Patent Publication Number: US-2005143670-A1

Title: Portable electrocardiograph

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a portable electrocardiograph capable of easily measuring and storing electrocardiographic waveforms.  
      2. Description of the Background Art  
      Generally, for diagnosing ischemic cardiomyopathies such as angina pectoris and myocardial infarction, an electrocardiogram of a patient is used. Known electrocardiographs used for measuring electrocardiographic waveforms include a stationary electrocardiograph and a portable electrocardiograph.  
      The stationary electrocardiograph is installed in a medical institution such as a hospital and is used in such a manner that electrodes are attached to a body of a patient who lies on a bed or the like to measure electrocardiographic waveforms. Measurement of the electrocardiographic waveforms by using the stationary electrocardiograph is advantageous in that various electrocardiographic waveforms (such as P waveform, QRS waveform, or ST waveform) can precisely be measured. On the other hand, there is a possibility that an abnormal waveform is not necessarily reproduced at the time of measurement, and a symptom of a patient sometimes cannot properly be observed at the time of diagnosis by a physician.  
      Portable electrocardiographs are roughly divided into a Holter electrocardiograph for continuously measuring and storing electrocardiographic waveforms while electrodes are attached to the body of the patient who lives daily life for one day to several days, and an event-type electrocardiograph for measuring and storing electrocardiographic waveforms when a subjective symptom to be measured such as palpitation or pant occurs.  
      In the Holter electrocardiograph, a state where the electrodes are attached to the body of the patient should be maintained for a long time. Accordingly, an adhesion-type electrode is normally adopted as each of a plurality of measurement electrodes. The adhesion-type electrode is implemented by applying a conductive adhesive on a surface of the measurement electrode. The electrode is attached to the body by means of an adhesive layer. It is noted that the adhesion-type electrode is electrically connected to a device main body via a connection cable extending from an electrode body.  
      In the Holter electrocardiograph, abnormal waveforms can reliably be measured. On the other hand, since the state where electrodes are attached to the patient should be maintained for one day to several days, the patient may feel unpleasant or pain.  
      Known event-type portable electrocardiographs include an electrocardiograph of a type in which an electrode for measuring electrocardiographic waveforms is always in contact with a prescribed site of the body and an electrocardiograph of a type in which a subject himself/herself contacts an electrode with the body when a subjective symptom to be measured occurs.  
      In the former event-type portable electrocardiograph, like the Holter portable electrocardiograph, the state where the electrode is always in contact with the body has to be maintained. As such, the adhesion-type electrode is employed. Here, the subject suffers from unpleasant feeling or pain, as in the case of the Holter portable electrocardiograph described above. In contrast, in the latter event-type portable electrocardiograph, the electrode should be brought into contact with the body only when necessary. Therefore, the event-type portable electrocardiograph is very easy to use for the subject.  
      As the latter event-type portable electrocardiographs, various electrocardiographs structured such that an electrode is provided on an outer surface of the device main body have been proposed.  
      For example, as shown in  FIG. 27 , Japanese Patent Laying-Open No. 61-41438 discloses a portable electrocardiograph  100 E structured such that a display unit  148  is provided on a front face  111  of a device main body  110  and three electrodes  121 ,  122  and  123  to be attached to the body are provided on a rear face  112 . Measurement is carried out by bringing three electrodes  121 ,  122  and  123  into contact with a chest of a subject.  
      As shown in  FIGS. 28A and 28B , Japanese Utility Model Laying-Open No. 3-91304 discloses a portable electrocardiograph  100 F structured such that electrode  121  is provided on front face  111  of device main body  110 , a supporting member  191  extending from the top of device main body  110  toward rear face  112  of device main body  110  is attached to a top face  113  of device main body  110  with a hinge  192 , and electrode  122  is provided on a surface of supporting member  191 . At the time of measurement, supporting member  191  is pivoted to open the electrocardiograph (see  FIG. 28C ), so that an electrode formation face of supporting member  191  and front face  111  of device main body  110  are located on substantially the same plane, and a electrocardiographic waveform is measured in a state where two electrodes  121  and  122  are brought into contact with the chest of the subject.  
      As shown in  FIGS. 29A and 29B , Japanese Utility Model Laying-Open No. 3-91305 discloses a portable electrocardiograph  100 G structured such that electrode  121  made of an electroconductive rubber is provided on front face  111  of device main body  110  and electrodes  122  and  123  are provided on a right side face  115  and a left side face  116  of device main body  110  respectively. At the time of measurement, the subject holds device main body  110  from rear face  112  side thereof so as to touch electrodes  122  and  123  provided on both side faces  115  and  116 , and brings electrode  121  provided on front face  111  into contact with the chest of the subject so as to measure an electrocardiographic waveform.  
      As shown in  FIG. 30 , Japanese Patent Laying-Open No. 2003-144403 discloses a portable electrocardiograph  100 H structured such that a negative electrode  121  and an indifferent electrode  123  are provided on top face  113  and a bottom face  114  respectively, that are opposing surfaces of device main body  110  having a substantially rectangular parallelepiped shape, and a positive electrode  122  is provided on left side face  116  which is a curved surface adjacent to the surfaces on which negative electrode  121  and indifferent electrode  123  are provided. On front face  111  of device main body  110 , display unit  148  for displaying a measurement result as well as an operation button portion  140  where various operation buttons represented by a power button  141  for turning on power are disposed are provided. At the time of measurement, the subject himself/herself holds negative electrode  121  and indifferent electrode  123  provided on top face  113  and bottom face  114  respectively from the rear side of device main body  110  with his/her right hand, and brings electrode  122  provided on left side face  116  of device main body  110  into contact with his/her chest so as to measure an electrocardiographic waveform.  
      Meanwhile, in Japanese Patent Laying-Open No. 9-56686 discloses a portable electrocardiograph structured so as to be capable of switching between Holter-type and event-type depending on a purpose of use. As shown in  FIG. 31 , in a portable electrocardiograph  100 I disclosed in Japanese Patent Laying-Open No. 9-56686, device main body  110  is divided into a main body portion  193  and an arm portion  194  connected to each other by a hinge mechanism. On top face  113  and bottom face  114  that are opposing surfaces of main body portion  193 , one measurement electrode  121  and indifferent electrode  123  are provided respectively. The other measurement electrode  122  is provided at a tip end of arm portion  194  on front face  111  of device main body  110 . In addition, a jack  150  for receiving a connector  182  of connection cables  181  extending from attachment portions  171  of the adhesion-type electrodes (a pair of measurement electrodes  121  and  122  and indifferent electrode  123 ) is provided in a prescribed position of main body portion  193 .  
      When this electrocardiograph is used as the event-type electrocardiograph, the adhesion-type electrodes are disconnected from device main body  110 . Then, one measurement electrode  121  and indifferent electrode  123  are brought into contact with the body by holding main body portion  193  with the right hand, and the other measurement electrode  122  provided at the tip end of arm portion  194  is pressed against the chest. On the other hand, when the electrocardiograph is used as the Holter-type portable electrocardiograph, connector  182  of connection cables  181  extending from the adhesion-type electrodes is inserted in jack  150  provided in device main body  110  in a direction shown with an arrow D in the drawing, and the adhesion-type electrode is attached to a prescribed site of the chest. In a state where connector  182  is inserted in jack  150 , measurement electrodes  121  and  122  as well as indifferent electrode  123  provided on an outer surface of device main body  110  are electrically disconnected from a circuit provided inside the device main body.  
      In such a portable electrocardiograph as disclosed in each document above, the contact portion between the electrode provided on the outer surface of a housing and the body should be kept stable during a measurement period of several tens of seconds. Unless stable contact is maintained, the measured waveform is disturbed by variation in a contact area between the electrode and the body, and the electrocardiographic waveform cannot precisely be measured in a stable manner.  
      The conventional portable electrocardiograph described above is intended to maintain contact between the electrode and the body by pressing a hand holding the electrocardiograph main body against abdomen or the like of the body at the time of measurement, and by fixing that hand. More specifically, a wrist, a forearm, an elbow or the like of the holding arm is pressed against the body, thereby preventing the holding hand from being moved during measurement and maintaining stable contact between the electrode and the body. This point will be described in more detailed manner with reference to portable electrocardiograph  100 H disclosed in Japanese Patent Laying-Open No. 2003-144403.  
       FIG. 32  is a perspective view of a measurement posture to be taken by the subject at the time of measuring an electrocardiographic waveform using portable electrocardiograph  100 H disclosed in Japanese Patent Laying-Open No. 2003-144403. As shown in  FIG. 32 , during measurement, a subject  200  presses a wrist portion of forearm  220  against the right side of the body while holding portable electrocardiograph  100 H with his/her right hand  210 , and also brings positive electrode  122  provided on left side face  116  of device main body  110  of portable electrocardiograph  100 H into direct contact with the skin of a lower left portion of a chest  250 . While maintaining this state for several tens of seconds, an electrocardiographic waveform is measured.  
       FIG. 33  shows a state where portable electrocardiograph  100 H is held with right hand  210 . As shown in  FIG. 33 , when subject  200  takes the measurement posture as shown in  FIG. 32 , he/she holds device main body  110  while covering the rear face side of device main body  110  with his/her palm, such that front face  111  of portable electrocardiograph  100 H faces upward. Device main body  110  is held with a forefinger  212 , a middle finger  213 , a ring finger  214 , and a little finger  215  of right hand  210  being lightly bent, so that any or all of the fingers come into contact with negative electrode  121  provided on top face  113  of device main body  110 . A thumb  211  extends along bottom face  114  of device main body  110  and comes in contact with indifferent electrode  123  provided on bottom face  114 , so as to hold device main body  110 . Then, the wrist portion of right hand  210  is pressed against the right side of the body, and right hand  210  is fixed such that positive electrode  122  formed on left side face  116  of device main body  110  is not apart from the body.  
      In measuring the electrocardiographic waveform in such a measurement posture, if the wrist portion of the right arm is not covered with clothing or the like, the right arm and the right side of the body are in direct contact with each other. Consequently, a measurement circuit (an electric circuit formed in the body from the positive electrode to the negative electrode) is short-circuited in this portion. In such a case, the measurement circuit no longer crosses over the heart, resulting in failure in precise measurement of the electrocardiographic waveform.  
      Even if the wrist portion of the right arm is covered with clothing or the like, in a state where the portable electrocardiograph is held with the right hand and pressed against the right side of the body, the subject has to put strength in his/her right arm in order to hold the portable electrocardiograph. Here, muscles in the right arm are under a tension, resulting in generation of a myoelectric potential. When the myoelectric potential is produced in the right arm forming a part of the measurement circuit, the myoelectric potential is in turn superposed as noise on the electrocardiographic waveform to be measured. In particular with regard to elderly people who have less flexibility of the body, the myoelectric potential produced when the measurement posture described above is taken is high, which will considerably interfere precise measurement of the electrocardiographic waveform.  
      A variety of techniques (as disclosed in Japanese Patent Laying-Open Nos. 2000-14653, 2001-346771, 61-206428, and the like) have conventionally been developed in order to solve the above-described problems. The technique disclosed in each document, however, is directed to removal with a filter of noise as result of a myoelectric potential component produced in muscles other than cardiac muscle and mixed in measurement data. Unless complete removal of the noise is achieved, precise electrocardiographic data cannot be obtained. On the other hand, complete removal of the noise is substantially impossible, and it has been extremely difficult to accurately and precisely measure each characteristic waveform in the electrocardiographic waveforms (such as P waveform, QRS waveform, ST waveform, or the like) even with these techniques.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to provide a portable electrocardiograph capable of precisely measuring an electrocardiographic waveform in a stable manner, without noise caused by a myoelectric potential produced in muscles other than cardiac muscle being superposed on the electrocardiographic waveform.  
      The inventors have conceived that superposition on the electrocardiographic waveform of the noise caused by the myoelectric potential produced in muscles other than cardiac muscle can be avoided by measuring the electrocardiographic waveform while a measurement posture preventing muscles in the right arm from being under tension is taken, and have found a measurement posture completely different from a posture taken in using a conventional portable electrocardiograph. More specifically, the inventors have found that superposition on the electrocardiographic waveform of the noise caused by the myoelectric potential produced in muscles in the right arm can considerably be suppressed by measuring the electrocardiographic waveform when such a posture that the right arm is supported by some kind of base or such a posture that the subject has his/her right arm vertically hang down is taken, thereby attaining precise measurement of the electrocardiographic waveform in a stable manner. The inventors have studied and developed a portable electrocardiograph allowing such a measurement posture, and finally completed the present invention.  
      A portable electrocardiograph according to the present invention measures an electrocardiographic waveform by measuring a potential difference produced between a first electrode and a second electrode brought into contact with a body surface. The first electrode is provided on an outer surface of a device main body, and the second electrode is drawn outside the device main body via a connection cable.  
      Preferably, in the portable electrocardiograph according to the present invention, the device main body has a substantially rectangular parallelepiped shape, and the first electrode is provided on an end surface located at one end in a longitudinal direction of the device main body.  
      Preferably, the connection cable is attached to the device main body in a detachable manner.  
      Preferably, in the portable electrocardiograph according to the present invention, the device main body includes wind-up means for winding up the connection cable in the device main body.  
      Preferably, in the portable electrocardiograph according to the present invention, the device main body includes a storage space accommodating the connection cable and the second electrode.  
      Preferably, in the portable electrocardiograph according to the present invention, the first electrode is to be brought into contact with a right hand, and the second electrode is to be brought into contact with a chest.  
      Preferably, in the portable electrocardiograph according to the present invention, the first electrode is to be brought into contact with a chest while the device main body is held with a left hand, and the second electrode is to be brought into contact with a right hand.  
      According to the present invention, superposition on the electrocardiographic waveform of the noise caused by the myoelectric potential produced in muscles other than cardiac muscle is avoided, thereby allowing precise measurement of the electrocardiographic waveform. Therefore, the present invention contributes to early detection of ischemic cardiomyopathies or the like, and allows proper diagnosis.  
      The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of an appearance of a portable electrocardiograph in a first embodiment of the present invention.  
       FIG. 2  is a front view of the portable electrocardiograph in the first embodiment of the present invention.  
       FIG. 3  is a top view of the portable electrocardiograph in the first embodiment of the present invention.  
       FIG. 4  is a bottom view of the portable electrocardiograph in the first embodiment of the present invention.  
       FIG. 5  is a right side view of the portable electrocardiograph in the first embodiment of the present invention.  
       FIG. 6  is a left side view of the portable electrocardiograph in the first embodiment of the present invention.  
       FIG. 7  is a perspective view of a measurement posture to be taken by a subject at the time of measuring an electrocardiographic waveform using the portable electrocardiograph in the first embodiment of the present invention.  
       FIG. 8  illustrates a measurement posture to be taken by the subject at the time of measuring an electrocardiographic waveform using the portable electrocardiograph in the first embodiment of the present invention, viewed from the above.  
       FIG. 9  illustrates a state where a device main body is held by the subject at the time of measuring an electrocardiographic waveform using the portable electrocardiograph in the first embodiment of the present invention.  
       FIG. 10  is a partially cut-away side view of another structural example of an external electrode that can be employed in the portable electrocardiograph in the first embodiment of the present invention.  
       FIG. 11  is a side view of yet another structural example of the external electrode that can be employed in the portable electrocardiograph in the first embodiment of the present invention.  
       FIG. 12  is a perspective view of an appearance of a portable electrocardiograph in a second embodiment of the present invention.  
       FIG. 13  is a front view of the portable electrocardiograph in the second embodiment of the present invention.  
       FIG. 14  is a top view of the portable electrocardiograph in the second embodiment of the present invention.  
       FIG. 15  is a bottom view of the portable electrocardiograph in the second embodiment of the present invention.  
       FIG. 16  is a right side view of the portable electrocardiograph in the second embodiment of the present invention.  
       FIG. 17  is a left side view of the portable electrocardiograph in the second embodiment of the present invention.  
       FIG. 18  is a perspective view of a measurement posture to be taken by a subject at the time of measuring an electrocardiographic waveform using the portable electrocardiograph in the second embodiment of the present invention.  
       FIG. 19  illustrates a measurement posture to be taken by the subject at the time of measuring an electrocardiographic waveform using the portable electrocardiograph in the second embodiment of the present invention, viewed from the above.  
       FIG. 20  illustrates a state where a device main body is held by the subject at the time of measuring an electrocardiographic waveform using the portable electrocardiograph in the second embodiment of the present invention.  
       FIG. 21  is a side view of another structural example of the external electrode that can be employed in the portable electrocardiograph in the second embodiment of the present invention.  
       FIG. 22  is a side view of yet another structural example of the external electrode that can be employed in the portable electrocardiograph in the second embodiment of the present invention.  
       FIG. 23  is a perspective view of another example of the measurement posture to be taken by the subject at the time of measuring an electrocardiographic waveform using the portable electrocardiograph in the second embodiment of the present invention.  
       FIG. 24  is a schematic perspective view of a structure of a portable electrocardiograph in a third embodiment of the present invention.  
       FIG. 25  illustrates a variation of the portable electrocardiograph in the third embodiment of the present invention.  
       FIG. 26  is a schematic perspective view of a structure of a portable electrocardiograph in a fourth embodiment of the present invention.  
       FIG. 27  is a perspective view of an example of a conventional portable electrocardiograph.  
       FIG. 28A  is a front view of another example of the conventional portable electrocardiograph.  
       FIG. 28B  is a left side view of the conventional portable electrocardiograph illustrated in  FIG. 28A .  
       FIG. 28C  is a left side view illustrating a state where the conventional portable electrocardiograph shown in  FIGS. 28A and 28B  is opened.  
       FIG. 29A  is a front view of yet another example of the conventional portable electrocardiograph.  
       FIG. 29B  is a right side view of the conventional portable electrocardiograph illustrated in  FIG. 29A .  
       FIGS. 30 and 31  are front views of yet other examples of the conventional portable electrocardiograph.  
       FIG. 32  illustrates a measurement posture to be taken by the subject at the time of measuring an electrocardiographic waveform using the portable electrocardiograph illustrated in  FIG. 30 .  
       FIG. 33  illustrates a holding state with a right hand at the time of measuring an electrocardiographic waveform using the portable electrocardiograph illustrated in  FIG. 30 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In the following, embodiments of the present invention will be described in detail with reference to the drawings.  
     First Embodiment  
      First, an overall structure of a portable electrocardiograph  100 A in the present embodiment will be described.  
      As shown in FIGS.  1  to  6 , in order to realize excellent usability, portable electrocardiograph  100 A in the present embodiment has such a light weight and a small size that it can be held by one hand. Portable electrocardiograph  100 A includes a device main body  110  and an external electrode unit  160 A.  
      A structure of device main body  110  will now be described. Device main body  110  has a flat and elongated, substantially rectangular parallelepiped shape. On its outer surfaces (front face  111 , rear face  112 , top face  113 , bottom face  114 , right side face  115 , and left side face  116 ), a display unit, an operation unit, electrodes and the like are disposed.  
      As shown in  FIGS. 1 and 2 , a measurement button  142  serving as an operation button for starting measurement is provided in a portion close to one end in the longitudinal direction (the direction shown with an arrow A in the drawing) of front face  111  of device main body  110 . In a portion close to the other end of front face  111  of device main body  110 , display unit  148  is provided. Display unit  148  is implemented, for example, by a liquid crystal display and serves to display a result of measurement or the like. The measurement result is displayed, for example, as electrocardiographic waveforms or numerical data as shown in  FIG. 1 .  
      As shown in  FIGS. 1 and 3 , power button  141  is disposed in a prescribed position in top surface  113  of device main body  110 . Power button  141  serves as an operation button for turning ON/OFF portable electrocardiograph  100 A.  
      As shown in  FIGS. 1 and 4 , various operation buttons are disposed in prescribed positions on bottom face  114  of device main body  110 . In shown portable electrocardiograph  100 A, a setting button  143 , a display button  144 , a left scroll button  145 , and a right scroll button  146  are disposed. Setting button  143  is used for making a variety of settings for portable electrocardiograph  100 A, while display button  144  is used for displaying a measurement result on display unit  148 . Left scroll button  145  and right scroll button  146  are used for scrolled display of a graph showing a measurement result or guide information displayed on display unit  148 .  
      As shown in  FIGS. 1 and 5 , on right side face  115  located at one end in the longitudinal direction of device main body  110 , first electrode (negative electrode)  121  representing one electrode out of a pair of measurement electrodes as well as indifferent electrode  123  for deriving a potential serving as a reference in potential variation in the body are disposed. Right side face  115  has a smoothly curved shape, such that a forefinger of the right hand of the subject is fitted thereto when the subject takes a measurement posture which will be described later. In addition, a concave portion  115   a  extending in an up-down direction is formed in right side face  115 . Concave portion  115   a  is in a shape to receive the forefinger of the right hand of the subject.  
      First electrode  121  and indifferent electrode  123  described above are formed with a conductive member, and electrically connected to a circuit formed inside device main body  110 . In addition, first electrode  121  and indifferent electrode  123  are disposed in concave portion  115   a  provided in right side face  115  such that their surfaces are exposed on the outer surface of device main body  110 . The first electrode  121  is located closer to top face  113  on right side face  115 , while indifferent electrode  123  is located closer to bottom face  114  on right side face  115 .  
      As shown in  FIG. 6 , on left side face  116  of device main body  110 , a jack  150  receiving connector  182  (see  FIG. 1 ) provided at the tip end of connection cable  181  of external electrode unit  160 A which will be described later is provided. Jack  150  serves as a connection terminal for electrically connecting second electrode  122  (see  FIG. 1 ) which will be described later to the circuit provided inside device main body  110 .  
      A structure of external electrode unit  160 A will now be described. As shown in  FIG. 1 , external electrode unit  160 A includes attachment portion  171 , connection cable  181 , and connector  182 . Attachment portion  171  represents a part for attaching second electrode  122  which will be described later to the body. In portable electrocardiograph  100 A in the present embodiment, what is called an adhesion-type electrode is adopted. On a main surface of attachment portion  171 , second electrode (positive electrode)  122  representing the other electrode of the pair of measurement electrodes is disposed. A conductive adhesive is applied to the surface of second electrode  122 , and second electrode  122  is attached to the body by means of the adhesive layer.  
      Connection cable  181  has one end electrically connected to second electrode  122 , and has the other end connected to connector  182 . Preferably, a highly flexible connection cable  181  is used, from the viewpoint of ease of use. Connector  182  is detachably inserted in jack  150  provided in device main body  110  described above. When connector  182  is inserted in jack  150 , second electrode  122  provided in external electrode unit  160 A is electrically connected to the circuit provided inside device main body  110 .  
      Next, a measurement posture to be taken by the subject in measuring an electrocardiographic waveform using portable electrocardiograph  100 A having the above-described structure will be described.  
      As shown in  FIGS. 7 and 8 , during measurement, a state in which connector  182  of external electrode unit  160 A is inserted in jack  150  of device main body  110  is maintained. Subject  200  presses down power button  141  provided on top face  113  of device main body  110 , so as to turn on portable electrocardiograph  100 A.  
      Then, the subject holds a portion closer to one end in the longitudinal direction of device main body  110  such that right side face  115  of device main body  110  is covered with forefinger  212  of right hand  210 . Right forearm  220  is placed on a base such as a desk  300 . Here, subject  200  preferably sits on a chair or the like, and takes a relaxed posture without imposing burden on the body.  
      Thereafter, attachment portion  171  of external electrode unit  160 A is stuck to chest  250 . More specifically, attachment portion  171  is stuck such that second electrode  122  provided in external electrode unit  160 A comes in contact with the skin on a fifth intercostal anterior axillary line of chest  250 . Then, the subject presses measurement button  142  provided on front face  111  of device main body  110  with his/her thumb  211  of right hand  210  holding device main body  110 , and maintains the measurement posture at ease for several tens of seconds until measurement of the electrocardiographic waveform is completed.  
      A state that portable electrocardiograph  100 A is held with right hand  210  will now be described.  
      As shown in  FIG. 9 , in this measurement posture, subject  200  holds with right hand  210  a portion closer to one end in the longitudinal direction of device main body  110  such that front face  111  of device main body  110  of portable electrocardiograph  100 A faces upward. Here, right side face  115  of device main body  110  is covered with forefinger  212  of right hand  210 , thumb  211  of right hand  210  is placed on front face  111  of device main body  110 , and the middle finger of right hand  210  is placed on the rear face of device main body  110 . That is, device main body  110  is held such that it is caught by three fingers.  
      In this state, forefinger  212  of right hand  210  is lightly bent such that the forefinger extends along curved right side face  115  and is inserted in concave portion  115   a  provided in right side face  115 . Forefinger  212  of right hand  210  is thus brought into contact with first electrode  121  and indifferent electrode  123  provided in concave portion  115   a.    
      When such a measurement posture is taken, first electrode  121  and indifferent electrode  123  provided on the outer surface of device main body  110  of portable electrocardiograph  100 A come in contact with forefinger  212  of right hand  210  of subject  200 , and second electrode  122  connected to device main body  110  via connection cable  181  comes in contact with chest  250  of subject  200 . In this manner, a measurement circuit is implemented by right hand  210  being in contact with first electrode  121 , forearm  220  without contacting chest  250 , a brachium  230  and a right shoulder  240  without contacting chest  250 , and chest  250  to which second electrode  122  is attached, in this order.  
      According to portable electrocardiograph  100 A in the present embodiment, a potential difference produced between first electrode  121  provided on the outer surface of device main body  110  and second electrode  122  drawn outside device main body  110  via connection cable  181  is measured, so as to measure the electrocardiographic waveform. With such a structure, the measurement posture as shown in  FIGS. 7 and 8  can be allowed.  
      In the measurement posture shown in  FIGS. 7 and 8 , right forearm  220  is placed on the base such as desk  300 . Accordingly, subject  200  does not have to put unnecessary strength into his/her right arm, and the electrocardiographic waveform can be taken with the subject taking a very relaxed posture. The muscles in the right arm are not under tension, and generation of the myoelectric potential is effectively suppressed. Consequently, noise caused by the myoelectric potential produced in the muscles in the right arm is not superposed on obtained measurement data, whereby the electrocardiographic waveform can precisely be measured in a stable manner.  
      In addition, according to portable electrocardiograph  100 A in the present embodiment, first electrode  121  provided on the outer surface of device main body  110  is provided on right side face  115  located at one end in the longitudinal direction of device main body  110 . Accordingly, when the electrocardiographic waveform is measured while the measurement posture as shown in  FIGS. 7 and 8  is taken, display unit  148  can visually be recognized during measurement. That is, measurement while checking the measurement data can be achieved.  
      Moreover, according to portable electrocardiograph  100 A in the present embodiment, external electrode unit  160 A including connection cable  181  is attached to device main body  110  in a detachable manner, thereby portability being improved.  
      Though the external electrode unit including the adhesion-type electrode has been described by way of example in the present embodiment, the external electrode unit connected to the device main body is not necessarily limited to the above-described type. For example, an external electrode unit including a suction-cup-type electrode or an external electrode unit including a pressed-type electrode may be adopted.  
      An external electrode unit  160 B shown in  FIG. 10  represents an external electrode unit including what is called a suction-cup-type electrode, and includes a negative pressure creating portion  172  and a suction cup portion  173 . Negative pressure creating portion  172  and suction cup portion  173  are formed, for example, with a rubber material, and suction cup portion  173  is covered with a conductive coating. The conductive coating implements second electrode  122 , and it is electrically connected to connection cable  181 .  
      In attaching the suction-cup-type electrode to the body, negative pressure creating portion  172  is pinched by fingers, so as to compress an internal space. Then, suction cup portion  173  is pressed against a prescribed site of the body, and the fingers that have been pinched negative pressure creating portion  172  are removed. Then, a negative pressure is caused in the internal space, and the suction-cup-type electrode is stuck and held to the body. When the external electrode unit including such a suction-cup-type electrode is employed as well, the electrocardiographic waveform can precisely be measured in a stable manner, as in employing the external electrode unit including the adhesion-type electrode.  
      An external electrode unit  160 C shown in  FIG. 11  represents an external electrode unit including what is called a pressed-type electrode, and includes a base body  174  and second electrode  122  provided on its outer surface. Second electrode  122  is formed with a conductive member, and electrically connected to connection cable  181 .  
      In bringing the pressed-type electrode into contact with the body, base body  174  is held with a left hand and pressed against a prescribed site of the body. When the external electrode unit including such a pressed-type electrode is employed as well, the electrocardiographic waveform can precisely be measured in a stable manner, as in employing the external electrode unit including the adhesion-type electrode.  
     Second Embodiment  
      An overall structure of a portable electrocardiograph  100 B in the present embodiment will now be described.  
      As shown in FIGS.  12  to  17 , in order to realize excellent usability, portable electrocardiograph  100 B in the present embodiment has such a light weight and a small size that it can be held by one hand, as in the portable electrocardiograph in the first embodiment described above. Portable electrocardiograph  100 B includes device main body  110  and an external electrode unit  160 D.  
      A structure of device main body  110  will now be described. Device main body  110  has a flat and elongated, substantially rectangular parallelepiped shape. On its outer surfaces (front face  111 , rear face  112 , top face  113 , bottom face  114 , right side face  115 , and left side face  116 ), a display unit, an operation unit, electrodes and the like are disposed.  
      As shown in  FIGS. 12 and 13 , display unit  148  is provided in a portion close to one end in the longitudinal direction (the direction shown with arrow A in the drawing) of front face  111  of device main body  110 . Display unit  148  is implemented, for example, by a liquid crystal display and serves to display a result of measurement or the like. The measurement result is displayed, for example, as electrocardiographic waveforms or numerical data as shown in  FIG. 12 . In a portion close to the other end of front face  111  of device main body  110 , measurement button  142  serving as an operation button for starting measurement is provided. In an end portion closer to one end of front face  111  of device main body  110 , an alignment mark  111   a  serving as an index in pressing first electrode  121  which will be described later against the body is formed.  
      As shown in  FIGS. 12 and 14 , power button  141  is disposed in a prescribed position in top surface  113  of device main body  110 . Power button  141  serves as an operation button for turning ON/OFF portable electrocardiograph  10 B. In a prescribed position on top face  113  of device main body  110 , jack  150  receiving connector  182  (see  FIG. 12 ) provided at the tip end of connection cable  181  of external electrode unit  160 D which will be described later is provided. Jack  150  serves as a connection terminal for electrically connecting second electrode  122  (see  FIG. 12 ) which will be described later to a circuit provided inside device main body  110 .  
      As shown in  FIGS. 12 and 15 , various operation buttons are disposed in prescribed positions on bottom face  114  of device main body  110 . In shown portable electrocardiograph  100 B, setting button  143 , display button  144 , left scroll button  145 , and right scroll button  146  are disposed. Setting button  143  is used for making a variety of settings for portable electrocardiograph  100 B, while display button  144  is used for displaying the measurement result on display unit  148 . Left scroll button  145  and right scroll button  146  are used for scrolled display of a graph showing a measurement result or guide information displayed on display unit  148 .  
      As shown in  FIGS. 12 and 16 , on right side face  115  located at one end in the longitudinal direction of device main body  110 , first electrode (positive electrode)  121  representing one electrode out of a pair of measurement electrodes is disposed. First electrode  121  is formed with a conductive member, and electrically connected to the circuit provided inside device main body  110 .  
      As shown in  FIG. 17 , on left side face  116  located at the other end in the longitudinal direction of device main body  110 , indifferent electrode  123  for deriving a potential serving as a reference in potential variation in the body is disposed. Indifferent electrode  123  is formed with a conductive member, and electrically connected to the circuit provided inside device main body  110 .  
      Left side face  116  has a smoothly curved shape, such that a forefinger of the left hand of the subject is fitted thereto when the subject takes a measurement posture which will be described later. In addition, a concave portion  116   a  extending in an up-down direction is formed in left side face  116 . Concave portion  116   a  is in a shape to receive the forefinger of the left hand of the subject.  
      A structure of external electrode unit  160 D will now be described. As shown in  FIG. 12 , external electrode unit  160 D includes a base body  175 , connection cable  181 , and connector  182 . Base body  175  is made of a box-shaped member having an opening in one surface, and includes second electrode (negative electrode)  122  on its inner bottom face. Base body  175  has such a shape as to receive in its inner space the forefinger of the right hand through the opening. Base body  175  is structured such that when the forefinger of the right hand is inserted therein, the forefinger tip comes in contact with second electrode  122 .  
      Connection cable  181  has one end electrically connected to second electrode  122 , and has the other end connected to connector  182 . Preferably, a highly flexible connection cable  181  is used, from the viewpoint of ease of use. Connector  182  is detachably inserted in jack  150  provided in device main body  110  described above. When connector  182  is inserted in jack  150 , second electrode  122  provided in external electrode unit  160 D is electrically connected to the circuit provided inside device main body  110 .  
      Next, a measurement posture to be taken by the subject in measuring an electrocardiographic waveform using portable electrocardiograph  100 B having the above-described structure will be described.  
      As shown in  FIGS. 18 and 19 , during measurement, a state in which connector  182  of external electrode unit  160 D is inserted in jack  150  of device main body  110  is maintained. Subject  200  presses down power button  141  provided on top face  113  of device main body  110 , so as to turn on portable electrocardiograph  100 B.  
      Then, forefinger  212  of right hand  210  is inserted in the inner space of base body  175  of external electrode unit  160 D, so as to bring forefinger  212  into contact with second electrode  122 . Right forearm  220  is placed on the base such as desk  300 . Here, preferably, thumb  211  of right hand  210  is brought into contact with a rear face of base body  175 . In this manner, base body  175  is held by forefinger  212  and thumb  211  in a stable manner, and contact between second electrode  122  and forefinger  212  of right hand  210  is maintained in a stable manner.  
      Then, the subject holds a portion closer to the other end in the longitudinal direction of device main body  110  such that left side face  116  of device main body  110  is covered with a forefinger  262  of a left hand  260 , and first electrode  121  provided on right side face  115  of device main body  110  is brought in direct contact with the skin on the fifth intercostal anterior axillary line located in a lower left portion of chest  250 . Here, subject  200  preferably sits on a chair or the like, and takes a relaxed posture without imposing burden on the body. Then, the subject presses measurement button  142  provided on front face  111  of device main body  110  with a thumb  261  of left hand  260  holding device main body  110 , and the subject maintains this measurement posture at ease for several tens of seconds until measurement of the electrocardiographic waveform is completed.  
      A state that portable electrocardiograph  100 B is held with left hand  260  will now be described.  
      As shown in  FIG. 20 , in this measurement posture, subject  200  holds a portion closer to the other end in the longitudinal direction of device main body  110  with left hand  260  such that front face  111  of device main body  110  of portable electrocardiograph  100 B faces upward. Here, left side face  116  of device main body  110  is covered with forefinger  262  of left hand  260 , thumb  261  of left hand  260  is placed on front face  111  of device main body  110 , and the middle finger of left hand  260  is placed on the rear face of device main body  110 . That is, device main body  110  is held such that it is caught by three fingers.  
      In this state, forefinger  262  of left hand  260  is lightly bent such that the forefinger extends along curved left side face  116  and is inserted in concave portion  116   a  provided in left side face  116 . Forefinger  262  of left hand  260  is thus brought into contact with indifferent electrode  123  provided in concave portion  116   a.    
      When such a measurement posture is taken, first electrode  121  provided on right side face  115  of device main body  110  of portable electrocardiograph  100 B comes in contact with chest  250  of subject  200 , and indifferent electrode  123  provided on left side face  116  of device main body  110  comes in contact with forefinger  262  of left hand  260  of subject  200 . In addition, second electrode  122  connected to device main body  110  via connection cable  181  comes in contact with forefinger  212  of right hand  210  of subject  200 . In this manner, a measurement circuit is implemented by right hand  210  being in contact with second electrode  122 , forearm  220  without contacting chest  250 , brachium  230  and right shoulder  240  without contacting chest  250 , and chest  250  to which first electrode  121  is attached, in this order.  
      According to portable electrocardiograph  100 B in the present embodiment, a potential difference produced between first electrode  121  provided on the outer surface of device main body  110  and second electrode  122  drawn outside device main body  110  via connection cable  181  is measured, so as to measure the electrocardiographic waveform. With such a structure, the measurement posture as shown in  FIGS. 18 and 19  can be allowed.  
      In the measurement posture shown in  FIGS. 18 and 19 , right forearm  220  is placed on the base such as desk  300 . Accordingly, subject  200  does not have to put unnecessary strength into his/her right arm, and the electrocardiographic waveform can be taken with the subject taking a very relaxed posture. The muscles in the right arm are not under tension, and generation of the myoelectric potential is effectively suppressed. Consequently, noise caused by the myoelectric potential produced in the muscles in the right arm is not superposed on obtained measurement data, whereby the electrocardiographic waveform can precisely be measured in a stable manner. Here, device main body  110  of portable electrocardiograph  100 B is held with the left hand. Therefore, the myoelectric potential produced in muscles in the left arm does not appear on the measurement circuit. That is, noise caused by the myoelectric potential is not superposed on the obtained electrocardiographic waveform.  
      In addition, according to portable electrocardiograph  100 B in the present embodiment, first electrode  121  provided on the outer surface of device main body  110  is provided on right side face  115  located at one end in the longitudinal direction of device main body  110 . Accordingly, the measurement posture to allow the measurement circuit to cross over the heart is realized in an ensured manner, and short-circuit of the measurement circuit due to contact of right hand  210 , forearm  220  and brachium  230  with chest  250  is prevented. When the electrocardiographic waveform is measured while the measurement posture as shown in  FIGS. 18 and 19  is taken as well, display unit  148  can visually be recognized during measurement. That is, measurement while checking the measurement data can be achieved.  
      Moreover, according to portable electrocardiograph  100 B in the present embodiment, external electrode unit  160 D including connection cable  181  is attached to device main body  110  in a detachable manner, thereby portability being improved.  
      Though the external electrode unit including the electrode receiving the right forefinger has been described by way of example in the present embodiment, the external electrode unit connected to the device main body is not necessarily limited to the above-described type. For example, an external electrode unit including a grip-type electrode or an external electrode unit including a pinched-type electrode may be adopted. In addition, though portable electrocardiograph  100 B in the present embodiment has indifferent electrode  123  disposed on left side face  116  of device main body  110 , indifferent electrode  123  may be provided in the external electrode unit instead of being disposed on device main body  110 , as will be described later.  
      An external electrode unit  160 E shown in  FIG. 21  represents an external electrode unit including what is called a grip-type electrode, and includes a base body  176  as well as second electrode  122  and indifferent electrode  123  provided on its outer surface. Second electrode  122  and indifferent electrode  123  are formed with a conductive member, and electrically connected to connection cable  181 .  
      In contacting the grip-type electrode with the body, base body  176  is gripped by the right hand. During measurement, attention should be paid not to release the hand. When the external electrode unit including such a grip-type electrode is employed as well, the electrocardiographic waveform can precisely be measured in a stable manner.  
      An external electrode unit  160 F shown in  FIG. 22  represents an external electrode unit including a pinched-type electrode, and includes a base body  177  as well as second electrode  122  and indifferent electrode  123  provided on its outer surface. Second electrode  122  and indifferent electrode  123  are formed with a conductive member, and provided on opposing main surfaces of base body  177  respectively. Second electrode  122  and indifferent electrode  123  are electrically connected to connection cable  181 .  
      In contacting the pinched-type electrode with the body, for example, the thumb of the right hand is brought into contact with indifferent electrode  123 , the forefinger and the middle finger of the right hand are brought into contact with second electrode  122 . In doing so, base body  177  is held with the right hand, and attention should be paid not to release the hand during measurement. When the external electrode unit including such a pinched-type electrode is employed as well, the electrocardiographic waveform can precisely be measured in a stable manner.  
      Portable electrocardiograph  100 B in the present embodiment may adopt external electrode unit  160 A including what is called the adhesion-type electrode described in the first embodiment above.  FIG. 23  shows a measurement posture in such a case.  
      As shown in  FIG. 23 , when external electrode unit  160 A including the adhesion-type electrode is employed, the device main body is held and pressed against the body with the left hand in a manner the same as in the measurement posture shown in  FIG. 18  as set forth above. Meanwhile, it is preferable to change a position where the adhesion-type electrode provided in external electrode unit  160 A contacts with the body. That is, the electrode is preferably attached to the right shoulder in measuring the electrocardiographic waveform. In this manner, second electrode  122 , right shoulder  240 , chest  250 , and first electrode  121  implement the measurement circuit in this order. Accordingly, regardless of a state of the right arm, superposition on the electrocardiographic waveform of the noise caused by the myoelectric potential produced in the muscles in the right arm is considerably suppressed. As a result, more precise measurement of the electrocardiographic waveform can be achieved.  
     Third Embodiment  
      A portable electrocardiograph  100 C in the present embodiment is intended to measure the electrocardiographic waveform in the measurement posture shown in  FIGS. 7 and 8 , in a manner similar to portable electrocardiograph  100 A in the first embodiment described above. Therefore, portions the same as those in the first embodiment described above are given the same reference characters in the drawings, and description thereof will not repeated.  
      As shown in  FIG. 24 , portable electrocardiograph  100 C in the present embodiment includes a cord reel  158  serving as wind-up means for winding up connection cable  181  of external electrode unit  160 A in device main body  110 . Connection cable  181  wound on cord reel  158  is drawn outside device main body  110  through an opening  116   b  provided in left side face  116  of device main body  110 , and its tip end is electrically connected to second electrode  122  provided in external electrode unit  160 A. Cord reel  158  turns in a direction shown with an arrow B in the drawing, so as to freely adjust a length of connection cable  181 .  
      According to such a structure, not only the length of connection cable  181  can be adjusted, but also connection cable  181  is wound by means of cord reel  158  during a period in which measurement is not performed. Accordingly, a portable electrocardiograph attaining excellent portability can be obtained.  
      As shown in  FIG. 25 , cord reel  158  may be provided in the external electrode unit. In such a case, cord reel  158  is attached to some midpoint of connection cable  181 .  
     Fourth Embodiment  
      A portable electrocardiograph  100 D in the present embodiment is intended to measure the electrocardiographic waveform in the measurement posture shown in  FIGS. 7 and 8 , in a manner similar to portable electrocardiograph  100 A in the first embodiment described above. Therefore, portions the same as those in the first embodiment described above are given the same reference characters in the drawings, and description thereof will not repeated.  
      As shown in  FIG. 26 , portable electrocardiograph  100 D in the present embodiment includes a storage space for accommodating connection cable  181  of external electrode unit  160 A on top face  113  of device main body  110 . More specifically, a cover  159  provided over top face  113  of device main body  110  is pivoted in a direction shown with an arrow C in the drawing, so as to permit take-out/storage of connection cable  181 .  
      Connection cable  181  is directly drawn out from device main body  110 , and has its tip end connected to connector  182 . Connector  182  is inserted in a jack  171   a  provided in attachment portion  171  of the adhesion-type electrode, so as to be electrically connected to second electrode  122 .  
      According to such a structure, connection cable  181  can be stored inside device main body  110  during a period in which measurement is not performed. Accordingly, a portable electrocardiograph attaining excellent portability can be obtained. In order to achieve further improvement in portability, a storage space for accommodating the adhesion-type electrode may be provided within device main body  110 .  
      Though embodiments based on the present invention have been described above, the present invention is not limited to those embodiments. The present invention aims to provide one electrode out of the measurement electrodes in the device main body of the portable electrocardiograph and the other electrode in a manner drawn outside the device main body, in order to adopt a measurement posture without putting unnecessary strength into the right arm for the purpose of suppressing generation of a myoelectric potential produced in muscles in the right arm during measurement of an electrocardiographic waveform. Therefore, a structure other than those can be modified as appropriate. For example, a position where an indifferent electrode is disposed or a position where a display unit, an operation unit, or the like is disposed can be modified as appropriate.  
      With regard to a position where the electrode is attached to the body, it is preferable to attach the electrode to the position described in the embodiments above, considering the purpose of precisely measuring an electrocardiographic waveform in a stable manner. Measurement, however, can be performed also when the electrode is attached to a different position.  
      Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.