U.S. patent application number 12/653114 was filed with the patent office on 2010-09-30 for apparatus and method for performing nerve conduction studies with localization of evoked responses.
Invention is credited to Shai N. Gozani, Xuan Kong, Ann Pavlik Meyer, Martin D. Wells.
Application Number | 20100249643 12/653114 |
Document ID | / |
Family ID | 46278847 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100249643 |
Kind Code |
A1 |
Gozani; Shai N. ; et
al. |
September 30, 2010 |
Apparatus and method for performing nerve conduction studies with
localization of evoked responses
Abstract
An apparatus and method for detecting physiological function,
for example, nerve conduction, is described. In one embodiment the
apparatus includes a housing including a stimulator shaped to fit a
first anatomical site and a detector shaped to fit a second
anatomical site. The housing automatically positions the detector
substantially adjacent to the second anatomical site when the
stimulator is positioned substantially adjacent to the first
anatomical site. The detector contains a plurality of individual
detection elements, whereby the response evoked by stimulation at
the first anatomical site is measured using one or more of these
detection elements at the second anatomical location.
Inventors: |
Gozani; Shai N.; (Brookline,
MA) ; Meyer; Ann Pavlik; (Newton, MA) ; Kong;
Xuan; (Acton, MA) ; Wells; Martin D.;
(Needham, MA) |
Correspondence
Address: |
PANDISCIO & PANDISCIO, P.C.
470 TOTTEN POND ROAD
WALTHAM
MA
02451-1914
US
|
Family ID: |
46278847 |
Appl. No.: |
12/653114 |
Filed: |
December 8, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10075217 |
Feb 14, 2002 |
7628761 |
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12653114 |
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09625502 |
Jul 26, 2000 |
6379313 |
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10075217 |
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09270550 |
Mar 16, 1999 |
6132386 |
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09625502 |
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09022990 |
Feb 12, 1998 |
5976094 |
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09270550 |
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08886861 |
Jul 1, 1997 |
5851191 |
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09022990 |
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60269126 |
Feb 15, 2001 |
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Current U.S.
Class: |
600/554 |
Current CPC
Class: |
A61B 5/6829 20130101;
A61B 5/389 20210101; A61B 2560/0412 20130101; A61B 2562/063
20130101; A61B 5/6824 20130101; A61B 5/742 20130101; A61B 5/1106
20130101; A61B 5/4041 20130101; A61B 5/296 20210101; A61B 5/05
20130101 |
Class at
Publication: |
600/554 |
International
Class: |
A61B 5/05 20060101
A61B005/05 |
Claims
1. An apparatus for assessing physiological function in an
individual comprising: a sensor, said sensor comprising: a
stimulator shaped to fit a first anatomical site, said
stimulator'generating a stimulus whereby application of said
stimulus stimulates a nerve at said first anatomical site; and a
detector shaped to fit a second anatomical site, said detector
comprising a plurality of electrodes for detecting a signal
generated in response to said stimulus; wherein said sensor
automatically positions said detector substantially adjacent to
said second anatomical site when said stimulator is positioned
substantially adjacent to said first anatomical site; and further
wherein said sensor comprises a processor for processing said at
least one signal from said detector to select at least one
electrode detecting at least one signal characteristic of said
anatomical site.
2. An apparatus for assessing physiological function in an
individual comprising: a sensor, said sensor comprising: a
stimulator shaped to fit a first anatomical site, said stimulator
generating a stimulus whereby application of said stimulus
stimulates a nerve at said first anatomical site; and a detector
shaped to fit a second anatomical site, said detector comprising a
plurality of electrodes for detecting a signal generated in
response to said stimulus; wherein said sensor comprises a
processor for processing said at least one signal from said
detector to select at least one electrode detecting at least one
signal characteristic of said anatomical site.
3. An apparatus for assessing physiological function in an
individual comprising: a sensor, said sensor comprising: a
stimulator shared to fit a first anatomical site, said stimulator
generating a stimulus whereby application of said stimulus
stimulates a nerve at said first anatomical site; and a detector
shaped to fit a second anatomical site, said detector comprising a
plurality of electrodes for detecting a signal generated in
response to said stimulus; wherein said sensor automatically
positions said detector substantially adjacent to said second
anatomical site when said stimulator is positioned substantially
adjacent to said first anatomical site.
4. The apparatus of claim 3 wherein said sensor is shaped to fit a
lower extremity of said individual.
5. The apparatus of claim 4 wherein said lower extremity comprises
the foot.
6. The apparatus of claim 3 further comprising a processor, said
processor for processing said at least one signal from said
detector to select at least one electrode detecting at least one
signal characteristic of said anatomical site.
7. The apparatus of claim 3 wherein said physiological function
comprises nerve conduction.
8. The apparatus of claim 7 wherein said nerve conduction comprises
conduction of the tibial nerve.
9. The apparatus of claim 7 wherein said nerve conduction comprises
conduction of the peroneal nerve.
10. The apparatus of claim 3 wherein said stimulator comprises a
shape to fit said first anatomical site, wherein said first
anatomical site comprises, a superficial location over the peroneal
nerve, and said detector comprises a shape to fit said second
anatomical site, wherein said second anatomical site comprises a
superficial location over the extensor digitorum brevis muscle of
the foot.
11. The apparatus of claim 3 wherein said stimulator comprises a
shape to fit said first anatomical site, wherein said first
anatomical site comprises a superficial location over the tibial
nerve, and said detector comprises a shape to fit said second
anatomical site, wherein said second anatomical site comprises a
superficial location over the abductor hallucis muscle of the
foot.
12. The apparatus of claim 3 wherein said first anatomical site
comprises the ankle ipsilateral to said second anatomical site.
13. The apparatus of claim 3 further comprising a positioning
indicator for location over a third anatomical site.
14. The apparatus of claim 11 wherein said third anatomical site
comprises the malleolus of the ankle joint.
15. The apparatus of claim 14 wherein said malleolus is ipsilateral
to said second anatomical site.
16. The apparatus of claim 3 wherein said detector is physically
connected to said stimulator by a semi-flexible connector.
17. The apparatus of claim 16 wherein said connector comprises a
strip comprising electrical traces for signaling between said
detector and said stimulator.
18. The apparatus of claim 3 wherein said electrodes comprise an
electrode array in communication with a processor.
19. The apparatus of claim 18 wherein said electrode array
comprises at least two independent interleaved bipolar recording
elements.
20. The apparatus of claim 3 wherein said signal comprises a
compound muscle action potential.
21. The apparatus of claim 20 wherein said compound muscle action
potential is recorded over a motor point.
22. The apparatus of claim 3 wherein the weighted sum of the
recordings of at least two electrodes comprises the detectable
signal.
23. A method for assessing physiological function in an individual,
comprising: (a) placing a sensor on an individual, said sensor
comprising: a stimulator shaped to fit a first anatomical site,
said stimulator generating a stimulus whereby application of said
stimulus stimulates a nerve at said first anatomical site; and a
detector shaped to fit a second anatomical site, said detector
comprising a plurality of electrodes for detecting at least one
signal generated in response to said stimulus; wherein said sensor
automatically positions said detector substantially adjacent to
said second anatomical site when said stimulator is placed
substantially adjacent said first anatomical site on the surface of
an individual; and (b) performing nerve conduction studies with at
least one electrode to assess physiological function in an
individual.
24. The method of claim 23 further comprising: (c) processing said
at least one signal generated at said second anatomical site to
select at least one electrode detecting said at least one signal
characteristic of said second anatomical site; (d) selecting at
least one electrode in response to said processing according to
step (c) from said plurality of electrodes; and (e) performing
nerve conduction studies of step (b) with said at least one
electrode selected in step (d).
25. The method of claim 23 wherein said nerve conduction studies
comprise measurement of an F-wave latency.
26. The method of claim 23 wherein said nerve conduction studies
comprise measurement of a motor latency.
27. The method of claim 23 wherein said nerve conduction studies
comprise measurement of a sensory latency.
28. The method of claim 23 wherein said nerve conduction studies
comprise measurement of a sensory amplitude.
29. The method of claim 24 wherein processing further comprises
amplitude comparison between a plurality of signals generated at
said second anatomical site.
30. The method of claim 24 wherein processing comprises frequency
spectrum comparison between a plurality of signals generated at
said second anatomical site.
31. The method of claim 23 wherein said at least one signal
generated at said second anatomical site comprises peripheral
evoked potentials.
32. The method of claim 29 wherein said amplitude comparison
comprises maximal peak to peak amplitude.
33. The method of claim 30 wherein said frequency spectrum
comparison comprises discrete Fourier transform analysis of said
plurality of signals generated at said second anatomical site and
comparison of the spectral components.
34. The method of claim 33 wherein said selected electrodes
comprise electrodes with more energy at low frequencies.
35. The method of claim 23 wherein said at least one signal
generated at said second anatomical site comprises compound muscle
action potential.
36. The method of claim 23 wherein said at least one signal
generated at said second anatomical site is recorded over a motor
point.
37. An apparatus for assessing physiological function in an
individual, comprising: stimulus means for producing a stimulus and
for applying the stimulus at a first anatomical site whereby a
nerve is stimulated; detecting means comprising a plurality of
electrodes for detecting at least one signal characteristic of a
second anatomical site generated in response to said stimulus; and
connecting means for connecting said stimulus means and said
detecting means wherein said connecting means automatically
position said detecting means substantially adjacent said second
anatomical site when said stimulating means are positioned
substantially adjacent first anatomical site.
38. The apparatus of claim 37 further comprising: processing means
for processing said at least one signal from said detecting means.
Description
REFERENCE TO PENDING PRIOR PATENT APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application Serial No. 06/269,126, filed Feb. 15, 2001, and is a
continuation-in-part of U.S. patent application Ser. No.
09/625,502, filed Jul. 26, 2000, which is a continuation of U.S.
patent application Ser. No. 09/270,550, filed Mar. 16, 1999 (now
U.S. Pat. No. 6,132,386), which is a continuation-in-part of U.S.
patent application Ser. No. 09/022,990, filed Feb. 12, 1998 (now
U.S. Pat. No. 5,976,094), which is a divisional application of U.S.
patent application Ser. No. 08/886,861, filed Jul. 1, 1997 (now
U.S. Pat. No. 5,851,191), all of which are hereby incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to apparatus and methods for the
assessment of neuromuscular function. More specifically, this
invention relates to apparatus and methods for diagnosing
peripheral nerve and muscle diseases based on the assessment of
neuromuscular function.
BACKGROUND OF THE INVENTION
[0003] Neuromuscular diseases, which represent disorders of the
peripheral nerves and muscles, are a common and growing health care
concern. The most prevalent neuromuscular disorders are carpal
tunnel syndrome (CTS), low back pain caused by spinal root
compression (i.e., radiculopathy), and diabetic neuropathy, which
is nerve degeneration associated with diabetes. These conditions
affect approximately thirty to forty million individuals each year
in the United States alone, and have an associated economic cost
greater then $100 billion annually. However, despite their
extensive impact on individuals and the health care system, the
detection and monitoring of such neuromuscular diseases are based
on outdated and inaccurate clinical techniques or rely on expensive
referrals to a specialist.
[0004] In particular, the effective prevention of neuromuscular
dysfunction requires early detection and subsequent action. Even
experienced physicians find it difficult to diagnose and stage the
severity of neuromuscular dysfunction based on symptoms alone. The
only objective way to detect many neuromuscular diseases is to
measure the transmission of neural signals. The gold standard
approach is a formal nerve conduction study by a clinical
neurologist, but this procedure has a number of significant
disadvantages. First, it requires a highly trained specialist. As a
result, it is expensive and generally requires weeks or months to
complete. Second, because they are not readily available, formal
nerve conduction studies are generally performed late in the
episode of care, thus serving a confirmatory role rather than a
diagnostic one.
[0005] Thus, there is a need for making accurate and robust nerve
conduction measurements available to a wide variety of health care
personnel in multiple settings, including the clinic, the office,
the field, and the workplace (all of which are sometimes
collectively referred to as "point-of-care" settings). However,
personnel in these environments generally do not have the
neurophysiological and neuroanatomical training to perform such
studies. In particular, the correct application of nerve conduction
studies requires appropriate placement of electrodes for both
stimulation of the nerve and detection of the evoked response from
the corresponding nerve or muscle. Therefore, in order to provide
effective nerve conduction studies in point-of-care settings, it is
necessary to simplify and automate the process of correct electrode
placement.
[0006] The prior art reveals a number of attempts to simplify the
assessment of neuromuscular function, such as in diagnosing CTS,
and to make such diagnostic measurements available to non-experts.
Rosier (U.S. Pat. No. 4,807,643) describes a portable device for
measuring nerve conduction velocity in patients. This instrument,
however, does not provide any assistance in the correct placement
of stimulation and detection electrodes. On the contrary, a skilled
operator with a fairly sophisticated knowledge of nerve and muscle
anatomy must ensure correct application of the device. Spitz et al.
(U.S. Pat. No. 5,215,100) and Lemmen (U.S. Pat. No. 5,327,902) have
also attempted to simplify nerve conduction studies. Specifically,
they proposed systems that measure nerve conduction parameters
between the arm or forearm and the hand, such as would be required
for diagnosing CTS. Both systems suffer from several significant
disadvantages, however. First, both systems are large, bulky, and
constructed from rigid structures that create a supporting fixture
for the arm and hand of an adult. This severely limits their
portability and increases their cost. Second, these systems are
only applicable to specific limbs and are not generally applicable
to numerous anatomical sites. Third, these devices require highly
trained operators who can make the appropriate adjustments on the
apparatus so as to ensure electrode contact with the proper
anatomical sites on the arm and hand. In particular, these systems
provide no physiological localization of the electrodes, and as a
result multiple placements are often required to find the correct
electrode location.
[0007] There have been some attempts to simplify the process of
nerve localization, primarily for the purpose of avoiding nerve
damage during surgical procedures. For example, Raymond et al.
(U.S. Pat. No. 5,775,331) describes a system for locating a nerve
by applying a stimulus to a plurality of stimulation sites (such as
the cavernosal nerve), recording a response to the stimulation
(such as the tumescence response), and modifying the stimulation
site according to an algorithm that utilizes the response. Although
this invention is useful in its intended application of nerve
preservation during surgery, it could not be used to simplify or
automate nerve conduction studies because it does not provide means
to locate the evoked response, leaving this difficult task to the
operator.
[0008] The present invention avoids the aforementioned
limitations.
SUMMARY OF THE INVENTION
[0009] In accordance with the present invention, an apparatus and
method are provided for the substantially automated, rapid, and
efficient assessment of neuromuscular function without requiring
the involvement of highly trained personnel. The assessment of
neuromuscular function is effected by stimulating a nerve, and then
measuring the response of a muscle innervated by that nerve. The
muscle response is detected by measuring the myoelectric potential
generated by the muscle in response to the stimulus.
[0010] More particularly, the apparatus and method of the invention
assess physiological function in, for example, the lower extremity
of an individual by using an electrode to apply a stimulus to a
nerve. The stimulus may be, for example, an electrical stimulus or
a magnetic stimulus. Other types of stimuli may also be used. A
detector, adapted for detecting the myoelectric potential generated
by a muscle in response to the stimulus, detects the response of
the muscle to the stimulus. An electronic controller then evaluates
the physiological function of the nerve. The function is then
correlated to the presence or absence of a neuromuscular pathology,
such as, for example, Carpal Tunnel Syndrome (CTS) or lumbosacral
radiculopathy.
[0011] In a preferred embodiment of the invention, there is
provided a sensor including a stimulator electrode and a
myoelectric detector. The stimulator electrode is adapted for
placement at a first anatomical site substantially adjacent to a
nerve, and the myoelectric detector is adapted for placement at a
second anatomical site substantially adjacent to a muscle
innervated by that nerve. In one embodiment, a semi-flexible
connector links the stimulator electrode and myoelectric detector
such that the connector automatically positions the myoelectric
detector at the second anatomical site when the stimulator
electrode is positioned at the first anatomical site, or vice
versa.
[0012] In one embodiment, the apparatus of the invention further
includes a processor for processing at least one signal detected by
the myoelectric detector which is characteristic of the second
anatomical site.
[0013] In a particular embodiment, the physiological function of an
individual which is to be assessed by the apparatus of the
invention is nerve conduction, such as conduction of the tibial
nerve or the peroneal nerve. Thus, in one embodiment, the first
anatomical site is a superficial location over the peroneal nerve
and the second anatomical site is a superficial location over the
extensor digitorum brevis muscle of the foot. Alternatively, the
first anatomical site is a superficial location over the tibial
nerve and the second anatomical site is a superficial location over
the abductor hallucis muscle of the foot. In another embodiment,
the sensor of the invention includes a positioning indicator for
location over a third anatomical site such as the medial or lateral
malleolus of the individual. In one embodiment the superficial
location is on the skin of the individual.
[0014] In one embodiment of the apparatus of the invention, at
least a portion of the body of the sensor is manufactured from a
plastic, such as MYLAR. In one embodiment of the invention, the
flexible connector is a strip which is rectangular, s-shaped, or
any other shape configured to position the myoelectric detector
over the second anatomical site when the stimulator electrode is
positioned over the first anatomical site. In one embodiment, the
connector includes electrical traces for carrying signals to the
stimulator electrode, and from the myoelectric detector, to an
electronic controller and monitor. In one embodiment, the traces
connect the stimulator electrode and the myoelectric detector to
the controller. In a particular embodiment of the invention, the
myoelectric detector includes an electrode array that includes at
least two independent interleaved bipolar recording electrodes. The
signals recorded from the recording electrodes include compound
muscle action potentials (CMAP's). In one embodiment, the compound
muscle action potential (CMAP) is recorded over a motor point. In
one embodiment of the invention, the detectable signal includes the
weighted sum of the recordings of at least two of the recording
electrodes.
[0015] The method of the invention relates to the assessment of
physiological function using appropriate apparatus. In one form of
the invention, a sensor, including a stimulator electrode and a
myoelectric detector, attached by a connector, is placed on the
skin of the individual overlying the anatomical location to be
studied. The stimulator electrode is placed at the first anatomical
site. When the stimulator electrode is positioned at the first
anatomical site, the myoelectric detector is automatically
positioned at the second anatomical site by the construction of the
connector.
[0016] With the sensor positioned as described above on the skin of
the individual, the stimulator electrode applies a stimulus to a
nerve (for example, the peroneal nerve or the tibial nerve). A
muscle innervated by the nerve (for example, the extensor digitorum
brevis muscle of the foot with respect to the peroneal nerve, or
the abductor hallucis muscle of the foot with respect to the tibial
nerve) responds and thereby generates a myoelectrical potential.
The signal generated by the myoelectrical potential is detected by
the electrode array of the myoelectric detector and processed by
the processor in communication with the myoelectric detector.
[0017] The processor processes the signals from the myoelectric
detector's electrode array to select which electrode(s) of the
electrode array is detecting at least one signal characteristic of
the second anatomical site. The electrode selected by the processor
as detecting at least one signal characteristic of the second
anatomical site is used to perform nerve conduction studies to
assess physiological function of the individual. The processor
further processes signals from the selected electrode to perform
the nerve conduction study. The processed signals are correlated to
physiological function of the nerve and muscle.
[0018] The invention will be understood further upon consideration
of the following drawings, description and claims. The drawings are
not necessarily to scale and emphasis instead is generally being
placed upon illustrating the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates one embodiment of a sensor formed in
accordance with the present invention placed on the lower extremity
of an individual;
[0020] FIG. 2 illustrates one embodiment of a sensor formed in
accordance with the present invention shaped to fit the foot of an
individual;
[0021] FIG. 2A is a cross-sectional view illustrating one way of
fabricating the sensor of the present invention;
[0022] FIG. 3 illustrates the embodiment of FIG. 2 positioned on
the foot of a patient;
[0023] FIG. 4 is a graph in the time domain of the muscle response
evoked and measured by an embodiment of the present invention;
[0024] FIG. 5 is a flowchart illustrating the steps in one
embodiment of the invention to select optimum recording electrode
pairs; and
[0025] FIG. 6 is a graph in the frequency domain showing the power
spectral density of muscle responses evoked and measured by one
embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] A primary objective of the present invention is to measure
evoked potentials in peripheral nerves and muscles. The process of
acquiring such measurements is commonly described as a nerve
conduction study. Typical nerve conduction measurements include
nerve impulse propagation latency (distal motor latency, DML, or
distal sensory latency, DSL), nerve impulse velocity (conduction
velocity, CV), the amplitude of the evoked neural signal (nerve
action potential, NAP, amplitude), and the amplitude of the
neurally evoked muscle signal (compound muscle action potential,
CMAP, amplitude).
[0027] The present invention includes a nerve conduction sensor and
associated algorithms. Taken together, the invention provides
mechanical and electronic localization to perform accurate and
reliable nerve conduction studies. Mechanical localization is a
process whereby mechanical means facilitate the placement of an
evoked response detector in the general vicinity of the nerve
segment or muscle to be measured. Subsequently, electronic
localization may be utilized to precisely investigate the
electrophysiological properties of the region and identify the
optimal location at which to measure the evoked response, so as to
obtain accurate and reliable measurements. Through utilization of
mechanical and electronic localization, the present invention
obviates the need for precise electrode placement and knowledge of
neuroanatomy. Instead, this knowledge is effectively encapsulated
within the mechanical and electronic localization means, thereby
allowing an effective nerve conduction study to be performed
without requiring the involvement of highly trained personnel.
[0028] In general, referring to FIG. 1, there is shown a nerve
conduction sensor 5 formed in accordance with the present
invention. Sensor 5 comprises a stimulator 10, a detector 15, a
connector 20, and an interface 25, all integrated in a unitary
housing. The stimulator 10 stimulated a peripheral nerve N at a
first anatomical site S1, for example, the ankle. The detector 15
detects an evoked signal at a second anatomical site S2, which is
either the nerve N stimulated by the stimulator 10 at a location
different from the first anatomical site S1 or, as shown in FIG. 1,
on a muscle M innervated by the stimulated nerve N, for example,
the extensor digitorum brevis muscle. Other first anatomical sites
S1 (for example, knee, wrist, and elbow) and other second
anatomical sites S2 (for example, foot, hand, and calf) are also
contemplated by the present invention and are not limited to the
first and second anatomical sites illustrated in FIG. 1.
[0029] An important aspect of the present invention is the
connector 20, which connects the stimulator 10 and the detector 15.
The connector 20 automatically positions the detector 15
substantially adjacent to the second anatomical site S2 when the
stimulator 10 is positioned at the first anatomical site S1, thus
mechanically localizing the evoked signal.
[0030] Another important aspect of the present invention relates to
the properties of the detector 15. In particular, the detector 15
preferably contains an element array 30 (FIG. 2) comprising a
plurality of individual detection elements. The evoked response
detected by the detector 15 is measured using one or more of the
detection elements of the element array 30, thus electronically
localizing the evoked signal.
[0031] FIG. 2 provides a detailed view of one embodiment of the
nerve conduction sensor 5, which includes the stimulator 10,
detector 15, connector 20, and interface 25. In a preferred
embodiment, the nerve conduction sensor 5 is formed from multiple
layers of materials. The primary base layer is preferentially
formed from a continuous sheet of MYLAR. Subsequent layers include
colored ink, conductive silver traces, insulating material,
silver-chloride pads, hydrogel, and medical grade adhesive. The
sensor is then applied to the skin of the individual so that the
operative elements face inwardly, toward the patient, and so that
the base layer faces outwardly, away from the patient. Details of
the general construction of such layered sensors are known in the
art. The connector 20 of the nerve conduction sensor 5 is
configured to mechanically orient the stimulator 10 and the
detector 15 relative to one another and the patient's anatomy. In
particular, the connector 20 ensures that placement of stimulator
10 at a first anatomical site S1, substantially determines the
orientation and position of the detector 15 at a second anatomical
site S2 as illustrated in FIG. 1. In accordance with the present
invention, the automatic positioning of the detector 15 need not be
precise but must be substantially in the vicinity of the second
anatomical site S2. The construction of connector 20 substantially
limits the range of anatomic sites over which the detector 15 can
be placed, so that anatomic sites that are physiologically
unrelated to the stimulation site S1 (e.g., anatomical site S3 in
FIG. 1.) are not accessible to the detector 15.
[0032] In a preferred embodiment, the connector 20 is formed from
MYLAR. However, other materials such as various plastics may also
be used. The particular connector configuration shown in FIG. 2 is
intended to be illustrative and other configurations may also be
used and should be considered to be within the scope of the present
invention. For example, in another embodiment, the stimulator 10
and the detector 15 are contiguous and attached. The construction
of connector 20 is limited only by the objective that placement of
the stimulator 10 at the first anatomical site S1 automatically
places the detector 15 substantially adjacent to the second
anatomical site S2. The converse will also hold, i.e., placement of
the detector 15 at the second anatomical site S2 automatically
places the stimulator 10 at the first anatomical site S1.
[0033] The stimulator 10 includes at least one stimulation element
35 (FIG. 2) that delivers a stimulus to a peripheral nerve. The
stimulus can be electrical, magnetic, optical, chemical, or
biological. In a preferred embodiment, the stimulus is an
electrical impulse and the stimulation element 35 includes a
plurality of layers of different materials which together form the
stimulation electrode. By way of example, and looking at FIG. 2A,
stimulation electrode 35 may include a mylar substrate 40, a layer
of conductive ink 45, a conductive gel 50 bordered by a foam mask
55, a layer of adhesive 60, and a release liner 62.
[0034] In a preferred embodiment of the invention illustrated in
FIG. 2, the stimulator 10 includes a temperature probe 65. When the
stimulator 10 is placed on the individual, the temperature probe
comes into contact with the test subject's skin and measures the
skin surface temperature. This temperature is then used for
calibrating the system. Other locations for the temperature probe
65 have been contemplated and include sites within the detector 15
and the connector 20.
[0035] Referring still to FIG. 2, in one embodiment of the
invention, the detector 15 includes an array 30 of detection
elements. The detection elements may be capable of detecting
bioelectrical, magnetic, optical, chemical or biological signals.
In a preferred embodiment, bioelectrical signals, and more
specifically biopotentials, are detected, and the array 30 includes
at least four electrodes 70, 75, 80 and 85 (collectively, the array
30), preferably arranged in a linear configuration such as shown in
FIG. 2. However, other configurations, such as a matrix of
electrodes, and different numbers of electrodes, have been
contemplated and should be considered within the scope of the
present invention.
[0036] The detector array 30 illustrated, for example, in FIG. 2
allows the detector 15 to adapt to variations in the anatomic
location, physical structure and physiological organization of the
second anatomical site S2, such as a muscle M. In a preferred
embodiment, the electrodes 70, 75, 80 and 85 are composed of a
plurality of layers of different materials with substantially the
same area. Again, construction such as that shown in FIG. 2A may be
used. In many applications, such as in the recording of electrical
signals, a distinct reference electrode is required. This reference
electrode essentially establishes a "zero point" that other
voltages may be referenced against. Such a reference electrode 90
is shown in FIG. 2. In this embodiment, the reference electrode 90
provides a reference voltage for acquisition of biopotentials
signals from detector array 30 of the detector 15. In one
embodiment, shown in FIG. 2, the reference electrode 90 is located
on the stimulator 10. In other embodiments, the reference electrode
90 is located on the detector 15, on the connector 20, or on
another part of the nerve conduction sensor 5.
[0037] The stimulator electrode 10 and the bioelectrical detector
15 are formed in the nerve conduction sensor 5 so as to make
contact with the skin of the individual when the nerve conduction
sensor 5 is in position on the individual. In one embodiment, the
nerve conduction sensor 5 may be configured for different sizes
(e.g., small, medium and large), for different nerves (e.g.,
median, ulnar, peroneal, and posterior tibial nerves), for
different muscles (e.g., extensor digitorum brevis, adductor
hallucis brevis), for right and left anatomical sites, and for
various anatomical sites (e.g., ankle, foot, hand, wrist).
[0038] Referring to FIG. 2, in one embodiment, the nerve conduction
sensor 5 has an interface 25 that serves as a communications port
between the nerve conduction sensor 5 and external devices, such as
an electronic controller 95 (see FIG. 3). The nerve conduction
sensor 5 also has a series of traces that provide communication
between the connector 25 and internal elements of the sensor. In a
preferred embodiment, illustrated in FIG. 2, these traces 100, 105,
110 and 115 are capable of transmitting electronic signals and are
embedded within a unitary housing of sensor 5. As shown in FIG. 2,
the nerve conduction sensor 5 includes traces 100 that communicate
signals from the stimulation elements 35 on the stimulator 10 to
the connector 25; traces 105 that communicate signals from the
element array 30 on the detector 15 to the connector 25; traces 110
that communicate signals from the reference electrode 90 to the
connector 25; and traces 115 that communicate electronic signals
from the temperature probe 65 to the connector 25. In one
embodiment, the traces are created by printing silver lines 45
(FIG. 2A) on the mylar substrate 40 which are in direct
communication with conductive gels 50 at both the stimulation and
detection sites. In this embodiment, the foam mask 55 is positioned
on top of these traces to prevent shorting.
[0039] Referring still to FIG. 2, in one embodiment, the nerve
conduction sensor 5 includes indicators 120 and 125 to aid in
positioning the sensor on the individual's extremity. In a
preferred embodiment, the nerve conduction sensor 5 includes
positioning indicators 120 and 125 to help place the stimulator 10
correctly; connector 20 then ensures that detector 15 is positioned
appropriately. In another embodiment, another positioning indicator
130 helps place the detector 15 correctly; connector 20 then
ensures that stimulator 10 is positioned appropriately. In yet
another embodiment, indicators 120, 125 and 130 are all provided on
a sensor 5.
[0040] According to a method of the invention, the positioning
indicators 120, 125 and 130 are placed on the skin of the
individual at particular anatomical sites, thereby aiding in the
placement and orientation of the nerve conduction sensor 5 on the
extremity of the individual. The positioning indicators 120, 125
and 130, shown in FIG. 2, are merely illustrative and other
embodiments with various positioning indicators and mechanisms
known to the skilled person are contemplated by the invention.
[0041] As illustrated in FIG. 3, the nerve conduction sensor 5 is
interfaced to an electronic controller 95. The electronic
controller 95 includes a generator t generate electrical stimuli
that stimulate the nerve N through the stimulator 10, a signal
detector to detect signals from a nerve N or muscle M (evoked by
stimulation by the stimulator 10) through the detector 15, a
processor to process the detected signals, and a display to
communicate the results to an operator or another electronic device
such as a computer. In one embodiment, the electronic controller 95
includes a controller detector to detect the evoked response from
detector 15 and a transmitter to transmit this information to a
remote processor for further processing and analysis. This
transmitter may be telephone lines, the Internet, or wireless
networks. In another embodiment, the electronic controller 95
includes an amplifier to amplify, a recorder to record, and a
processor to process bioelectrical signals generated by detector
15.
[0042] One embodiment of the controller 95 contains two
differential amplifiers each of which is connected to two
electrodes within the electrode array 30. In one particular
embodiment, one differential amplifier is electronically connected
to electrodes 70 and 80, through connector 25 and traces 105, and
another differential amplifier is electronically connected to
electrodes 75 and 85, through connector 25 and traces 105. This
configuration thus represents two differential bipolar recordings.
Other configurations by which the electrodes 30 are connected to
the amplifier have been contemplated and should be considered
within the scope of the present invention.
[0043] In another aspect, the invention is a method for performing
nerve conduction studies. As an illustrative example, motor nerve
conduction studies may be performed with the nerve conduction
sensor 5. This is accomplished by placing the stimulator electrode
10 of the sensor 5 over the nerve N to be studied, for example the
peroneal nerve at the ankle. The connector 20 of the sensor 5 then
automatically places the detector 15 substantially adjacent to a
muscle M innervated by the nerve N, for example the extensor
digitorum brevis muscle on the lateral aspect of the mid foot.
After the detector 15 is put in contact with the individual's skin,
one or more of the detection electrodes in array 30 are selected,
preferably according to an algorithm described below and
illustrated in FIG. 5. Subsequently, myoelectrical activity is
recorded from the muscle M in response to stimulation of the nerve
N by the stimulator 10. The motor nerve conduction study is thus
carried out by repeatedly stimulating the nerve N and recording the
resulting evoked responses by the chosen detection electrodes in
array 30. The evoked response thus detected provides information on
the function of the nerve and muscle and may include the distal
motor latency (DML), the compound action potential (CMAP)
amplitude, the F-wave latency, the F-wave amplitude, the refractory
period, the activity dependence, the stimulation threshold, and
other nerve conduction parameters familiar to those knowledgeable
in the art. The particular detection electrodes in array 30 do not
need to be constant throughout the nerve conduction study. In other
words, some of the detection electrodes can be used in one part of
the study, and other electrodes can be used in a different part of
the study.
[0044] In a preferred embodiment of the invention, the electronic
controller 95 (FIG. 3) and the nerve conduction sensor 5 are
configured so that the electronic controller acquires two signals
formed from two interleaved pairs of detection electrodes in array
30. Signals thus recorded are called bipolar signals. An embodiment
of a bipolar signal 135 is illustrated in FIG. 4. The signal 135
has a number of features that are important both for the assessment
of nerve conduction parameters such as those described above, as
well as for the determination of the anatomical and physiological
relationship between the detection electrodes and the underlying
muscle M. One feature is the latency 140 of the signal. The latency
140 represents the time between the stimulation of nerve N and
arrival of the impulse at the innervated muscle M. Latency 140, and
its associated parameter velocity, are generally considered to be
the most important nerve conduction parameters. In this respect it
should be appreciated that diseased nerves have a longer latency
than normal nerves. In addition, the specific electrode located
closest to the muscle motor point 145 (FIG. 1) will typically have
the lowest latency among the electrode array 30.
[0045] Another feature of the signal 135 is the maximum rising
slope 150 of the signal. This parameter represents the
depolarization of the muscle tissue M. The maximum rising slope 150
is particularly important because the signal recorded over the
motor point 145 (FIG. 1) generally has a larger slope 150 than a
biopotential recorded away from the motor point 145.
[0046] Another feature of the signal 135 is the peak-to-peak
amplitude 155 of the signal 135. This parameter represents the
overall size of the muscle action potential. This is an important
characteristic, inasmuch as diseased nerves typically have a lower
amplitude 155 than healthy nerves. In addition, signals 135
recorded over the motor point 145 generally have larger
peak-to-peak amplitude 155 than those recorded away from the motor
point 145.
[0047] The aforementioned features of signal 135 should only be
considered to be representative of those used to determine nerve
conduction and muscle structure. Other features have been
contemplated and should be considered within the scope of the
present invention.
[0048] As mentioned above, the performance of nerve conduction
studies with the nerve conduction sensor 5 requires selection of
one or more electrodes from array 30 from which the evoked response
is measured and nerve conduction parameters; such as the distal
motor latency, are determined. In the illustrative example of a
motor nerve conduction study, the evoked response must be recorded
from the motor point--which is the region of the muscle innervated
by the nerve. The objective of the electrode array 30 is to provide
means for sampling the evoked response from all or a section of the
muscle, and to determine the single electrode or combination of
electrodes that best represent the evoked response from the motor
point. In the most general case, the evoked response is a weighted
sum of one or more electrodes. However, in a preferred embodiment,
the single electrode that best represents the motor point response
is used.
[0049] FIG. 5 illustrates a preferred algorithm for utilizing the
signals 135 recorded from the electrode array 30 to select the
optimal electrode(s) 70, 75, 80, 85 for performance of nerve
conduction studies. In process step 160, two signals S.sub.1 and
S.sub.2 are acquired. In a preferred embodiment, these signals are
differentially recorded from two interleaved pairs of electrodes
70, 80, and 75, 85 and typically have a waveform shape and feature
set similar to those shown, for example, in FIG. 4. In this
embodiment, S.sub.1=V(E.sub.70)-V(E.sub.80) and
S.sub.2=V(E.sub.75)-V(E.sub.85), where V(E.sub.X) is the
biopotential at electrode E.sub.X, and E.sub.70 and E.sub.75 form
the positive differential inputs and E.sub.80 and E.sub.85 form the
negative differential inputs of their respective signals. These
signals are only illustrative and embodiments have been
contemplated in which different combinations of electrodes are
utilized, such as 70, 75, and 80, 85, or 70, 85, and 75, 80, in
which each of the electrodes is recorded relative to a common
indifferent electrode, and in which the electronic controller 95
has means to dynamically create various combinations of
differential recordings. In addition, although the illustrative
algorithm is described in terms of two signals, it can be applied
to a greater number of signals formed from recordings of the
electrode array 30.
[0050] According to one embodiment of the invention, predetermined
signal features (latency, amplitude and slope, respectively) are
calculated for each of the two signals S.sub.1 and S.sub.2 in
process steps 165, 170 and 175. In a preferred embodiment, these
parameters are independent of the optimal polarity of the signals.
In other words, the same parameters are calculated for S.sub.i and
-S.sub.i. Furthermore, these parameters are illustrative and
additional parameters may be used. After calculation of the signal
features, the algorithm continues with process step 180, in which
the latencies (L.sub.1 and L.sub.2) of the two signals are compared
to determine if they are within a predetermined range, .sigma., of
one another. In a preferred embodiment, the predetermined range is
between about 0.1 and 0.7 ms, preferably 0.4 ms. If the latency
difference is within the predetermined value, then the algorithm
continues with process step 185. In this step, a score (f.sub.1 and
f.sub.2) is determined for each signal from the non-latency
parameters by creating a linearly weighted sum of these parameters
using predetermined coefficients. Subsequently, in process step
190, the scores are compared for equality. If they are equal then
the algorithm continues with process step 195. If they are not
equal then the algorithm continues with process step 200. If the
latency difference is not within the predetermined range as
determined in step 180, then the algorithm continues with process
step 195. In step 195, a score is determined for each signal based
entirely on its corresponding latency. In a preferred embodiment,
this score is inversely proportional to the latency such that a
shorter latency will yield a higher score. As an example, the
following scoring function has been contemplated.
f i = 1 L i ##EQU00001##
[0051] Upon completing the score calculation in process step 195,
the algorithm continues with process step 200 in which the scores
for the two signals (f.sub.1 and f.sub.2, regardless of whether
calculated in process step 185 or 195) are compared. If the first
signal has a greater or equal score to the second signal, then the
algorithm continues with process step 205 in which the first signal
is chosen for subsequent processing and then the algorithm proceeds
to process step 210. If in process step 200, the first signal has a
lower score than the second signal, then the algorithm proceeds to
process step 215 in which the second signal is chosen for
subsequent processing before continuing with process step 210.
[0052] In process step 210 the latency of the chosen signal
(S.sub.1 if from process step 205 and S.sub.2 if from process step
215) is calculated for each polarity yielding two latencies,
L.sub.+ and L.sub.-. The algorithm then proceeds to process step
220 where the latencies are compared. If the positive polarity
latency (L.sub.+) is less than or equal to the negative polarity
latency (L.sub.-), then the algorithm proceeds to process step 225
where the optimal recording electrode is reported as the positive
input to the differential recording. For example, in the embodiment
in which the first signal is formed from a differential recording
of electrodes 70 and 80, the reported electrode would be electrode
70. If in process step 220, the negative polarity latency (L.sub.-)
is less than the positive polarity latency (L.sub.+), then the
algorithm proceeds to process step 230 where the optimal recording
electrode is reported as the negative input to the differential
recording. For example, in the embodiment in which the first signal
is formed from a differential recording of electrodes 70 and 80,
the reported electrode would be electrode 80.
[0053] In the preferred algorithm shown in FIG. 5, a set of
predetermined linear weights is utilized in process step 185 to
generate a score indicating which signal is optimal. In the
preferred embodiment, these weights are obtained by performing a
linear regression between an ensemble of signals and an expert's
assessment of their optimality. As an illustrative example, a set
of signals is obtained with the nerve conduction sensor and then a
neurophysiological expert assigns an optimality score to them.
Subsequently, the scoring function is calculated by performing a
linear regression between the signals and the expert score. In one
embodiment, the expert score indicates whether the electrodes from
which the signal was obtained are over the muscle motor point.
Although the scoring function in the illustrative algorithm is
linear, it may also be non-linear. For example, in another
embodiment, the scoring function is determined by logistic
regression analysis. In yet another embodiment, the scoring
function is neural network trained by a technique such as backwards
propagation. In yet another embodiment, a combination of fuzzy
logic and expert system based technique can be used to derive the
scoring function.
[0054] In the illustrative algorithm of FIG. 5, time domain
features of the recorded signal are utilized to determine the
optimal electrode. However, frequency based analysis has also been
contemplated, either independently or in conjunction with above
time-domain analysis. FIG. 6 shows the power spectrum of two
bipoloar signals recorded with the nerve conduction sensor 5. The
horizontal axis 235 shows frequency. The vertical axis 240 shows
the power spectral density, which was calculated by taking the
discrete Fourier transform of each signal and then normalizing the
spectral energy to the maximum value. This allows the resulting
power spectral densities 245 and 250 to be compared. A signal
recorded over the motor point 145 will have a simpler morphology
than one recorded away from the motor point 145. As a result, the
signal recorded from the motor point 145 can be determined by that
which concentrates more towards lower frequencies. In the
illustrative example shown in FIG. 6, signal 245 has proportionally
more energy at lower frequencies than does signal 250. Thus, signal
245 is expected to be closer to the motor point 145. Features
derived from other transformations such as wavelet and
multi-resolution analysis can also be used to determine motor
point.
[0055] While the present invention has been described in terms of
certain exemplary preferred embodiments, it will be readily
understood and appreciated by one of ordinary skill in the art that
it is not so limited, and that many additions, deletions and
modifications to the preferred embodiments may be made within the
scope of the invention as hereinafter claimed. Accordingly, the
scope of the invention is limited only by the scope of the appended
claims.
* * * * *