microprocessor 104 at
approximately 48 pulses per second which is
multiplexed at the pulse amplifier's output responsive
to microprocessor 104 into 2 channels, each having a
rate of 24 pulses per second. If the gluteus maximus
and the quads are stimulated, then no step is
activated, and the pulse rate is 96 pulses per second
divided into 4 channels each having a rate of 24
pulses per second responsive to the microprocessor
~04.
The distribution of the stimuli as determined by
microprocessor 104 is shown in Figs. 5A-D, showing the
envelopes of stimuli pulse trains for stand and sit-
down functions as applied to Right Quads (Fig. 5A) and
Left Quads (Fig. 5C), and to the right and left
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peroneal nerves for activating. Right Step (Fig. 5B)
and Left step (Fig. 5D).
In addition, microprocessor circuit 104 computes
the actual stimulus level per a given function and
outputs via 128 to display circuit 106. Display
circuit 106 can be an LED light-bar display, or
alternatively a numerical read-out display. The
display can be mounted on the stimulator box 100.
The microprocessor 104 also determines when the
quads' stimulus level at any one of the two quads
reaches a level close to the maximal level, as
determined by 104 responsive to the inputs via 112, -
and then activates an audible alarm 108 to warn the
patient that he cannot increase the level any further.
This aspect is important since the patient has no
sensation at the quads and cannot determine the degree
of fatigue at the stimulated muscle. When walking
with the FES system of the present invention, the
patients~ arms carry only 2% to 5% of his body weight
according to measurements, whereas his stimulated leg
muscles carry 95~ to 98%. Whenever the patient feels
that his arms which support him on the walker carry
increased weight, he will tend to increase quads ~ -
stimuli levels at the appropriate arm side. However,
when he reaches the maximum level he must be given
time to sit down (possibly, to go to a chair). Hence,
the alarm of 108 is to be activated in sufficient time
before that complete fatigue level is reached, this
level being also adjustable by processor 104
responsive to inputs at 112. The audible alarm can be
mounted on the stimulator box 100.
The microprocessor circuit 104 also computes
fail-safe provisions to: (i) guarantee that a step
can be taken only at one leg at a time; (ii)
guarantees that, if no input is received from the -;
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walker mounted switches 101 or from the panel switches
107 on the stimulator box 100, concerning commands to
one leg or to both, then the patient will always be or
remain in the ~'stand~ (both quads "on") mode, to
guarantee that with a failure in link 121 or 122, be
it an acoustic, IR, radio frequency or wire link or
transmitter or receiver failure, that the patient will
remain standing and will not fall ~and, of course, he
still has the walker support); (iii) guarantees that
after every step the system automatically returns to
the "stand~ mode (of both quads being stimulated), and
in certain realizations the microprocessor 104 also
computes a fail-safe provision that a step is limited
in time so that even if a step switch is stuck in the
"step" mode, then after a predetermined reasonable
time (of the order of a second) the concerned leg is
returned to "stand" (quads) mode by an appropriate
microprocessor-controlled decision and channel
switching. In certain realizations the latter
situation also provides for an appropriate warning
signaI, audible or visible or both, to alert the
patient to that faulty situation.
Additional safety features are ;41so associated
with the "sit-down" mode. First, since the computer
is determining when to take steps,- it can time events
precisely. As one additional safety feature, when
going to a sit-down mode, the system increases
stimulus level to both the right and left quadriceps
muscles via the electrodes for attachment thereto,
thus giving extra support to the quads for sitting,
since the person may already be fatigued at this point
where they are ready to sit-down. The increase in
level is in the range of ten to twenty percent (10% -
20%).
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Referring to Figs. 7A-B, Fig. 7A shows the
stimulus level plotted vertically versus time plotted
horizontally for the right quadriceps muscle, and Fig.
7B illustrates the stimulus level versus time for the
left quadriceps muscle. Note that at the time
indicated, TSD indicating the time of the sit-down
command from the standing position as received and
recognized by the computer, that the stimulus levels
to both the right and left quadriceps muscles are
increased, by between ten to twenty percent
preferably, for a short time duration (on the order
of seconds) prior to decreasing the stimulus level by
ramping the level of the stimulus signals to the right
and left quadriceps to the zero level of full sitting.
In accordance with another aspect of the present -
invention, directed to the safety feature of
preventing falls, the system provides an increased
level of stimulus to the standing remaining quad for
the duration of a step by the other leg during each
step, by a predetermined increase level value. This
provides a safety mechanism to prevent possible falls
of a patient while taking a step. When taking a step,
all of the patient's weight is on the leg not
stepping, the stepping leg being in the air (being
moved to produce a step). The computing portion of
the system determines both when to take the step, and
at the appropriate time of taking the step, increases
the stimulus to the remaining quad by between ten and
twenty percent above the then steady state level.
Referring to Figs. 8A-D, Figs. 8A and 8B
illustrate stimulus level versus time waveforms for
the right quadriceps (Fig. 8A) and left quadriceps
(Fig. 8B). Figs. 8C and 8D illustrate step occurrence
versus time waveforms for step right (Fig. 8C) and
step left (Fig. 8D). Each of Figs. 8A-8D is plotted
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against the same time axis in the horizontal
direction. As illustrated in Figs. 8A-C, when step
right occurs as indicated by the positive pulse on
Fig. 8C, the stimulus level to the right quadriceps
(Fig. 8A) is turned of. during leg movement to produce
the step, while at that same time, the stimulus level
to the left quadriceps is incremented as illustrated
on Fig. 8B, approximately 15% over the steady state
level. ~An increase within the range of approximately
10 to 20% is acceptable). Thus, the stimulus level to
the left quadriceps is increased temporarily during
the step occurrence of the right step, corresponding
to the turning off of the stimulus to the right
quadriceps. Similarly, referring to Figs. 8A, 8B and
8D, at the step occurrence of step left, the positive
pulse in Fig. 8D, the stimulus to the left quadriceps,
Fig. 8B, is turned off, while the stimulus level to
the right quadriceps, Fig. 8A, is increased by the
predefined value to increase the level of stimulus to
the standing leg, the right leg, during the left step.
To provide extra smooth landing of a given leg after
a step has been taken with that leg, it may be
advisable not to stimulate the quadriceps of that leg
with a sharp instantaneous voltage rise, but to
provide a voltage ramp rise-time of the stimuli to
these quadriceps after each step.
Referring to Fig. 9, in accordance with another
aspect of the present invention, the system measures
its own output current such as between the opto-
isolator 205 (or multiplexer means 10$) and the
electrodes 102 (or alternatively it can measure the
voltaqe drop over a fixed impedance R at that
location), and couples the measurement value back to
its input for determination of whether the output
current (or voltage) drop is below a predefined
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threshold. As illustrated in Fig. 9, the output
current to one electrode is determined by measuring
the voltage drop (VD) across a fixed impedance R. The
voltage (VD) is compared to a predefined threshold
level (V~) (illustrated as being variable for
different preset predefined levels) by a comparator
300. The output of the comparator 300 is coupled to
an input of the system's microprocessor 104. The
predefined threshold, in a preferred embodiment, is
approximately 50% of the lowest output level to any
electrode. Alternatively, by trial and error, other
thresholds can be chosen. If there is a drop below
this predefined threshold, this implies that enough
current is not being output to some channel (or
channels), i.e. such as an electrode is loose or
disconnected. The computing unit 104 of the apparatus
then provides for an audible sound alarm and/or visual
alarm for the user/patient, and disallows any step,
but maintains the patient in a standing mode (at least
on one leg since during a step one leg is in the air,
preferably increasing the stimulation level to the
remaining electrode). This stimulation level can be
increased by increasing either the peak voltage, pulse
frequency, pulse width, or a combination of these. In
addition, it has been shown in the literature (of
Kralj and Bajd book, page 127, Fig. 3) that by
increasing pulse width and/or pulse frequency during
a "TAKE S~EP" mode, one achieves a higher step (a
larger angle of hip joint flexion). Whereas the
figure of p. 127 related to the CUTANEOUS FEMORIS
nerve, our experience over many tests with patients
indicates similar increases of step height (namely, of
hip flexion angle) also when a peroneal nerve is being
stimulated. If the other leg happens to be the one
disconnected (the one being stood on is the one where
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the electrode disconnects), then the patient could
fall, except as self-supported by his/her arms on a
walker unit.
To avoid excessively high voltages at the output
of the pulse-amplifier circuit 103, that output may
also be connected, in parallel, to a ZNR type voltage
sensitive load. This load presents to that output a
load of no more than a few thousand ohms, if the
voltage at that output reaches a certain predetermined
value of between 50 and 130V, and which otherwise
presents an additional open circuit.
A battery supply 111, as illustrated, consists of
8 AAA 1.5 VDC batteries, which supplies power to all
the circuits of the stimulator box 100 via 130. The
battery supply is also coupled to activate a low-
battery voltage warning via circuit 109 to provide the
audible warning 108 and also a visual flashing warning
light 110. The "low-battery" warning sound is
programmed by the processor 104 to differ from the
sound of the stimulus-level-saturation alarm discussed
above.
Fig. 6 illustrates a specific embodiment of the
stimulator box 100 of Fig. 1, for a wired link 121,
with corresponding numerals indicating like elements.
Specific electronic device designations are
illustrated in Fig. 6, such as the Hitachi HD63701
processor, 104.
While there have been described herein various
illustrated embodiments, it will be understood by
those skilled in the art that various other
embodiments emanate from those disclosed. This
description is illustrative and not limiting, and the
true scope of this invention is as set forth in the
appended claims.
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