Note: Descriptions are shown in the official language in which they were submitted.
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'Title: WIRELESS PHYSIOLOGICAL MONITORING SYSTEM
t=field Of The Invention
(0001, The invention relates to a wireless physiological monitoring
system that can be used to measure a wide variety of physiological signals
from a patient for monitoring the patient andlor diagnosing certain medical
conditions.
Backer~und Of 'The Inventi~n
(0002) The measurement of physiological signals from a patient for
monitoring the patient and~or diagnosing a particular medical condition
conventionally requires medical instrumentation to be physically attached to
the patient. This includes attaching electrodes to the patient at the
measurement site and then transmitting the measured signals to the medical
instrumentation via cables. In some cases, this can result in many cables
being connected between the patient and the medical instrumentation. For
instance, for multimodality intraoperative monitoring measurements, there
may be anywhere from 4. to 32 measurement channels, for electromyography
(EMG) measurements there may be 1 to 4 measurement channels, for
electrocardiogram (ECG) measurements, there may be ten measurement
channels and for measuring brain potentials, there may be more than 128
channels in cases where signets are measured from the cortex.
[0003, The plurality of cables connecting the patient to the medical
instrumentation provides many disadvantages. The cables are uncomfortable
for the patient and limit the mobility of the patient. It is important for the
patient
to remain mobile so that the patient does not develop any blood clots. The
cables also make it difficult to perfarm any tests on the patient which
require
the patient to move. Further, in some cases, the cables may be stiff and can
easily become detached from the patient especially when the patient moves.
(0004] The plurality of cables connecting the patient to the medical
instrumentation are also cumbersome for the medical personnel that interact
with the patient. In particular, the entire set-up can be confusing and in
some
cases requires expertise for arranging all of the different electrodes and
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cables. Accordingly, the time required for attaching or removing the
electrodes
and cables to or from the patient can be quite Icing. This can be detrimental
in
situations in which speed is of the essence. In addition, the medical
personnel
may accidentally trip or become entangled in the cables. Further, in thE~
operating room, the cables to the patient are not accessible during surgery
since the cables are in the "sterile field". This is a problem when
troubleshooting faulty cables since cables in the operating room are
routinelyr
run over by people and heavy equipment and therefore subject to a high
failure rate.
Summary Of The Invention
[0005, The inventors have developed a wireless physiological
monitoring system that includes, at a minimum, at least one wireless sensor
and a monitoring device which are linked to one another in a wireless fashion
for measuring physiological signals from a patient for monitoring the patient.
The wireless physiological monitoring system may also be used to perform
diagnostic tests on the patient. To perform certain diagnostic tests, the
wireless physiological monitoring system may further include a wireless
stimulator that is synchronized with the wireless sensor for performing
certain
diagnostic tests such as nerve conduction velocity tests, for example.
[0006, In one instance, the wireless sensor may be a wireless surface
electrode assembly. In another instance, the wireless sensor may be a
wireless needle assembly. In both cases, the sensors preferably include
electrical leads for obtaining active, reference and common voltage
measurements. This results in better signal quality for the measured
physiological signals since the common mode voltage can be measured and
removed from both the measured active and reference voltages. The wireless
needle assembly is also advantageous in that it requires no external surface
electrodes to operate.
(0007 For both the wireless surface electrode assembly and the
wireless needle assembly, the sensors include a releasably attachable
wireless adapter that provides a wireless connection between the sensor and
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the monitoring device, and a measurement module, for measuring
physiological signals from the patient. The measurement module is
disposable and the wireless adapter may be reused with another
measurement module to form another wireless sensor.
[0008] In one instance, the wireless adapter may communicate
according to the Bluetooth communication protocol.
[0009] Further, in one embodiment, the wireless adapter includes a
processor and a pre-processing stage for processing the measured
physiological signals prior to transmitting corresponding wireless signals to
the monitoring device. The wireless adapter may also include a memory unit
for storing the raw measured or processed physiological signals.
[0010] The wireless physiological monitoring system of the invention
advantageously allows for faster application and removal of the sensors to a
patient since there are no cables that need to be attached. When the wireless
needle assembly is used as the wireless sensor, the medical practitioner
simply places the needle assembly into the recording site and receives high
quality signals through the wireless connection without the need to prepare
and "wire-up'° the patient. The wireless physiological monitoring
system
provides better signal quality for the measured physiological signals since
there are no cables which can pick up electromagnetic interference; this is a
common problem with conventional equipment. There is also no leakage
current once the measured physiological signals have been converted to
wireless signals. Furthermore, since all of the components of the wireless
physiological monitoring system are totally wireless, the mobility of the
patient
is not compromised.
[0011] In a first aspect, the invention provides a wireless physiological
monitoring system for measuring physiological signals from a patient. The
system comprises a monitoring device having a first transceiver; at least one
wireless sensor disposed on a measurement site on the patient for measuring
a physiological signal, the at least one wireless sensor having a second
transceiver for transmitting a corresponding wireless physiological signal to
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the first transceiver; and, at least one wireless stimulator having a third
transceiver, the at least one wireless stimulator being adapted to provide a
stimulation current to the patient in response to at least one of a command
signal transmitted by the first transceiver of the monitoring device and
manual
actuation.
[0012] 1n one embodiment, the at least one wireless sensor includes <~
wireless adapter having the second transceiver; and, a measurement module
having an active conductor and a reference conductor for receiving voltages
used to produce a differential voltage measurement indicative of the,
physiological signal, the measurement module further including a common
conductor for receiving another voltage for rerr~oving common mode voltage
from the differential measurement. The second transceiver transmits the
differential measurement as the wireless physiological signal.
[0013] In another embodiment, a wireless surface electrode assembly
is used for the at least one wireless sensor. The measurement module of the
wireless electrode assembly comprises: a base having an electrical interface
connected to the active, reference and common conductors, the base having
a shape complementary to that of the wireless adapter for releasable
attachment to the wireless adapter; an active electrode for placement on the
patient, the active electrode being connected to the active conductor; a
reference electrode for placement on the patient, the reference electrode
being connected to the reference conductor; and, a common electrode for
placement on the patient, the common electrode being connected to the
common conductor.
[0014] The active and reference electrodes are located approximately
equidistantly from the common electrode.
[0015] In another embodiment, a wireless needle assembly is used for
the at least one wireless sensor. The measurement module of the wireless
needle assembly comprises: a base having an electrical interface connected
to the active, reference and common conductors, the base having a shape
complementary to that of the wireless adapter for releasable attachment to the
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wireless adapter; and, a shaft which houses the active, reference and
common conductors, wherein a first conductor is disposed centrally along the
longitudinal axis of the shaft, a second conductor is disposed concentrically
about the first conductor, a first insulator is disposed in between the first
and
second conductors, a third conductor is disposed concentrically about the
second conductor, and a second insulator is disposed in between the second
and third conductors.
[0016, In a second aspect, the invention provides a wireless
physiological monitoring system for measuring physiological signals from a
patient. The system comprises a monitoring device having a first transceiver;
and, at least one wireless sensor disposed on a measurement site on the
patient for measuring a physiological signal. The at least one wireless sensor
includes a wireless adapter having a second transceiver; and, a measurement
module having an active conductor and a reference conductor for receivingi
voltages used to produce a differential voltage measurement indicative of the
physiological signal, the measurement module further including a common
conductor for receiving another voltage for removing common mode voltage
from the differential measurement. The second transceiver transmits a
wireless physiological signal corresponding to the differential voltage
measurement to the first transceiver of the monitoring device.
(0017, In one embodiment, the system further comprises at least one
wireless stimulator having a third transceiver, the at least one wireless
stimulator being adapted to provide a stimulation current to the patient in
response to at least one of a command signal transmitted by the first
transceiver of the monitoring device and manual actuation.
[0018' In a third aspect, the invention provides a wireless sensor for
measuring a physiological signal from a patient, the wireless sensor being
disposed on a measurement site on the patient. The wireless sensor
comprises: a wireless adapter having a transceiver; and, a measurement
module having an active conductor and a reference conductor for receiving
voltages used to produce a differential voltage measurement indicative of the
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physiological signal, the measurement module further including a common
conductor for receiving another voltage for removing common mode voltage
from the differential measurement. The transceiver transmits a wireless
physiological signal corresponding to the differential voltage measurement.
Brief Description ~f The Drawings
r0019] For a better understanding of the invention and to show more
clearly how it may be carried into effect, reference will now be made, by way
of example only, to the accompanying drawings which show exemplary
embodiments of the invention and in which:
Figure 1 shows an exemplary embodiment of a wireless
physiological monitoring system in accordance with the invention;
Figure 2a shows a top view of an exemplary embodiment of a
wireless surface electrode assembly for use as a wireless sensor in the
system of Figure 1 in accordance with the invention;
Figures 2b shows an exploded side view of an exemplary
embodiment of a wireless surface electrode assembly for use as a wireless
sensor in the system of Figure 1 in accordance with the invention;
Figure 3a shows an exploded side view of an exemplary
embodiment of a wireless needle assembly for use as a wireless sensor in the
system of Figure 1 in accordance with the invention;
Figure 3b shows a magnified view of an exemplary embodiment
of the tip of the wireless needle assembly of Figure 3a; and,
Figure 4 shows an exemplary embodiment of a wireless adapter
for use with either the wireless surface electrode assembly of Figures 2a and
2b or the wireless needle assembly of Figures 3a and ;fib.
Detailed Descriation ~f The Embodiments Of 'The Invention
X0020] It will be appreciated that for simplicity and clarity of illustration,
elements shown in the figures have not necessarily been drawn to scale. For
example, the dimensions of some of the elements may be exaggerated
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relative to other elements for clarity. Further, where considered appropriate,
reference numerals may be repeated among the figures to indicate
corresponding or analogous elements. In addition, numerous specific details
are set forth in order to provide a thorough understanding of the invention.
However, it will be understood by those of ordinary skill in the art that the
invention may be practiced without these specific details. In other
instarices,
well-known methods, procedures and components have not been described iin
detail so as not to obscure the invention.
[0021, Referring first to Figure 1, shown therein is an exemplary
embodiment of a wireless physiological monitoring system 10. The wireless
physiological monitoring system 10 comprises a monitoring device 12 and at
least one wireless sensor 14. Typically there are a plurality of wireless
sensors 14, three of which are shown for exemplary purposes. The wireless
sensors 14 are attached to a patient 16 and each measures a desired
physiological signal from the patient 16. Examples of physiological signals
include an electroencephalographic (EEG) signal, an electrooculographic:
(EOG) signal, an electromyographic (EMG) signal or an electrocardiographic:
(ECG) signal. The measured physiological signal may be pre-processed by
the wireless sensor 14. The wireless sensors 14 then transmit corresponding
wireless physiological signals 18 to the monitoring device 12. The
transmission frequency may be in the Wireless Medical Telemetry Services
(WMTS) band or the Industry Scientific and Medical (ISM) band or any other
band approved for this activity. The WMTS band includes frequency ranges of
608 to 614 MHz, 1395 to 14.00 MHz and 1429 to 1432 MHz. The ISM band
includes the frequency range of 2.4 to 2.4835 GHz. The structure of the
wireless sensor 14 is discussed in more detail below.
[0022, The monitoring device 12 may perform a number of functions on
the wireless physiological signals 18. For instance, the monitoring device 12
may simply store the wireless physiological signals 18 for later downloading
to
a computing device which processes the wireless physiological signals 18. In
this case, the monitoring device 12 may sirr~ply be a storage device.
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. _ _
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Alternatively, the monitoring device 12 may itself process the wireless
physiological signals 18 as well as possibly display the wireless
physiological
signals 18 of the processed version. Accordingly, the monitoring device 12
may be a suitable computing device such as a laptop computer, a personal
computer (PC) or an application specific hardware device.
(0023 In one exemplary embodiment, the monitoring device 12
comprises a processor 20, a memory unit 2 2, a transceiver 24 with an
antenna 26, a power supply 28 and a display 30 connected as shown in
Figure 1. The processor 20 controls the operation of the monitoring device 12
and initiates monitoring and/or diagnostic tests on the patient 16 via the
wireless sensors 14. In particular, the processor 20 sends commands via the
transceiver 24 to the wireless sensors 14 to initiate monitoring or diagnostic
tests and also to synchronise with the wireless sensors 14. The processor 20
may be any suitable processing element, such as a PC central processing
unit (CPU) chip, and in some instances may be a digital signal processor
(DSP). The transceiver 24 operates according to a suitable wireless
communication protocol. In one instance, the communication protocol may be
the Bfuetooth communication protocol as discussed in more detail below.
(0024 The processor 20 receives the wireless physiological signals 18
and stores the wireless physiological signals 18 in the memory unit 22. The
memory unit 22 may be any suitable memory device such as a hard drive or
flash memory or the like. The wireless physiological signals 18 can then be
downloaded, via the transceiver 24, or anoi:her suitable communications
device (not shown), to another computing device for processing. Alternatively,
prior to storage or after storage, the processor 20 may then process the
wireless physiological signals 18 according to a processing algorithm that is
suitable for the type of monitoring or diagnostic test that is being
performed.
For instance, noise reduction algorithms may be applied to the signals 18 to
improve the signal to noise ratio. In addition, pattern recognition or other
detection algorithms may be applied to the signals 18 to detect certain events
in the signals 18. These noise reduction and pattern recognition algorithm s
.r _,.: M . .. ": . ~ . . ~E,.. . :,... . . , . .:...,.. . .
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are commonly known to those skilled in the art and will not be discussed
further.
[0025 The processor 20 may display the wireless physiological signals
18 or the processed version of the signals 18 on the display unit 30. The
display 30 may be a monitor, an BCD, and 'the like. The power supply 2;8
provides power to the various components of the monitoring device 12. The
power supply 28 may be a rechargeable battery or may be a computer power
supply unit that is connected to mains power.
[0026] The wireless physiological monitoring system 10 may further
comprise at least one wireless stimulator 32 for performing certain diagnostic
tests on the patient 15 such as nerve conduction velocity tests. In
particular,
the wireless stimulator 32 is used to generate a stimulation current to
creai;e
an action potential in a nerve of the patient 16.
[002'T~ The wireless stimulator 32 includes a stimulation processor 34,
a stimulation generation unit 36, a stimulation transceiver 38 with an antenna
40, a stimulation interface 42, two prongs 44 and a battery 46 connected as
shown in Figure 1. The wireless stimulator 32 may optionally include battery
charging circuitry 48. The stimulation processor 34 controls the operation of
the wireless stimulator 32 and may be a DSP or a microcontroller. The
stimulation processor 34 instructs the stimulation generation unit 36 to
generate a stimulation current when the stimulation transceiver 38 receives an
appropriate command signal from the monitc,ring device 12 or when it is
manually actuated.
[0028, The stimulation generation unit 3f~ includes circuitry to create the
stimulation current having different characteristics depending on the part of
the patient 16 to which the stimulation current is being applied. In general,
the
stimulation current is preferably a controlled constant amplitude current and
may include a single pulse or multiple pulses where each pulse may be
monophasic or biphasic. For example, when the stimulation current is applied
to the hand of the patient 18, the amplitude may be up to 100 milliamps, the
duration of up to 1 millisecond and the maximum voltage is limited to 400
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volts. However, when the wireless stimulator 32 is applied to the head of the
patient 16, it is used to generate motor-evoked potentials and requires higher
amplitude voltages and current. In such an instance, the maximum voltage
amplitude is limited to 1000 V, the maximum current amplitude is limited to
1.5
A and the maximum pulse duration is less than 1 ms.
[0029] The stimulation interface 42 allows a medical practitioner to
control the wireless stimulator 32. In one embodiment, the stimulation
interface 42 includes a button, a dial and a small display (all not shown).
The
button may be manually actuated to start and stop the stimulation current,
an~nd
the dial may be used to change the intensity of the stimulation current. The
display shows the intensity of the stimulation current and the remaining
charge on the battery. Alternatively, as previously mentioned, the wireless
stimulator 32 may be controlled from the monitoring device 12 over tlhe
wireless link. In both cases, the same level of synchronization is needed
between the wireless stimulator 32 and the corresponding wireless sensors
14 that are used to measure the response to the stimulation current.
j0030] During a diagnostic test, the two prongs 44 of the wireless
stimulator 32 are applied to a test site on the skin of the patient 16 to
stimulate
the desired nerve. One of the prongs is a cathode terminal and the other
prong is an anode terminal. The wireless stimulator 32 also has touch-proof
adapter connections (not shown) to stimulate through smaller external
electrodes or needles for cases in which the prongs 44 are not appropriate.
[0031] The wireless stimulator 32 is powered by the battery 46. In one
embodiment, the battery 4is a rechargeable battery. Accordingly, when the
wireless stimulator 32 is not in use, the wireless stimulator 32 is placed in
a
charging stand (not shown) for recharging the battery 46. In this case, the
stimulation processor 34 engages the battery charging circuitry 48 to recharge
the battery 46.
[0032] There are some diagnostic tests in which it is beneficial to have
two wireless stimulators. One example of such a diagnostic test is a collision
study. One of the wireless stimulators is used to generate multiple action
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potentials resulting in a muscle or nerve response from the patient 16 and the
other wireless stimulator is used to generate a second action potential in a
different nerve that cancels out an undesirable response detected at the
recording site. For this diagnostic test, the timing between the delivery of
the
stimulation currents provided by the two wireless stimulators must be
controlled to an accuracy of a few hundred microseconds.
[0033] Referring now to Figures 2a and 2b, shown therein is an
exemplary wireless surface electrode assembly 50 for use as at least one of
the wireless sensors 14 in the wireless physiological monitoring system 10.
The wireless surface electrode assembly 50 includes a measurement module
52 and a wireless adapter 54. The measurement module 52 includes three
conductive electrodes: an active electrode 56, a reference electrode 58 and a
common electrode 60. The three electrodes 56, 58 and 60 are used so that a
differential measurement is made for the desired physiological signal and so
that the common mode of the differential measurement can be removed. The
common electrode 60 is preferably equidistant to both the active and
reference electrodes 58 and 5so that the voltage measured by the common
electrode 60 is common to both the active and reference electrodes 56 and
58. The signal provided by the common electrode 60 also allows for removing
muscle artifacts from the physiological signals measured by the active and
reference electrodes 56 and 5 8. The electrodes can be made of any
biocompatible conductive material with suitable mechanical properties, such
as silver-silver chloride, gold, silver, tin, platinum or alloys thereof, or
carbon.
[0034] Each of the electrodes 56, 58 and 60 are wired to a base 62 of
the measurement module 52 and are electrically insulated from one another.
The base may be made of any biocompatible material with suitable
mechanical properties, such as Nylon, Teflon or PVC. The base 62 further
includes three electrical contacts (not shown) on a top portion thereof that
interface with corresponding electrical contacts (not shown) on the bottom of
the wireless adapter 54. The wireless adapter 54 includes components for
transmitting the wireless physiological signal 18 that corresponds to the
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physiological signal measured by the electrode assembly 50 to the monitoring
device 12. An exemplary implementation of the wireless adapter 54 is
described below.
[0035] The wireless adapter 54 has a shape that is complementary to
that of the measurement module 52 so that the wireless adapter 54 makes a
snap-fit or friction-fit connection with the measurement module 52. The
connection is also such that the wireless adapter 54 is releasably attachable
to the measurement module 52. Accordingly, the wireless adapter 54 can be
attached to a measurement module 52, used for physiological monitoring or
diagnostic testing on the patient 16, and then detached from the
measurement module 52 once monitoringJtesting is completed so that the
wireless adapter 54 can be reused and the measurement module 52 can be
discarded.
[0036] The wireless surface electrode assembly 50 further includes an
adhesive portion preferably applied to a section of each of the electrodes 56,
5~ and 60 to hold the wireless surface electrode assembly 50 in place once
the assembly 50 has been attached to the patient 15. Alternatively, or in
addition, a piece of tape, or other adhesive means, may be applied to the
electrodes 56, 58 and 60 of the wireless surface electrode assembly 50 to
hold it in place. The electrodes may also be glued on with a suitable glue
such
as collodion. Alternatively, the wireless surface electrode assembly 50 may be
built into gloves that are worn and held in place by a medical practitioner
that
is obtaining physiological signals from the patient 16.
[0037] Referring now to Figures 3a and 3b, shown therein are an
exploded side view, and a magnified view of the tip, respectively, of an
exemplary embodiment of a wireless needle assembly 70, for use as at least
one of the wireless sensors 14. in the wireless physiological monitoring
system
10.
[0038] The wireless needle assembly 70 includes a measurement
module 72 and the wireless adapter 54. The measurement module 72
includes a shaft with a needle tip 74 disposed at the end; the shaft and
needle
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tip having three concentric conductors: an active conductor 76, a reference
conductor 78 and a common conductor 80. The active and reference
conductors 76 and 78 are separated by an insulator 82. The reference and
common conductors 78 and 80 are separated by an insulator 84. The three
conductors 76, 78 and 80 are used, in a similar manner to wireless sensor 50,
so that a differential measurement may be made far the desired physiological
signal and so that the common mode component of the differential
measurement may be removed.
[0039' The common conductor 80 is advantageously in close proximity
to both of the active conductor 76 and the reference conductor 78 so that it
provides a close approximation to the common mode voltage of the active and
reference conductors 76 and 78. It should be noted that the location of the
reference, common and active conductors 76, 78 and 80 are interchangeable.
For instance, the center conductor 76 may instead be the common conductor
and the outer electrode 80 may be the active conductor. However, it is
preferable for the active and reference conductars 76 and 78 to remain close
to one another to eliminate any far field effects in the measured voltages.
Accordingly, the common conductor 80 is preferably the outer conductor.
[0040] Each of the conductors 76, 78 and 80 are wired to a base 86 of
the measurement module 72. The base 86 further includes three electrical
contacts on a top portion thereof that interface with corresponding electrical
contacts on the bottom of the wireless adapter 54. Similar to the wireless
surface electrode assembly 50, the wireless adapter 54 has a shape that is
complementary to that of the measurement module 72 so that the wireless
adapter 54 is releasably attachable to the measurement module 72.
Accordingly, the wireless adapter 52 !s reusable and the measurement
module 72 is disposable. The entire wireless needle assembly 70 is small
enough to facilitate clinical use. Further, the tip 74 of the wireless needle
assembly 70 may come in different lengths and diameters to facilitate
measurement at muscles or nerves of different sixes and depths.
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[0041, In use, the wireless needle assembly 70 is inserted into a
desired measurement site on the patient. To hold the wireless needle
assembly 70 in place, a piece of tape, or other adhesive means, may be
applied to the wireless needle assembly 70. The wireless needle assembly 70
may also be held in place by the hand of the medical practitioner who is
measuring physiological signals from the patient 16. Alternatively, the
wireless
needle assembly 70 may not need any tape or adhesive if it is inserted to an
adequate depth. In another alternative, the tip of the wireless needle
assembly 70 may have a hook or corkscrew shape to hold it in place.
[0042] It should also be noted that the wireless adapter 54 may be
used with other needles having a different number of conductors. For
instance, the wireless adapter 54 may be combined with a measurement
module that has a standard monopolar conductor configuration or with a
measurement module that has a standard bipolar conductor configuration. In
these cases, if a differential voltage measurement is to be made while
removing common-mode voltage, extra surface electrodes can be attached to
the measurement module. For instance, in the case of a needle measurement
module having a standard monopolar (single active electrode) conductor
configuration, a common surface electrode and a reference surface electrode
may be added. In the case of a needle measurement module having a
standard bipolar conductor configuration (having active and reference
electrodes), only a common surface electrode need be added.
[0043 Referring now to Figure 4, shown therein is an exemplary
embodiment of the wireless adapter 54 for use with either the wireless surface
electrode assembly 50 or the wireless needle assembly 70. The wireless
adapter 54 includes a processing unit 90, a signal interface 92, a pre-
processing stage 94, an analog-to-digital converter (ADC) 96, a memory unit
98, a battery 100, a transceiver 102 and an antenna 104 connected as shown
in Figure 4. The processing unit 90 controls the operation of the wireless
adapter 54 and may be a DSP or the like.
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[0044] The electrical interface 92 provides an electrical connection to
the active, common and reference leads of the measurement modules 52 or
72 to receive measurement signals 10G. The measurement signals 106 are
then processed by the pre-processing stage 94 which includes a filtering
stage followed by an amplification stage (both not shown). The filtering stage
includes high pass filters (i.e. one for each of the active and reference
measurement signals) to remove the contact potential component from the
measurement signals 106 and provide filtered signals. It may also have a sine
wave generator used for measuring impedance of the electrodes. The cutoff-
frequency of the high pass filters is approximately 0.1 Hz to 20 hiz.
[0045] The amplification stage includes a differential amplifier for
amplifying the filtered signals thereby providing pre-processed physiological
signal 108. The gain factor of the amplifiers is selected so that the pre-
processed physiological signal 108 does not saturate the input stage of the
ADC 96. This depends on the type of physiological signals that are measured
by the corresponding measurement module 52 or 72 (i.e. since different
physiological signals have different amplitudes). The particular type of
physiological signal that is being measured may be transmitted by the
monitoring device 12 to the wireless adapter 54 so that the processing unit 90
can vary the gain of the amplification stage in the pre-processing stage 94.
[0046] The ADC 96 digitizes the pre-processed physiological signal 108
to provide a digitized physiological signal 110. The processing unit 90 sends
the digitized physiological signal 110 to the transceiver 102 for transmitting
the corresponding physiological wireless signal 18 via the antenna 104. The
wireless physiological signal 18 may be transmitted at different rates
depending on the type of physiological measurement that is made.
[0047] Prior to sending the digitized physiological signals 110 to the
transceiver 102, the processing unit 90 may store the digitized physiological
signals 110 in the memory unit 98. In an alternative, the digitized signals
110
may not be transmitted and may instead simply be stored in the memory unit
98 for downloading at a later time.
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[0048] In another alternative, the processing unit 90 may perform
further processing on the digitized physiological signals 110 according to the
type of physiological signal that is being recorded so that the transceiver
102
sends processed data that corresponds to the measured physiological signal
rather than the actual measured physiological signals. The processed data
may be readily displayed on the display 30 of the monitoring device 12. In
another alternative, the processing unit may perform further processing on
the digitized physiological signal 110 according to the type of physiological
signal that is being recorded so that the transceiver 102 sends averaged data
collected over multiple stimulation sweeps.
[0049] The battery 100 of the wireless adapter 54 is a low voltage
battery and the other components of the wireless adapter 54 are also adapted
for low voltage operation. This reduces the possibility of electrical shock to
the
patient 16. In addition, this ensures that the battery 100 can operate for a
long
time before requiring replacement. In an alternative, the battery 100 may be
rechargeable and the wireless adapter 54 may have an interface (not shown)
to the battery 100 so that the battery 100 can be plugged into a battery
charger and recharged.
[0050] Any suitable wireless communication protocol may be used for
the monitoring device 12, the wireless sensor 14 and the wireless stimulator
32. In one embodiment, the Bluetooth standard is used as the wireless
communication protocol. The Bluetooth standard provides a universal radio
interface in the 2.4~ GHz frequency band that enables low power electronic
devices to wirelessly communicate with each other. In accordance with the
Bluetooth standard, the monitoring device 12, the wireless sensors 14 and the
wireless stimulator 32 behave as nodes grouped in an ad-hoc network
referred to as a piconet. The monitoring device 12 behaves as a master node
and the wireless sensors 14 and the wireless stimulator 32 behave as slave
nodes. The monitoring device 12 and each of the wireless sensors 14 and the
wireless stimulator 32 is provided with a unique address so that the wireless
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physiological signals 15 from various wireless sensors 14 can be
distinguished from one another.
[0051] Each node in the Bluetooth network has an internal "native"
clock that determines the timing of the corresponding transceiver. The
communication channel between the master nodes and the slave nodes is
defined by a frequency hopping sequence derived from the address of the
master node. The master node provides its native clock as a time slot
reference. Each time slot supports full-duplex communication initiated by the
master node: during the first part of the time slot the master node polls a
slave
node and during the second part of the time slot the corresponding slave node
responds.
[0052] During operation, the wireless sensors 14 are instructed by the
monitoring device 12 to start and stop data transmission so that power and
bandwidth is not wasted. Accordingly, the wireless sensors 14 are usually in a
"listening mode" to wait for commands from the monitoring device 12. In
particular, when the wireless adapter 54 is attached to one of the
measurement modules 50 or 70, the wireless adapter 54 turns on, joins the
piconet, identifies itself to monitoring device 12 and listens for commands.
The wireless adapter 54 turns off when it is disconnected from the
measurement module 50 or 70.
(0053] Some of the physiological monitoring and diagnostic tests
performed by the physiological wireless monitoring system 10 require
stringent timing requirements for the wireless sensors 14 andlor the wireless
stimulator 32. One example is nerve conduction diagnostic tests and evoked
potential monitoring in which synchronization is preferably done to within
approximately +/- 50 microseconds.
[0054] With the Biuetooth communication standard, the modulation rate
of the master node is approximately 1 Mbit/sec which allows for
synchronization down to 1 microsecond. This synchronization can be
accomplished by adding extra hardware counting circuitry to the slave nodes,
or by using the processors of the slave nodes, to keep track of the modulation
CA 02507789 2005-05-17
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rate of the master node. Each slave node will count at the same rate, but will
have different zero points based on the time at which they started counting.
[0055] The method of aligning the respective zero points is to have the
slave node transmit a timing message to the master node and have the
master node immediately respond. The slave node then measures the
number of counts of the master modulation rate taken for the round trip and
divides by two to get the tr ansit time. This is done many times, 50 times for
example, to get an average transit time and the average clock offset (this is
more accurate than individual measurements). The slave node then adjusts
its native clock based on the average clock offset less the transit time to
achieve the stated accuracy. This synchronization procedure is done each
time a connection is established between a slave node and the master node.
[0056] An example of a diagnostic test that can be performed with the
wireless physiological monitoring system 10 is the Palmar nerve response, in
which the prongs 44 of the wireless stimulator 32 are placed in contact with
the skin above the desired nerve to inject a stimulation current. One of the
wireless sensors 14 is placed on a finger in close proximity to the desired
nerve to measure the resulting action potential of the desired nerve. The
Palmar nerve response usually occurs in about 1 millisecond. Measuring the
latency of this response involves finding the take-off point or peak amplitude
of the action potential. An error of 50 microseconds in synchronization
results
in a 5% error in the response, which is at the limit of what is diagnostically
acceptable.
[0057] Some other examples of diagnostic tests and physiological
monitoring that can be done with the wireless physiological monitoring system
10 include the blink reflex and recording somatosensory evoked potentials.
These tests are demanding in that multiple action potentials are averaged
together. This is done since the amplitude of the response is similar to the
noise level in the measured signal, which is typically about 1 rnicrovolt. Any
errors in timing between stimulus delivery and data acquisition results in a
flattened peak in the averaged response making it difficult to determine the
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latency of the response. If the synchronization errors exceed 50 microseconds
then the quality of the responses is considered to be poor. Another example
of physiological monitoring is the ECG which is typically recorded at a
sampling rate of 200 Hz and requires 5 milliseconds of synchronization
5 accuracy.
[0058] Bandwidth may be a factor in some of the monitoring/diagnostic
tests that require multiple recording electrodes, such as multimodality
monitoring during surgery in which somatosensory evoked potentials, motor
evoked potentials, brainstem auditory evoked responses ~BAERs), EMG and
10 EEG are simultaneously recorded using up to 16 data channels that each
acquire data at a sampling rate of 60 KHz or higher. Actually EEG and ECG
signals require a sampling rate of 200 Hz, BAERs require a sampling rate of
60 kHz while most other evoked potentials require a sampling rate of 20 kHz.
In addition, 16 bits are preferably used per sample. This results in a maximum
15 possible data rate of approximately 15 Mbits/sec, which exceeds the
capability of the Bluetooth standard, but is still within the range of 802.118
wireless communication sfiandards.
[0059] Unfortunately, the power consumption of devices that operate
under the 802.118 wireless standard is 3 times higher than devices that
20 operate under the BBuetooth communication standard. This may be overcome
by recording at a high speed triggered by the stimulus and storing the
recorded and optionally processed physiological signals in the memory unit 98
of the wireless sensors 14 and then transmitting the recorded physiological
signals from the wireless sensors 14 to the monitoring device 12 at lower
25 speeds after the physiological response has occurred. This technique is
applicable whenever continuous monitoring of the unprocessed waveform
data is not required, such as for channels related to evoked potentials where
only the averaged signals over multiple recording sweeps need be
transmitted.
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[0060] However, this technique does not work for channels related to
EMG data which require continuous data transmission, but the EMG data can
be sampled at lower frequencies.
[0061] It should further be noted that by storing and transmitting the
data periodically, the transceiver 102 of the wireless adapter 54 can be
turned
off when not being used thereby saving power and extending the fife of the
battery 100. In addition, to save power consumption, data bandwidth can be
reduced by employing at least one of decimation, averaging and compression.
However, the power consumption due to the added processing must be
smaller than the savings in power consumption due to transmitting a reduced
amount of data.
[0062] The wireless physiological monitoring system of the invention is
particularly well suited for wireless monitoring of ECG, EIVIG and EEG
monitoring and can be used clinically, intra-operatively and in an Intensive
Care Unit (iCU). In use, the wireless sensors 14 may be color-coded andlor
numbered according to the corresponding placement location on the patient
16. Accordingly, a medical practitioner simply needs to refer only to the
color-
coding andlor numbering when attaching the wireless sensors 14 to the
patient 16.
[0063] In order to conduct auditory or visual evoked potential testing,
the wireless physiological monitoring system 10 may further include at least
one of a wireless auditory stimulator and a wireless visual stimulator (both
not
shown). The wireless auditory stimulator may be a set of wireless
headphones or at least one wireless inserfi earphone that may be used to
present an auditory stimulus t~ the patient 16. The auditory stimulus may be a
steady state waveform such as a tone, or a transient waveform such as a
click, or some form of noise or a combination thereof in which the waveforms
have a selectable phase, frequency and intensity. The wireless visual
stimulator may be a set of goggles with a wireless link. The goggles may be
used to provide steady state or transient visual stimuli such as a flash of
light
to at least one eye of the patient 16. In both the auditory and visual cases,
the
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wireless sensors 14 are placed at the appropriate location on the patient 16
to
record the resulting evoked potential.
j0064, It should be understood that various modifications can be made
to the embodiments described and illustrated herein, without departing from
the invention.
