Abstract:
An apparatus for and method of conducting a nerve conduction study is provided. In response to predetermined stimulation from an excitation device, a signal is generated that travels through a human body. The apparatus includes a sensing electrode operatively engagable with the human body downstream of the excitation device for sensing the signal. The apparatus further includes a pressure mounting structure operatively connected to the sensing electrode for controlling the pressure at which the sensing electrode engages the body. The pressure mounting structure includes a pressure source and a pressure sensor. A controller receives a pressure signal from the pressure sensor and the signal from the sensor electrode. The controller includes software to normalize the amplitude of the signal based on the pressure at which the sensing electrode engages the body.

Description:
REFERENCE TO GOVERNMENT GRANT 
   This invention was made with United States government support awarded by the following agencies: NSF 144 KR91. The United States has certain rights in this invention. 

   FIELD OF THE INVENTION 
   The invention relates generally to conduction analysis of a selected muscle or nerve, and in particular, to an apparatus for and method of studying an amplitude of a conduction signal generated by a selected muscle or nerve in response to electrical stimulation. 
   BACKGROUND OF THE INVENTION 
   Doctors often encounter patients having problems with a particular muscle or nerve (e.g., pinched nerve in the back or neck). Typically, a doctor examines the health of the problematic muscle or nerve by performing an electromyogram (EMG) test. An EMG test generally includes two parts, a nerve conduction study and a needle examination. 
   The nerve conduction study generally relies on the premise that a nerve is something like an electrical wire. To see if the wire is functioning properly, one delivers an electrical current and evaluates the conductibility of the wire. Analogously, the nerve conduction study includes delivering an electrical current to a selected nerve or muscle and analyzing the nerve&#39;s conductibility. How well the selected nerve or muscle conducts the electrical current provides an indication of the health of the nerve or muscle. The physician generally performs the nerve conduction study by attaching a recording or sensing electrode to the surface of the skin of the patient and delivering the electrical current with a pair of electrodes. With delivery of the electrical current, the sensing electrode acquires response signals, referred to as compound motor action potential (CMAP) signals from the selected nerve or muscle. The amplitude of the acquired CMAP signal indicates how many nerve or muscle cells are firing together, and the velocity of the acquired CMAP signal gives an indication of the type of fibers firing. Even though amplitude information is an important parameter in evaluating the functional performance of a nerve or muscle, physicians generally rely only on the conduction velocity to evaluate the performance of the nerve. Physicians do not rely upon amplitude because it has a high level of variance and lesser degree of reproducibility. 
   Therefore, it is a primary object and feature of the present invention to provide an apparatus for enhancing evaluation of the functional performance of a selected nerve or muscle based on a nerve conduction study. 
   It is a further object and feature of the present invention to provide an apparatus for and method of studying the effect of pressure on a sensing electrode in regard to the amplitude level of a conduction signal acquired during a nerve conduction study. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, an apparatus and a method is provided to perform a nerve conduction study that enhances evaluation of the functional performance of a nerve or muscle. The present invention shows how an amount of applied pressure on the sensing electrode directly affects the amplitude of the recorded CMAP signal. The apparatus provides known levels of force or pressure on the sensing electrode, and acquires test information used in calibrating the amplitude of the acquired CMAP signal. The calibrated amplitude information enhances accuracy and precision in the evaluation of the functional performance of the selected nerve or muscle. 
   In one embodiment, the invention provides an apparatus for sensing the amplitude of a signal generated in response to electrical stimulation from an excitation device operatively engaging a human body. The apparatus includes a sensing electrode operatively engagable with the human body downstream of the excitation device for sensing the signal generated in response to electrical stimulation by the excitation device. The apparatus further includes a pressure mounting structure operatively connected to the sensing electrode for controlling the pressure at which the sensing electrode engages the body. The pressure mounting structure may include a pressure source operatively connected to the sensing electrode for applying the pressure at which the sensing electrode engages the body. The pressure mounting structure may further include a pressure electrode that generates a pressure signal representative of the value of the pressure at which the sensing electrode engages the body. 
   The apparatus may further include a controller electrically connected to receive the pressure signal from the pressure electrode and the signal from the sensing electrode. The controller is configured to perform the steps of determining a pressure normalization ratio from pressure signals acquired from the pressure sensor, and normalizing the acquired conduction signal from the sensing electrode based on the pressure normalization ratio. 
   In another embodiment, the invention provides for a method for sensing the amplitude of a signal traveling through a human body, the signal generated in response to electrical stimulation from an excitation device operatively engaging the body. The method includes the steps of acquiring the signal from the sensing electrode, exerting a pressure on the sensing electrode, acquiring a pressure signal representative of the pressure at which the sensing electrode engages the body, determining a pressure normalization ratio based on the acquired pressure signal, and normalizing the signal based on the pressure normalization ratio. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings furnished herewith illustrate a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the following description of the illustrated embodiment. 
       FIG. 1  is a schematic representation of a first embodiment of an apparatus to study nerve conduction in accordance with the present invention; 
       FIG. 2  is a schematic diagram of the apparatus of  FIG. 1  having a platform in accordance with the present invention; 
       FIG. 3  is a schematic diagram of the apparatus of  FIG. 2  rotated to a changed position; 
       FIG. 4  is a schematic diagram of an alternative embodiment of an apparatus to study nerve conduction in accordance with the present invention; and 
       FIG. 5  is a flow diagram of a first embodiment of a method of nerve conduction study in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a schematic representation of a first embodiment of an apparatus  10  in accordance with the present invention. The apparatus  10  generally includes an excitation source  15 , an excitation electrode  20 , a sensing electrode  25 , a pressure source  30 , a pressure sensor  35 , an input device  40 , an output device  45 , a light source  50 , and a controller  55 . The following description of the present invention refers to a physician performing a nerve conduction study on a selected nerve located in a hand of a patient. Yet, the operators (e.g., researchers, technicians, etc.) of the apparatus  10  can vary. Likewise, the selected nerve can vary. Furthermore, the present invention can be used to study other nerves as well as miscellaneous muscles. 
   The excitation source  15  provides electrical current to the excitation electrode  20  positioned on the patient. One embodiment of the excitation source  15  is a current generator electrically connected to the excitation electrode  20 . The physician touches the skin surface of the patient with the electrode  20  at a position to deliver the electrical current to the selected nerve. An electrical ground is typically connected to the patient to complete the current path. The type of excitation source  15  and/or excitation electrode  20  and the level/duration of electrical current can vary. The physician delivers the electrical current to the patient at a location to generate a response from the selected nerve. The nerve reacts to the electrical current by providing a conduction signal, referred to as a compound motor action potential (CMAP) signal. The CMAP signal provides a recordable reaction that reflects the performance function of the selected nerve. 
   The physician positions the sensing electrode  25  at the skin surface to acquire the CMAP signal response from the selected nerve. The type and location of the sensing electrode  25  can vary. The sensing electrode  25  provides the CMAP signal to the controller  55  for processing. The CMAP signal generally includes a velocity and an amplitude level. 
   The pressure source  30  applies a measurable force normal to the sensing electrode  25  acquiring the CMAP signal. One embodiment of the pressure source  30  includes a micrometer. The pressure sensor  35  provides a pressure signal representative of a value of the applied pressure by the pressure source  30  to the controller  55 . One embodiment of the pressure sensor  35  includes a load cell (discussed later) positioned between the pressure source  30  and the sensing electrode  25 . An exemplary load cell is manufactured by ENTRAN®. The types of pressure sources  30  (e.g., hands, vises, etc.) and pressure sensors  35  (e.g., strain gauges, etc.) can vary. 
   The input device  40  is configured to provide input information to the controller  55 . The input information can include the type of sensing electrode  25 , the selected nerve or muscle under study, patient biography, etc. The types of input devices  40  (e.g., keyboards, touch-screen panels, switches, push-buttons, etc.) can vary. The output device  45  is configured to display output information from the controller  55  for viewing by the physician. The output device  45  can provide a display of a pressure reading from the pressure electrode, an acquired CMAP waveform, an amplitude level and velocity of the CMAP waveform, etc. The type of output device  45  (e.g., display screen, monitor, LCDs, etc.) can also vary. 
   The light source  50  illuminates over the general area of the skin surface receiving the sensing electrode  25 . One embodiment of the light source  50  illuminates a grid  56  configured to provide a reference for placement of the sensing electrode  25 . The type, of reference (e.g., bulls eye, etc.), color, activation (e.g., manual, automatic, etc.), and position of the light source  50  can vary. The illumination of the grid  56  provides a reference for placing the sensing electrode  25  at the same position on the body. 
   The controller  55  is electrically connected to the excitation source  15 , the sensing electrode  25 , the pressure sensor  35 , the input device  40 , the output device  45 , and the light source  50 . One embodiment of the controller  55  includes a processor  57  configured by one or more modules of software to operate the apparatus. The processor  57  includes a program storage  58  and a memory storage  59 . The program storage  58  contains the one or modules of software that configure the processor  57 . The memory storage  59  provides for storage of data received by the controller  55  (e.g., pressure readings, CMAP signals, etc.). 
   A power supply  60  provides electrical power to the apparatus  10 . In one embodiment, the power supply  60  supplies power to the excitation source  15 , the pressure sensor  35 , the input  40  and output  45  devices, the light source  50 , and the controller  55 . In other embodiments of the apparatus  10 , one or more of the above elements can have its own power supply. 
     FIG. 2  shows a first embodiment of the apparatus  10  having a pressure mounting structure  65 . The pressure mounting structure  65  is operatively connected to the sensing electrode  25  for controlling the pressure at which the sensing electrode  25  engages the hand  67  of the patient. In addition, it is intended that pressure mounting structure  65  orient the sensing electrode  25  at a user selected location on the hand  67 , as hereinafter described. Of course, other embodiments of the apparatus  10  and pressure mounting structure  65  can be configured to analyze other miscellaneous nerves or muscles on feet, arms, legs, etc. 
   The pressure mounting structure  65  includes a platform  70  attached to or mounted with a vertical support  75 . The platform  70  includes a flat, rigid surface that can be part of a support stand or a separate panel component. The vertical support  75  is a rigid structure mounted to the platform  70  by a pair of fasteners (e.g., bolts and nuts, screws, spot-weld, etc.). The vertical support  75  and/or platform  70  are configured to provide support for receiving and bearing against the hand  67  of the patient. The pressure mounting structure  65  further includes a horizontal support  80  having a first end  81   a  attached normal relative to the vertical support  75 , and an opposite second end  81   b . A vertical adjuster  82  is mounted to second end  81   b  of horizontal support  80  and is configured to variably adjust the vertical position of the horizontal support  80  and attached pressure source  30 , pressure sensor  35 , and sensing electrode  25  relative to the hand  67  positioned on the platform  70 . The vertical adjuster  82  includes a slide  83  moveable along a channel  84  vertically extending along the vertical support  75 . The adjuster  82  is attached by a pair of fasteners (e.g., bolt and nut, screw, spot-weld, etc.) to the horizontal support  80 . The type vertical hold (e.g., tightening screw, pinch against channel, etc.) to maintain the position of the adjuster  82  and attached horizontal support  80  can vary. 
   The pressure mounting structure  65  further includes an angle positioning device operatively connected to the second end  81   b  of horizontal support  80  for controlling an angle at which the sensing electrode  25  engages the hand. In the depicted embodiment, the angle positioning device includes a dial  85  rotatably mounted to the second end  81   b  of the horizontal support  80 . The dial  85  is in pivotal support of the pressure source  30  and sensing electrode  25 . The dial  85  is configured to position the sensing electrode  25 , the pressure source  30 , and the pressure electrode  35  at various desired rotational angles for engaging the hand  67  of the patient. The dial  85  includes a disc  86  attached at the center by a hinge  87  to the second end  81   b  of the horizontal support  80 . A bracket  89  attached to the disc  86  supports the pressure source  30 . The type of fastener and/or bracket  89  can vary. The composition (e.g., wood, plastic, metal, etc.) of the above-described elements of the support structure  65  can vary. The type of angular position holder (e.g., tightening screw, friction, etc.) to maintain the angular position of the disc  86  and to attach disc  86  relative to the platform  70  can vary. The horizontal support  80  and dial  85  are configured to allow the pressure source  30 , pressure sensor  35 , and sensing electrode  25  to engage various locations of the patient&#39;s hand  67  at various positions against the platform  70  and/or vertical support  75 . 
   As shown in  FIG. 2 , the pressure source  30  includes a micrometer  90  having one end  92  configured to bias the sensing electrode  25  against a hand  67  supported against the platform  70 . The other end of the micrometer  90  includes an adjustment knob  95 . The physician can slide the vertical adjustment  82  and horizontal support  80  and rotate the dial  85  to change position of the micrometer  90  so as to provide a controlled application of pressure to the sensing electrode  25 . 
   Pressure sensor  35  may include a load cell  100  positioned between the first end  92  of the micrometer  90  and the sensing electrode  25 . The load cell  100  can have its own power supply or receive electrical power from the controller  55 . The load cell  100  provides the pressure signal to the controller  55 . Light source  50  is disposed between the load cell and the sensing electrode  25 . Alternatively, the light source  50  can be positioned at other locations (e.g., underneath the hand, designated support, etc.). The sensing electrode  25  is attached to the apparatus  10 . Alternatively, the sensing electrode  25  can be individually positioned on the patient&#39;s hand  67  separate from the remaining elements of the apparatus  10 . 
   The controller  55  controls activation of the light source  50 . For example, the controller  55  may provide a signal that activates the light source upon detecting the sensing electrode  25  making contact with the hand  67 . Alternatively, the controller  55  may provide the electrical power to the light source based on a manual/automatic switch disposed at the controller or at the light source itself. 
   The controller  55  is also electrically connected to the sensing electrode  25  and the load cell  100 . The excitation source  15  is shown separated from the controller  55 . Of course, another embodiment of the apparatus  10  can include the excitation source  15  adjacent the controller  55  in a housing. An electrical ground is attached to the arm of the patient to complete the electrical circuit with the excitation source  15  and electrode  20 . 
     FIG. 3  shows another illustration of the apparatus  10  at a rotated position relative to the patient&#39;s hand  67  supported against the vertical support  75  and platform  70  of the apparatus  10 . The dial  85  is configured to position the micrometer  90 , load cell  100 , light source  50 , and sensing electrode  25  in various rotational positions to properly apply normal pressure to and acquire an adequate conduction signal from the sensing electrode  25  positioned on the hand  67  of the patient. 
     FIG. 4  shows yet another embodiment of an apparatus  200  for performing a nerve conduction study on a patient. The apparatus  200  includes a sensing electrode  225  configured to acquire a conduction signal from the hand  67 . The apparatus  200  also includes a pressure source  230  having a micrometer  290  and an adjustment knob  295  coupled with a strap  297 . The adjustment knob  295  is configured to change the tension of a strap  297  wrapped around at least a portion of the hand  67 , thereby applying a controlled pressure to the sensing electrode  225 . By increasing the tension of the strap  297 , the physician can controllably increase the application of pressure applied by the micrometer  290  against the sensing electrode  225 . A load cell  300  acquires a reading of the applied pressure by the pressure source  230 . The type of pressure source  230  (e.g., human, vise, etc.) and strap  297  (e.g., perforated, belt, etc.) can vary. A controller  355  is electrically connected to receive signals from the sensing electrode  225  and the load cell  300  similar to the apparatus described in  FIG. 2 . 
   Other embodiments of the apparatus  10  and  200  may include elements having individual displays, controls, and power supplies. 
   Having described the basic architecture of several embodiments of the apparatus  10  of the present invention, a method  400  of operation of the apparatus  10  will now be described as shown in  FIG. 5 . It is envisioned that the method  400  of operation can be modified for other embodiments of the apparatus  10 . Furthermore, it is envisioned that not all the acts may be required, that some of the acts may be modified, or that the order of the acts may vary. 
   As shown in  FIG. 5  and at act  405 , a physician activates or starts the apparatus  10 . The patient positions a hand  67  on the apparatus  10  for nerve conduction study. The light source  50  can illuminate the grid  56  to provide a reference for positioning the sensing electrode  25  at the same location on the hand. At act  410 , a physician positions the excitation electrode  20  and the sensing electrode  25  on the patient. In one embodiment, the physician positions an excitation electrode  20  at or near the elbow of the patient. The physician positions the sensing electrode  25  near a selected nerve in the patient&#39;s hand  67 . The excitation electrode  20  is connected to the excitation source  15 . A second electrode positioned on the patient is connected to electrical ground. At act  415 , the physician determines whether the position of the sensing electrode  25  should be adjusted to more adequately acquire a CMAP signal from the selected nerve. At act  420 , the physician applies pressure to the sensing electrode  25 . In one embodiment and as shown in  FIG. 2 , the physician applies pressure by adjusting the extended position of the micrometer  90  biased against the sensing electrode  25  and the hand  67  of the patient. The change in extended position of the micrometer  90  applies additional pressure on the sensing electrode  25 . The apparatus  10  is configured to provide repeatable degrees of pressure to the sensing electrode  25 . 
   The physician has a choice to select a research option (act  425 ) or clinical option (act  430 ) for performing the nerve conduction study. The research option is configured to study the general effect of variable pressure on the conduction signal acquired by the sensing electrode  25 . The clinical option is generally configured to perform a nerve conduction study of a selected nerve of a patient. If the research option (act  425 ) is selected, the physician determines whether the desired pressure is placed on the sensing electrode  25  (act  435 ). If not, then the physician adjusts the application of pressure by the pressure source  30  (act  420 ). 
   At act  440 , the physician applies electrical stimulation, or delivers the electrical current, to the excitation electrode  20 . Again, the physician can select a research option (act  445 ) or a clinical option (act  450 ). If the physician selects the clinical option (act  450 ), then the physician determines whether the pressure source  30  is applying adequate pressure to the sensing electrode  25 . Inadequate pressure on the sensing electrode  25  can reduce the clarity at the conduction signal (act  455 ). If the pressure is inadequate then the physician adjusts the pressure applied by the pressure source  30  to the sensing electrode  25  (act  420 ). 
   At act  460 , the controller  55  acquires the pressure signal from the pressure sensor  35  and the conduction signal from the sensing electrode  25 . At act  470 , the controller  55  determines a pressure normalization ratio. In one embodiment, determining the pressure normalization ratio is determined during calibration of the apparatus  10 . The act of determining the pressure normalization ratio includes the physician determining a change in the amplitude level of the acquired conduction signal caused by a known application of pressure by the pressure source  30  to the sensing electrode  25 . In one embodiment, the pressure normalization ratio is based on a linear relationship. Thereby, the pressure normalization ratio equals the gradient (e.g., change in amplitude/0.1 lb. change in pressure) of a straight line representing the change in amplitude of the conduction signal caused by a known application of pressure on the sensing electrode  25 . In another embodiment, a non-linear relationship can be used to determine the pressure normalization ratio. If based on a non-linear relationship, a physician can use a look-up table of tangential values representing the change in amplitude of the conduction signal for a known application of pressure by the pressure source  30  to the sensing electrode  25 . 
   At act  475 , the controller normalizes the conduction signal with respect to the pressure normalization ratio. In one embodiment, normalizing the conduction signal includes multiplying the acquired conduction signal by the pressure normalization ratio. Act  480  is the end of operation of the apparatus  10 . 
   By normalizing the effect of pressure on the amplitude of the nerve conduction signal, a physician can place more confidence in the accuracy of the measured amplitude values of the acquired conduction signal. This acquired amplitude information provides performance information in addition to the measured velocity of the nerve conduction signal. While conduction velocity provides information regarding the state of the nerve conduction pathways, the amplitude of the nerve conduction signal provides insight about the health of nerve cells in the area. Thereby, the present invention provides the physician with an apparatus of and a method for studying and acquiring amplitude information of nerve conduction studies that enable a more thorough evaluation of the performance of a studied nerve or muscle. 
   The apparatus  10  and the method  400  can be used to perform tests in nerve conduction performed to evaluate for anterior horn disease, root lesions related to compressed spinal nerve roots, plexus lesions, compression/entrapment neuropathies, distal myopathies, neuromuscular transmission defects, polyneuropathies, trauma, etc. These disfunctions/diseases can be associated with various nerves or muscles located in various areas of the body (e.g., foot, leg, hand, spine, etc.). For example, a nerve conduction study may be performed to evaluate nerve damage above and below a trauma to the knee, including nerves in the foot. The apparatus  10  is configured to support the various areas of the foot in providing a repeatable pressure to a sensing electrode for acquiring conduction signal data generated by the selected nerve(s) in the foot. 
   Various modes of carrying out the invention are contemplated as being within the scope of the following claim particularly pointing out and distinctly claiming the subject matter, which is regarded as the invention.