Patent Publication Number: US-2012046572-A1

Title: Nerve stimulator measuring device

Description:
This is a continuation-in-part application based on U.S. patent application (Ser. No. 11/021,299) filed Dec. 23, 2004 and the provisional patent applications (Ser. No. 60/532,029) filed on Dec. 23, 2003, and (Ser. No. 60/541,511) filed on Feb. 3, 2004. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to devices used to measure nerve conduction in peripheral nerves and more particularly, to such devices that measure the conduction time and amplitude of a test signal applied to a nerve. 
     2. Description of the Related Art 
     It is common practice in medicine to measure the electrical conduction on a peripheral nerve. For example, when diagnosing carpel tunnel syndrome it is common for a physician to measure the electrical conduction in the median nerve as it extends from the forearm, through the wrist and into the hand. During the test procedure, the physician measures the length of time and the amplitude of a test signal applied to the nerve having a known length. To perform the test, recording sensors are attached to the patient&#39;s forearm and a nerve stimulator is positioned over the nerve. 
     When testing for carpel tunnel syndrome, the recording sensors and the nerve stimulator&#39;s cathode probe must be spaced apart at selected distances (8 cm, 10 cm, and 14 cm) on the hand and forearm. Heretofore, physicians have used a ruler or measuring tape and an ink marker to first mark the specific locations of the recording electrodes and the nerve stimulator on the patient&#39;s skin before the test is performed. Often, several tests are performed on the same hand and forearm during the visit, which requires manually marking the skin reference points. The act of measuring and marking several sets of reference points on the forearm and hand is very time consuming. Also, because the sets of reference points are relatively close, a wrong set of reference points may be used during the test that produces inaccurate readings. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a nerve stimulator measuring device that enables a physician to easily and quickly determine the proper position of the nerve stimulator. 
     It is another object of the invention to provide such a device that may be used with a standard electrical nerve stimulator that uses a cathode probe and an anode probe that are positioned against or adjacent to the skin. 
     It is another object of the invention to provide such a device that enables a physician to determine different locations of the cathode probe from the electrical sensor without using an ink marker. 
     It is another object of the invention to provide such a device that is wireless thereby eliminating wires that typically extend from the device to the recording machine. 
     These and other objects are met by the nerve stimulator measuring device with a tape measure attached thereto used to measure the distance between the electrical sensor and the cathode probe. In the first embodiment, the tape measure is located in an outer housing that attaches or is integrally formed on the cathode probe on a standard electrical nerve stimulator. The outer housing includes two bores designed to receive the anode and cathode probes on the electrical nerve stimulator. During assembly, the outer housing is positioned over the two probes with the tape measure disposed therebetween. An index marking or line formed on the outer surface of the outer housing is aligned with the center axis on the cathode probe. 
     In a second embodiment, the nerve stimulator comprises an outer housing with a tape receiver cavity formed there that holds a spool upon which a flexible tape measure is wound and unwound. The spool is coupled to a tape retraction mechanism that automatically rewinds the tape measure on the spool. Mounted on the outer surface of the outer housing is a stimulator activation button coupled to an electric test signal generator and a tape retraction button coupled to the tape retraction mechanism. 
     In the second embodiment, disposed on the distal end of the tape measure used with the second embodiment, are three recording sensors. Wires extend from the three recording sensors to an optional wireless transmitter located inside the outer housing. During operation, the wireless transmitter transmits the detected electrical signal information from the sensors to a wireless receiver connected to a nearby recording machine. The three wires that connect to the three recording sensors are mounted on the tape measure and are extended and retracted into the outer housing with the tape measure. Also mounted on the outer housing is a signal intensity control switch that the user manually operates to adjust the size of the signal generated by the stimulator probes. 
     In three other embodiments of the invention, a linear skin distance measuring device is attached to the electrical nerve stimulator. In two embodiments, a linear skin distance measuring device is attached to one or both probes on the electrical nerve stimulator. In another embodiment, the linear skin distance measuring device is attached to the body of the electrical nerve stimulator. In each embodiment, the linear skin distance measuring device is designed to measure the distance the electrical nerve stimulator travels moved to a desired location on the skin over the nerve to be tested from an electrode sensor attached to the skin. An electric nerve generator is connected to the anode and cathode probes on the electrical nerve stimulator. The electrical nerve stimulator is positioned over the electrode sensor and then manually moved to the desired location over the nerve. A display on the device informs the healthcare worker the precise distance traveled. When the desired distance is achieved, the test is then performed. 
     When the first embodiment is used to diagnose carpel tunnel syndrome, the recording sensors are first attached to the forearm over the median nerve. The free end of the tape measure is then centrally aligned over the first recording sensor and the electrical stimulator with the outer housing attached thereto is pulled towards the hand to the desired length (8 cm, 10 cm, or 14 cm) required for the test. The electrical nerve stimulator is then held so that the cathode probe is aligned on the skin adjacent to the desired distance on the tape. The electrical nerve stimulator is then activated and a reading is obtained. When additional tests are to be conducted, the recording sensor is again used as a reference point for the free end of the tape. The electric nerve stimulator is moved to the new testing point so that the desired distance is displayed on the tape. The electrical nerve stimulator is then held so that the cathode probe is then pressed against the skin adjacent to the new distance. 
     When the second embodiment is used to diagnose carpel tunnel syndrome, the end of the tape measure is pulled from the outer housing so that the three electrical sensors are longitudinally aligned at a desired location of a desired nerve on the forearm. The outer housing is then pulled towards the hand so that the anode and cathode stimulator prongs are positioned at a desired location. (8 cm, 10 cm, or 14 cm) on the tape measure. The stimulator button is then pressed to activate the electrical nerve stimulator. The optional signal intensity switch is used to adjust the desired signal intensity. When additional tests are to be conducted, the nerve sensor probes are moved to a new location on the tape measure and the stimulator button is activated. When the test is completed the tape retraction button is activated to automatically retract the tape measure into the outer housing. 
     In the third and fourth embodiments, the handheld electrical nerve stimulator is perpendicularly aligned over the skin adjacent to an electrode sensor. The distance measuring device is then activated and begins to measure the distance the handheld electrical nerve stimulator is moved over the surface of the skin. When the handheld electrical nerve stimulator is positioned at the desired location on the skin, the distance reading on the display is then recorded and the two probes are then pressed the skin. The electric nerve generator is then activated and a test is then conducted. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the first embodiment of the nerve stimulator measuring device disclosed herein. 
         FIG. 2  is a side elevational view of another embodiment of the nerve stimulator measuring device. 
         FIG. 3  is a top plan view of the first embodiment of the nerve stimulator measuring device shown in  FIG. 1 . 
         FIG. 4  is a side elevational view of the first embodiment of the nerve stimulator measuring device shown in  FIGS. 1 and 3 . 
         FIG. 5  is a top plan view of the second embodiment of the nerve stimulator measuring device shown in  FIG. 2 . 
         FIG. 6  is a side elevational view of the second embodiment of the nerve stimulator measuring shown in  FIGS. 2 and 5 . 
         FIG. 7  is a perspective view of a third embodiment of the nerve stimulator measuring device used with a magnetic nerve stimulator. 
         FIG. 8  is a second perspective view of the third embodiment of an electromagnetic nerve stimulator measuring device shown in  FIG. 7 . 
         FIG. 9  is a perspective view of two tab sensors directly connected to the distal end of tape  30 . 
         FIG. 10  is a perspective view of the distal end of the tape with two wrap sensors attached thereto. 
         FIG. 11  is an illustration showing a fourth embodiment of the nerve stimulator measuring device used to measure the conductivity of a nerve on a patient&#39;s hand. 
         FIG. 12  is a top plan view of the fourth embodiment of a nerve stimulator measuring device. 
         FIG. 13  is a right side elevational view of the fourth embodiment of the nerve stimulator measuring device shown in  FIGS. 11 and 12 . 
         FIG. 14  is a left side elevational view of the nerve stimulator measuring device shown in  FIGS. 11-13 . 
         FIG. 15  is a front elevational view of the nerve stimulator measuring device shown  FIGS. 11-14 . 
         FIG. 16  is a rear elevational view of the nerve stimulator measuring shown in  FIGS. 11-15 . 
         FIG. 17  is a top plan view of a third embodiment of the tape measure. 
         FIG. 18  is a sectional view taken along line  18 - 18   FIG. 17 . 
         FIG. 19  is a perspective view of tape measure shown in  FIGS. 17 and 18  rolled onto a spool. 
         FIG. 20  is a front elevational view of a handheld electrical nerve stimulator with a linear distance measuring device mounted on the lower end of the stimulator&#39;s body with a lower platform that slides up and down over the anode and cathode probes. 
         FIG. 21  is a side elevational view of the measure device shown in  FIG. 20 . 
         FIG. 22  is a top plan view of the measure device shown in  FIGS. 20 and 21 . 
         FIG. 23  is a side elevational view of another embodiment of a linear distance measuring device mounted on the end of the nerve stimulator with a lower platform that slides over one probe on the electrical nerve stimulator. 
         FIG. 24  is a top plan view of the embodiment shown in  FIG. 23 . 
         FIG. 25  is a side elevational of another embodiment of the nerve stimulator with an optical linear measuring unit built therein. 
         FIG. 26  is another embodiment of the nerve stimulator with an optical linear measuring unit that uses a roller ball to measure the distance traveled over a surface. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Shown in the accompanying  FIGS. 1-26  are six embodiments of an electrical nerve stimulator measuring device used to measure the distance of conductivity in a peripheral nerve. Referring to the first embodiment shown in  FIGS. 1 ,  3 , and  4 , the device  10  comprises an outer housing  20  with two side ears  11 ,  12  that attach to the anode and cathode probes  78 ,  80 , respectively, on a handheld electrical nerve stimulator  70 . 
     Located inside the outer housing  20  is a retractable spool  31  with a flexible tape  30  with length measure units  32  printed thereon. In the preferred embodiment, the two ears  11 ,  12  include two bores  24 ,  26  designed to slidingly receive the anode and cathode probes,  78 ,  80  respectively. The outer housing  20  is aligned on the probes  78 ,  80  so that the tape measure  30  unwinds around a center axis that is perpendicular to the longitudinal axis of the two probes  78 ,  80 . 
     The second embodiment of the device  10 ′, shown in  FIGS. 2 ,  5  and  6 , comprises the tape measure  30  also disposed inside an outer housing  20 ′ designed to be coaxially aligned around the cathode probe  80 . The outer housing  20 ′ includes a center bore  28  that receives the cathode probe  80  on the electrical nerve stimulator  70 . A portion  27  of the outer housing  20 ′ extends laterally and includes a second bore  29  designed to slidingly receive the anode probe  78 . The spool  31  for the tape measure  30  is aligned inside the outer housing  20 ′ so that it unwinds around a center axis coaxially aligned with the cathode probe  80 . When properly assembled on the electrical nerve stimulator  70 , the anode probe  78  extends through the second bore  29  and prevents the outer housing  20 ′ from rotating on the stimulator  70 . 
       FIGS. 7 and 8  show a third embodiment of the measuring device, denoted  10 ″, design to be used with an electro-magnetic nerve stimulator  85 . Device  10 ″ comprises two clamping members  86 ,  87  located on the opposite sides of a cylindrical shaped outer housing  20 ″. Like the first two embodiments, located inside the outer housing  20 ″ is a retractable spool  31  with a flexible tape measure  30  wound thereon. Formed on the side of the outer housing  20 ″ is an exit port  88  through which the distal end of the tape measures  30  extends. The two clamping members  86 ,  87  are designed to extend and adjustably squeeze around the circular body of the electrical nerve stimulator  85 . A threaded bolt  100  and nut  99  are used to apply a clamping force to the two clamping members  86 ,  87 . The outer housing  20  is aligned on the two clamping members  86 ,  87  to that its center axis is perpendicular to the longitudinal axis on the two clamping members  86 ,  87 . When properly assembled, the exit port  88  is aligned over the center axis of the center opening  89  on the electrical nerve stimulator  85 . 
     In the first three embodiments  10 ,  10 ′,  10 ″, an optional index marking or surface  84  may be printed or formed on the outer body  20 ,  20 ′, or  20 ″ that denotes the reference point for the tape measure  30 . 
     As shown in  FIGS. 1 and 2 , during use, the two recording sensors  90 ,  92  are positioned on the skin over or proximal end of the nerve  95 . The end of the tape measure  30  is then grasped and aligned with the center axis of the recording sensor  90 ,  92 . The electrical nerve stimulator  70  is then pulled toward the hand to unwind the tape measure  30  from the outer housing  20 ,  20 ′. Using the index mark on the outer housing  20  and the length measurement units  32  on the tape measure  30 , the electrical nerve stimulator  70  is then positioned so that its cathode probe  80  is placed at the desired location on the skin over the nerve  95  and adjacent to the desired distance shown on the tape measure  30 . The electrical nerve stimulator  70  is then activated and a reading is obtained. When additional tests are to be conducted, the first recording sensor  90  is used as a reference point, and the tape measure  30  unwound from the outer housing  20  until the desired length is indicated. The electrical nerve stimulator  70  is then selected and the cathode probe  80  is then aligned over the skin adjacent to the new desired distance. 
     When using the third embodiment of the device  10 ″, the electro-magnetic stimulator  85  is held so that the center axis of the central opening  89  is longitudinally aligned over the nerve  95 . The stimulator  85  is held so that the exit port  88  of the device  10 ″ is positioned directly over the nerve  95 . The end of the tape measure  30  is then pulled and positioned over the sensor. The distance indicia on the tape measure  30  at the exit port  88  or surface  84  is then read. With devices  10 ,  10 ′ and  10 ″, the recording sensors  90  and  92  may be attached or formed in the distal end of the tape measure  30 . As shown in  FIG. 9 , the recording sensors  90 ,  92  may be “button-like” tab connectors  91 ,  93 , respectively, that connect to the lead wires  95 ,  96  that connect to the recording machine. In  FIG. 10 , the connectors  91 ,  93  are replaced with two strap connectors  97 ,  98 , respectively, that wrap around tape measure  30  and connect to lead wires  95 ,  98 , respectfully. 
     Shown in the accompanying  FIGS. 11-18 , is a fourth embodiment of the device, denoted  10 ′″ also used to measure the distance of conductivity in a peripheral nerve  95 . Referring to  FIGS. 11 ,  13 , and  14 , the device  10 ′″ comprises an outer housing  20 ′″ with anode and cathode probes  78 ,  80 , respectively, are longitudinally aligned and extending from one end. Mounted inside the outer housing  20 ′″ is a tape measure receiver cavity  35  that holds a spool  37  and a tape retraction mechanism (not shown) that automatically rewinds the tape measure  30  onto the spool  37 . 
     The three recording sensors  43 ,  44 ,  45  are mounted longitudinally near the distal end  31  of the tape measure  30 . Printed on the front surface  32  of the tape measure  30  are metric or English distance markings  36  that enable the user to determine the distance from the closest recording sensor. Also mounted on the outer surface of the outer housing  20 ′″ is a tape retraction button  65  coupled to the tape retraction mechanism  39  which when activated, automatically retracts the tape measure  30  into the outer housing  12 . 
     As shown in  FIG. 12 , an electric test signal generator  49  is mounted on a printed circuit board  48  disposed inside the outer housing  12 ′″. Wires from the two prong stimulators  78 ,  80  connect to a printed circuit board  48 . During operation, the test signal generator  49  produces a test signal to the two prong stimulators  78 ,  80 . It should be understood however, that the electrical test signal generator  49  may be eliminated from the outer housing  20 ′″ and mounted in an external device (not shown) that is connected to the outer housing  20 ′″ via a cable  67 . Also mounted on the outer surface of the outer housing  20 ′″ is a stimulator activation button  50  coupled to the electric test signal generator  49 . A test single intensity dial  52  is also provided to allow the user to adjust the intensity of the test signal. 
     Located inside the outer housing  20 ′″ is an optional wireless transmitter  55  connected printed circuit board  48 . During operation, the wireless transmitter  55  transmits detected electrical signal information from three sensors  43 ,  44 ,  45  to a wireless receiver  58  connected to a nearby recording machine  60  shown in  FIG. 11 . When the wireless transmitter  55  is not provided in the device, the three wires connect directly to main cable  46  that runs to the recording machine  60 . Located inside the outer housing  20 ′″ is a 9 volt battery  62  that provides electricity to the probes  78 ,  80  and to the printed circuit board  48   
     When device  10 ′″ is used to diagnose carpel tunnel syndrome, the distal end  31  of the tape measure  30  is pulled from the outer housing  12  so that the three electrical sensors  43 ,  44 ,  45  are aligned at the desired location on the hand  82 . The outer housing  20 ′″ is then pulled so that the anode and cathode stimulator prongs  78 ,  80  are positioned at a desired location (8 cm, 10 cm, or 14 cm) on the tape measure  30  along the forearm. The stimulator button  50  is then pressed to activate the electrical test signal generator  49 . The optional signal intensity dial  52  is used to adjust the signal intensity. When additional tests are to be conducted, the nerve sensor probes  78 ,  80  are moved to a new location on the tape measure  30  and the stimulator button  50  is activated. When the test is completed the tape retraction button  65  is activated to automatically retract the tape measure  30  into the outer housing  20 ′″. 
       FIGS. 20-24  show two additional embodiments of the invention denoted  200 ,  300  in which a manual linear distance measuring device  202 ,  302  is selectively attached or integrally mounted on the end of the electrical nerve stimulator  70 . In  FIGS. 20-22 , the linear skin distance measuring device  202  includes a main body  205  that securely attached to the upper ends of one or both probes  78 ,  80  or to the nerve stimulator  70 . Located below the main body  205  is a moveable lower platform  210  with a rotating wheel  220  mounted on an axle  221  designed to roll over the surface of the skin  99 . Coupled to the rotating wheel  220  and mounted on the main body  205  is an indicator or display  230  that informs the healthcare worker the linear distance traveled by the rotating wheel  220  during use. 
     The lower platform  210  includes two bores  212 ,  214 , designed to slide over the two probes  78 ,  80 , respectively. The rotating wheel  220  is mounted on an axle  221  held between two, transversely aligned, rigid supports  222 ,  224  that extend downward from the lower platform  210 . A transducer  228  is provided for converting the rotational movement into a digital format. The two rigid supports  222 ,  224  are parallel and spaced apart so that the rotating wheel  220  may rotate freely between them. The rigid supports  222 ,  224  are also slightly shorter than the diameter of the rotating wheel  220  so that the two supports  222 ,  224  are above the skin  99  as the lower surface of the rotating wheel  220  contacts and rotate over the skin  99 . During use, the rotating wheel  220  rolls over the skin surface when the nerve stimulator  70  is moved laterally (directions f 1  and f 2 ) as shown in  FIG. 20 . 
     As shown in  FIG. 22 , the lower platform  210  includes two lateral ears  226 ,  228  which the healthcare worker presses against using his or her finger to force the rotating wheel  220  against the skin  99 . During use, the lower platform  220  is force downward over the two probes  78 ,  80  to press the rotating wheel  220  against the skin  99  as the nerve stimulator  70  is moved laterally to the designed skin position over the skin  99   
     In the preferred embodiment, the rotating wheel  220  is biased upward towards the main body  205  when not in use thereby enabling the nerve stimulator  70  to be used in a normally manner without the linear distance measuring device  200 . Attached to the two support arms  222 ,  224  are two t-shaped posts,  225 ,  227 , respectively, that extend vertically upward and into a void space created inside the main body  205 . Springs  236 ,  238  are attached to the two posts  225 ,  227 , respectively, which press against the inside surface of the main body  205  to biased the lower platform  210  upward. 
       FIG. 22  is a top plan view of the measure device shown in  FIGS. 20 and 21  with a LCD display  230  mounted on the front surface of the main body  205 . Mounted on the sides of the main body  205  is a ON/OFF switch  242  and a RESET switch  244 . The display  230  and the two switches  242 ,  244  are connected to a PCB  248  mounted inside the main body  205 . A battery  250  is mounted inside the main body  205  and electrically connected to the PCB  248 . 
       FIG. 23  is a side elevational view of the nerve stimulator  70  with another embodiment of a linear distance measuring device, denoted  302 , with the main body  305  mounted on the upper ends of one of the two probes  78 ,  80  and the lower platform  310  that slides up and down over one probe  78  or  80 . Mounted on the lower platform  310  is a T-shaped post  312  that extends into the void cavity formed in the main body  305 . A spring  314  is positioned around the post  312  which extends through a bore  307  formed on the bottom surface of the main body  50 . During use, the spring  314  presses against the inside surface of the main body  305  and acts as a biasing means to hold the lower platform  310  upward over the probe  78  when not in use. 
     The main body  305  includes display  330 , a PCB  336 , a battery  338  and an ON/OFF switch  342  and a RESET switch  344 . The lower platform  310  includes a rear cylindrical member  318  that slides over one probe  78  or  80 . Located in front of the cylindrical member  318  is a rigid support member  338 . A rotating wheel  320  is mounted on an axle  321  and inside the space created between the cylindrical member  318  and the rigid member  338 . Located inside is a transducer  328  used to convert rotational movement into a digital format. 
     The lower platform  310  is sufficiently wide and long so that a portion of the lower platform  310  extends laterally and forward to the main body  305  and exposed. The exposed portions may be used as pressing surfaces for the user&#39;s finger tips to press the lower platform  310  and the rotating wheel  320  when moving the nerve stimulator  70  into a desired location. 
     In each embodiment, the linear skin distance measuring device  200 ,  300  is designed to measure the distance the electrical nerve stimulator travels moved to a desired location on the skin over the nerve to be tested from an electrode sensor attached to the skin  99 . An electric nerve generator is connected to the anode and cathode probes on the electrical nerve stimulator  70 . The electrical nerve stimulator is positioned over the electrode sensor and then manually moved to the desired location over the nerve. A display  230 ,  330  on the device  200  or  300 , respectively, informs the healthcare worker the precise distance traveled. When the desired distance is achieved, the test is then performed. 
       FIGS. 24 and 25  show another embodiment of the nerve stimulator, generally indicated by the reference number  400 , with an optical measuring unit  410  built therein which is used to measure the linear distance the nerve stimulator  400  is moved across the surface. The nerve stimulator  400  includes a light emitter means  412  located inside a longitudinally aligned neck housing  405 . In the preferred embodiment, the neck housing  405  is longitudinally aligned between the two probes  78 ,  80 . The light emitter means  412  transmits light through an orifice  407  located at the tip of the neck housing  405 . Located inside the neck housing  405  is a light receiver  420  that senses the light emitted from the light emitter means  412  and reflected from the skin surface. In an alternative embodiment shown in  FIG. 25 , a rolling ball  440  may be place between the orifice  407  and skin surface to create a more accurate reading. The roller ball  440  may include a lattice-shaped pattern  442  formed on its outer surface which has varying light reflecting characteristics, the variations in the light reflected from the rolling ball  440  can be easily sensed by the light receiver  420  when the rolling ball  440  rolls across the skin surface. 
     The light emitter means  412  may be a light emitting diode which has small power consumption and high light intensity. The light emitted from the light emitter means  412  is reflected off the skin surface or incident to the rolling ball  440  disposed at the lower tip portion of the neck housing  405 . 
     Connected to the light receiver  420  is a conversion and output unit  460  that converts the variations in the light sensed by the light receiver  420  into an electrical signal and outputs the electrical signal. That is, when the sensor  400  is moved over the skin surface, light emitted from the light emitter means  412  is reflected from the surface or rolling ball  440  having the lattice-shaped pattern  442  continuously varies and the conversion and output unit  460  converts the variations in the light sensed by the light receiver  420  into an electrical signal and then outputs the electrical signal. 
     A calculation unit  480  is disposed inside the nerve sensor  400  and calculates the real distance using the electrical signal input from the conversion and output unit  460 . The calculator unit  480  is also electrically connected to a LCD display  500  that indicated the distance measured. The calculator unit  480  is electrically connected to an ON/OFF switch  510 . 
     The input button unit  490  is disposed inside the neck housing  405  and inputs a signal to the calculation unit  480  indicating that the orifice  407  or rolling ball  440  is positioned at the first point A or the second point B. 
     During operation, the user grasps the body of the nerve stimulator  400  and holds in vertically upright. The tip of the neck housing  405  or the rolling ball  440  is placed on the first point A, the input button unit  490  is pressed to indicate to the calculation unit  480  that the present position of the rolling ball  440  is the first point A. Then the nerve stimulator  400  is moved over the nerve path so that the orifice  407  or rolling ball  440  remains in contact with the skin. As the nerve stimulator  400  is moved, the light emitted through the orifice  407  and reflected off the skin or incident on the rolling ball  420  is sensed by the light receiver  420 . The variation in the light sensed by the light receiver  420  is converted into an electrical signal that is output to the calculation unit  440 . The nerve stimulator  400  is moved to the second point B. Then, when the orifice  407  or rolling ball  480  reaches the second point B, the input button unit  490  is pressed to indicate to the calculation unit  480  that the present position of the housing  10  is the second point B. Then, the calculation unit  480  recognizes the second point B and calculates a distance over which the orifice  407  or rolling ball  420  has rolled from the first point A to the second point B. The distance is then shown on the display  500 . 
     In compliance with the statute, the invention described herein has been described in language more or less specific as to structural features. It should be understood however, that the invention is not limited to the specific features shown, since the means and construction shown is comprised only of the preferred embodiments for putting the invention into effect. The invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the amended claims, appropriately interpreted in accordance with the doctrine of equivalents.