Abstract:
Vascular endothelial function in terms of flow-mediated dilation (FMD) of peripheral arteries can be assessed reliably by measuring beat-to-beat pulse-wave conduction time (PCT) simultaneously for two symmetric segments of arteries locating on the right and left sides of body. When reactive hyperemia is induced in the peripheral tissues on one side, the time dependent changes in PCT caused by FMD on that side can be detected as the beat-to-beat differences in PCT between two sides (ΔPCT). ΔPCT would provide a sensitive and specific assessment of the FMD response, because the influences of the systemic changes in hemodynamic and neurohumoral factors common to both sides are subtracted out. In addition, measurement of PCT requires no skillful technique and is advantageous in that the apparatus is inexpensive.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a Divisional of application Ser. No. 10/822,843 filed Apr. 13, 2004 now U.S. Pat. No. 7,131,949. The disclosure of the prior application is incorporated by reference herein in their entirety. 

   BACKGROUND 
   1. Field of the Invention 
   This invention relates to a method and apparatus for assessing vascular endothelial function. 
   2. Description of the Related Art 
   Vascular endothelium is a cell group that constitute a layer of lining blood vessels, functioning not only to line the inner wall of blood vessels and separate blood components from body tissues but also to produce or release substances which control the biological characteristics of blood vessels including dimension, elasticity, permeability and reactivity. Since impairment of vascular endothelial function is found in earlier stages of arteriosclerosis where arteriosclerosis has not yet developed or clinically manifested, it is possible to prevent the development or treat the arteriosclerosis earlier by detecting the impairment of vascular endothelial function. 
   A non-invasive method for assessing flow-mediated dilation induced by reactive hyperemia by using an ultrasonic device is known as a method for assessing vascular endothelial function (for example, as shown in the non-patent literature 1). The above reactive hyperemia is a transient increase in organ blood flow that takes place following a brief period of ischemia (arterial occlusion) and subsequent release. The flow-mediated dilation is a reaction in which an increased arterial blood flow stimulates vascular endothelium of the artery concerned, thus secreting from vascular endothelium endothelium-derived relaxing factors (EDRF; nitrogen monoxide and analogous substances), which are substances to dilate blood vessels, resulting in an increase in the diameter of the artery concerned. As a result, since endothelium-derived relaxing factors are secreted at a smaller quantity when the vascular endothelial function is impaired, the diameter of the artery will not increase as expected even after an increase in arterial blood flow caused by the reactive hyperemia. Thus, vascular endothelial function can be assessed by referring to the extent of the increase in diameter of the artery with the peripheral reactive hyperemia. 
   In the method described in the non-patent literature 1, an ultrasonic probe was used to provide consecutive images of an artery by which a maximum increase rate of the arterial diameter after release from ischemia in relation to that before the ischemia was calculated to assess vascular endothelial function based on the maximum increase rate. The above maximum increase rate is called % FMD (flow mediated dilatation), which is about 10% for healthy adults. 3 to 4% FMD is indicative of endothelial dysfunction and likely that arteries in major organs have already been atherosclerotic or may have an increased risk for arteriosclerosis. 
   Methods for inducing release of endothelium-derived relaxing factors from vascular endothelium include methods for causing the above hyperemic reaction or increased blood flow and for injecting into an artery substances stimulating the release of EDRF such as acetylcholine. 
   [Non-Patent Literature 1] 
   Page 104 to 106, “Pulse Wave Velocity,” First edition compiled by Toshio Ozawa and Yoshiaki Masuda, Published by Medical Review Co., Ltd. May 1, 2002 
   However, the following problems are found in the method for calculating % FMD by referring to the vasodilation response assessed by an ultrasonic device. First, a major problem with the method is the large variation in results, as high as 2 to 3%, among examiners and laboratories. Since the % FMD is considered normal at about 10% and abnormal at 3 to 4%, a variation of as high as 2 to 3% poses a serious problem. The great variation is due to the need for skill in detecting correct signals such as placing an ultrasonic probe vertically to a vessel, and variation in the point of time in determining a diameter of the vessel because it is necessary to detect from consecutive images of a pulsating blood vessel the timing when the greatest dilation of the vessel takes place after release from ischemia, and also to determine a diameter of the blood vessel at the end of diastolic phase of the heart. Therefore, it may take several months to acquire this skill, and it is reported that % FMD is not reliable unless the result is obtained from an examiner with substantial experience (for example, about six-months). Second, this method has an inevitable theoretical limitation. The arterial diameter shows not only pulsation but also spontaneous variations. The arterial diameter is dependent on heart rate and blood pressure, both of which show, even in a short term, physiological fluctuation such as those relating respiration and Mayer wave (10-second rhythm). Also, neurohumoral, thermoregulatory and emotional factors (which could accompany arterial occlusion) affect the vascular tone directly and indirectly through heart rate and blood pressure. The influences of these systemic factors confound the assessment of endothelium-dependent vascular responses and partly contribute to the large variation of % FMD. Finally, in case of the brachial artery, the diameter of blood vessel is about 5 mm and expected change of the diameter would be less than 0.5 mm, or dilation corresponding to less than 10% of a diameter of the vessel. Thus, such exact detection requires a high-performance and highly priced ultrasonic device, which is another problem. 
   SUMMARY OF THE INVENTION 
   This invention has been made in view of these problems, with the objective of providing a method and apparatus for assessing vascular endothelial function, which realize a highly reliable assessment of vascular endothelial function with excluding the influences of the systemic factors, do not require a great amount of skill, and is low in cost. 
   The above object may be achieved according to a first aspect of this invention, which provides a method for assessing vascular endothelial function, comprising; (a) a stimulation step of giving stimulation for inducing a release of endothelium-derived relaxing factors from vascular endothelium to a specified region of the artery in a living body, (b) a pre-stimulation measurement step of measuring, before said stimulation step, almost simultaneously first pulse-wave-conduction-velocity-relating information which is a pulse-wave-conduction-velocity-relating information related to the velocity at which a pulse conducts through the first segment including a part or a whole of the specified region of the artery and second pulse-wave-conduction-velocity-relating information which is said pulse-wave-conduction-velocity-relating information of the artery in the second segment almost symmetric to said first segment with respect to the median plane, (c) a post-stimulation measurement step of measuring said first pulse-wave-conduction-velocity-relating information and said second pulse-wave-conduction-velocity-relating information after said stimulation step, and (d) a comparative value calculation step of calculating respectively the pre-stimulation comparative value representing a difference or ratio of the first pulse-wave-conduction-velocity-relating information to the second pulse-wave-conduction-velocity-relating information obtained at said pre-stimulation measurement step and the post-stimulation comparative value representing a difference or ratio of the first pulse-wave-conduction-velocity-relating information to the second pulse-wave-conduction-velocity-relating information obtained at said post-stimulation measurement step. 
   In the first preferred form of the method according to the first aspect of the invention, said first segment is a segment from the heart to a specified point on said artery and said second segment is a segment almost symmetric to a segment from the heart to a specified point on said artery with respect to the median plane. 
   the second preferred form of the method according to the first aspect of the invention, (a) in said pre-stimulation measurement step, an almost simultaneous measurement is carried out for third pulse-wave-conduction-velocity-relating information which is said pulse-wave-conduction-velocity-relating information at the predetermined third segment closer to the central side rather than said first segment with regard to said artery and also for fourth pulse-wave-conduction-velocity-relating information which is said pulse-wave-conduction-velocity-relating information at a fourth segment almost symmetric to said third segment with respect to the median plane, in addition to the first pulse-wave-conduction-velocity-relating information and the second pulse-wave-conduction-velocity-relating information, (b) in said post-stimulation measurement step, an almost simultaneous measurement is carried out for the third pulse-wave-conduction-velocity-relating information and the fourth pulse-wave-conduction-velocity-relating information, in addition to the first pulse-wave-conduction-velocity-relating information and the second pulse-wave-conduction-velocity-relating information, and (c) in said comparative value calculation step, respective calculations are carried out for the pre-stimulation comparative value on the central side representing a difference or ratio of the third pulse-wave-conduction-velocity-relating information to the fourth pulse-wave-conduction-velocity-relating information obtained at said pre-stimulation measurement step and also for the post-stimulation comparative value on the central side representing a difference or ratio of the third pulse-wave-conduction-velocity-relating information to the fourth pulse-wave-conduction-velocity-relating information obtained at said post-stimulation measurement step, in addition to the pre-stimulation comparative value on the peripheral side representing a difference or ratio of the first pulse-wave-conduction-velocity-relating information to the second pulse-wave-conduction-velocity-relating information obtained at said pre-stimulation measurement step and the post-stimulation comparative value on the peripheral side representing a difference or ratio of the first pulse-wave-conduction-velocity-relating information to the second pulse-wave-conduction-velocity-relating information obtained at said post-stimulation measurement step. 
   In the third preferred form of the method according to the first aspect of the invention, said comparative value calculation step is a step of calculating successively said post-stimulation comparative values, and further comprising vascular endothelial dysfunction judgment step for judging the presence and extent of vascular endothelial dysfunction on the basis of the fact that an absolute value of a difference between a peak value of the post-stimulation comparative value and the pre-stimulation comparative value calculated successively by the comparative value calculation step is at or lower than a predetermined judgment standard value. 
   The object may also be achieved according to a second aspect of the present invention, which provides a method for assessing vascular endothelial function, comprising; (a) a stimulation step of giving stimulation for inhibiting the release of endothelium-derived relaxing factors from vascular endothelium and also for inhibiting vascular dilation resulting from the release of said endothelium-derived relaxing factors to a specified region of the artery in a living body, (b) a pre-stimulation measurement step of measuring, before said stimulation step, almost simultaneously first pulse-wave-conduction-velocity-relating information which is pulse-wave-conduction-velocity-relating information related to the velocity at which a pulse conducts through the first segment including a part or a whole of the specified region of the artery and second pulse-wave-conduction-velocity-relating information which is said pulse-wave-conduction-velocity-relating information of the artery in the second segment almost symmetric to said first segment with respect to the median plane, (c) a post-stimulation measurement step of measuring said first pulse-wave-conduction-velocity-relating information and said second pulse-wave-conduction-velocity-relating information after said stimulation step, and (d) a comparative value calculation step of calculating respectively the pre-stimulation comparative value representing a difference or ratio of the first pulse-wave-conduction-velocity-relating information to the second pulse-wave-conduction-velocity-relating information obtained at said pre-stimulation measurement step and the post-stimulation comparative value representing a difference or ratio of the first pulse-wave-conduction-velocity-relating information to the second pulse-wave-conduction-velocity-relating information obtained at said post-stimulation measurement step. 
   In the first preferred form of the method according to the second aspect of the invention, said first segment is a segment from the heart to a specified point on said artery and said second segment is a segment almost symmetric to a segment from the heart to a specified point on said artery with respect to the median plane. 
   In the second preferred form of the method according to the second aspect of the invention, (a) in said pre-stimulation measurement step, an almost simultaneous measurement is carried out for third pulse-wave-conduction-velocity-relating information which is said pulse-wave-conduction-velocity-relating information at the predetermined third segment closer to the central side rather than said first segment with regard to said artery and also for fourth pulse-wave-conduction-velocity-relating information which is said pulse-wave-conduction-velocity-relating information at a fourth segment almost symmetric to said third segment with respect to the median plane, in addition to the first pulse-wave-conduction-velocity-relating information and the second pulse-wave-conduction-velocity-relating information, (b) in said post-stimulation measurement step, an almost simultaneous measurement is carried out for the third pulse-wave-conduction-velocity-relating information and the fourth pulse-wave-conduction-velocity-relating information, in addition to the first pulse-wave-conduction-velocity-relating information and the second pulse-wave-conduction-velocity-relating information, and (c) in said comparative value calculation step, respective calculations are carried out for the pre-stimulation comparative value on the central side representing a difference or ratio of the third pulse-wave-conduction-velocity-relating information to the fourth pulse-wave-conduction-velocity-relating information obtained at said pre-stimulation measurement step and also for the post-stimulation comparative value on the central side representing a difference or ratio of the third pulse-wave-conduction-velocity-relating information to the fourth pulse-wave-conduction-velocity-relating information obtained at said post-stimulation measurement step, in addition to the pre-stimulation comparative value on the peripheral side representing a difference or ratio of the first pulse-wave-conduction-velocity-relating information to the second pulse-wave-conduction-velocity-relating information obtained at said pre-stimulation measurement step and the post-stimulation comparative value on the peripheral side representing a difference or ratio of the first pulse-wave-conduction-velocity-relating information to the second pulse-wave-conduction-velocity-relating information obtained at said post-stimulation measurement step. 
   In the third preferred form of the method according to the second aspect of the invention, said comparative value calculation step is a step of calculating successively said post-stimulation comparative values, and further comprising vascular endothelial dysfunction judgment step for judging the presence and extent of vascular endothelial dysfunction on the basis of the fact that an absolute value of a difference between a peak value of the post-stimulation comparative value and the pre-stimulation comparative value calculated successively by the comparative value calculation step is at or lower than a predetermined judgment standard value. 
   The object may also be achieved according to a third aspect of the present invention, which provides an apparatus for assessing vascular endothelial function, comprising; (a) an arterial occlusion apparatus for occluding arteries to cause ischemia of a specified region of tissue in a living body for more than a predetermined time, (b) a pulse-wave-conduction-velocity-relating information measurement apparatus for measuring successively said first pulse-wave-conduction-velocity-relating information which is a pulse-wave-conduction-velocity-relating information related to the velocity at which a pulse conducts through the artery in the first segment including a part or a whole of the specified region of said artery and the second pulse-wave-conduction-velocity-relating information which is said pulse-wave-conduction-velocity-relating information of the artery in the second segment almost symmetric to said first segment with respect to the median plane, and (c) comparative value calculating means for calculating the pre-ischemic comparative value representing a difference or ratio of said first pulse-wave-conduction-velocity-relating information to said second pulse-wave-conduction-velocity-relating information before ischemia (arterial occlusion) by said arterial occlusion apparatus and also for calculating the post-ischemic comparative value representing a difference or ratio of said first pulse-wave-conduction-velocity-relating information to said second pulse-wave-conduction-velocity-relating information after release from ischemia (arterial occlusion) by said arterial occlusion apparatus. 
   In the first preferred form of the apparatus according to the third aspect of the invention, said first segment is a segment from the heart to a specified point on said artery and said second segment is a segment almost symmetric to a segment from the heart to a specified point on said artery with respect to the median plane. 
   In the second preferred form of the apparatus according to the third aspect of the invention, said comparative value calculating means is for calculating successively said post-ischemic comparative value, and further comprising vascular endothelial dysfunction judgment means for judging the presence and extent of vascular endothelial dysfunction on the basis of the fact that an absolute value of a difference between a peak value of the post-ischemic comparative value and the pre-ischemic comparative value calculated successively by the comparative value calculating means is at or lower than a predetermined judgment standard value. 
   In the third preferred form of the apparatus according to the third aspect of the invention, said comparative value calculating means is for calculating successively said post-ischemic comparative value, and further comprising an output apparatus for illustrating graphically changes over time in comparative values calculated successively by said comparative value calculating means. 
   In the fourth preferred form of the apparatus according to the third aspect of the invention, (a) said first segment is closer to the peripheral side than a region of arterial occlusion by said arterial occlusion apparatus, (b) said pulse-wave-conduction-velocity-relating information measurement apparatus is for measuring almost simultaneously the third pulse-wave-conduction-velocity-relating information which is said pulse-wave-conduction-velocity-relating information at the specified third segment closer to the central side rather than said region of arterial occlusion and the fourth pulse-wave-conduction-velocity-relating information which is said pulse-wave-conduction-velocity-relating information at the fourth segment almost symmetric to said third segment with respect to the median plane, in addition to said first pulse-wave-conduction-velocity-relating information and the second pulse-wave-conduction-velocity-relating information, and (c) said comparative value calculating means is for calculating respectively the pre-ischemic comparative value on the central side representing a difference or ratio of said third pulse-wave-conduction-velocity-relating information to said fourth pulse-wave-conduction-velocity-relating information obtained before ischemia by said arterial occlusion apparatus and post-ischemic comparative value on the central side representing a difference or ratio of the third pulse-wave-conduction-velocity-relating information to the fourth pulse-wave-conduction-velocity-relating information obtained after release from ischemia (arterial occlusion) by said arterial occlusion apparatus, in addition to the pre-ischemic comparative value on the peripheral side representing a difference or ratio of said first pulse-wave-conduction-velocity-relating information to the second pulse-wave-conduction-velocity-relating information obtained before ischemia by said arterial occlusion apparatus and post-ischemic comparative value on the peripheral side representing a difference or ratio of said first pulse-wave-conduction-velocity-relating information to said second pulse-wave-conduction-velocity-relating information obtained after release from ischemia (arterial occlusion) by said arterial occlusion apparatus. 
   According to the first aspect of the present invention, since the first pulse-wave-conduction-velocity-relating information to be measured at the post-stimulation measurement step is affected by dilation of the vessels and reduced elasticity of the vessel walls due to the release of endothelium-derived relaxing factors from vascular endothelium in the stimulation step, it varies depending on the first pulse-wave-conduction-velocity-relating information to be measured at the pre-stimulation measurement step. The first pulse-wave-conduction-velocity-relating information by itself shows spontaneous variations due to the influence of systemic fluctuations in blood pressure, heart rate and other factors, which obscure the changes after the stimulations. However, in the first invention, the second pulse-wave-conduction-velocity-relating information is also measured. Since this second pulse-wave-conduction-velocity-relating information is pulse-wave-conduction-velocity-relating information at the second segment almost symmetric to the first segment with respect to the median plane, it is approximately similar to the first pulse-wave-conduction-velocity-relating information in the spontaneous variations. A comparative value to be calculated at the comparative value calculation step is a difference or ratio of the first pulse-wave-conduction-velocity-relating information to the second pulse-wave-conduction-velocity-relating information. Therefore, the comparative value is not affected by the influence of the systemic fluctuations in blood pressure, heart rate and other factors. Since comparison of the pre-stimulation comparative value and the post-stimulation comparative value would make clear the change in stimulation-derived first pulse-wave-conduction-velocity-relating information, vascular endothelial function can be assessed at a high reliability by referring to the assessment of vascular endothelial function on the basis of comparison of the pre-stimulation comparative value with the post-stimulation comparative value. In addition, measurement of the pulse-wave-conduction-velocity-relating information does not require a great amount of skill and is also advantageous in that an apparatus is inexpensive. 
   In the first aspect of the present invention, stimulation is given for inducing the release of endothelium-derived relaxing factors from vascular endothelium during the stimulation step, whereas in the second aspect of the present invention, stimulation is given to a living body for inhibiting the release of endothelium-derived relaxing factors from the vascular endothelium and also for inhibiting vascular dilation due to the release of endothelium-derived relaxing factors. This is the only difference between them, with the same effect obtained also from the second aspect of the present invention. 
   The first preferred forms of the first, second and third aspects of the invention show specific modes of the first and the second segments. As shown herein, where one end of the first segment is the heart, the segment partially overlaps with the second segment. However, in executing the invention other than the first preferred forms of the first, second and third aspects of the invention, the first segment may or may not partially overlap with the second segment. 
   In the second forms of the first and second aspects of the invention, the pulse-wave-conduction-velocity-relating information at the first segment closer to the peripheral side rather than a local site where stimulation is given and the pulse-wave-conduction-velocity-relating information at the second segment, which constitutes a pair with the first segment, are referred to in the comparative value calculation step to calculate the comparative value before or after the stimulation closer to the peripheral side rather than the local site. In addition, the third and the fourth pulse-wave-conduction-velocity-relating information before and after the stimulation are calculated respectively at the-third segment on the central side of an artery where the stimulation is given and at the fourth segment, which constitutes a pair with the third segment. The third and the fourth pulse-wave-conduction-velocity-relating information are referred to in the comparative value calculation step to calculate the comparative value on the central side before and after the stimulation. It is thus possible to separate vascular endothelial function of an artery to be stimulated into those on the peripheral side and those on the central side and evaluate them at the same time. 
   The third forms of the first and second aspects of the invention shows a specific embodiment for judging vascular endothelial function on the basis of the pre-stimulation comparative value and post-stimulation comparative value. 
   According to the third aspect of the invention, when the first pulse-wave-conduction-velocity-relating information measured by the apparatus for measuring pulse-wave-conduction-velocity-relating information after the release from ischemia (arterial occlusion) by the arterial occlusion apparatus is affected by dilation of the vessels and reduced elasticity of the vessel walls due to the flow-mediated dilation response after the release from ischemia, it undergoes changes in the first pulse-wave-conduction-velocity-relating information to be measured before ischemia. The first pulse-wave-conduction-velocity-relating information by itself shows spontaneous variations due to the influence of systemic fluctuations in blood pressure, heart rate and other factors, which obscure the changes after release from ischemia. However, in the third aspect of the invention where the second pulse-wave-conduction-velocity-relating information is measured, the second pulse-wave-conduction-velocity-relating information is the pulse-wave-conduction-velocity-relating information at the second segment almost symmetric to the first segment with respect to the median plane. Since the spontaneous variations are approximately similar to the first pulse-wave-conduction-velocity-relating information and a comparative value to be calculated at the comparative value calculating means is a difference or ratio of the first pulse-wave-conduction-velocity-relating information to the second pulse-wave-conduction-velocity-relating information, the comparative value is not affected by the spontaneous variations due to the influence of systemic fluctuations in blood pressure, heart rate and other factors. Therefore, since comparison of the pre-ischemic comparative value with the post-ischemic comparative value would make clear the changes caused by the reactive hyperemia in the first pulse-wave-conduction-velocity-relating information, vascular endothelial function can be assessed at high reliability by referring to the assessment of vascular endothelial function on the basis of comparison of the pre-ischemic comparative value and the post-ischemic comparative value. In addition, measurement of the pulse-wave-conduction-velocity-relating information does not require a great amount of skill and is advantageous in that the apparatus is inexpensive. 
   In the second form of the third aspect of the invention, the vascular endothelial dysfunction determination means is used to judge the presence and extent of vascular endothelial dysfunction by referring to a peak of the comparative value calculated after the release from ischemia (arterial occlusion) by the comparative value calculating means and also to a comparative value before ischemia, which is advantageous in making an automatic judgment of the vascular endothelial function. 
   In the third form of the third aspect of the invention, changes over time in post-ischemic comparative values are graphically given by an output apparatus, and a point in time when the blood vessel diameter dilates to the greatest extent after release from ischemia appears as a peak in a graph showing changes over time in the post-ischemic comparative values. Therefore, it is possible to determine easily a point in time when the blood vessel diameter undergoes the greatest dilation by referring to the graph. 
   In the fourth form of the third aspect of the invention, the pulse-wave-conduction-velocity-relating information at the first segment closer to the peripheral side rather than the arterial occlusion site and the pulse-wave-conduction-velocity-relating information at the second segment, which constitutes a pair with the first segment, are referred to in the comparative value calculating means to calculate the comparative value before or after the ischemia closer to the peripheral side rather than the arterial occlusion site. In addition, the third and the fourth pulse-wave-conduction-velocity-relating information before and after the ischemia are respectively calculated at the third segment on the central side of an artery to be occluded and at the fourth segment, which constitutes a pair with the third segment. The third and the fourth pulse-wave-conduction-velocity-relating information are referred to by the comparative value calculating means to calculate the comparative value on the central side before and after the ischemia. It is thus possible to separate vascular endothelial function of an artery to be occluded into those on the peripheral side and those on the central side and evaluate them at the same time. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, advantages and technical and industrial significances of the present invention will be better understood by reading the following detailed description of presently preferred embodiment of the invention, when considered in connection with the accompanying drawings, in which: 
       FIG. 1  is a block diagram explaining the structure of the vascular endothelial function assessment apparatus used in the present invention; 
       FIG. 2  is a view showing a state where the cuff and the pressure pulse wave detecting probe provided in the vascular endothelial function assessment apparatus of  FIG. 1  are attached to the patient; 
       FIG. 3  is a view showing in detail the structure of the pulse wave detection probe of  FIG. 1 ; 
       FIG. 4  is a view showing the press surface of the pulse wave sensor provided in the pressure pulse wave detecting probe of  FIG. 3 ; 
       FIG. 5  is a functional block diagram explaining major control function of the CPU provided in the vascular endothelial function assessment apparatus of  FIG. 1 ; 
       FIG. 6  is a view explaining the optimum hold-down pressure HDPO determined by the hold-down pressure control means of  FIG. 5 ; 
       FIG. 7  is a view showing the right pulse-wave conduction time, left pulse-wave conduction time and conduction time difference calculated by the pulse-wave conduction time calculating means and conduction time difference calculating means of  FIG. 5 ; 
       FIG. 8  is a view showing the right pulse-wave conduction time, left pulse-wave conduction time and conduction time difference calculated by the pulse-wave conduction time calculating means and conduction time difference calculating means of  FIG. 5 ; 
       FIG. 9  is a view showing the right pulse-wave conduction time, left pulse-wave conduction time and conduction time difference calculated by the pulse-wave conduction time calculating means and conduction time difference calculating means of  FIG. 5 ; 
       FIG. 10  is a view showing the right pulse-wave conduction time, left pulse-wave conduction time and conduction time difference calculated by the pulse-wave conduction time calculating means and conduction time difference calculating means of  FIG. 5 ; 
       FIG. 11  is a flowchart describing major control operations of the CPU in the functional block diagrams of  FIG. 5 , showing a signal collection routine; 
       FIG. 12  is a flowchart describing the major control operations of the CPU in the functional block diagrams of  FIG. 5 , showing a signal computation routine; 
       FIG. 13  is a functional block diagram explaining major control function of the CPU provided in the vascular endothelial function assessment apparatus of the second embodiment of the invention; 
       FIG. 14  is a view showing changes over time in the conduction time ratio R (PCT) calculated by the left pulse-wave conduction time PCT L  and right pulse-wave conduction time PCT R  of  FIG. 7  through  FIG. 10 ; 
       FIG. 15  is a view showing a state where the cuff and pressure pulse wave detecting probe provided in the vascular endothelial function assessment apparatus of the third embodiment are attached to the patient; 
       FIG. 16  is a flowchart describing major control operations of the electronic control device of the third embodiment, showing a signal collection routine; and 
       FIG. 17  is a flowchart describing major control operations of the electronic control device of the third embodiment, showing a signal computation routine. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   An embodiment of the present invention will be hereinafter described with reference to the drawings.  FIG. 1  is a block diagram illustrating the structure of vascular endothelial function assessing apparatus  10  to which the invention is applied.  FIG. 2  is a view showing a state where the a cuff  14  and a pressure pulse wave detecting probe  18  provided in the vascular endothelial function assessing apparatus  10  in  FIG. 1  are attached to a patient  12 . 
   As shown in  FIG. 2 , the cuff  14  is attached to an upper arm (the left upper arm in this instance) of the patient  12 , and two pressure pulse wave detecting probes  18  are respectively attached to the left and right wrists of the patient  12 . 
   As shown in  FIG. 1 , the cuff  14  is connected through a piping  20  to a pressure control valve  22  and a pressure sensor  24 , and the pressure control valve  22  is further connected through a piping  26  to a pneumatic pump  28 . The pressure control valve  22  controls a highly pressurized air produced by the pneumatic pump  28  to supply it into the cuff  14 , or controls the pressure inside the cuff  14  by releasing air inside the cuff  14 . 
   The pressure sensor  24  detects a pressure inside the cuff  14  to supply a pressure signal SP indicating the pressure to a static pressure valve-specific circuit  30 . The static pressure valve-specific circuit  30  is provided with a low-pass filter and is able to discriminate a cuff pressure signal SC representing a stationary pressure contained in the pressure signal SP, that is, pressing pressure of the cuff  12 (hereinafter referred to as cuff pressure PC), thus supplying the cuff pressure signal SC through an A/D converter (not illustrated) to an electronic control device  32 . 
   A plural number of electrodes  16  are attached at specified sites of the patient  12  to measure an electrocardiogram. No particular restriction is given to a method for introducing the electrocardiogram, and any method such as a bipolar limb lead and chest lead can be used. The above electrodes  16  are connected to an electrocardiograph  34 , which amplifies an electrocardiographic signal SE introduced from the electrodes  16  and supplies it through the A/D converter (not illustrated) to the electronic control device  32 . The above electrocardiographic signal SE represents an action potential of cardiac muscles, namely, an electrocardiogram. 
   Two units of the pressure pulse wave detecting probes  18  are identical in structure. As displayed in detail in  FIG. 3 , these are provided with a container-like sensor housing  38 , a case  40  accommodating the sensor housing  38 , a screw axis  44  which is screwed down to the sensor housing  38  and is also able to move the sensor housing  38  toward a radial artery  42  through rotational driving, as well as a driving part  46  which is housed inside the case  40  and provided with a motor (not illustrated) for rotating and driving the screw axis  44 . The above case  40  is also provided with an attachment band  48 . 
   The thus structured pressure pulse wave detecting probe  18  is attached through the attachment band  48  to the wrist  52  in an easily attachable and detachable manner so that an open end of the sensor housing  38  is located opposite to the body surface  50 . 
   A pressure pulse wave sensor  54  is provided inside the above sensor housing  38  through a diaphragm  56  in such a manner that it can be moved relatively toward the sensor housing  38  and also projected through an opening end of the sensor housing  38 . A pressure chamber  57  is constituted with the sensor housing  38 , diaphragm  56  and others. As shown in  FIG. 1 , the pressure chamber  57  is structured so as to receive highly pressurized air from the pneumatic pump  58  through the pressure control valve  60 , by which the pressure pulse wave sensor  54  is pressed against the body surface  50  by HDP (hold down pressure) in accordance with the pressure inside the pressure chamber  57 . 
   The above sensor housing  38  and the diaphragm  56  constitute a hold-down apparatus  62  for pressing the pressure pulse wave sensor  54  toward the radial artery  42 . A motor made up of the screw axis  44  and the driving part  46  (not illustrated) constitutes a width-direction moving apparatus  64  for moving a hold-down pressure position at which the pressure pulse wave sensor  54  is pressed toward the body surface  50  in the width direction of the radial artery  42 . 
   As shown in  FIG. 4 , a number of semiconductor pressure sensitive elements (hereinafter simply referred to as pressure sensitive elements) E are arranged on a press surface  66  of the above pressure pulse wave sensor  54  along a width direction of the radial artery  42 , namely, in such a manner that an interval between them can be longer than a diameter of the radial artery  42  in a direction of moving the pressure pulse wave sensor  54  in parallel with the screw axis  44  and also in a constant space (for example, 0.2 mm apart from each other). 
   When the thus structured pressure pulse wave detecting probe  18  is pressed toward the radial artery  42  above the body surface  50  of the wrist  52 , a pressure pulse wave sensor  54  detects a radial artery pulse wave RW produced from the radial artery  42  and transmitted to the body surface  50 . As shown in  FIG. 1 , the pressure pulse wave signal SM representing the radial artery pulse wave is supplied through the A/D converter (not illustrated) to the electronic control device  32 . In the following explanation, a pressure pulse wave signal SM outputted from the pressure pulse wave sensor  54  attached to the left wrist is designated as a left pressure pulse wave signal SM L ; a radial artery pulse wave RW represented by the left pressure pulse wave signal SM L , as a left radial artery pulse wave RW L ; a pressure pulse wave signal SM outputted from the pressure pulse wave sensor  54  attached to the right wrist, as a right pressure pulse wave signal SM R ; and a radial artery pulse wave RW represented by the right pressure pulse wave signal SM R , as a right radial artery pulse wave RW n . 
   The electronic control device  32  is configured with a so called microcomputer provided with CPU  68 , ROM  70 , RAM  72  and I/O port (not illustrated) and others. In compliance with the program previously stored in the ROM  70 , the CPU  68  utilizes the memory function of the RAM  72  and executes signal processing, thus outputting driving signals from the I/O port, controlling the pressure control valve  22  and the pneumatic pump  28  through a driving circuit (not illustrated) for attaining control of the cuff pressure PC, and outputting driving signals to the pneumatic pump  58  and the pressure control valve  60  through a driving circuit (not illustrated) for attaining adjustment of the pressure inside the pressure chamber  57  as well. Further, the CPU  68  is used to perform computations on the basis of signals supplied from the electronic control device  32 , by which pulse-wave conduction time PCT and conduction time difference ΔPCT are calculated, and the thus calculated pulse-wave conduction time PCT and conduction time difference ΔPCT are displayed on a display  74  which serves as an output apparatus. 
     FIG. 5  is a functional block diagram explaining major control functions of the CPU  68  in the vascular endothelial function-assessing apparatus  10  as shown in  FIG. 1 . The cuff pressure controlling means  60  functioning as arterial occlusion controlling means judges the cuff pressure PC on the basis of the cuff pressure signal SC supplied from the static pressure valve-specific circuit  30  and controls the pressure control valve  22  and the pneumatic pump  28 , thereby instantly elevating the cuff pressure PC up to a predetermined pressure level P 1  (for example, 250 mmHg) which is higher than the highest blood pressure BP sys  at a site of wearing the cuff  14 , followed by maintaining the cuff pressure PC for a predetermined time determined by a simulation (for example, for 5 minutes), and reducing the cuff pressure PC to an atmospheric pressure at a subsequent stage. Further, in the present embodiment, an arterial occlusion apparatus  82  is provided with the cuff  14 , pressure control valve  22  for controlling the cuff pressure PC, pneumatic pump  28 , pressure sensor  24  and cuff pressure controlling means  80 . The arterial occlusion apparatus  82  is used to occlude arteries in the upper arm, and a reactive hyperemia then takes place at peripheral tissues downstream from a site of arterial occlusion when the occlusion is released, thereby increasing blood flow at arteries (namely, the brachial artery and connected arteries upstream or downstream therefrom) perfusing the tissues, which stimulates and induces endothelium-derived relaxing factors from vascular endothelium at the above specified regions or those where increased blood flow is found. Then, the arteries undergo dilation of the diameter after release of the endothelium-derived factors. 
   An optimum-hold-down position control means  84  is used to judge whether or not hold-down pressure position changing conditions can be attained on the basis of the fact that, of plural pressure sensitive elements E provided on a pressure pulse wave sensor  54 , an element that can detect a maximum pressure (hereinafter the element is referred to as maximum pressure detecting element EM) is positioned at a site corresponding to a predetermined number or a distance from an edge of the arrangement used as a reference. Then, when the hold-down pressure position changing conditions are attained, the following hold-down pressure position changing operations are carried out. More particularly, in the hold-down pressure position changing operations, the pressure pulse wave sensor  54  is temporarily separated from the body surface  50 , the width-direction moving apparatus  64  is used to move a hold-down apparatus  62  and a pressure pulse wave sensor  54  at a specified distance and then the hold-down apparatus  62  is used to press the pressure pulse wave sensor  54  by exerting a relatively small predetermined first hold-down pressure HDP 1 . Then, judgment is made again as to whether or not the above hold-down pressure position changing conditions can be attained, with the status kept as it is, and the above operations and judgment procedures are carried out until the hold-down pressure position changing conditions are no longer attained, more particularly, the above maximum pressure detecting element EM is approximately positioned at the center of the arrangement. The predetermined number or predetermined distance from an edge of the arrangement under the above hold-down pressure position changing conditions is determined on the basis of a diameter of the artery (radial artery  42  in the present embodiment) pressed by the pressure pulse wave sensor  54 , for example, it will be set to be ¼ of the diameter. 
   In an hold-down pressure control means  86 , the pressure pulse wave sensor  54  is positioned at an optimally pressed site by the optimum-hold-down position control means  84 , and the hold-down apparatus  62  is then used to allow hold-down pressure HDP of the pressure pulse wave sensor  54  to change successively according to pulsation in a predetermined hold-down pressure range or allow the hold-down pressure to change continuously at a relatively mild and constant rate in a predetermined hold-down pressure range. An optimum hold-down pressure HDPO is determined on the basis of the radial artery pulse wave RW obtained in the course of changes in the hold-down pressure HDP, and the hold-down apparatus  62  is used to maintain the hold-down pressure HDP of the pressure pulse wave sensor  54  in a range of an optimum hold-down pressure HDPO. In this instance, the optimum hold-down pressure HDPO is designated as a hold-down pressure by which the side pressed by the pressure pulse wave sensor  54  on a blood vessel wall of the radial artery  42  derived from the hold-down pressure HDP of the pressure pulse wave sensor  54  is rendered almost flat. For example, as shown in  FIG. 6 , the HDPO is a hold-down pressure value in a specified range, a center of which is in the middle of a flat area formed by the curve (shown by the dotted line in  FIG. 6 ) connected with a lower peak value (rising point) RW min  of the radial artery pulse wave RW in a two-dimensional graph showing the size of the radial artery pulse wave RW obtained from a maximum pressure detecting element EM of the pressure pulse wave sensor  54  and the hold-down pressure HDP of the pressure pulse wave sensor  54 , when the hold-down pressure HDP is increased continuously in a range containing a sufficient optimum hold-down pressure HDPO. 
   A pulse-wave conduction time calculating means  88  is used to calculate respectively the right pulse-wave conduction time PCT R  which is a conduction time of a pulse wave from the heart to the right wrist and the left pulse-wave conduction time PCT L  which is a conduction time of a pulse wave from the heart to the left wrist, on the basis of electrocardiographic signal SE supplied successively from the electrocardiograph  34  and the right pressure pulse wave signal SM R  and the left pressure pulse wave signal SM L  supplied successively from the respective maximum pressure detecting elements EM of two pressure pulse wave sensors  54 . Namely, a difference between the time when a specified site (R-wave in this embodiment) of the electrocardiogram represented by the electrocardiographic signal SE is detected and the time when a specified site (rising point in this embodiment) of the right radial artery pulse wave RW R  represented by the right pressure pulse wave signal SM R  is detected is calculated as the right pulse-wave conduction time PCT R , whereas a difference between the time when a specified site (R-wave) of the electrocardiogram represented by the electrocardiographic signal SE is detected and the time when a specified site (rising point) of the left radial artery pulse wave RW L  represented by the pressure pulse wave signal SM 1  is detected is calculated as the left pulse-wave conduction time PCT L . Specifically, the pulse-wave conduction time PCT calculated on the basis of the electrocardiogram is a conduction time of a pulse wave from the heart to the right (left) wrist to which pre-ejection period from the time when the cardiac muscle starts to contract to the time when blood is ejected is added. 
   In the pulse-wave conduction time calculating means  88 , as explained above, the right pulse-wave conduction time PCT R  and the left pulse-wave conduction time PCT L  are calculated over time respectively in terms of values for each pulse or an average of a few pulses by referring to a period from the time when the cuff pressure PC is controlled by the cuff pressure control means  80  and arteries in the left upper arm are occluded by the cuff  14  at a specified time (before 5 minutes in this embodiment) to the time when a specified time has passed after the arterial occlusion is released (5 minus in this embodiment). Since no left radial artery pulse wave RW L  takes place while the arteries are occluded in the left upper arm, no calculation can be made for the left pulse-wave conduction time PCT L . Changes over time in the thus calculated right pulse-wave conduction time PCT R  and the left pulse-wave conduction time PCT L  are displayed graphically on the display  74 . 
   In this embodiment, the first segment covers an area from the heart to the left wrist and the second segment covers an area from the heart to the right wrist. The above left pulse-wave conduction time PCT L  and the right pulse-wave conduction time PCT R  respectively correspond to the first pulse-wave-conduction-velocity-relating information and the second pulse-wave-conduction-velocity-relating information. The electrocardiograph  34 , two pressure pulse wave sensors  54 , optimum-hold-down position control means  84 , hold-down pressure control means  86  and pulse-wave conduction time calculating means  88  give functions as a pulse-wave-conduction-velocity-relating information measurement apparatus  90 . 
   When the first segment covering an area from the heart to the left wrist is compared with the second segment covering an area from the heart to the right wrist, it is found that these two segments are almost symmetrical with respect to the median plane of the patient  12 . Since the aortic artery and its branches are not symmetrical, these two segments are not completely symmetrical with respect to the median plane. 
   A conduction time difference calculating means  92 , which functions as comparative value calculating means, is to calculate the conduction time difference ΔPCT corresponding to the comparative value, on the basis of the pulse-wave conduction time PCT calculated over time in terms of a value for each pulse or an average of a few pulses in the above pulse-wave conduction time calculating means  88 . Changes over time in the thus calculated conduction time difference ΔPCT are displayed graphically on the display  74 . The above conduction time difference ΔPCT can be obtained by subtracting the time-corresponding right pulse-wave conduction time PCT R  from the left pulse-wave conduction time PCT L  calculated by the pulse-wave conduction time calculating means  88 , representing a difference in these two pulse-wave conduction times PCT L  and PCT R  based on the same pulsation or point in time. 
     FIG. 7  through  FIG. 10  are graphs showing the right pulse-wave conduction time PCT R  and the left pulse-wave conduction time PCT L  calculated by the pulse-wave conduction time calculating means  88  as well as the conduction time difference ΔPCT calculated by the conduction time difference calculating means  92 . In  FIG. 7  through  FIG. 10 , measurement is carried out in different patients, and the left brachial artery is occluded for 5 minutes, which corresponds to a part from 5 to 10 minutes in the graph. As shown in these graphs, the left pulse-wave conduction time PCT L  shows spontaneous variations, although such variations vary among individuals. Thus, no clear changes after the release from ischemia are obtained for the left pulse-wave conduction time PCT L  itself. The right pulse-wave conduction time PCT R  for the second segment, which is almost symmetrical to the segment for measuring the left pulse-wave conduction time PCT L  with respect to the median plane, shows the spontaneous variations similar to those observed in the left pulse-wave conduction time PCT L . This indicates that these spontaneous variations reflect the effects of systemic factors common to the both sides of body. Therefore, conduction time difference ΔPCT is free from the variations due to the influence of the systemic factors. 
   Prior to an explanation about the assessment of vascular endothelial function based on the conduction time difference ΔPCT, changes in the pulse-wave conduction time PCT with reactive hyperemia will be explained by referring to the Moens-Korteweg formula as shown in Expression 1.
 
 PWV= ( Eh/ 2 ρR ) 1/2   (Expression 1)
         wherein E represents Young&#39;s modulus; h, thickness of blood vessel wall; ρ, density of blood; and R, radius of a blood vessel.       

   This is a well known formula regarding pulse wave conduction velocity PWV, by which Expression 2 can be obtained by referring to the relationship between the pulse wave conduction velocity PWV and the pulse-wave conduction time PCT.
 
 PCT=D/PWV=D (2ρ R ) 1/2 /( Eh ) 1/2   (Expression 2)
         wherein D represents conduction distance.       

   Expression 2 shows that an increase in blood vessel radius R, a decrease in blood vessel wall thickness h, and a decrease in elasticity E result in a longer pulse-wave conduction time PCT. 
   arm to which the cuff  14  is attached due to the reactive hyperemia, endothelium-derived relaxing factors are released from the vascular endothelium to cause dilation of blood vessels (increase in the radius and decrease in the wall thickness) and lower the elasticity of blood vessels in association with the dilation at a blood flow-increased area, thus resulting in an increase in the pulse-wave conduction time PCT (delayed). However, when vascular endothelial function is impaired, blood vessels will not dilate nearly as much on reactive hyperemia and the pulse-wave conduction time PCT will not increase nearly as much either. It is therefore possible to evaluate vascular endothelial function at the segment where the left pulse-wave conduction time PCT L  is measured (or segment from the heart to the left wrist) by referring to the extent of the increase in the left pulse-wave conduction time PCT L  due to the reactive hyperemia. As shown in  FIG. 7  through  FIG. 10 , the left pulse-wave conduction time PCT L  shows large spontaneous variations, which makes it difficult to judge the extent of the increase with the reactive hyperemia. However, the conduction time difference ΔPCT is free from the spontaneous variations and therefore an increase in the pulse-wave conduction time with the reactive hyperemia can be clearly detected. 
   There may be many ways for evaluating changes in conduction time difference ΔPCT with reactive hyperemia. The evaluation can be made on the basis of, for example, an increased quantity in the peak of the conduction time difference ΔPCT after the release from ischemia in relation to the conduction time difference ΔPCT before the ischemia or an increased rate of the peak of the conduction time difference ΔPCT after the release from the ischemia in relation to the conduction time difference ΔPCT before the ischemia. Where the increased quantity and increased rate are large, vascular endothelial function is judged to be normal. In the patients shown in  FIG. 7  through  FIG. 10 , those in  FIG. 7  through  FIG. 9  are judged normal in the vascular endothelial function whereas those in  FIG. 10  are judged abnormal in the vascular endothelial function. 
   When reverting to  FIG. 5 , in vascular endothelial dysfunction judgment means  94 , the conduction time difference ΔPCT after the release from ischemia calculated by the conduction time difference calculating means  92  is referred to determine the peak value, and the conduction time difference ΔPCT before start of the ischemia is subtracted from the peak value to obtain a difference between the conduction time difference ΔPCT before the ischemia and that after the ischemia, or the peak value is divided by the conduction time difference ΔPCT before the start of the ischemia to calculate the ratio of the conduction time difference ΔPCT before the ischemia to that after the ischemia (the difference or the ratio in this instance must always be positive). Where the thus obtained difference and ratio are at or less than a predetermined judgment standard value established by simulations, it is judged that they show an impairment of vascular endothelial function. In this instance, character r symbols showing such an impairment are displayed on the display  74 . A value obtained at one specified point (for example, immediately before the start of ischemia) may be used in calculating the conduction time difference ΔPCT before start of ischemia. In this embodiment, an average value obtained for a certain time before the start of ischemia (for example, 3 minutes) is used to remove variation in the value. 
     FIG. 11  and  FIG. 12  are flowcharts showing major control operations of the CPU  68  indicated in the functional block diagram of  FIG. 5 .  FIG. 11  illustrates a signal collecting routine and  FIG. 12  illustrates a signal computation routine. 
   In step SA 1  of  FIG. 11  (hereinafter, the word, step, is omitted), judgment is made as to whether hold-down position changing conditions (APS starting conditions) are attained or not under conditions where, of pressure sensitive elements E arranged on the press surface  66  of pressure pulse wave sensor  54 , the maximum pressure detecting element EM is positioned at a specified number or specified distance from the arrangement. When this judgment is denied, steps after SA 3  to be described later will be carried out. 
   In contrast, when the judgment on SA 1  is affirmed, namely, where the pressure pulse wave sensor  54  is positioned inappropriate in relation to the radial artery  42 , APS control routine for SA 2  is carried out, which is equivalent to the optimum-hold-down position control means  84 . In the APS control routine, the width-direction moving apparatus  64  is controlled to determine an optimum hold-down position so that, of individual pressure detecting elements E in the pressure pulse wave sensor  54 , a pressure detecting element E which is able to detect a maximum amplitude is positioned approximately at the center of the arrangement of the pressure detecting elements E, and this pressure detecting element E is designated as the maximum pressure detecting element EM. The pressure pulse wave signal SM explained below means a pressure pulse wave signal SM detected by the maximum pressure detecting element EM determined in this step of SA 2 . 
   Where judgment is made on the SA 1  as explained above or the above SA 2  is carried out, HDP control routine for SA 3  which is equivalent to the hold-down pressure control means  86  is carried out as a subsequent step. More particularly, the pressure control valve  60  is controlled to elevate continuously the hold-down pressure HDP of the pressure pulse wave sensor  54 , during which a hold-down pressure which attains the maximum amplitude of the radial artery pulse wave RW detected by the maximum pressure detecting element EM is designated as an optimum hold-down pressure HDPO, and the hold-down pressure HDP of the pressure pulse wave sensor  54  is retained in the optimum hold-down pressure HDPO. 
   In the subsequent SA 4 , electrocardiographic signal SE, right pressure pulse wave signal SM R  and left pressure pulse wave signal SM L  are read in for every sampling period at a specified point in time. Then, in SA 5 , judgment is made as to whether or not 5 minutes passed after the start of reading the signals at SA 4 . Where judgment on the SA 5  is denied, the SA 4  will be repeated to continue reading of the electrocardiographic signal SE, right pressure pulse wave signal SM R  and left pressure pulse wave signal SM L . These steps of SA 4  and SA 5  will function as a pre-stimulation measurement step in combination with the SB 1  through SB 5  ( FIG. 12 ) to be described later and used for calculating the left pulse-wave conduction time PCT L  and the right pulse-wave conduction time PCT R  on the basis of signals obtained in SA 4  and SA 5 . 
   Where judgment on the SA 5  is affirmed, steps from SA 6  through SA 9  corresponding to the stimulation step will be carried out. In SA 6 , the cuff pressure signal SC is at first referred to judge the cuff pressure PC and control the pneumatic pump  28  and the pressure control valve  22 , thereby controlling the cuff pressure PC within the previously described pressure value P 1  to start arterial occlusion on the left upper arm. 
   In the subsequent SA 7 , electrocardiographic signal SE and right pressure pulse wave signal SM R  are read in for every sampling period at a specified point in time. Then, in SA 8 , judgment is made as to whether or not 5 minutes passed after the start of arterial occlusion. Where this judgment is denied, the SA 7  will be repeated to continue reading of the electrocardiographic signal SE and the right pressure pulse wave signal SM R . Where judgment on SA 8  is affirmed, the pneumatic pump  28  is stopped to control the pressure control valve  22 , thereby reducing the cuff pressure PC down to an atmospheric pressure to release arterial occlusion. Once the arterial occlusion is released, a reactive hyperemia takes place at tissues peripheral to a site of arterial occlusion and results in an increase in arterial blood perfusing through the tissues, which stimulates to induce the release of endothelium-derived relaxing factors from vascular endothelium at an area where blood flow has increased. 
   In the subsequent SA 10 , as with the SA 4 , the electrocardiographic signal SE, right pressure pulse wave signal SM R  and left pressure pulse wave signal SM L  are read in for every sampling at a specified point in time. Then, in SA 11 , judgment is made as to whether or not 5 minutes passed after the start of reading the signals in SA 10  after the release from arterial occlusion. Where this judgment is denied, the SA 10  will be repeated to continue reading of the electrocardiographic signal SE, right pressure pulse wave signal SM R  and left pressure pulse wave signal SM L . These SA 10  and SA 11  will function as a post-stimulation measurement step in combination with the SB 1  through SB 5  ( FIG. 12 ) to be described later and used for calculating the left pulse-wave conduction time PCT L  and the right pulse-wave conduction time PCT R  on the basis of signals obtained in SA 10  and SA 11 . 
   In contrast, where judgment on the SA 11  is affirmed, the signal collecting routine is completed to carry out the signal computation routine as shown in  FIG. 12 . 
   In conducting the signal computation routine as shown in  FIG. 12 , an electrocardiogram represented by the electrocardiographic signal SE read in the steps of SA 4 , SA 7  and SA 10  is referred to determine a detection time of R-wave for each pulse in the initial step of SB 1 , and an electrocardiogram represented by the left pulse wave signal SM L  read in the steps of SA 4 , SA 7  and SA 10  is referred to determine a rising point of the left radial artery pulse wave RW L  for each pulse in the subsequent SB 2 , and an electrocardiogram represented by the right pulse wave signal SM R  read in the steps of SA 4 , SA 7  and SA 10  is referred to determine a rising point of the right radial artery pulse wave RW R  for each pulse in the next step of SB 3 . 
   Then, in the subsequent SB 4 , a difference between the detection time of individual electrocardiogram R-waves determined in SB 1  and the detection time of rising points of individual left radial artery pulse waves RW L  determined in SB 2  is referred to calculate over time the left pulse-wave conduction time PCT L  in terms of a value for each pulse or an average of a few pulses, and in the subsequent SB 5  a difference between the detection time of individual electrocardiogram R-waves determined in SB 1  and the detection time of the individual right radial artery pulse waves RW R  determined in SB 3  is referred to calculate over time the right pulse-wave conduction time PCT R  in terms of a value for each pulse or an average of a few pulses. 
   In the subsequent SB 6  equivalent to the conduction time difference calculating means  92  and the comparative value calculation step, the right pulse-wave conduction time PCT R  calculated in SB 5  is subtracted from the left pulse-wave conduction time PCT L  calculated in SB 4  to calculate over time the conduction time difference ΔPCT 5 minutes before ischemia (namely, pre-ischemic comparative value) and the conduction time difference ΔPCT 5 minutes after ischemia (namely, post-ischemic comparative value) in terms of a value for each pulse or an average of a few pulses. 
   In the subsequent SB 7 , changes over time in the left pulse-wave conduction time PCT L , right pulse-wave conduction time PCT R  and conduction time difference ΔPCT calculated in the above SB 4  through SB 6  are illustrated graphically as shown in  FIG. 7  through  FIG. 10 . 
   Then, the steps of SB 8  through SB 12  equivalent to the vascular endothelial dysfunction judgment means 94 and vascular endothelial dysfunction judgment step will be carried out. In the SB 8 , with regard to values of the conduction time difference ΔPCT 5 minutes before ischemia calculated in SB 6 , those of conduction time difference ΔPCT 3 minutes before ischemia are averaged. Then, in SB 9 , a peak of the conduction time difference ΔPCT after the release from ischemia calculated in SB 6  is determined. Thereafter, in the subsequent SB 10 , the average of the conduction time difference ΔPCT 3 minutes before ischemia calculated in SB 8  is subtracted from the peak of the conduction time difference ΔPCT after the release from ischemia determined in SB 9  to calculate the difference between the conduction time difference ΔPCT before ischemia and that after ischemia. 
   Then, in SB 11 , where a difference between the conduction time difference ΔPCT before ischemia and that after ischemia calculated in the above SB 10  is at or lower than the predetermined judgment standard value, the vascular endothelial function are judged to be impaired, and where the difference is greater than the predetermined judgment standard value, the vascular endothelial function is judged to be normal. In SB 12 , the message showing the judgment results will be displayed on the display  74 . 
   According to the above embodiment, the left pulse-wave conduction time PCT L  measured by the pulse-wave-conduction-velocity-relating information measurement apparatus  90  after the release from ischemia (arterial occlusion) by the arterial occlusion apparatus  82  is affected by dilation of the vessels and reduced elasticity of the vessel walls due to the flow-mediated dilation response after the release from ischemia undergoes changes in the left pulse-wave conduction time PCT L  measured before ischemia. However, the left pulse-wave conduction time PCT L  by itself shows spontaneous variations, which obscure the changes with reactive hyperemia. However, in this embodiment where a right pulse-wave conduction time PCT R  is measured, the right pulse-wave conduction time PCT R  is a pulse-wave conduction time PCT for the second segment almost symmetrical to the first segment with respect to the median plane and therefore similar to the left pulse-wave conduction time PCT L  in spontaneous variations due to the influences of systemic factors. Further, since the conduction time difference ΔPCT calculated by the conduction time difference calculating means  92  (SB 6 ) is a difference between the left pulse-wave conduction time PCT L  and the right pulse-wave conduction time PCT R , the conduction time difference ΔPCT is free of spontaneous variations due to the influences of systemic fluctuations in blood pressure, heart rate and other factors. Therefore, since comparison of the conduction time difference ΔPCT before ischemia with that after ischemia would make clear the change in the left pulse-wave conduction time PCT L  with reactive hyperemia, the vascular endothelial function can be assessed at a high reliability by referring to the assessment of vascular endothelial function on the basis of comparison of the conduction time difference ΔPCT before ischemia with that after ischemia. In addition, measurement of the pulse-wave conduction time PCT does not require a great amount of skill and is advantageous in that the apparatus is inexpensive. 
   According to the above embodiment, the vascular endothelial dysfunction judgment means  94 (from SB 8  through SB 12 ) is used to make an automatic judgment of the vascular endothelial dysfunction on the basis of the fact that a difference between the peak of the conduction time difference ΔPCT after the release from ischemia calculated by the conduction time difference calculating means  92 (SB 6 ) and the conduction time difference ΔPCT before ischemia is at or lower than a predetermined judgment standard value. 
   Further, according to the above embodiment, since the vascular endothelial dysfunction judgment means  84  is provided with the display  74  which graphically illustrates changes over time in the conduction time difference ΔPCT calculated by the conduction time difference calculating means  92 (SB 6 ), it is able to determine easily a point in time when the blood vessel dilated to the greatest extent by referring to graphically illustrated changes over time in the conduction time difference ΔPCT. 
   In the above embodiment, the first segment covers an area from the heart to the wrist  52  in which arteries are occluded by the arterial occlusion apparatus  82 , or including a relative long area from the heart to the wrist  52 . The first segment has accordingly a longer pulse-wave conduction time PCT. Thus, since the conduction time difference ΔPCT calculated by the conduction time difference calculating means 92(SB 6 ) has a greater change after the release from ischemia than that before ischemia, it is possible to examine the vascular endothelial function at a higher reliability. 
   Next, an explanation will be made about the second embodiment of the invention. In making an explanation about the second embodiment, parts having the same structure with the first embodiment will be given the same symbol and omitted from explanation. 
   The second embodiment is different from the first embodiment only in that calculation is made for the conduction time ratio R (PCT) in place of the conduction time difference ΔPCT of the first embodiment, providing similar effects as in the first embodiment. Hereinafter an explanation will be made about the difference between the first embodiment and the second embodiment. 
     FIG. 13  is a functional block diagram describing major control functions of the CPU  68  in the vascular endothelial function assessment apparatus of the second embodiment. 
   The conduction time ratio calculating means  96  which functions as comparative value calculating means is used to calculate a ratio of the conduction time PCT based on mutually equal pulsations or points in time, namely, conduction time ratio R (PCT), by dividing the left pulse-wave conduction time PCT L  by the right pulse-wave conduction time PCT R , each of which is calculated over time in terms of a value for each pulse or an average of a few pulses by the pulse-wave conduction time calculating means  88 . Changes over time in the thus calculated conduction time ratio R (PCT) are displayed graphically on the display  74 . 
     FIG. 14  is a view illustrating changes over time in the conduction time ratio R (PCT) calculated by the left pulse-wave conduction time PCT L  and the right pulse-wave conduction time PCT R  shown in  FIG. 7  through  FIG. 10 , wherein (a), (b), (c) and (d) represent changes over time in the conduction time ratio R (PCT) calculated by the left pulse-wave conduction time PCT L  and the right pulse-wave conduction time PCT R  respectively in  FIG. 7 ,  FIG. 8 ,  FIG. 9  and  FIG. 10 . As apparent from the comparison of the graph shown in  FIG. 14  with lower graphs shown in  FIG. 7  through  FIG. 10 , it is found that the conduction time ratio R (PCT) is almost similar to the change with the conduction time difference ΔPCT. 
   When returning to  FIG. 13 , the vascular endothelial dysfunction judgment means  98  is different from the vascular endothelial dysfunction judgment means 84 of the first embodiment only in that the conduction time ratio R (PCT) is used in place of the conduction time difference ΔPCT. More particularly, the vascular endothelial dysfunction judgment means  98  is used to determine a peak value by referring to the conduction time ratio R (PCT) after the release from ischemia calculated by the conduction time ratio calculating means  96 , and the conduction time ratio R (PCT) before start of ischemia is subtracted from the peak value to obtain a difference between the conduction time ratio R (PCT) before ischemia and that after ischemia, or the peak value is divided by the conduction time ratio R (PCT) before start of ischemia to obtain a ratio of the conduction time ratio R (PCT) before ischemia to that after ischemia. Where the thus obtained difference or ratio is at or lower than a predetermined judgment standard value determined by simulations, it is judged that the vascular endothelial function is impaired, and characters or symbols showing such impairment are displayed on the display  74 . 
   Next, an explanation will be made regarding the third embodiment of this invention.  FIG. 15  is a view showing a state where the cuff  14  and pressure pulse wave detecting probe  18  provided in the vascular endothelial function assessment apparatus of the third embodiment are attached to the patient  12 . As shown in  FIG. 15 , the third embodiment is provided with four pressure pulse wave detecting probes  18 , which are attached to the right and left wrists, a site of the left upper arm downstream from the cuff  14  and a site of the right upper arm symmetrical to the site with respect to the median plane. In the third embodiment, the pulse-wave-conduction-velocity-relating information measurement apparatus  90  of the first embodiment to which the pressure pulse wave detecting probe  18  attached to the above right upper arm is structurally added is used as a pulse-wave-conduction-velocity-relating information measurement apparatus. 
   The third embodiment is different from the first embodiment only in a larger number of pressure pulse wave detecting probes  18  by 2 and the control functions of the electronic control device  32 .  FIG. 16  and  FIG. 17  are flowcharts showing major control operations of the electronic control device  32  of the third embodiment.  FIG. 16  is a signal collection routine and  FIG. 17  is a signal computation routine. 
     FIG. 16  is similar in content with  FIG. 11  of the previously described first embodiment, except for an increased number of signals collected in steps SA 4 - 1 , SA 7 - 1  and SA 10 - 1 . More particularly, in SA 4 - 1  and SA 10 - 1 , a pressure pulse wave signal on the right central side SM RC  which is a signal from the pressure pulse wave detecting probe  18  attached to the right upper arm closer to the central side than the right wrist and a pressure pulse wave signal on the left central side SM LC  which is a signal from the pressure pulse wave detecting probe  18  attached to the left upper arm closer to the central side than the left wrist are read in, in addition to the electrocardiographic signal SE, a pulse wave signal on the right peripheral side SM RE  which is a signal from the pressure pulse wave detecting probe  18  attached to the right wrist and a pressure pulse wave signal on the left peripheral side SM LE  which is a signal from the pressure pulse wave detecting probe  18  attached to the left wrist. In SA 7 - 1 , the pulse wave signal on the right central side SM RC  is read in, in addition to the electrocardiographic signal SE and the right pulse wave signal on the peripheral side SM RE . Further, in  FIG. 16 , steps of SA 4 - 1  through SA 5  will function as a pre-stimulation measurement step in combination with steps SC 1  through SC 5  ( FIG. 17 ) to be described later, and steps SA 10 - 1  through SA 11  will function as a post-stimulation measurement step in combination with the steps SC 1  through SC 5  ( FIG. 17 ). 
   The computation routine of  FIG. 17  will be carried out after completion of the signal collection routine of  FIG. 16 . An electrocardiogram represented by the electrocardiographic signal SE read in the steps SA 4 - 1 , SA 7 - 1  and SA 10 - 1  of  FIG. 16  is referred to determine a detection point in time of R-wave for each pulse at first in SC 1 . Electrocardiograms represented by a pulse wave signal on the left peripheral side SM LE  and a pulse wave signal on the left central side SM LC  read in the steps SA 4 - 1 , SA 7 - 1  and SA 10 - 1  are referred to determine a rising point of the left radial artery pulse wave RW L  and a rising point of the left brachial artery pulse wave BW L  for each pulse. Then, in the subsequent SC 3 , electrocardiograms represented by a pulse wave signal on the right peripheral side SM RE  and a pulse wave signal on the right central side SM RC  read in the steps SA 4 - 1 , SA 7 - 1  and SA 10 - 1  are referred to determine a rising point of the right radial artery pulse wave RW R  and a rising point of the right brachial artery pulse wave BW R  for each pulse. 
   In the subsequent SC 4 , a difference between the time when a rising point of each left brachial artery pulse wave BW L  determined in SC 2  is detected and the time when a rising point of each left radial artery pulse wave RW L  is detected is referred to make an over time calculation of the pulse-wave conduction time on the left peripheral side PCT LE  in terms of a value for each pulse or an average of a few pulses. Further, a difference between the time when each R-wave of the electrocardiogram determined in SC 1  is detected and the time when a rising point of each left brachial artery pulse wave BW L  determined in SC 2  is detected is referred to make an over time calculation of the pulse-wave conduction time on the left central side PCT LC  in terms of a value for each pulse or an average of a few pulses. In the third embodiment of this invention, the above-mentioned pulse-wave conduction time on the left peripheral side PCT LE  and the pulse-wave conduction time on the left central side PCT LC  are equivalent respectively to the first pulse-wave-conduction-velocity-relating information and the third pulse-wave-conduction-velocity-relating information, and their measurement segments, namely, a segment from the left upper arm to the left wrist and a segment from the heart to the left upper arm are equivalent respectively to the first segment and the third segment. 
   Then, in SC 5 , a difference between the time when a rising point of each right brachial artery pulse wave BW R  determined in SC 2  is detected and the time when a rising point of each right radial artery pulse wave RW R  is detected is referred to make an over time calculation of the pulse-wave conduction time on the right peripheral side PCT RE  in terms of a value for each pulse or an average of a few pulses. Further, a difference between the time when each R-wave of the electrocardiogram determined in SC 1  is detected and the time when a rising point of each right brachial artery pulse wave BW R  determined in SC 2  is detected is referred to make an over time calculation of the pulse-wave conduction time on the right central side PCT RC  in terms of a value for each pulse or an average of a few pulses. In the third embodiment of this invention, the above-mentioned pulse-wave conduction time on the right peripheral side PCT RE  and the pulse-wave conduction time on the right central side PCT RC  are equivalent respectively to the second pulse-wave-conduction-velocity-relating information and the fourth pulse-wave-conduction-velocity-relating information, and their measurement segments, namely, a segment from the right upper arm to the right wrist and a segment from the heart to the right upper arm are equivalent respectively to the second segment and the fourth segment. 
   Then, in the subsequent SC 6  equivalent to the comparative value calculating means and comparative value calculation step, the pulse-wave conduction time on the right peripheral side PCT RE  calculated in SC 5  is subtracted from the pulse-wave conduction time on the left peripheral side PCT LE  calculated in SC 4  to make an over time calculation of the conduction time difference on the peripheral side ΔPCT E  for 5 minutes before ischemia (namely, pre-ischemic comparative value on the peripheral side) and the conduction time difference on the peripheral side ΔPCT E  for 5 minutes after the release from ischemia (namely, post-ischemic comparative value on the peripheral side) in terms of a value for each pulse or an average of a few pulses. Further, the pulse-wave conduction time on the right central side PCT RC  calculated in SC 5  is subtracted from the pulse-wave conduction time on the left central side PCT LC  calculated in SC 4  to make an over time calculation of the conduction time difference on the central side ΔPCT c  for 5 minutes before ischemia (namely, pre-ischemic comparative value on the central side) and the conduction time difference on the central side for 5 minutes after the release from ischemia ΔPCT c  (namely, post-ischemic comparative value on the central side) in terms of a value for each pulse or an average of a few pulses. 
   In the subsequent SC 7 , changes over time in the pulse-wave conduction time on the left and right peripheral sides PCT LE  and PCT RE , pulse-wave conduction time on the left and right central sides PCT LC , PCT RC , conduction time difference on the peripheral side ΔPCT E  and conduction time difference on the central side ΔPCT C  calculated in the above-mentioned steps of SC 4  through SC 6  are given graphically on the display  74 . 
   Then, steps of SC 8  through SC 12  equivalent to the vascular endothelial dysfunction judgment means and vascular endothelial dysfunction judgment step are carried out. In SC 8 , respectively averaged are the conduction time difference on the peripheral side ΔPCT E  and the conduction time difference on the central side ΔPCT C  for 3 minutes before start of ischemia, with regard to the conduction time difference on the peripheral side ΔPCT E  and the conduction time difference on the central side ΔPCT C  for 5 minutes before ischemia calculated in SC 6 . 
   Then, in the subsequent SC 9 , the respective determinations are made for the peak of the conduction time difference on the peripheral side ΔPCT E  after release from ischemia and the peak of the conduction time difference on the central side ΔPCT C  after release from ischemia calculated in SC 6 . Then, in SC 10 , the average of the conduction time difference on the peripheral side ΔPCT E  for 3 minutes before ischemia calculated in SC 8  is subtracted from the peak of the conduction time difference on the peripheral side ΔPCT E  after the release from ischemia determined in SC 9  to calculate a difference between the conduction time difference on the peripheral side PCT E  before ischemia and that after ischemia. Further, the average of the conduction time difference on the central side ΔPCT C  for 3 minutes before ischemia calculated in SC 8  is subtracted from the peak of the conduction time difference on the central side ΔPCT C  after release from ischemia determined in SC 9  to calculate a difference between the conduction time difference on the central side ΔPCT C  before ischemia and that after ischemia. 
   Then, in the subsequent SC 11 , where a difference between the conduction time difference on the peripheral side ΔPCT E  before ischemia and that after ischemia as calculated in the above SC 10  is at or lower than a predetermined judgment standard value for the conduction time difference on the peripheral side ΔPCT E , it is judged that the vascular endothelial function in the segment from the left upper arm to the left wrist are impaired. Where the difference between the conduction time difference on the peripheral side ΔPCT E  before ischemia and that after ischemia is greater than the predetermined judgment standard value, it is judged that the vascular endothelial function in the segment from the left upper arm to the left wrist are normal. Further, where the difference between the conduction time difference on the central side ΔPCT C  before ischemia and that after ischemia calculated in the above SC 10  is at or lower than the predetermined judgment standard value for the conduction time difference on the central side ΔPCT C , it is judged that the vascular endothelial function in the segment from the heart to the left upper arm are impaired. Where the difference between the conduction time difference on the central side ΔPCT C  before ischemia and that after ischemia is greater than the predetermined judgment standard value, it is judged that the vascular endothelial function from the heart to the left upper arm are normal. Then, in SC 12 , the message showing the results obtained in the above SC 1  are displayed on the display  74 . 
   According to the above third embodiment, in SC 6  (comparative value calculating means and comparative value calculation step), the pulse-wave conduction time on the left peripheral side PCT LE  at the first segment closer to the peripheral side than the left upper arm, which is a site of arterial occlusion, pulse-wave conduction time on the right peripheral side PCT RE  at the second segment, which constitutes a pair with the first segment, are referred to calculate a conduction time difference on the peripheral side ΔPCT E  (comparative value) before and after ischemia closer to the peripheral side than the site of arterial occlusion. In addition, the pulse-wave conduction time on the left central side PCT LC  and the pulse-wave conduction time on the right central side PCT RC  before and after ischemia are respectively calculated at the third segment on the central side of the left brachial artery and at the fourth segment, which constitutes a pair with the third segment. In SC 6  (comparative value calculating means and comparative value calculation step), the pulse-wave conduction time on the left central side PCT LC  and pulse-wave conduction time on the right central side PCT RC  are referred to calculate the conduction time difference on the central side ΔPCT C  (comparative value) before and after ischemia on the central side. Therefore, it is possible to separate the vascular endothelial function of the left brachial artery into those on the peripheral side and those on the central side and also make a simultaneous evaluation of them. 
   An explanation has been made in detail about the embodiments of this invention by referring to the drawings, however, other embodiments may be applied to the invention. 
   For example, in the above embodiments, a reactive hyperemia after transient ischemia is used to attain an increase in the arterial blood flow as a type of stimulation for inducing the release of endothelium-derived relaxing factors from vascular endothelium. A necessary hyperemic reaction can be obtained by warming or exercise of the hand. Thus, such warming or exercise may be used in place of arterial occlusion (ischemia) inducing reactive hyperemia. Further, in addition to inducing the release of endothelium-derived relaxing factors from vascular endothelium by the blood flow increasing response, administration of drugs such as acetylcholine is able to induce the release of endothelium-derived relaxing factors from vascular endothelium. Thus, these drugs may be administered in place of a type of stimulation for releasing endothelium-derived relaxing factors. Such administration methods include direct arterial injection, application of a drug on the skin at a specified region to be stimulated and systemic administration, for example, a method by which the blood flow into the above region can be blocked only for a period when blood concentrations of the drug are relatively high to prevent delivery of the drug into local areas for a certain period only. 
   Increased blood flow by reactive hyperemia is a type of stimulation for inducing the release of endothelium-derived relaxing factors. In contrast, stimulations may be given for inhibiting the release of endothelium-derived relaxing factors and for inhibiting the vascular dilation due to the release of endothelium-derived relaxing factors. When such stimulations are applied, since these stimulations are common to the previously-described embodiments in that a stimulus is given to change a diameter of the blood vessel, they can provide the same effect as obtained in the previously-described embodiments. These stimulations include administration of drugs, oxidation stress, inflammable cytokines (for example, interleukin 1, interleukin 6 and tumor necrosis factors) and hypoxia. In this instance, the oxidation stress takes place by smoking, mental stress, high levels of low-density lipoprotein and ischemic reperfusion. The drugs include nitrogen monoxide synthetase inhibitors which inhibit the release of nitrogen monoxide which is an endothelium-derived relaxing factor, a nitric acid agent which gives a prior saturation to vasodilation response due to endogenous endothelium-derived relaxing factors and nitrogen monoxide by itself. The drugs may be administered similarly as those inducing the release of the previously-described endothelium-derived relaxing factors. 
   In the previous embodiments, pulse-wave conduction time PCT is computed after all the signals are collected for measuring the pulse-wave conduction time PCT. The pulse-wave conduction time PCT may also be computed for each reading of a pulse or a few pulses. 
   In the previous embodiments, the pulse-wave conduction time PCT is calculated as pulse-wave-conduction-velocity-relating information. Pulse wave conduction velocity PWV may also be calculated in place of the pulse-wave conduction time PCT. 
   In the previous embodiments, the arterial occlusion apparatus  82  is used to carry out arterial occlusion at the upper arm. It may be also possible to carry out arterial occlusion at the forearm, wrist, femoral region, lower leg and ankle. Where arterial occlusion is carried out at these regions, arteries at occlusion sites (for example, the femoral artery) or arteries connecting with their upstream or downstream arteries undergo an increase in blood flow after the release from occlusion. Sites to be stimulated by increased blood flow are the arteries of occlusion sites and arteries connecting with their upstream or downstream arteries. Thus, in the first segment, the end of the upstream side includes, for example, the base of ascending aorta, cervical portion and upper arm, whereas the end of the downstream includes ankle and tips of the digits at the side where reactive hyperemia is carried out. Further, where arterial occlusion is carried out at the upper arm as explained in the previous embodiment, the first segment or the third segment is not restricted by the previous embodiments, and the end of the upstream in the first segment and the end of the downstream in the third segment may be the cervical portion, or the end of the downstream in the first segment may be the tips of the fingers. 
   In the previous embodiments, an electrocardiograph is used as a heartbeat-synchronous signal detection apparatus for detecting the electrocardiographic signal SE as a heartbeat-synchronous signal. A phonocardiographic microphone may be used as a heartbeat-synchronous signal detection apparatus for measuring a cardiac sound signal (phonocardiogram). 
   Further, in the previous first embodiment, the conduction time difference ΔPCT is calculated by subtracting the right pulse-wave conduction time PCT R  from the left pulse-wave conduction time PCT L . The conduction time difference ΔPCT may also be calculated by subtracting the left pulse-wave conduction time PTC L  from the right pulse-wave conduction time PTC R . Similarly, in the second embodiment, the conduction time ratio R (PCT) may be calculated by dividing the right pulse-wave conduction time PTC R  by the left pulse-wave conduction time PCT L . 
   In the previous embodiments, the conduction time difference ΔPCT before start of ischemia (or conduction time ratio R (PCT)) is subtracted from the peak of the conduction time difference ΔPCT after the release from ischemia (or conduction time ratio R (PCT)) to calculate the difference. It may be also possible that the peak of the conduction time difference ΔPCT after the release from ischemia (or conduction time ratio R (PCT))is subtracted from the conduction time difference ΔPCT before start of ischemia (or conduction time ratio R (PCT)) to obtain the difference. 
   In the previous embodiments, the display  74  is used as an output apparatus. It may be also possible that the output apparatus is a printer. 
   It is further to be understood that various other changes may be made in the present invention, without departing from the spirit of the present invention.