Abstract:
A portable electrocardiograph and method of use are disclosed. According to one aspect of the present invention, a portable electrocardiograph is provided which includes: a rectangular housing having at least a first outer surface and a second outer surface; a first electrode provided on the first outer surface of the housing; an electrode formation face provided on the second outer surface of the housing; and a second electrode provided within the electrode formation face; wherein the electrode formation face includes an electrode region in which the second electrode is positioned and a non-electrode region which is positioned so as to surround the electrode region.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a portable electrocardiograph capable of easily measuring and storing electrocardiographic waveforms.  
         [0003]     2. Description of the Background Art  
         [0004]     Generally, for diagnosing ischemic cardiomyopathies such as angina pectoris and myocardial infarction, an electrocardiograph of the patient is used. Known electrocardiographs for measuring electrocardiographic waveforms include stationary electrocardiographs and portable electrocardiographs.  
         [0005]     Stationary electrocardiographs are generally found in medical institutions such as hospitals, and they measure waveforms by attaching electrodes to the body of a patient who lies on a bed or the like. The use of a stationary electrocardiograph is advantageous because it is able to measure various electrocardiographic waveforms (such as P waveform and QRS waveform) very precisely. However, stationary electrocardiographs suffer from the fact that, in many cases, the events they are seeking to monitor have past and therefore a proper diagnosis is not possible.  
         [0006]     Portable electrocardiographs generally include Holter electrocardiographs and event-type electrocardiographs. Holter electrocardiographs are used to continuously measure and store electrocardiographic waveforms using electrodes which are attached to the body of a patient on a continual basis over a period of days. Event-type electrocardiographs operate by having electrodes applied to the body when a subjective symptom to be measured such as palpitation or pain occurs.  
         [0007]     Holter electrocardiographs are very reliable for measuring abnormal waveforms. However, since this method requires that the electrodes remain attached for a period of days, patients are greatly inconvenienced and subject to a great deal of pain and discomfort.  
         [0008]     The event-type electrocardiographs generally fall into one of two categories. A first category is comprised of devices which use electrodes which are always in contact with a predetermined region of the body. A second category is comprised of devices which are applied to the body when a subjective symptom to be measured occurs, and the test subject himself/herself makes an electrode comes in contact with the body.  
         [0009]     In the first category of event-type portable electrocardiographs, like the Holter portable electrocardiograph, a state where the electrode is always in contact with the body has to be maintained, so that the test subject is inconvenienced. In contrast, in the second category of event-type portable electrocardiographs, it is sufficient to attach the electrode to the body when necessary, so that the portable cardiograph is very easy-to-use for the test subject.  
         [0010]     Within the second category of event-type portable electrocardiographs, devices using various configurations of electrodes and body surfaces have been proposed.  
         [0011]     For example, Japanese Patent Laying-Open No. 61-41438 discloses, as shown in  FIG. 20 , a portable electrocardiograph  100 D having a configuration in that a display  150  is provided on a front face  102  side of a housing  101  of an electrocardiograph monitor and three electrodes  110 ,  120  and  130  to be attached to the body of a test subject are provided on a rear face  103  side. Measurement is carried out by making the three electrodes  110 ,  120  and  130  come into contact with the chest of the test subject.  
         [0012]     Japanese Utility Model Laying-Open No. 3-91304 discloses a portable electrocardiograph  100 E having a configuration in that, as shown in  FIGS. 21A and 21B , the electrode  110  is attached to the front face  102  of the housing  101 , a supporting member  191  extending from the top of the housing  101  along the rear face  103  side of the housing  101  is attached to a top face  104  of the housing  101  by using a hinge  192 , and the electrode  120  is provided on the surface of the supporting member  191 . At the time of measurement, the supporting member  191  is swung (see  FIG. 21C ), an electrode formation face of the supporting member  191  and the front face  102  of the housing  101  are arranged to be almost in the same plane, and electrocardiographic waveforms are measured in a state where the two electrodes  110  and  120  are in contact with the chest of the test subject.  
         [0013]     Japanese Utility Model Laying-Open No. 3-91305 discloses a portable electrocardiograph  100 F having a configuration in that, as shown in  FIGS. 22A and 22B , the electrode  110  made of electroconductive rubber is provided on the front face  102  of the housing  101  and the electrodes  120  and  130  are provided on a right side face  106  and a left side face  107 , respectively, of the housing  101 . At the time of measurement, the test subject holds the housing  101  from the rear face  103  side of the housing so as to make contact with the electrodes  120  and  130  provided on both of the side faces  106  and  107  and makes the electrode  110  provided on the front face  102  come into contact with the chest of the test subject to measure electrocardiographic waveforms.  
         [0014]     Japanese Patent Laying-Open No. 2003-144403 discloses a portable electrocardiograph  100 G having a configuration in that, as shown in  FIG. 23 , a negative electrode  110  and a neutral electrode  130  are provided on the top face  104  and a bottom face  105 , respectively, which are opposite surfaces of the housing  101  having an almost rectangular parallelepiped shape, and a positive electrode  120  is provided on the left side face  107  which is a curved surface adjacent to the faces on which the negative electrode  110  and the neutral electrode  130  are provided. On the front face  102  of the housing  101 , the display  150  for displaying a measurement result and an operation button part  140  in which various operation buttons typified by a power source button  141  for turning on the power source are provided.  
         [0015]     At the time of measurement, the test subject himself/herself holds the negative electrode  110  and the neutral electrode  130  provided on the top face  104  and the bottom face  105 , respectively, from the rear side of the housing  101  by his/her right hand and makes the electrode provided on the left side face  107  of the housing  101  come into contact with his/her chest to measure electrocardiographic waveforms.  
         [0016]     In such a portable electrocardiograph having an electrode on the outer surface of the housing, the contact portion between the electrode and the body has to be kept stable throughout the entire measurement period, which may be tens seconds. In the case where stable contact is not maintained, the measured electrocardiographic waveforms are disturbed and cannot be measured with precision.  
         [0017]     In the conventional portable electrocardiographs, the contact between the electrode and the measured body is generally maintained by manually pressing the electrocardiograph main body against the measured body at the time of measurement. More specifically, the wrist of the holding hand, forearm, elbow or the like is pressed against the body of the user, thereby preventing the holding hand from being moved during measurement and stably maintaining the contact between the electrode and the body. This point will be described more specifically with reference to portable electrocardiograph  100 G disclosed in Japanese Patent Laying-Open No. 2003-144403.  
         [0018]      FIG. 24  is a diagram showing a measurement posture to be taken by the test subject at the time of measuring electrocardiographic waveforms by using the portable electrocardiograph  100 G disclosed in Japanese Patent Laying-Open No. 2003-144403. As shown in  FIG. 24 , upon measurement, a test subject  200  presses the wrist portion of a forearm  220  against a portion of the right side of the body while holding the portable electrocardiograph  100 G with his/her right hand  210  while also contacting the positive electrode  120  provided on the left side face  107  of the housing  101  of the portable electrocardiograph  100 G with the skin of a left lower part of a chest  250 . While maintaining contact for tens of seconds, electrocardiographic waveforms are measured.  
         [0019]      FIG. 25  shows a state where the portable electrocardiograph  100 G is held by the right hand  210 . As shown in  FIG. 25 , the test subject  200  holds the housing  101  while covering the rear face side of the housing  101  with the palm so that the front face  102  of the portable electrocardiograph  100 G faces upward. The housing  101  is held by lightly bending a forefinger  212 , a middle finger  213 , a ring finger  214  and a little finger  215  of the right hand  210  so that any or all of them come into contact with the negative electrode  110  provided for the top face  104  of the housing  101 . A thumb  211  extends along the bottom base  105  of the housing  101  to hold the housing  101  while being in contact with the neutral electrode  130  provided on the bottom face  105 . The wrist portion of the right hand  210  is pressed against the right side of the body and the right hand  210  is fixed so that the positive electrode  120  formed on the left side face  107  of the housing  101  is not apart from the body.  
         [0020]     In the case of measuring the electrocardiographic waveforms in such a measurement posture, if the wrist of the right hand is covered with cloth, the right hand and the right side of the body are not in direct contact with each other. Consequently, a measurement circuit in this portion (an electric circuit formed in the body from the positive electrode to the negative electrode) can be prevented from being short-circuited, so that electrocardiographic waveforms can be measured with high precision. In the case where the test subject does not wear cloth or wears cloth such as a short-sleeve shirt with which the wrist is not covered, the right hand and the right side of the body come into direct contact with each other. In this portion, the measurement circuit is short-circuited. Consequently, the measurement circuit does not cross the heart, so that electrocardiographic waveforms cannot be measured with precision. In such a state, it is difficult to detect ischemic cardiomyopathies of an early stage and the object itself of measuring electrocardiographic waveforms may be lost.  
         [0021]     However, if the wrist is not fixed by pressing the right hand against the right side of the body, the contact between the electrode and the body becomes unstable and a large disturbance occurs in the measured electrocardiographic waveforms. In many cases, the test subject uses a portable electrocardiograph when he/she feels palpitation, pant, dizzy or the like. In such a state, it is very difficult to stably maintain the contact between the electrode and the body and the body moves inevitably at the time of measurement.  
       SUMMARY OF THE INVENTION  
       [0022]     An object of the present invention is to provide a portable electrocardiograph which consistently enables stable contact between an electrode and the human body.  
         [0023]     A portable electrocardiograph according to a first aspect of the present invention allows a user to measure electrocardiographic waveforms by holding a first electrode provided on an outer surface of a housing element, while pressing a second electrode provided on an outer surface of the housing element against the user&#39;s body. An electrode formation face as a face on which the second electrode is provided on the outer surface of the housing includes, in plan view, an electrode region at which the second electrode is positioned and a non-electrode region which is positioned so as to surround the electrode region. The non-electrode region is formed to be flat.  
         [0024]     In the portable electrocardiograph according to the first aspect of the present invention, preferably, the electrode region is positioned at a center portion of the electrode formation face.  
         [0025]     In the portable electrocardiograph according to the first aspect of the present invention, preferably, a main face of the electrode region is formed to be flat.  
         [0026]     In the portable electrocardiograph according to the first aspect of the present invention, preferably, the main face of the electrode region is flush with a main face of the non-electrode region.  
         [0027]     In the portable electrocardiograph according to the first aspect of the present invention, preferably, the main face of the electrode region may be positioned so as to be projected from the main face of the non-electrode region.  
         [0028]     In the portable electrocardiograph according to the first aspect of the present invention, preferably, a plurality of projections are provided in the non-electrode region.  
         [0029]     In the portable electrocardiograph according to the first aspect of the present invention, preferably, when the main face of the electrode region is positioned so as to be projected from that of the non-electrode region and a plurality of projections are provided in the non-electrode region, the electrode formation face is constructed so that a distance between the apex of each of the plurality of projections and the main face of the non-electrode region is equal to or shorter than a distance between the main face of the projected electrode region and the main face of the non-electrode region.  
         [0030]     In the portable electrocardiograph according to the first aspect of the present invention, preferably, a plurality of recesses are provided in the non-electrode region.  
         [0031]     In the portable electrocardiograph according to the first aspect of the present invention, preferably, the housing has an almost rectangular parallelepiped shape, the first electrode is provided in a grip region including a first end face positioned at an end in the longitudinal direction of the housing, and the second electrode is provided on a second end face positioned at the other end in the longitudinal direction of the housing.  
         [0032]     In the portable electrocardiograph according to the first aspect of the present invention, preferably, the housing has an almost rectangular parallelepiped shape, the first electrode is provided in a grip region positioned adjacent to a first end face positioned at an end in the longitudinal direction of the housing, and the second electrode is provided on a second end face positioned at the other end in the longitudinal direction of the housing.  
         [0033]     A portable electrocardiograph according to a second aspect of the present invention includes: a housing having an almost rectangular parallelepiped shape; a first electrode provided in a grip region positioned adjacent to an end in the longitudinal direction of the housing; and a second electrode provided on a second end face positioned at the other end in the longitudinal direction of the housing. The user measures electrocardiographic waves by holding the grip region by his/her right hand and, simultaneously, pressing the second end face against the limbs other than the holding hand or the trunk. The second end face includes an electrode region on which the second electrode is positioned and a non-electrode region which is positioned so as to surround the electrode region. The non-electrode region is formed to be flat.  
         [0034]     According to the present invention, it is possible to provide a portable electrocardiograph which enables stable contact between an electrode and the human body.  
         [0035]     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  
       [0036]      FIG. 1  is a perspective view showing the outside structure of a portable electrocardiograph in a first embodiment of the present invention;  
         [0037]      FIG. 2  is a front view of the portable electrocardiograph in the first embodiment of the present invention;  
         [0038]      FIG. 3  is a top view of the portable electrocardiograph in the first embodiment of the present invention;  
         [0039]      FIG. 4  is a right side view of the portable electrocardiograph in the first embodiment of the present invention;  
         [0040]      FIG. 5  is a left side view of the portable electrocardiograph in the first embodiment of the present invention;  
         [0041]      FIG. 6  is a rear view of the portable electrocardiograph in the first embodiment of the present invention;  
         [0042]      FIG. 7  is a diagram showing a measurement posture to be taken by the test subject at the time of measuring electrocardiographic waveforms by using the portable electrocardiograph in the first embodiment of the present invention;  
         [0043]      FIG. 8A  is a front view of the portable electrocardiograph in the first embodiment of the present invention, showing a state where the portable electrocardiograph is held by the right hand at the time of measuring electrocardiographic waveforms;  
         [0044]      FIG. 8B  is a rear view of the portable electrocardiograph in the first embodiment of the present invention, showing a state where the portable electrocardiograph is held by the right hand at the time of measuring electrocardiographic waveforms;  
         [0045]      FIG. 9  is a diagram showing from above a measurement posture to be taken in the case where the test subject does not wear cloth at the time of measuring electrocardiographic waveforms by using the portable electrocardiograph in the first embodiment of the present invention;  
         [0046]      FIG. 10  is a diagram showing from above a measurement posture to be taken in the case where the test subject wears cloth at the time of measuring electrocardiographic waveforms by using the portable electrocardiograph in the first embodiment of the present invention;  
         [0047]      FIG. 11  is a front view of a portable electrocardiograph used as a comparative example in a verification test of contact stability;  
         [0048]      FIG. 12  is a left side view of the portable electrocardiograph used as the comparative example in the verification test of contact stability;  
         [0049]      FIG. 13  is a diagram showing electrocardiographic waveforms measured by the portable electrocardiograph in the comparative example in the verification test of contact stability;  
         [0050]      FIG. 14  is a diagram showing electrocardiographic waveforms measured by a portable electrocardiograph in an example of the present invention in a verification test of contact stability;  
         [0051]      FIG. 15  is a diagram showing comparison between contact stability of the electrocardiographic waveforms in the comparative example and that of the electrocardiographic waveforms in the example of the present invention in the verification test of contact stability;  
         [0052]      FIG. 16  is a front view of a portable electrocardiograph in a second embodiment of the present invention;  
         [0053]      FIG. 17  is a left side view of the portable electrocardiograph in the second embodiment of the present invention;  
         [0054]      FIG. 18  is a front view of a portable electrocardiograph in a third embodiment of the present invention;  
         [0055]      FIG. 19  is a left side view of the portable electrocardiograph in the third embodiment of the present invention;  
         [0056]      FIG. 20  is a perspective view showing an example of a conventional portable electrocardiograph;  
         [0057]      FIG. 21A  is a front view showing another example of the conventional portable electrocardiograph;  
         [0058]      FIG. 21B  is a left side view showing the conventional portable electrocardiograph illustrated in  FIG. 21A ;  
         [0059]      FIG. 21C  is a left side view showing a state where the conventional portable electrocardiograph illustrated in  FIG. 21A  is open;  
         [0060]      FIG. 22A  is a front view showing still another example of the conventional portable electrocardiograph;  
         [0061]      FIG. 22B  is a right side view of the conventional portable electrocardiograph illustrated in  FIG. 22A ;  
         [0062]      FIG. 23  is a front view showing yet another example of the conventional portable electrocardiograph;  
         [0063]      FIG. 24  is a diagram showing a measurement posture to be taken by the test subject at the time of measuring electrocardiographic waveforms by using the conventional portable electrocardiograph illustrated in  FIG. 23 ; and  
         [0064]      FIG. 25  is a diagram showing a state where the conventional portable electrocardiograph illustrated in  FIG. 23  is held by the right hand to measure electrocardiographic waveforms. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0065]     Hereinafter, embodiments of the present invention will be described with reference to the drawings.  
       First Embodiment  
       [0066]     First, the structure of a portable electrocardiograph  100 A in the first embodiment will be described. As shown in FIGS.  1  to  6 , the portable electrocardiograph  100 A in this embodiment is formed light and small so as to be easily handled and can be held by one hand. The portable electrocardiograph  100 A has a housing  101  of a flat and elongated almost rectangular parallelepiped shape. On the outer surfaces (front face  102 , rear face  103 , top face  104 , bottom face  105 , right side face  106 , left side face  107  and curved face  108 ), a display unit, an operation unit, electrodes and the like are arranged.  
         [0067]     As shown in  FIGS. 1 and 2 , a grip part  160  as a grip region is provided adjacent to an end in the longitudinal direction (the direction of the arrow A in the figure) of the housing  101 . The grip part  160  is a portion provided so that the test subject can stably hold the main body of the portable electrocardiograph  100 A at the time of measurement. At the time of measurement, the grip part  160  is covered with the right hand of the test subject. The grip part  160  includes a right side face  106  as a first end face positioned at one end in the longitudinal direction of the housing  101 , portions adjacent to one end of each of the front face  102 , the rear face  103 , the top face  104  and the bottom face  105 , and a curved face  108  continued to the right side face  106  and the top face  104 .  
         [0068]     For the grip part  160  on the front face  102  side of the housing  101 , a measurement button  142  as an operation button for starting measurement is provided. A rest  148  on which the thumb of the right hand is rested at the time of measurement is provided on the front face  102  of the housing  101  so as to be adjacent to the measurement button  142 .  
         [0069]     At the front face  102  adjacent to the other end in the longitudinal direction of the housing  101 , a display  150  is positioned. The display  150  is constructed by, for example, a liquid crystal display and is a portion for displaying a result of measurement. The measurement result is displayed as, for example, electrocardiographic waveforms or numerical data as shown in  FIG. 1 .  
         [0070]     Below the display  150  in the front face  102 , various operation buttons are disposed. In the illustrated portable electrocardiograph  100 A, in the front face  102  of the housing  101 , a setting button  143 , a display button  144 , a left scroll button  145  and a right scroll button  146  are disposed.  
         [0071]     The setting button  143  is an operation button for making various settings of the portable electrocardiograph  100 A. The display button  144  is an operation button used for displaying a measurement result on the display  150 . The left scroll button  145  and the right scroll button  146  are operation buttons for scrolling and displaying a graph of a measurement result, guide information and the like to be displayed on the display  150 .  
         [0072]     As shown in  FIGS. 1 and 3 , the power source button  141  is disposed in a predetermined position in the top face  104  of the housing  101 . The power source button  141  is an operation button for operating ON/OFF of the portable electrocardiograph  100 A.  
         [0073]     As shown in  FIGS. 1, 3  and  4 , a recess  108   a  is provided in the curved face  108  of the housing  101 . The recess  108   a  extends along the extension direction of the curved face  108 . In a predetermined position in the recess  108   a , the negative electrode  110  as a first electrode is provided. The negative electrode  110  is made of an electroconductive material and has a shape which is slightly projected to the outside from the curved face of the recess  108   a  and is exposed in the recess  108   a . The recess  108   a  is formed in a shape for accepting the forefinger of the right hand.  
         [0074]     As shown in  FIGS. 1 and 5 , the positive electrode  120  as a second electrode is provided for the left side face  107  as a second end face positioned at the other end in the longitudinal direction of the housing  101 . The positive electrode  120  is made of an electroconductive material and is positioned at a center position in the left side face  107  of the housing  101 . A contact face  121  with the body, which is the main face of the positive electrode  120  is formed to be flat. Around the positive electrode  120 , a flat face  107   a  made of an insulating material is formed. The flat face  107   a  is flush with the contact face  121  of the positive electrode  120 .  
         [0075]     Specifically, the left side face  107  of the housing  101  as an electrode formation face is constructed by an electrode region at which the positive electrode  120  is positioned (i.e., the contact face  121  of the positive electrode  120 ) and a non-electrode region (i.e., the flat face  107   a ) positioned so as to surround the electrode region and formed to be flat. The main face of the electrode region and that of the non-electrode region are flush with each other.  
         [0076]     The contact face  121  of the positive electrode  120  has an almost rectangle shape and, preferably, the length of one side of the contact face  121  lies in the range from 20 mm to 30 mm. The width of the non-electrode region extending from the border with the electrode region to the end of the electrode formation face is, preferably, at least 2 mm. In the portable electrocardiograph  100 A in this embodiment, the size of the electrode region (L 11 ×L 12    FIG. 5 ) is 30 mm×20 mm and the size of the electrode formation face (L 13 ×L 14  in  FIG. 5 ) is 62 mm×27 mm. The width of the non-electrode region from the border with the electrode region to the end of the electrode formation face (D 11  and D 12  in  FIG. 5 ) is 16 mm in the longitudinal direction of the electrode formation face and is 3.5 mm in the transverse direction.  
         [0077]     As shown in  FIG. 6 , in the grip part  160  on the rear face  103  side of the housing  101 , the neutral electrode  130  as an indifferent electrode is positioned. The neutral electrode  130  is made of an electroconductive material and extends in the vertical direction on the rear face  103  of the housing  101 . The neutral electrode  130  extends in the direction crossing the longitudinal direction on the rear face  103  of the housing  101  and is inclined so that its upper end portion (an end portion on the top face  104  side) is positioned to the right side face  106  side more than its lower end portion (an end portion on the bottom face  105  side). The neutral electrode  130  is an electrode for detecting potential fluctuations occurring in the human body at the time of measurement and for obtaining a correction value for removing an error component included in a measurement result.  
         [0078]     Next, a measurement posture to be taken by the test subject in the case of using the portable electrocardiograph  100 A having the above configuration will be described.  
         [0079]     As shown in  FIG. 7 , at the time of measurement, the test subject  200  makes the positive electrode  120  provided on the left side face  107  of the housing  101  come into direct contact with the skin on the fifth intercostal anterior axillary line positioned at a lower left portion of the chest  250  while holding the grip part  160  of the portable electrocardiograph  100 A by the right hand  210 . The measurement button  142  provided on the front face  102  of the housing  101  is depressed by the thumb  211  of the right hand  210 , and the thumb  211  of the right hand  210  is rested on the rest  148 . While maintaining the state for tens of seconds, electrocardiographic waveforms are measured.  
         [0080]     The gripping state of the portable electrocardiograph  100 A by the right hand  210  will now be described.  
         [0081]     As shown in  FIG. 8A , in the measurement posture, the test subject  200  holds the grip part  160  of the housing  101  by the right hand  210  while covering the right side face  106  of the housing  101  with the palm so that the front face  102  of the portable electrocardiograph  100 A faces upward. At this time, the thumb  211  is lightly bent and attached to the housing  101  so that the thumb  211  of the right hand  210  comes into contact with the rest  148  provided adjacent to one end of the front face  102  of the housing  101 . The forefinger  212  is lightly bent so as to be along the curved face  108  of the housing  101  and is fit in the recess  108  a provided in the curved face  108  so as to come into contact with the negative electrode  110 . Further, as shown in  FIG. 8B , the grip part  160  of the rear face  103  of the housing  101  is held by the middle finger  213 , the ring finger  214  and the little finger  215  of the right hand  210 . At this time, at least one of the middle finger  213 , the ring finger  214  and the little finger  215  on the rear face  103  side of the housing  101  comes into contact with the neutral electrode  130  provided on the rear face  103  of the housing  101 .  
         [0082]     As shown in  FIG. 9 , in the portable electrocardiograph  100 A in this embodiment, at the time of measurement, the housing  101  is held so that the right side face  106  of the housing  101  may be covered with the palm of the right hand  210 . Consequently, the wrist of the right hand  210  is always apart from the chest  250  only by predetermined distance. Accordingly, the right arm (the forearm  220  and the upper arm  230 ) does not come into contact with the chest  250 . As a result, a measurement circuit is constructed extending from the right hand  210  holding the negative electrode  110  and the neutral electrode  130  via the forearm  220  which is not in contact with the chest  250  and the upper arm  230  and a right shoulder  240  which are also not in contact with the chest  250  to the chest  250  against which the positive electrode is pressed. Consequently, the measurement posture by which the measurement circuit is constructed so as to cross the heart can be realized with reliability, and the measurement circuit can be prevented from being short-circuited due to contact between the right hand  210 , the forearm  220  and the upper arm  230  and the chest  250 .  
         [0083]     As shown in  FIG. 10 , when the test subject  200  wears cloth  300  covering the right elbow, the right hand  210  can be fixed by making the right elbow come in contact with the right side of the body. By taking the measurement posture that the right elbow is pressed against the right side of the body, the measurement posture shown in  FIG. 10  can be maintained for tens of seconds without moving the right hand  210 . As a result, the electrocardiographic waveforms can be measured stably with high precision.  
         [0084]     As described above, in the portable electrocardiograph  100 A in this embodiment, the left side face  107  as the electrode formation face includes the electrode region at which the position electrode  120  is positioned and the non-electrode region formed to be flat so as to surround the electrode region. With such a configuration, the contact stability between the contact face  121  of the positive electrode  120  and the chest  250  is improved, the measurement voltage value is not varied, and electrocardiographic waveforms can be measured stably with high precision. Those are effects attained by providing the non-electrode region in the electrode formation face. This point will be described in detail below.  
         [0085]     There are various noise components entering a voltage value obtained at the time of measurement. One of the noise components which exerts an influence on the voltage value most is a change in the contact area between the positive electrode and the chest which occurs due to movement of the test subject. When the contact area between the positive electrode and the chest changes, the contact resistance in the portion largely fluctuates and large variations occur in the voltage value obtained. To suppress variations in the measured voltage value, the test subject has to maintain the measurement posture as shown in  FIG. 7  without moving the right hand and the chest at the time of measurement. However, in many cases, the test subject feels palpitation, pant, dizzy or the like at the time of measurement and it is very difficult for the test subject to maintain the measurement posture. Consequently, the body of the test subject moves inevitably at the time of measurement.  
         [0086]     In the portable electrocardiograph  100 A in this embodiment, however, the non-electrode region formed so as to surround the contact face  121  is positioned around the contact face  121  of the positive electrode  120  as the electrode region. Consequently, fluctuations of the contact region which occur due to movement of the right hand  210  and the chest  250  occur only in the non-electrode region and hardly occur in the electrode region. Therefore, the contact with the chest  250  of the positive electrode  120  positioned at the center portion of the electrode formation face is maintained more stably. Even if the test subject moves, a change does not occur in the contact area between the positive electrode  120  and the chest  250 . As a result, a measurement voltage value can be obtained accurately. Thus, the electrocardiographic waveforms can be measured stably with high precision.  
         [0087]     As described above, by employing the portable electrocardiograph  100 A as in this embodiment, also in the case where the test subject takes the measurement posture as shown in  FIG. 9 , stable contact between the electrode and the body can be realized without fixedly pressing the hand holding the electrocardiograph main body against another region of the body, and electrocardiographic waveforms can be stably measured with high precision. In the case where the test subject takes the measurement posture as shown in  FIG. 10 , the right hand is stabilized by pressing the right elbow against the chest, so that electrocardiographic waveforms can be measured more precisely and stably.  
         [0088]     In the case of employing the portable electrocardiograph  100 A as in this embodiment, electrocardiographic waveforms can be measured by pressing the positive electrode as the second electrode against the palm of the left hand or the inner side of the thigh of the left leg.  
         [0089]     A test of verifying how much electrocardiographic waveforms are stabilized by employing the structure of the portable electrocardiograph  100 A will be described below.  
         [0090]     In the test, the portable electrocardiograph  100 A was used as an example and a portable electrocardiograph  100 H shown in  FIG. 12  was used as a comparative example. The portable electrocardiographs were used under the same conditions and stabilities of the measured electrocardiographic waveforms were compared with each other, thereby evaluating the contact stability between the electrode and the body.  
         [0091]     First, the structure of the portable electrocardiograph  100 H used as a comparative example will be described. As shown in  FIGS. 11 and 12 , the structure of the portable electrocardiograph  100 H is similar to that of the portable electrocardiograph  100 A except for the structure of the left side face  107  of the housing  101  as an electrode formation face.  
         [0092]     As shown in  FIGS. 11 and 12 , the positive electrode  120  as the second electrode is provided on the left side face  107  as a second end face positioned at the other end in the longitudinal direction of the housing  101  of the portable electrocardiograph  100 H. The positive electrode  120  is made of an electroconductive material and extends from the rear face  103  of the housing  101  via the left side face  107  to the front face  102 . That is, the positive electrode  120  is formed so that the entire left side face  107  of the housing  101  serves as the contact face  121  with the body. Consequently, the non-electrode region provided on the left side face  107  of the portable electrocardiograph  100 A does not exist in the portable electrocardiograph  100 H.  
         [0093]     The contact face  121  as a main face of the electrode  120  of the portable electrocardiograph  100 H has a rectangular shape and is formed to be flat. The size is 62 mm×27 mm.  
         [0094]     The differences between the structure of the portable electrocardiograph  100 H as the comparative example and the structure of the portable electrocardiograph  100 A as the example of the present invention will be summarized as shown in Table 1.  
                                                         TABLE 1                                       Presence/                       absence           Size of   of non-       Shape of           electrode   electrode   Size of electrode   contact           region   region   formation face   face                                    Com-   62 mm × 27 mm   Absence   62 mm × 27 mm   Flat       parative       example       Example   30 mm × 20 mm   Presence   62 mm × 27 mm   Flat       of       the present       invention                  
 
         [0095]      FIG. 13  is a diagram showing electrocardiographic waveforms obtained by the test subject himself/herself in the measurement posture as shown in  FIG. 7  by using the portable electrocardiograph  100 H.  FIG. 14  is a diagram showing electrocardiographic waveforms measured by the test subject himself/herself in the measurement posture as shown in  FIG. 7  by using the portable electrocardiograph  100 A. In the diagrams, the horizontal axis denotes time, and the vertical axis denotes a measured voltage value.  
         [0096]     In the case of using the portable electrocardiograph  100 H in which the entire left side face  107  serves as the contact face  121  of the positive electrode  120  as shown in  FIGS. 11 and 12 , it is understood that large variations occur in the measured voltage values as shown in  FIG. 13 . The magnitude of a variation in the measured voltage value is about 1.5 V at the maximum. It is understood that a large fluctuation occurs in the measured voltage value in short time. The fluctuation occurs when the contact area between the positive electrode  120  and the chest changes due to movement of the wrist, chest or the like of the test subject and a large fluctuation occurs in the contact resistance in the portion.  
         [0097]     In contrast, it is understood that in the case of using the portable electrocardiograph  100 A in which the contact face  121  of the positive electrode  120  is positioned at the center portion of the left side face  107  and the non-electrode region is formed around the contact face  121  as shown in FIGS.  1  to  6 , the measured voltage value is very stable as shown in  FIG. 14 . The magnitude of variations of the measured voltage value is about 0.3 V and is suppressed to about ⅕ of the variation in the portable electrocardiograph  100 H. The reason is considered as follows. Also in the case where the wrist, chest or the like of the test subject moves, fluctuations in the contact state between the left side face  107  as the electrode formation face and the chest of the test subject occur only in the non-electrode region and hardly occur in the electrode region, so that the stable contact between the positive electrode  120  and the chest is assured.  
         [0098]      FIG. 15  is a diagram showing electrocardiographic waves obtained by enlarging the electrocardiographic waves shown in  FIGS. 13 and 14  in the time base direction and overlapped for comparison. It is understood from  FIG. 15  that, in measured waveforms in the example of the present invention, an electrocardiographic wave obtained by a single stroke has an almost same shape as that of other electrocardiographic waves and is measured stably and precisely. In contrast, in the measured waveforms in the comparative example, a disturbance occurs also in each of the electrocardiographic waves, obtained by a single stroke, and the electrocardiographic waves are not measured stably and precisely. Consequently, it is difficult to determine if the electrocardiographic waves are abnormal or it is a measurement error in the measured waveforms in the comparative example, and measurement itself of abnormal waveforms can be meaningless. On the other hand, in the measured waveforms in the example of the present invention, abnormal electrocardiographic waves and normal ones can be discriminated from each other with reliability and the present invention largely contributes to early finding of ischemic cardiomyopathies.  
       Second Embodiment  
       [0099]     First, the structure of a portable electrocardiograph  100 B in a second embodiment will be described. The same reference numerals will be given to components similar to those in the foregoing first embodiment and their description will not be repeated here.  
         [0100]     As shown in  FIGS. 16 and 17 , the portable electrocardiograph  100 B in this embodiment is different from the portable electrocardiograph  100 A in the first embodiment only with respect to the structure of the left side face  107  as the electrode formation face of the housing  101 .  
         [0101]     The portable electrocardiograph  100 B in this embodiment has the positive electrode  120  as the second electrode on the left side face  107  of the housing  101 . The positive electrode  120  is made of an electroconductive material and is positioned at the center portion of the left side face  107  of the housing  101 . Around the positive electrode  120 , the flat face  107   a  made of an insulating material is formed. The contact face  121  with the body as the main face of the positive electrode  120  is provided so as to be projected from the main face of the flat face  107   a . The contact face  121  of the positive electrode  120  is formed to be flat.  
         [0102]     Specifically, the left side face  107  of the housing  101  as an electrode formation face is constructed by an electrode region in which the positive electrode  120  is positioned (i.e., the contact face  121  of the positive electrode  120 ) and a non-electrode region (i.e., the flat face  107   a ) positioned so as to surround the electrode region and formed to be flat. The main face of the electrode region is provided so as to be projected from the main face of the non-electrode region.  
         [0103]     The contact face  121  of the positive electrode  120  has an almost rectangle shape and, preferably, the length of one side of the contact face  121  lies in the range from 20 mm to 30 mm. The distance between the main face of the electrode region positioned so as to be projected from the main face of the non-electrode region and the main face of the non-electrode region is preferably 1 mm or less. The width of the non-electrode region extending from the border with the electrode region to the end of the electrode formation face is, preferably, at least 2 mm or more. In the portable electrocardiograph  100 B in this embodiment, the size of the electrode region (L 21 ×L 22  in  FIG. 17 ) is 30 mm×20 mm, the distance (H 21  in  FIG. 16 ) between the main face of the electrode region and the main face of the non-electrode region is 0.5 mm, and the size of the electrode formation face (L 23 ×L 24  in  FIG. 17 ) is 62 mm×27 mm. The width of the non-electrode region extending from the border with the electrode region to the end of the electrode formation face (D 21  and D 22  in  FIG. 17 ) is 16 mm in the longitudinal direction of the electrode formation face and is 3.5 mm in the transverse direction.  
         [0104]     Around the positive electrode  120  on the left side face  107  of the housing  101 , a plurality of projections  107   b  are provided. The projection  107   b  is a part functioning as an anti-slip so as not to cause a positional deviation of the positive electrode  120  on the surface of the body at the time of measurement.  
         [0105]     Preferably, the projection  107   b  is formed so that its height is the same or lower than the main face of the electrode region positioned so as to be projected. In the portable electrocardiograph  100 B in this embodiment, the height (H 22  in  FIG. 16 ) of the projection is 0.5 mm.  
         [0106]     By providing the contact face  121  with the body of the positive electrode  120  so as to be projected from the left side face  107  of the housing  101 , the test subject can easily recognize the position of the positive electrode  120 , so that the measurement position is easily specified. In this case, by providing a plurality of projections in the non-electrode region, the positional deviation between the positive electrode and the body at the time of measurement can be prevented, so that the contact between the contact face of the electrode and the body can be stably maintained.  
       Third Embodiment  
       [0107]     First, the structure of a portable electrocardiograph  100 C in a third embodiment will be described. The same reference numerals will be given to components similar to those in the foregoing first embodiment and their description will not be repeated here.  
         [0108]     As shown in  FIGS. 18 and 19 , the portable electrocardiograph  100 C in this embodiment is different from the portable electrocardiograph  100 A in the first embodiment only with respect to the structure of the left side face  107  as the electrode formation face of the housing  101 .  
         [0109]     The portable electrocardiograph  100 C in this embodiment has the positive electrode  120  as the second electrode on the left side face  107  of the housing  101 . The positive electrode  120  is made of an electroconductive material and is positioned at the center portion of the left side face  107  of the housing  101 . Around the positive electrode  120 , the flat face  107   a  made of an insulating material is formed. The contact face  121  with the body as the main face of the positive electrode  120  is provided so as to be projected from the main face of the flat face  107   a . The contact face  121  of the positive electrode  120  is formed to be flat.  
         [0110]     Specifically, the left side face  107  of the housing  101  as an electrode formation face is constructed by an electrode region in which the positive electrode  120  is positioned (i.e., the contact face  121  of the positive electrode  120 ) and a non-electrode region (i.e., the flat face  107   a ) positioned so as to surround the electrode region and formed to be flat. The main face of the electrode region is provided so as to be projected from the main face of the non-electrode region.  
         [0111]     The contact face  121  of the positive electrode  120  has an almost rectangle shape and, preferably, the length of one side of the contact face  121  lies in the range from 20 mm to 30 mm. The distance between the main face of the electrode region positioned so as to be projected from the main face of the non-electrode region and the main face of the non-electrode region is preferably 1 mm or less. The width of the non-electrode region extending from the border with the electrode region to the end of the electrode formation face is, preferably, at least 2 mm or more. In the portable electrocardiograph  100 C in this embodiment, the size of the electrode region (L 31 ×L 32  in  FIG. 19 ) is 30 mm×20 mm, the distance (H 31  in  FIG. 18 ) between the main face of the electrode region and the main face of the non-electrode region is 0.5 mm, and the size of the electrode formation face (L 33 ×L 34  in  FIG. 19 ) is 62 mm×27 mm. The width of the non-electrode region extending from the border with the electrode region to the end of the electrode formation face (D 31  and D 32  in  FIG. 19 ) is 16 mm in the longitudinal direction of the electrode formation face and is 3.5 mm in the transverse direction.  
         [0112]     Around the positive electrode  120  on the left side face  107  of the housing  101 , a plurality of recesses  107   c  are provided. The recess  107   c  is a part functioning as an anti-slip so as not to cause a positional deviation of the positive electrode  120  on the surface of the body at the time of measurement.  
         [0113]     The depth of the recess  107   c  is preferably 0.3 mm to 1 mm. In the portable electrocardiograph  100 C in this embodiment, the depth of the recess is 0.5 mm.  
         [0114]     By providing the contact face  121  with the body of the positive electrode  120  so as to be projected from the left side face  107  of the housing  101 , the test subject can easily recognize the position of the positive electrode  120 , so that the measurement position is easily specified. In this case, by providing a plurality of recesses in the non-electrode region, the positional deviation between the positive electrode and the body at the time of measurement can be prevented, so that the contact between the contact face of the electrode and the body can be stably maintained.  
         [0115]     Although the foregoing first to third embodiments have been described by using, as examples, the portable electrocardiographs each constructed so that the grip region includes a first end face positioned adjacent to one end in the longitudinal direction of the housing, the present invention is not limited to the portable electrocardiographs having such a structure. Naturally, the present invention can be also applied to a portable electrocardiograph having a structure in which the grip region does not include a first end face, that is, a portable electrocardiograph intended to have a gripped state such that the one end face is not covered with the right hand.  
         [0116]     Although the foregoing first to third embodiments have been described by using, as examples, the portable electrocardiographs each having three electrodes of the positive electrode, the negative electrode and the neutral electrode, the neutral electrode is not an essential electrode. The present invention can be applied to any portable electrocardiograph as long as it has a pair of measurement electrodes of at least a positive electrode and a negative electrode on the outer surface of the housing.  
         [0117]     Further, although the foregoing first to third embodiments have been described by using, as examples, the portable electrocardiographs each having the display in the outer surface of the housing, the present invention can be naturally also applied to a portable electrocardiograph having a separately provided display. It is considered that a portable electrocardiograph having a separately provided display outputs measured electrocardiographic waveforms to an external display by radio or by wire.  
         [0118]     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.