U.S. patent application number 11/130221 was filed with the patent office on 2005-11-24 for wireless physiological monitoring system.
Invention is credited to Kurtz, Ronald Leon, Mumford, John Robert.
Application Number | 20050261559 11/130221 |
Document ID | / |
Family ID | 35376119 |
Filed Date | 2005-11-24 |
United States Patent
Application |
20050261559 |
Kind Code |
A1 |
Mumford, John Robert ; et
al. |
November 24, 2005 |
Wireless physiological monitoring system
Abstract
Embodiments of the invention relate to a wireless physiological
monitoring system. The system includes at least one wireless sensor
and a monitoring device which are linked to one another of a
wireless fashion for measuring physiological signals of a patient.
The at least one wireless sensor is located on the patient and may
comprise a wireless surface electrode assembly or a wireless needle
assembly. The system may also comprise a wireless stimulator
syncronized with the wireless sensor for performing certain
diagnostic tests, such as nerve conduction velocity tests, for
example. The wireless sensor preferably includes active, reference
and common conductors. The common conductor can be used to measure
the common mode voltage of the patient in the vicinity of the
testing, and this voltage can then be subtracted from the measured
active and reference voltages.
Inventors: |
Mumford, John Robert;
(Mississauga, CA) ; Kurtz, Ronald Leon; (Oakville,
CA) |
Correspondence
Address: |
BERESKIN AND PARR
40 KING STREET WEST
BOX 401
TORONTO
ON
M5H 3Y2
CA
|
Family ID: |
35376119 |
Appl. No.: |
11/130221 |
Filed: |
May 17, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60571890 |
May 18, 2004 |
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60571944 |
May 18, 2004 |
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60571942 |
May 18, 2004 |
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Current U.S.
Class: |
600/300 ;
128/903 |
Current CPC
Class: |
A61N 1/0502 20130101;
A61B 5/4041 20130101; A61N 1/0456 20130101; A61B 5/0002 20130101;
A61N 1/36017 20130101 |
Class at
Publication: |
600/300 ;
128/903 |
International
Class: |
A61B 005/00 |
Claims
1. A wireless physiological monitoring system for measuring
physiological signals from a patient, comprising: 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 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.
2. The system of claim 1, wherein the at least one wireless sensor
includes a wireless adapter comprising: 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 removing common mode voltage from the
differential measurement.
3. The system of claim 2, wherein the second transceiver transmits
the differential measurement as the wireless physiological
signal.
4. The system of claim 3, wherein the at least one wireless sensor
comprises a wireless surface electrode assembly comprising the
measurement module.
5. The system of claim 4, wherein 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.
6. The system of claim 5, wherein the active and reference
electrodes are located approximately equidistantly from the common
electrode.
7. The system of claim 3, wherein the at least one wireless sensor
comprises a wireless needle assembly comprising the measurement
module.
8. The system of claim 7, wherein 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 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.
9. The system of claim 7, wherein 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 wireless adapter; a needle
shaft comprising the active and reference conductors; and a surface
electrode comprising the common conductor.
10. The system of claim 7, wherein 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 wireless adapter; a needle
shaft comprising the active conductor; and surface electrodes
comprising the reference and common conductors, respectively.
11. A wireless physiological monitoring system for measuring
physiological signals from a patient, comprising: 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 including a
wireless adapter having a 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 removing common mode voltage from the differential
measurement;
12. The system of claim 11, wherein the second transceiver
transmits the differential measurement as the wireless
physiological signal.
13. The system of claim 12, wherein the at least one wireless
sensor comprises a wireless surface electrode assembly comprising
the measurement module.
14. The system of claim 13, wherein 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.
15. The system of claim 14, wherein the active and reference
electrodes are located approximately equidistantly from the common
electrode.
16. The system of claim 12, wherein the at least one wireless
sensor comprises a wireless needle assembly comprising the
measurement module.
17. The system of claim 16, wherein 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 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.
18. The system of claim 16, wherein 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 wireless adapter; a needle
shaft comprising the active and reference conductors; and a surface
electrode comprising the common conductor.
19. The system of claim 16, wherein 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 wireless adapter; a needle
shaft comprising the active conductor; and surface electrodes
comprising the reference and common conductors, respectively.
20. A wireless sensor for measuring a physiological signal from a
patient, the wireless sensor being disposed on a measurement site
on the patient, the system comprising: a wireless adapter having a
transceiver a measurement module having an active conductor and a
reference conductor for receiving voltages used to produce a
differential voltage measurement indicative of the physiologicial
signal, the measurement module further including a common conductor
for receiving another voltage for removing common mode voltage from
the differential measurement, wherein the transceiver transmits a
wireless physiological signal corresponding to the differential
voltage measurement.
21. The sensor of claim 20, wherein the wireless sensor comprises a
wireless surface electrode assembly.
22. The sensor of claim 21, wherein 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.
23. The sensor of claim 22, wherein the active and reference
electrodes are located approximately equidistantly from the common
electrode.
24. The sensor of claim 20, wherein the wireless sensor comprises a
wireless needle assembly.
25. The sensor of claim 24, wherein 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 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.
26. The sensor of claim 24, wherein 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 wireless adapter; a needle
shaft comprising the active and reference conductors; and a surface
electrode comprising the common conductor.
27. The sensor of claim 24, wherein 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 wireless adapter; a needle
shaft comprising the active conductor; and surface electrodes
comprising the reference and common conductors, respectively.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/571,944 filed on May 18, 2004, the
entire contents of which are hereby incorporated by reference, U.S.
Provisional Patent Application Ser. No. 60/571,890, filed on May
18, 2004, the entire contents of which are hereby incorporated by
reference and U.S. Provisional Patent Application Ser. No.
60/571,942 filed on May 18, 2004, the entire contents of which are
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] 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 and/or diagnosing
certain medical conditions.
BACKGROUND OF THE INVENTION
[0003] 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 signals are measured
from the cortex.
[0004] 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 perform 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.
[0005] 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 cables. Accordingly,
the time required for attaching or removing the electrodes and
cables to or from the patient can be quite long. 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 routinely run
over by people and heavy equipment and therefore subject to a high
failure rate.
SUMMARY OF THE INVENTION
[0006] 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.
[0007] 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.
[0008] 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 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.
[0009] In one instance, the wireless adapter may communicate
according to the Bluetooth communication protocol.
[0010] 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.
[0011] 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.
[0012] 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 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.
[0013] In one embodiment, the at least one wireless sensor includes
a 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 removing common mode voltage from the
differential measurement. The second transceiver transmits the
differential measurement as the wireless physiological signal.
[0014] 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.
[0015] The active and reference electrodes are located
approximately equidistantly from the common electrode.
[0016] 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 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.
[0017] 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 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 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.
[0018] 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.
[0019] 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 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 OF THE DRAWINGS
[0020] 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:
[0021] FIG. 1 shows an exemplary embodiment of a wireless
physiological monitoring system in accordance with the
invention;
[0022] FIG. 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 FIG. 1 in accordance with the invention;
[0023] FIGS. 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 FIG. 1 in accordance with the
invention;
[0024] FIG. 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 FIG. 1 in accordance with the
invention;
[0025] FIG. 3b shows a magnified view of an exemplary embodiment of
the tip of the wireless needle assembly of FIG. 3a; and,
[0026] FIG. 4 shows an exemplary embodiment of a wireless adapter
for use with either the wireless surface electrode assembly of
FIGS. 2a and 2b or the wireless needle assembly of FIGS. 3a and
3b.
DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION
[0027] 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 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 instances, well-known methods, procedures and
components have not been described in detail so as not to obscure
the invention.
[0028] Referring first to FIG. 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 1400 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.
[0029] 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 simply be a storage device. 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.
[0030] In one exemplary embodiment, the monitoring device 12
comprises a processor 20, a memory unit 22, a transceiver 24 with
an antenna 26, a power supply 28 and a display 30 connected as
shown in FIG. 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 synchronize 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 Bluetooth communication protocol
as discussed in more detail below.
[0031] 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 another 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 algorithms are commonly known to those skilled
in the art and will not be discussed further.
[0032] 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 LCD, and the
like. The power supply 28 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.
[0033] The wireless physiological monitoring system 10 may further
comprise at least one wireless stimulator 32 for performing certain
diagnostic tests on the patient 16 such as nerve conduction
velocity tests. In particular, the wireless stimulator 32 is used
to generate a stimulation current to create an action potential in
a nerve of the patient 16.
[0034] 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 FIG. 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
monitoring device 12 or when it is manually actuated.
[0035] The stimulation generation unit 36 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 16, the amplitude may be up
to 100 milliamps, the duration of up to 1 millisecond and the
maximum voltage is limited to 400 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.
[0036] 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, and 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 the 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.
[0037] 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.
[0038] The wireless stimulator 32 is powered by the battery 46. In
one embodiment, the battery 46 is 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.
[0039] 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 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.
[0040] Referring now to FIGS. 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 56 and 58 so 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 58. 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.
[0041] 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 physiological signal measured by the electrode assembly 50
to the monitoring device 12. An exemplary implementation of the
wireless adapter 54 is described below.
[0042] 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
monitoring/testing is completed so that the wireless adapter 54 can
be reused and the measurement module 52 can be discarded.
[0043] The wireless surface electrode assembly 50 further includes
an adhesive portion preferably applied to a section of each of the
electrodes 56, 58 and 60 to hold the wireless surface electrode
assembly 50 in place once the assembly 50 has been attached to the
patient 16. 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.
[0044] Referring now to FIGS. 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.
[0045] 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 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 for the desired physiological
signal and so that the common mode component of the differential
measurement may be removed.
[0046] 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 conductors 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.
[0047] 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 is 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 sizes and depths. Further details of the needle used by
wireless needle assembly 70 are shown and described in co-pending
U.S. patent application Ser. No. ______, filed May 17, 2005 and
entitled "Needle Having Multiple Electrodes", the entire contents
of which is hereby incorporated by reference.
[0048] 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.
[0049] 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.
[0050] Referring now to FIG. 4, shown therein is an exemplary
embodiment of the wireless adapter 54 for use with either the
wireless surface electrode assembly 60 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
FIG. 4. The processing unit 90 controls the operation of the
wireless adapter 54 and may be a DSP or the like.
[0051] 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 106.
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 Hz.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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 90 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.
[0056] 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.
[0057] 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 physiological signals 18 from various
wireless sensors 14 can be distinguished from one another.
[0058] 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.
[0059] 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.
[0060] 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
and/or 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.
[0061] With the Bluetooth 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 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.
[0062] 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 transit 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.
[0063] 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.
[0064] 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 microvolt. 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 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 accuracy.
[0065] 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 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 possible data rate of
approximately 15 Mbits/sec, which exceeds the capability of the
Bluetooth standard, but is still within the range of 802.11 g
wireless communication standards.
[0066] Unfortunately, the power consumption of devices that operate
under the 802.11 g wireless standard is 3 times higher than devices
that operate under the Bluetooth 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 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.
[0067] 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.
[0068] 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 life 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.
[0069] The wireless physiological monitoring system of the
invention is particularly well suited for wireless monitoring of
ECG, EMG 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 and/or numbered according to
the corresponding placement location on the patient 16.
Accordingly, a medical practitioner simply needs to refer only to
the color-coding and/or numbering when attaching the wireless
sensors 14 to the patient 16.
[0070] 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 insert earphone that may be used to present an
auditory stimulus to 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 wireless
sensors 14 are placed at the appropriate location on the patient 16
to record the resulting evoked potential.
[0071] It should be understood that various modifications can be
made to the embodiments described and illustrated herein, without
departing from the invention.
* * * * *