Abstract:
A blood rheology measurement device measures a blood rheology of blood flowing through an artery inside of a living body from outside of the living body. The blood rheology measurement device has a sensor that detects a flow rate of blood flowing through the artery and a pulsatile displacement that varies with an elapse of time. The pulsatile displacement corresponds to a displacement of the artery in a diameter direction thereof due to expansion and contraction of the artery resulting from a pulsatile motion of the heart. A calculating section calculates the blood rheology of blood flowing through the artery on the basis of the blood flow rate and the pulsatile displacement detected by the sensor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to measurement device and method of a body fluid circulating in a living body, more particularly to a blood rheology measurement device and a blood rheology measurement method for use in grasping a condition of blood to perform evaluation of health, diagnosis of disease, evaluation of effects of medicine and the like. 
     2. Description of the Related Art 
     As one of inspection items for judging a human health condition, there has been noted blood rheology measurement focusing on a fluidity of blood. As means for measuring blood rheology, there is developed a micro channel array type blood fluidity measurement device to measure a time for which a certain amount of blood sampled from a subject passes through a micro channel array (see, e.g., “Measurement of Fluidity of Whole Blood by use of Capillary Blood Vessel Model” by Yuji Kikuchi (Food Research Result Information, No. 11 issued in 1999)). At present, the micro channel array type blood fluidity measurement device is regarded as a standard machine in blood rheology measurement. 
     However, in the measurement by the micro channel array type blood fluidity measurement device, it is surely necessary to sample the blood. The measurement is performed by a medical institution only, and anyone cannot readily inspect the health condition anywhere. The sampling of the blood imposes a large physical and mental burden on the subject, and a limit of the number of times when the measurement can be performed per day is several times at most. Therefore, there is a problem that data continued in time series cannot be easily obtained. 
     In addition, it is considered that there is a strong correlation between the blood rheology and a blood flow rate in a living body. That is, it is considered that the blood flow rate is slow at a high viscosity of the blood, and high at a low viscosity. Therefore, the measurement of the blood flow rate in the living body indirectly makes it possible to known the blood rheology (see, e.g., Japanese Patent Application Laid-Open No. 2003-159250). 
     On the other hand, to calculate an index of the blood rheology on the basis of the blood flow rate in a blood vessel, in addition to the measurement of the blood flow rate, it is necessary to perform measurement of a blood pressure of the living body by use of a cuff as described in Japanese Patent Application Laid-Open No. 2003-159250. As a method of calculating the blood rheology, that is, an index of kinematic viscosity of the blood by use of this blood pressure value and the blood flow rate, there is a method based on a concept that a blood flow pressure in an artery as an object is approximated by means of the blood pressure value. 
     However, in the method of calculating the blood rheology, that is, the index of the kinematic viscosity of the blood by use of the blood pressure value and the blood flow rate, there is a problem that a measurement error is large because the blood flow pressure in the artery is approximated by means of the blood pressure value. Furthermore, it is essential to miniaturize the device which measures the blood rheology of a portion such as wrist or fingertip, but this is disadvantageously difficult from viewpoints of a mechanism for the blood pressure measurement, intricacy of the mechanism and the like. 
     Consequently, an object of the present invention is to provide a miniaturized blood rheology measurement device and a blood rheology measurement method which are capable of simply measuring blood rheology of a portion such as wrist or fingertip with a high precision without requiring blood pressure measurement. 
     SUMMARY OF THE INVENTION 
     To solve the above-described problem, the present invention is, characterized by: detecting an artery blood flow rate, a pulsatile displacement, an artery diameter, an artery wall thickness, a heartbeat frequency, and a phase difference or an amplitude ratio of the blood flow rate and the pulsatile displacement, which change with elapse of time, by use of a sensor including ultrasonic wave transmitting and receiving elements for transmitting and receiving ultrasonic waves between the surface of a living body and an artery blood flow in the living body; and calculating a blood kinematic viscosity by use of one of the phase difference and the amplitude ratio, the blood vessel diameter, and the heartbeat frequency to obtain an index value of a blood rheology. 
       FIG. 11  is a characteristic diagram showing effects of the present invention. There is shown a correlation between a kinematic viscosity υ which is an index value of blood rheology calculated from the phase difference of the blood flow rate and the pulsatile displacement measured by the blood rheology device in the present invention and a whole blood passing time T which is an index of blood rheology by a blood sampling system by use of a micro channel array. The ordinate indicates υ. In  FIG. 11 , a value of υ is small close to an origin of the ordinate, and the value of υ is large when ascending the ordinate. As described in detail, the small value of υ means that a viscosity of blood is large. 
     On the other hand, the abscissa indicates a whole blood passing time T. In  FIG. 11 , a value of T is small close to the origin of the ordinate, and the value of T is large on the right side. That is, the small value of the whole blood passing time T means that the blood being measured is fluid blood. That is, υ indicates a large value. On the other hand, the large value of the whole blood passing time T means that the blood being measured is viscous blood having a high viscosity. That is, the high viscosity indicates the small value of υ. In consideration of these relations, as shown in  FIG. 11 , it can be considered that there is a significant correlation between υ and the whole blood passing time T. 
     Therefore, as seen from  FIG. 11 , the blood rheology measurement device of the present invention is capable of measuring the blood rheology of wrist or fingertip with a good precision without, requiring blood pressure measurement. Therefore, it is possible to supply a simple, high-precision, and miniature blood rheology measurement device. As a result, anyone other than a specialist can readily check rheology correctly without sampling the blood from a subject, and the device is usable in checking a health condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a constitution of a blood rheology measurement device in the present invention; 
         FIG. 2  is a second block diagram showing a constitution of a blood rheology measurement device in the present invention; 
         FIG. 3  is a schematic diagram of an artery which pulsates in synchronization with a heartbeat in the present invention; 
         FIG. 4  is a characteristic diagram showing calculation processing for calculating an index of a blood rheology in the present invention; 
         FIG. 5  is a characteristic diagram showing the calculation processing for calculating the index of the blood rheology in the present invention; 
         FIG. 6  is a schematic diagram showing the calculation processing for calculating the index of the blood rheology in the present invention; 
         FIG. 7  is a schematic diagram showing the calculation processing for calculating the index of the blood rheology in the present invention; 
         FIG. 8  is a schematic diagram showing a structure of a sensor unit and blood rheology measurement in the present invention; 
         FIG. 9  is a second schematic diagram showing the structure of the sensor unit and the blood rheology measurement in the present invention; 
         FIG. 10  is an explanatory view showing a blood flow rate waveform and a pulsatile displacement waveform in the present invention; and 
         FIG. 11  is a characteristic diagram showing effects of the present invention. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1  ultrasonic sensor 
           2  transmitting element 
           3  receiving element 
           4  ultrasonic sensor 
           5  transmitting element 
           6  receiving element 
           7  ultrasonic sensor 
           8  transmitting element 
           9  receiving element 
           10  continuous ultrasonic wave transmitting circuit 
           11  continuous ultrasonic wave detecting circuit 
           12  ultrasonic wave circuit 
           13  burst generation circuit 
           14  burst detecting circuit 
           15  ultrasonic wave burst circuit 
           16  blood flow rate calculation processing unit 
           17  blood vessel information calculation processing unit 
           18  rheology calculation processing unit 
           19  waveform information calculation processing unit 
           20  heartbeat calculation processing unit 
           21  parameter calculation processing unit 
           22  rheology index calculation processing unit 
           23  output unit 
       
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a block diagram of a constitution of a blood rheology measurement device in the present invention. A sensor unit is constituted of a pair of wave sensors  1  and  4 , and an ultrasonic sensor  7  independent of the pair of ultrasonic sensors. The ultrasonic sensor  1  is constituted of a transmitting element  2  and a receiving element  3 , the ultrasonic sensor  4  is constituted of a transmitting element  5  and a receiving element  6 , and the ultrasonic sensor  7  is constituted of a transmitting element  8  and a receiving element  9 . The transmitting elements  2  and  5  are connected to a continuous ultrasonic wave generation circuit  10 , an electric signal generated by the continuous ultrasonic wave generation circuit  10  is converted into a mechanical ultrasonic wave, and the ultrasonic wave is transmitted into a living body. 
     An ultrasonic signal reflected by a blood flow in an artery and involving the Doppler signal is converted into the electric signal by the receiving elements  3  and  6 , the signal is input into a continuous ultrasonic wave detecting circuit  11 , and the Doppler electric signal is detected. An ultrasonic wave circuit  12  is constituted of two types of circuits which are the continuous ultrasonic wave generation circuit  10  and the continuous ultrasonic wave detecting circuit  11 . A burst generation circuit  13  outputs an electric burst signal to the connected transmitting element  8  to drive the transmitting element  8 . The transmitting element  8  converts the electric burst signal into an ultrasonic burst signal to emit the ultrasonic burst signal into the living body. The emitted ultrasonic burst signal is reflected by the artery, and converted into the electric signal by the receiving element  9 . Thereafter, the signal is input into a burst detecting circuit  14 , and the burst ultrasonic wave reflected by the artery is detected as the electric signal in the burst detecting circuit  14 . An ultrasonic burst circuit  15  is constituted of two types of circuits which are the burst generation circuit  13  and the burst detecting circuit  14 . 
     The Doppler electric signal detected by the continuous ultrasonic wave detecting circuit  11  includes a blood flow rate signal component which involves a periodic change synchronized with a living body heartbeat. A device for separately extracting the electric signal corresponding to a blood flow rate, that is, a blood flow rate signal from the Doppler electric signal is a blood flow rate calculation processing unit  16 . The electric signal corresponding to the reflected burst ultrasonic wave detected by the burst detecting circuit  14  includes artery pulsatile displacement and shape information involving the periodic change synchronized with the living body heartbeat. A device for separately extracting the artery pulsatile displacement and shape information from the electric signal is a blood vessel information calculation processing unit  17 . 
     The blood flow rate signal output from the blood flow rate calculation processing unit  16  and a blood vessel information signal output from the blood vessel information calculation processing unit  17  are input into a rheology calculation processing unit  18  of the present invention. The rheology calculation processing unit  18  is constituted of: a waveform information calculation processing unit  19 ; a heartbeat frequency calculation processing unit  20 ; a parameter calculation processing unit  21 ; and a rheology index calculation processing unit  22 . A rheology index detected by the rheology calculation processing unit  18  is output via an output unit  23 . As described above,  FIG. 1  shows an embodiment in which the ultrasonic sensor unit for measuring the blood flow rate and the ultrasonic sensor for measuring blood vessel information are disposed independently of each other. 
       FIG. 2  shows a block diagram of a constitution of a second blood rheology measurement device in the present invention. A sensor unit is constituted of a pair of ultrasonic sensors  1  and  24 . A transmitting element  25  and a receiving element  26  constituting the ultrasonic sensor  24  are connected to both of an ultrasonic wave circuit  12  and an ultrasonic burst circuit  15  via a switch circuit  27 . This switch circuit  27  periodically switches a circuit to be connected to the ultrasonic sensor  24  to the ultrasonic wave circuit  12  or the ultrasonic burst circuit  15 . 
     That is, the ultrasonic sensor  24  comes to have a function of both of blood flow rate detection and blood vessel information detection. A blood flow rate is detected based on measurement of the Doppler deflection amount of an ultrasonic frequency, and blood vessel information is detected based on measurement of a delay time or the like of a reflected burst wave. Therefore, a time width capable of measuring these measurement physical amounts may be set to a switching period of the switch circuit  27  shown in  FIG. 2 , and this is merely a design matter.  FIG. 2  shows an embodiment in which the ultrasonic sensor unit for measuring the blood flow rate also has a sensing function of measuring the blood vessel information. 
     The embodiments have been described above in which a plurality of ultrasonic sensors for measuring the blood flow rate are used. However, the present invention is not especially limited to the use of the plurality of ultrasonic sensors. For example, one ultrasonic sensor, that is, the only ultrasonic sensor  1  constituted of the transmitting element  2  and the receiving element  3  may be used. However, two ultrasonic sensors are preferably used as in the present embodiment. This is because when two ultrasonic sensors are used as in the present embodiment ( FIGS. 8 and 9 ) in which the sensors are disposed at such angles that ultrasonic wave emitting directions and recording sensitivity orientation directions are not parallel to one another, an unseen flowing direction in the blood vessel is specified, and high-precision measurement can be stably performed irrespective of a finger contact position. 
     First, there will be described hereinafter a theoretical background of calculation processing performed by the rheology calculation processing unit  18  in the present invention.  FIG. 3  is a schematic diagram of an artery which pulsates in synchronization with heartbeats. On the basis of a pressure distribution  29  in an artery  28 , the blood flow generates a blood flow rate distribution  30  in a Z-axis direction which is an axial direction of the artery and radial directions. Needless to say, this pressure distribution  29  is correlated with a blood pressure value. Furthermore, since an artery wall  31  has elasticity, the artery wall  31  causes a vibration displacement in the Z-axis direction and the radial directions. This vibration displacement is a shown pulsatile displacement  32 . Furthermore, the pulsatile displacement  32  propagates as a wave through the artery wall in the Z-axis direction together with pulses. This wave is a pulse wave  33 . In  FIG. 1 , it is possible to analytically obtain the pressure distribution  29 , the blood flow rate distribution  30 , and the pulsatile displacement  32  in accordance with the Navier Stokes equation in hydromechanics and a dynamic equation of the artery wall. That is, assuming that: a heartbeat angular frequency is ω; a pulse wave number is k; an inner diameter of the artery  28  is R; a thickness, Young&#39;s modulus, density, and Poisson&#39;s ratio of the artery wall  31  are h, E, ρ 0 , and σ, respectively; the pressure distribution  29  of the artery  28  is P; an axial-direction rate component of the blood flow rate distribution  30  is V; and the pulsatile displacement of the artery radius direction is ξ, P, V, and ξ are determined in accordance with the following equation by use of the Bessel function J 0 : 
                   P   =       P   0     +       P   m     ⁢       J   0     ⁡     (   kr   )       ⁢     ⅇ     j   ⁡     (       ω   ⁢           ⁢   t     -   kz     )                     Equation   ⁢           ⁢     (   1   )                 V   =         R     ρ   ⁢           ⁢   Eh         ⁢     Φ     ⁢       P   m     [     1   +           J   0     ⁡     (     j   ⁢     j     ⁢   α   ⁢     r   R       )           j   0     ⁡     (     j   ⁢     j     ⁢   α     )         ⁢       [       2   ⁢     1             ⁢   Φ       ⁢     (     1   -     σ             ⁢   2         )       -     (     1   -     2   ⁢           ⁢   σ       )       ]       (     F   -     2   ⁢           ⁢   σ       )           ]     ⁢     ⅇ     j   ⁡     (       ω   ⁢           ⁢   t     -   kz     )                   Equation   ⁢           ⁢     (   2   )                   ξ   =       P   m     ⁢       R   2     Eh     ⁢       (       F   ⁢           ⁢   Φ   ⁢           ⁢   σ     -     F   ⁢           ⁢     σ   2       +   F   -     Φ   ⁢           ⁢   σ       )       (     F   -     2   ⁢           ⁢   σ       )       ⁢     ⅇ     j   ⁡     (       ω   ⁢           ⁢   t     -   kz     )             ,           Equation   ⁢           ⁢     (   3   )                 
wherein φ and F are dimensionless functions defined in accordance with the following equation:
 
                         Φ   =       ⁢       (         1   2     ⁢   γ     +   σ   -     1   4     +       5   -     4   ⁢           ⁢   σ         4   ⁢     (     1   -   F     )           )     +                     ⁢           (         -     1   2       ⁢   γ     -   σ   +     1   4     +           -   4     ⁢           ⁢   σ     +   5         4   ⁢   F     -   4         )     2     -       (     1   -     σ   2       )     ⁢     (           2   ⁢           ⁢   γ     +   1       1   -   F       -   1     )                         Equation   ⁢           ⁢     (   4   )                 F   =     2   ⁢         ∑     n   =   0     ∞     ⁢     [         (     -   1     )     n     ⁢     1       P   n           n         ⁢     Γ   ⁡     (     1   +   n   +   1     )           ⁢       (         j     3   2       ⁢   α     2     )       1   +     2   ⁢   n           ]           j     3   2       ⁢   α   ⁢       ∑     n   =   0     ∞     ⁢     [         (     -   1     )     n     ⁢     1       P   n           n         ⁢     Γ   ⁡     (     n   +   1     )           ⁢       (         j     3   2       ⁢   α     2     )       2   ⁢   n         ]                     Equation   ⁢           ⁢     (   5   )                 
Moreover; assuming that the artery wall thickness is h, the artery wall density is ρ 0 , and the artery radius is R, a dimensionless parameter is defined in accordance with the following equation:
 
                   γ   =         ρ   o     ⁢   h       ρ   ⁢           ⁢   R               Equation   ⁢           ⁢     (   6   )                 
Furthermore, α can be defined as follows by use of the blood kinematic viscosity υ, the heartbeat frequency ω, and the radius R:
 
     
       
         
           
             
               
                 
                   α 
                   = 
                   
                     R 
                     ⁢ 
                     
                       
                         ω 
                         v 
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     7 
                     ) 
                   
                 
               
             
           
         
       
     
     Each of the blood flow rates detected in the embodiments shown in  FIGS. 1 and 2  is detected as a waveform having, as an amplitude, a maximum rate component in the blood flow rate distribution V given by the equation (2). This maximum rate component V m  is approximately given by the following equation. 
                       V   m     =         R     ρ   ⁢           ⁢   Eh         ⁢     Φ     ⁢       P   m     ⁡     [     1   +       K       J   0     ⁡     (     j   ⁢     j     ⁢   α     )         ⁢       [       2   ⁢     (     1   -     σ   2       )       -     Φ   ⁡     (     1   -     2   ⁢           ⁢   σ       )         ]       Φ   ⁡     (     F   -     2   ⁢           ⁢   σ       )             ]       ⁢     ⅇ     j   ⁡     (       ω   ⁢           ⁢   t     -   kz     )             ,           Equation   ⁢           ⁢     (   8   )                 
wherein K is not described in detail, but indicates a value which depends on a value of α in a range of 0.65 to 1.
 
     From the above-described analysis results, a phase difference δ between the maximum rate component V m  and the pulsatile displacement ξ in the axial direction, which periodically fluctuates in synchronization with the heartbeat angular vibration ω in the artery, is determined in accordance with the equation (9) from the equations (3) and (8). 
                         δ   =       ⁢       arg   ⁡     (       Φ     +       K       J   0     ⁡     (     j   ⁢     j     ⁢   α     )         ⁢       [       2   ⁢     (     1   -     σ   2       )       -     Φ   ⁡     (     1   -     2   ⁢           ⁢   σ       )         ]         Φ     ⁢     (     F   -     2   ⁢           ⁢   σ       )             )       -                     ⁢     arg   ⁡     (         F   ⁢           ⁢   Φ   ⁢           ⁢   σ     -     F   ⁢           ⁢     σ   2       -   F   -     Φ   ⁢           ⁢   σ         F   -     2   ⁢           ⁢   σ         )                     Equation   ⁢           ⁢     (   9   )                 
It is found that this phase difference δ is determined by only dimensionless constants α, σ, and γ irrespective of the pressure amplitude P m  in the artery. This is because the dimensionless functions F and Φ appearing in the equation (9) are functions of α, σ, and γ.
 
     Moreover, an amplitude ratio μ of the maximum rate distribution V m  and the pulsatile displacement ξ in the axial direction, which periodically fluctuates in synchronization with the heartbeat angular vibration ω in the artery, is similarly determined in accordance with the (equations (10) and (11) from the equations (3) and (8). 
                   μ   =       1   R     ⁢         E   ρ     ⁢     h   R         ⁢   Γ             Equation   ⁢           ⁢     (   10   )                   Γ   =       abs   ⁡     [       Φ     +       K       J   0     ⁡     (     j   ⁢     j     ⁢   α     )         ⁢       [       2   ⁢     (     1   -     σ   2       )       -     Φ   ⁡     (     1   -     2   ⁢           ⁢   σ       )         ]         Φ     ⁢     (     F   -     2   ⁢           ⁢   σ       )             ]         abs   ⁡     [       (       F   ⁢           ⁢   Φ   ⁢           ⁢   σ     -     F   ⁢           ⁢     σ   2       +   F   -     Φ   ⁢           ⁢   σ       )       (     F   -     2   ⁢           ⁢   σ       )       ]           ,           Equation   ⁢           ⁢     (   11   )                 
wherein Γ denotes a standardized amplitude ratio. It is found that this amplitude ratio μ is determined by the only artery inner diameter R, artery wall thickness h, blood density ρ, artery Young&#39;s modulus E, and dimensionless constants α, σ, and γ irrespective of the pressure amplitude P m  in the same manner as in the phase difference δ given by the equation (9).
 
       FIG. 4  is a characteristic diagram obtained by theoretically calculating dependence, on α, of the phase difference δ between the maximum blood flow rate V m  and the pulsatile displacement ξ, calculated in accordance with the equation (9), and is a characteristic diagram showing calculation processing of an index of the blood rheology in the present invention. The ordinate indicates α, and the abscissa indicates the phase difference δ. It is found that a characteristic curve  34 -A of this characteristic diagram does not change largely with the following typical values of σ and γ of a living tissue, and is substantially determined by a change of the value of α:
 
σ=0.4 to 0.6, and γ=0.0 to 0.3.
 
As defined by the equation (7), α is determined by the heartbeat vibration ω, the blood kinematic viscosity υ, and the artery inner radius R. Therefore, when the phase difference δ, the heartbeat vibration ω, and the artery inner diameter R are measured, the blood kinematic viscosity υ can be detected irrespective of the pressure P in the artery. That is, the blood kinematic viscosity υ can be detected without measuring the blood pressure.
 
       FIG. 5  is a characteristic diagram obtained by theoretically calculating a relation between the standardized amplitude ratio Γ of the maximum blood flow rate Vm and the pulsatile displacement ξ calculated by the equation (11) and α defined by the equation (7), and is a characteristic diagram for calculating the index of the blood rheology in the present invention. The ordinate indicates α, and the abscissa indicates the standardized amplitude ratio Γ. It is found that a characteristic curve  34 -B of this characteristic diagram does not change largely with the following typical values of σ and γ of the living tissue, and is substantially determined by the change of the value of α:
 
σ=0.4 to 0.6, and γ=0.0 to 0.3.
 
As defined by the equation (7), α is determined by the heartbeat vibration ω, the blood kinematic viscosity υ, and the artery inner radius R. Therefore, when the standardized amplitude ratio Γ, the heartbeat vibration ω, the artery inner diameter R, and the artery wall thickness h are measured, the Young&#39;s modulus E and the blood density ρ in the living tissue hardly have any individual difference, and are regarded as certain values. Therefore, the blood kinematic viscosity υ can be detected irrespective of the pressure P in the artery. That is, the blood kinematic viscosity υ can be detected without measuring the blood pressure in the same manner as in the phase difference.
 
     Incidentally, in a conventional method of detecting the blood rheology, the maximum blood flow rate V m  calculated in accordance with the equation (2) is divided by the blood pressure value instead of the pressure amplitude P m . The theoretical background of the calculation processing in the present invention has been described above. Moreover, j appearing in the equations (1) to (9) is an imaginary number (square root of −1), and the calculated value is a complex number, but needless to say, an actually significant physical amount is a real part in the same manner as in an alternating current theory of electronic engineering. 
       FIGS. 6 and 7  are principle diagrams showing the calculation processing in the blood vessel information calculation processing unit  17  of the blood rheology measurement device in the present invention.  FIG. 6  is a principle diagram in a case where there is used the ultrasonic sensor  7  for measuring the blood vessel information in the blood rheology measurement device of the present invention described with reference to  FIG. 1 . 
     The transmitting element  8  of the ultrasonic wave of the ultrasonic sensor  7  attached to skin  35  emits a transmission burst wave  36  to an artery  37 . Since the emitted ultrasonic burst wave is reflected by an artery outer wall  38  and an artery inner wall  39  of the artery  37 , four types of reflected burst waves are detected by the receiving element  9 . These four types of reflected burst waves are a first reflected burst wave  40 , a second reflected burst wave  41 , a third reflected burst wave  42 , and a fourth reflected burst wave  43 . Among these four types of reflected burst waves, the first and fourth reflected burst waves  40  and  43  are waves reflected by the artery outer wall  38  of the artery  37 , and the second and third reflected burst waves  41  and  42  are waves reflected by the artery inner wall  39 . In  FIG. 6 , a distance between the artery  37  and the skin  35  is an artery distance  44 , and an angle between the artery  37  and the skin  35  is an artery angle  45 . 
     These four types of reflected burst waves are detected by the receiving element  9  at different times.  FIG. 7  is a characteristic diagram showing output intensities of four types of burst waves observed by the receiving element  9 . In  FIG. 7 , the ordinate indicates signal intensities of a reflected burst signal waveform  46  and a transmitted burst signal waveform  51 , and the abscissa indicates time. The transmission burst wave  36  described with reference to  FIG. 6  is periodically emitted from the transmitting element  8  into the living body. This emission period ε is sufficiently smaller than a heartbeat period. A time when an n-th transmission burst wave  36  is emitted is a time T n  when the transmitted burst waveform  51  described with reference to  FIG. 7  appears. The signal intensity of the transmitted burst waveform  51  is V n . Here, assuming that a first burst wave emission time is 0, the n-th burst wave emission time T n  is as follows by use of the emission period ε:
 
T n =εn (1 2)              Equation (12)

     The reflected burst signal waveform  46  reflected by the artery  37  has four peak outputs. That is, they are a first reflected burst signal  47 , a second reflected burst signal  48 , a third reflected burst signal  49 , and a fourth reflected burst signal  50 . In this case, the first reflected burst wave  40  corresponds to the first reflected burst signal  47 , the second reflected burst wave  41  corresponds to the second reflected burst signal  48 , the third reflected burst wave  42  corresponds to the third reflected burst signal  49 , and the fourth reflected burst wave  43  corresponds to the fourth reflected burst signal  50 . The first to fourth reflected burst signals appear behind the appearance time T n  of the transmitted burst signal waveform  51 , and are observed at time T n   (1) , T n   (2) , T n   (3) , and T n   (4) , respectively. However, this delay amount is sufficiently smaller than the emission period of the transmission burst wave  36 . Signal intensities are V n   (1) , V n   (2) , V n   (3) , and V n   (4) , respectively. 
     The artery  37  described with reference to  FIG. 6  pulsates accompanying the periodic motion of the heart. Therefore, the times T n   (1)  to T n   (4)  when the signal waveforms appear and the signal intensities V n   (1)  to V n   (4)  periodically change with respect to time. This time period is nothing but the heartbeat period of the living body. 
     In the blood vessel information calculation processing unit  17  described with reference to  FIGS. 1 and 2  in the present invention, the reflected burst signal waveform  46  and the transmitted burst signal waveform  51  described with reference to  FIG. 7  are measured at arbitrary times. As waveform information, the times T n   (1)  to T n   (4)  when the signal waveforms appear and the signal intensities V n   (1)  to V n   (4)  are measured. Parameters shown in Table 1, that is, delay time differences Δτ and signal intensity ratios are detected from these measured values. 
                                                   TABLE 1                       Delay time   Signal intensity           difference Δτ   ratio                                        First reflected   Δτ 1 (n) = T n   (1)  − T n     a 1 (n) = V n   (1) /V n             burst signal           Second reflected   Δτ 2 (n) = T n   (2)  − T n   (1)     a 2 (n) = V n   (2) /V n             burst signal           Third reflected   Δτ 3 (n) = T n   (3)  − T n   (2)     a 3 (n) = V n   (3) /V n             burst signal           Fourth reflected   Δτ 4 (n) = T n   (4)  − T n   (3)     a 4 (n) = V n   (4) /V n             burst signal                        
Numeric values shown in Table 1 are measured every emission of the transmitted burst signal waveform  51 . The number of times of emission is a sampling number. The blood vessel shape information and the pulsatile displacement of the artery  37  are detected using the parameters shown in Table 1. There will be described hereinafter calculation processing to detect the blood vessel shape information and the pulsatile displacement.
 
     The blood vessel shape information detected by the blood vessel information calculation processing unit  17  in the present invention are an artery inner diameter  52 , an artery outer diameter  53 , an artery wall thickness  54 , an artery wall thickness  55 , and a ratio (artery wall thickness/artery inner diameter) between the artery inner diameter and the artery wall thickness shown in  FIG. 6 . 
     The artery radius R in the above-described theoretical equations (1) to (11) is equal to a time average value of the artery inner diameters  52  detected by the blood vessel information calculation processing unit  17  in the present invention. The artery inner diameter  52  periodically changes in synchronization with the heartbeat frequency. The artery inner diameter  52  is proportional to a delay time difference Δτ 3 (n) between the second reflected burst signal  48  and the third reflected burst signal  49  shown in  FIG. 7 . That is, assuming that the artery inner diameter  52  at the n-th emission time of the transmission burst wave  36  is D 1  (n), the following equation results. 
                       D   1     ⁡     (   n   )       =       1   2     ⁢   C   ⁢           ⁢   Δ   ⁢           ⁢       τ   3     ⁡     (   n   )       ⁢           ⁢   sin   ⁢           ⁢   θ             Equation   ⁢           ⁢     (   13   )                 
From the time average value of D 1  (n), the artery inner diameter R is as follows:
 
                     R   =       1     4   ⁢   m       ⁢   C   ⁢           ⁢   sin   ⁢           ⁢   θ   ⁢       ∑     l   =   0       m   -   1       ⁢     Δ   ⁢           ⁢       τ   3     ⁡     (   l   )               ,           Equation   ⁢           ⁢     (   14   )                 
wherein m denotes the sampling number.
 
     Similarly, the artery outer diameter  53  is proportional to a delay time difference between the first reflected burst signal  47  and the fourth reflected burst signal  50  shown in  FIG. 7 . That is, the artery outer diameter is proportional to a sum of Δτ 2 (n), Δτ 3 (n), and Δτ 4 (n) shown in Table 1. Therefore, assuming that the artery outer diameter  53  at the n-th emission time of the transmission burst wave  36  is D 2  (n), the following equation results. 
                       D   2     ⁡     (   n   )       =       1   2     ⁢     C   ⁡     [       Δ   ⁢           ⁢       τ   2     ⁡     (   n   )         +     Δ   ⁢           ⁢       τ   3     ⁡     (   n   )         +     Δ   ⁢           ⁢       τ   4     ⁡     (   n   )           ]       ⁢           ⁢   sin   ⁢           ⁢   θ             Equation   ⁢           ⁢     (   15   )                 
From the time average value of D 2  (n), an average value D 2  of the artery outer diameters  53  is as follows:
 
     
       
         
           
             
               
                 
                   
                     D 
                     2 
                   
                   = 
                   
                     
                       1 
                       
                         2 
                         ⁢ 
                         m 
                       
                     
                     ⁢ 
                     
                       C 
                       ⁡ 
                       
                         [ 
                         
                           
                             
                               ∑ 
                               
                                 l 
                                 = 
                                 0 
                               
                               
                                 l 
                                 = 
                                 
                                   m 
                                   - 
                                   1 
                                 
                               
                             
                             ⁢ 
                             
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   τ 
                                   2 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   l 
                                   ) 
                                 
                               
                             
                           
                           + 
                           
                             
                               ∑ 
                               
                                 l 
                                 = 
                                 0 
                               
                               
                                 l 
                                 = 
                                 
                                   m 
                                   - 
                                   1 
                                 
                               
                             
                             ⁢ 
                             
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   τ 
                                   3 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   l 
                                   ) 
                                 
                               
                             
                           
                           + 
                           
                             
                               ∑ 
                               
                                 l 
                                 = 
                                 0 
                               
                               
                                 L 
                                 = 
                                 
                                   m 
                                   - 
                                   1 
                                 
                               
                             
                             ⁢ 
                             
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   τ 
                                   4 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   l 
                                   ) 
                                 
                               
                             
                           
                         
                         ] 
                       
                     
                     ⁢ 
                     sin 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     θ 
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     16 
                     ) 
                   
                 
               
             
           
         
       
     
     Furthermore, the artery wall thickness  54  is proportional to a time average of delay time differences between the first reflected burst signal  47  and the second reflected burst signal  48 , and the artery wall thickness  55  is proportional to a time average of delay time differences between the third reflected burst signal  49  and the fourth reflected burst signal  50 . That is, assuming that the average value of the artery wall thicknesses  54  is h 1 , and the average value of the artery wall thicknesses  55  is h 2 , the values are detected as follows. 
                     h   1     =       1     2   ⁢   m       ⁢   C   ⁢           ⁢   sin   ⁢           ⁢   θ   ⁢       ∑     l   =   0       m   -   1       ⁢     Δ   ⁢           ⁢       τ   2     ⁡     (   l   )                     Equation   ⁢           ⁢     (   17   )                   h   2     =       1     2   ⁢   m       ⁢   C   ⁢           ⁢   sin   ⁢           ⁢   θ   ⁢       ∑     l   =   0       m   -   1       ⁢     Δ   ⁢           ⁢       τ   4     ⁡     (   l   )                     Equation   ⁢           ⁢     (   18   )                 
Since h 1  is equal to h 2 , there is not any problem even in a case where either value is adopted as the value h of the artery wall thickness  31 . If the values largely differ from each other, there is not any problem even in a case where the average value of h 1  and h 2  is adopted. That is, the following equation may be established:
 
                   h   =       1   2     ⁢     (       h   1     +     h   2       )               Equation   ⁢           ⁢     (   19   )                 
Furthermore, a ratio h/R between the artery inner diameter R and the artery wall thickness h is obtained as follows by use of the equations (14), and (17) to (19):
 
     
       
         
           
             
               
                 
                   
                     
                       h 
                       
                         
                             
                         
                         ⁢ 
                         R 
                       
                     
                     = 
                     
                       
                         
                           
                               
                           
                           ⁢ 
                           
                             h 
                             
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                         
                         
                           
                               
                           
                           ⁢ 
                           R 
                         
                       
                       = 
                       
                         2 
                         ⁢ 
                         
                           
                             
                                 
                             
                             ⁢ 
                             
                               
                                 ∑ 
                                 
                                   l 
                                   ⁢ 
                                   
                                       
                                   
                                   = 
                                   
                                       
                                   
                                   ⁢ 
                                   0 
                                 
                                 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     m 
                                     ⁢ 
                                     
                                         
                                     
                                     - 
                                     
                                         
                                     
                                     ⁢ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   τ 
                                   
                                     
                                         
                                     
                                     ⁢ 
                                     2 
                                   
                                 
                                 ⁢ 
                                 
                                   ( 
                                   l 
                                   ) 
                                 
                               
                             
                           
                           
                             
                                 
                             
                             ⁢ 
                             
                               
                                 ∑ 
                                 
                                   l 
                                   ⁢ 
                                   
                                       
                                   
                                   = 
                                   
                                       
                                   
                                   ⁢ 
                                   0 
                                 
                                 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     m 
                                     ⁢ 
                                     
                                         
                                     
                                     - 
                                     
                                         
                                     
                                     ⁢ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   τ 
                                   
                                     
                                         
                                     
                                     ⁢ 
                                     3 
                                   
                                 
                                 ⁢ 
                                 
                                   ( 
                                   l 
                                   ) 
                                 
                               
                             
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   or 
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       h 
                       
                         
                             
                         
                         ⁢ 
                         R 
                       
                     
                     = 
                     
                       
                         
                           
                               
                           
                           ⁢ 
                           
                             h 
                             
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                         
                         
                           
                               
                           
                           ⁢ 
                           R 
                         
                       
                       = 
                       
                         2 
                         ⁢ 
                         
                           
                             
                                 
                             
                             ⁢ 
                             
                               
                                 ∑ 
                                 
                                   l 
                                   ⁢ 
                                   
                                       
                                   
                                   = 
                                   
                                       
                                   
                                   ⁢ 
                                   0 
                                 
                                 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     m 
                                     ⁢ 
                                     
                                         
                                     
                                     - 
                                     
                                         
                                     
                                     ⁢ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   τ 
                                   
                                     
                                         
                                     
                                     ⁢ 
                                     4 
                                   
                                 
                                 ⁢ 
                                 
                                   ( 
                                   l 
                                   ) 
                                 
                               
                             
                           
                           
                             
                                 
                             
                             ⁢ 
                             
                               
                                 ∑ 
                                 
                                   l 
                                   ⁢ 
                                   
                                       
                                   
                                   = 
                                   
                                       
                                   
                                   ⁢ 
                                   0 
                                 
                                 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     m 
                                     ⁢ 
                                     
                                         
                                     
                                     - 
                                     
                                         
                                     
                                     ⁢ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   τ 
                                   
                                     
                                         
                                     
                                     ⁢ 
                                     3 
                                   
                                 
                                 ⁢ 
                                 
                                   ( 
                                   l 
                                   ) 
                                 
                               
                             
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   or 
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       h 
                       
                         
                             
                         
                         ⁢ 
                         R 
                       
                     
                     = 
                     
                       
                         
                           
                             
                                 
                             
                             ⁢ 
                             
                               h 
                               
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                           
                           
                             
                                 
                             
                             ⁢ 
                             
                               2 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               R 
                             
                           
                         
                         ⁢ 
                         
                           ( 
                           
                             
                               h 
                               
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             + 
                             
                               h 
                               
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                           
                           ) 
                         
                       
                       = 
                       
                         
                           
                             
                                 
                             
                             ⁢ 
                             
                               
                                 
                                   ∑ 
                                   
                                     l 
                                     ⁢ 
                                     
                                         
                                     
                                     = 
                                     
                                         
                                     
                                     ⁢ 
                                     0 
                                   
                                   
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       m 
                                       ⁢ 
                                       
                                           
                                       
                                       - 
                                       
                                           
                                       
                                       ⁢ 
                                       1 
                                     
                                   
                                 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   Δ 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     τ 
                                     
                                       
                                           
                                       
                                       ⁢ 
                                       2 
                                     
                                   
                                   ⁢ 
                                   
                                     ( 
                                     l 
                                     ) 
                                   
                                 
                               
                               ⁢ 
                               
                                   
                               
                               + 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   ∑ 
                                   
                                     l 
                                     ⁢ 
                                     
                                         
                                     
                                     = 
                                     
                                         
                                     
                                     ⁢ 
                                     0 
                                   
                                   
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       m 
                                       ⁢ 
                                       
                                           
                                       
                                       - 
                                       
                                           
                                       
                                       ⁢ 
                                       1 
                                     
                                   
                                 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   Δ 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     τ 
                                     
                                       
                                           
                                       
                                       ⁢ 
                                       4 
                                     
                                   
                                   ⁢ 
                                   
                                     ( 
                                     l 
                                     ) 
                                   
                                 
                               
                             
                           
                           
                             
                                 
                             
                             ⁢ 
                             
                               
                                 ∑ 
                                 
                                   l 
                                   ⁢ 
                                   
                                       
                                   
                                   = 
                                   
                                       
                                   
                                   ⁢ 
                                   0 
                                 
                                 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     m 
                                     ⁢ 
                                     
                                         
                                     
                                     - 
                                     
                                         
                                     
                                     ⁢ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   τ 
                                   
                                     
                                         
                                     
                                     ⁢ 
                                     3 
                                   
                                 
                                 ⁢ 
                                 
                                   ( 
                                   l 
                                   ) 
                                 
                               
                             
                           
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     20 
                     ) 
                   
                 
               
             
           
         
       
     
     Next, there will be described calculation processing to detect the pulsatile displacement. The pulsatile displacement is detected from a change amount of the artery inner diameter  52  with elapse of time or a change amount of the artery outer diameter with elapse of time. That is, the amount is detected as follows by use of the equations (13) to (16): 
                       ξ   1     =         1   2     ⁢       D   1     ⁡     (   n   )         -   R       ;   or           Equation   ⁢           ⁢     (   21   )                   ξ   2     =         1   2     ⁢       D   2     ⁡     (   n   )         -       1   2     ⁢       D   2     .                 Equation   ⁢           ⁢     (   22   )                 
Since ξ 1  is usually equal to ξ 2 , there is not any problem even in a case where either value is adopted as the value ξ of the pulsatile displacement. If the values largely differ from each other, there is not any problem even in a case where the average value of ξ 1  and ξ 2  is adopted. That is, the following equation may be established:
 
     
       
         
           
             
               
                 
                   ξ 
                   = 
                   
                     
                       1 
                       2 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           ξ 
                           1 
                         
                         + 
                         
                           ξ 
                           2 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     23 
                     ) 
                   
                 
               
             
           
         
       
     
     As another method, the pulsatile displacement may be determined utilizing a fact that the artery distance  44  shown in  FIG. 6  is proportional to a change of the delay time difference Δτ 1 (n) with elapse of time, between the appearance time T n   (1)  of the first reflected burst signal  47  and the appearance time T n  of the transmitted burst signal waveform  51  shown in Table 1. 
     As to the actual reflected burst wave in the living body, since the reflected wave from each tissue in the living body exists, there exist many reflected waves other than the reflected waves from the artery shown in  FIG. 7 . Therefore, it is necessary to detect the reflected wave from the artery from a large number of reflected waves. First, a large characteristic of the reflected wave from the artery lies in that a periodic fluctuation is involved in synchronization with the heartbeat frequency. This periodic fluctuation is observed in not only the delay time difference Δτ but also the amplitude intensity ratios shown in Table 1. Furthermore, among the amplitude intensity ratios, the amplitude intensity ratio of the first reflected burst wave is proportional to a size of an artery outer shape D 2 . 
     The blood flow rate measured by the blood rheology measurement device of the present invention is a flow rate of the blood flowing through the artery having a maximum outer diameter (inner diameter) in a portion to be measured. Therefore, signals having the delay time differences and the amplitude intensities synchronized with the heartbeat frequency are detected, and the reflected burst wave having the maximum amplitude intensity ratio is selected from these signals to select the reflected wave from the artery. 
     Next, a size θ of the artery angle  45  shown in the equations (10) to (18) is detected by the blood flow rate calculation processing unit  16  shown in  FIG. 1  as described later.  FIG. 8  is a schematic diagram showing a position relation between a structure of a sensor unit of the present invention and the artery in the living body, and is a schematic diagram showing the blood rheology measurement device of the present invention in the embodiment of  FIG. 1 . A pair of ultrasonic sensors  1  and  4 , and an ultrasonic sensor  7  are disposed on the same sensor substrate  56 . The pair of ultrasonic sensors are tilted to form a sensor angle  57  so that emitting and receiving directivity directions of a continuous ultrasonic wave are not parallel to one another. A size of the sensor angle  57  is ψ. The ultrasonic sensor  7  for transmitting and receiving the burst wave is disposed in an intermediate position between the ultrasonic sensors  1  and  4   
     Moreover, the ultrasonic sensors  1  and  4  are connected to the ultrasonic wave circuit  12  shown in  FIG. 1 . The ultrasonic sensors  1  and  4  transmit continuous ultrasonic waves to an artery  60 , and receive reflected continuous ultrasonic waves to a flow of blood flowing through the artery  60 . A blood flow rate component is detected from frequency components of the received ultrasonic waves by a blood flow rate calculation processing unit  16 . The ultrasonic sensor  7  transmits and receives a burst wave, and pulsatile displacement and blood vessel shape information are detected by a blood vessel information calculation processing unit  17  via a burst detecting circuit  14 . As to a transmitting element  2  and a receiving element  3 , a transmitting element  5  and a receiving element  6 , and a transmitting element  8  and a receiving element  9  constituting the ultrasonic sensors  1 ,  4  and  7 , materials are piezoelectric ceramics. 
     The sensor substrate  56  is disposed on a living body surface  61  via an acoustic matching layer  58 . An angle formed by the artery  60  present in a living tissue  59  and the sensor substrate  56  is an artery angle  45 , and its size is θ. The continuous ultrasonic waves transmitted from the ultrasonic sensors  1  and  4  to the artery  60  are reflected by a blood flow  62  in the artery  60 , and received as reflected ultrasonic waves involving the Doppler shift (frequency shift) due to the Doppler effect by the receiving elements of the ultrasonic sensors  1  and  4 . 
     The Doppler shift amounts of the received continuous ultrasonic waves are detected by a continuous ultrasonic wave detecting circuit  11  and the blood flow rate calculation processing unit  16 . Furthermore, the blood flow rate calculation processing unit  16  determines an artery angle θ and a blood flow rate V. That is, assuming that the Doppler shift amount observed by the ultrasonic sensor  1  is Δf 1 , the Doppler shift amount observed by the ultrasonic sensor  4  is Δf 2 , and the blood flow rate of the blood flow  62  is V, Δf 1  and Δf 2  are obtained as follows: 
                       Δ   ⁢           ⁢     f   1       =         2   ⁢   V     C     ⁢     cos   ⁡     (     θ   -   φ     )           ;   and           Equation   ⁢           ⁢     (   24   )                   Δ   ⁢           ⁢     f   2       =         2   ⁢   V     C     ⁢       cos   ⁡     (     θ   +   φ     )       .               Equation   ⁢           ⁢     (   25   )                 
Therefore, V and θ can be determined using these two equations as simultaneous equations. As a result, sin θ of the equations (10) to (18) can be determined as follows:
 
                       sin   ⁢           ⁢   θ     =                Δ   ⁢           ⁢     f   1       -     Δ   ⁢           ⁢     f   2              ⁢   cos   ⁢           ⁢   φ               (       Δ   ⁢           ⁢     f   1       +     Δ   ⁢           ⁢     f   2         )     2     ⁢     sin   2     ⁢   φ     +         (       Δ   ⁢           ⁢     f   1       -     Δ   ⁢           ⁢     f   2         )     2     ⁢     cos   2     ⁢   φ             ,           Equation   ⁢           ⁢     (   26   )                 
wherein a value of θ is obtained. The value can be substituted into the equation (24) or (25) to detect the blood flow rate V.
 
       FIG. 9  is a second schematic diagram showing a positional relation between a structure of a sensor unit of the present invention and an artery in a living body, and is a schematic diagram corresponding to the embodiment of  FIG. 2  showing a blood rheology measurement device of the present invention. A pair of ultrasonic sensors  1  and  24  are disposed on the same sensor substrate  63 . The pair of ultrasonic sensors are tilted to form a sensor angle  57  so that emitting and receiving directivity directions of ultrasonic waves are not parallel to one another in the same manner as in  FIG. 8 . A size of the sensor angle  57  is ψ. Furthermore, materials of a transmitting element  2  and a receiving element  3 , and a transmitting element  25  and a receiving element  26  constituting the ultrasonic sensors  1  and  24  are piezoelectric ceramics. 
     As described with reference to  FIG. 2 , in the sensor structure shown in  FIG. 9 , the transmitting element  25  an dh receiving element  26  constituting the ultrasonic sensor  24  are connected to both of the ultrasonic wave circuit  12  and the ultrasonic burst circuit  15  shown in  FIG. 1  via a switch circuit  27 . The switch circuit  27  periodically switches the circuit to be connected to the ultrasonic sensor  24  to the ultrasonic wave circuit  12  or the ultrasonic burst circuit  15 . That is, the size θ of an artery angle  64  to be obtained can be determined by use of the Doppler shift amount Δf 2  observed by the ultrasonic sensor  24  and the Doppler shift amount Δf 1  observed by the ultrasonic sensor  1  as follows. 
                     tan   ⁢           ⁢   θ     =         Δ   ⁢           ⁢     f   1       -     Δ   ⁢           ⁢     f   2     ⁢   cos   ⁢           ⁢   2   ⁢           ⁢   φ         Δ   ⁢           ⁢     f   2     ⁢   sin   ⁢           ⁢   2   ⁢           ⁢   φ               Equation   ⁢           ⁢     (   27   )                 
Furthermore, the blood flow rate V is described as follows.
 
     
       
         
           
             
               
                 
                   V 
                   = 
                   
                     
                       1 
                       
                         2 
                         ⁢ 
                         f 
                       
                     
                     ⁢ 
                     C 
                     ⁢ 
                     
                       
                         
                           
                             Δ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               f 
                               2 
                               2 
                             
                           
                           + 
                           
                             Δ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               f 
                               1 
                               2 
                             
                           
                           - 
                           
                             2 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             Δ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               f 
                               1 
                             
                             ⁢ 
                             Δ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               f 
                               2 
                             
                             ⁢ 
                             cos 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             φ 
                           
                         
                       
                       
                         sin 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         φ 
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     28 
                     ) 
                   
                 
               
             
           
         
       
     
       FIG. 10  is an explanatory view showing a waveform (blood flow rate waveform)  65  of a blood flow rate signal which periodically changes in synchronization with a heartbeat signal calculated and processed in the blood flow rate calculation processing unit  16 , and a pulsatile displacement waveform  66  which similarly periodically changes in synchronization with a heartbeat signal calculated and processed in the blood vessel information calculation processing unit  17 . The ordinate indicates an output intensity, indicates a rate intensity in the blood flow rate waveform  65 , and indicates a detected pulsatile displacement ξ in accordance with the equation (21), (22), or (23) in the pulsatile displacement waveform  66 . The abscissa indicates time, and both of the blood flow rate waveform  65  and the pulsatile displacement waveform  66  shown in the drawing have N peak values in a range of a time interval ΔT. 
     That is, the blood flow rate waveform  65  has N peak values V p (1) to V p (N), and the pulsatile displacement waveform  66  has N peak values ξ p (1) to ξ p (N). These peak values are measured values from a base line  67  of the blood flow rate waveform  65 , and measured values from a base line  68  of the pulsatile displacement waveform  66 . Therefore, these peak values are amplitude intensities of both of the waveforms. 
     Table 2 compiles and shows the peak value V p (1) of the blood flow rate waveform  65  and an appearance time τ V (n), and the peak value ξ p (n) of the pulsatile displacement waveform  66  and an appearance time τ h (n) shown in  FIG. 10 . 
                                                       TABLE 2                               Pulsatile displacement           Blood flow rate waveform   waveform            Peak   Peak appearance   Peak   Peak appearance   Peak       number   time   value   time   value               1   τ V (1)   V P (1)   τ h (1)   ξ P (1)       2   τ V (2)   V P (2)   τ h (2)   ξ P (2)       3   τ V (3)   V P (3)   τ h (3)   ξ P (3)       n   τ V (n)   V P (n)   τ h (n)   ξ P (n)       N   τ V (N)   V P (N)   τ h (N)   ξ P (N)                    
The N peak values of the blood flow rate waveform  65  shown in Table 2 correspond to the maximum blood flow rate V m  of a blood flow rate distribution given by the equation (2).
 
     Next, there will be described hereinafter the waveform information calculation processing unit  19 , the heartbeat frequency calculation processing unit  20 , the parameter calculation processing unit  21 , and the rheology index calculation processing unit  22  built in the rheology calculation processing unit  18  of the present invention. The waveform information calculation processing unit  19  which is a first calculation processing unit detects the waveform information (peak value) shown in Table 2. As a calculation processing method concerning a waveform in this waveform information calculation processing unit  19 , a calculation processing method is adopted in which a peak detecting method or the like using a comparator is used. 
     Next, the heartbeat frequency calculation processing unit  20  which is a second calculation processing unit obtains a time interval of peak value appearance of the blood flow rate waveform  65  or the pulsatile displacement waveform  66  in the waveform information shown in  FIG. 2  in accordance with the following calculation processing equation (1):
 
Δτ( n )=τ v ( n )−τ v ( n− 1)
 
or
 
Δτ( n )=τ h ( n )−τ h ( n− 1)  Calculation processing equation (1).
 
Furthermore, a heartbeat frequency F is detected by the following second calculation processing equation (2).
 
                   F   =     N       ∑     n   =   1     N     ⁢     Δτ   ⁡     (   n   )                   Calculation   ⁢           ⁢   processing   ⁢           ⁢   equation   ⁢           ⁢     (   2   )                 
This calculation processing method is a calculation processing method on the basis of the peak value, but may be based on minimum values of the blood flow rate waveform  65  and the pulsatile displacement waveform  66  shown in FIG.  10  without any essential problem.
 
     The parameter calculation processing unit  21  which is a third calculation processing unit built in the rheology calculation processing unit  18  of the present invention detects at least one of a phase difference and an amplitude ratio by means of calculation processing from both of the blood flow rate waveform  65  and the pulsatile displacement waveform  66 . 
     First, detection of the phase difference will be described. In the detection of the phase difference, time differences of N peak appearance times of the blood flow rate waveform  65  and the pulsatile displacement :waveform  66  are obtained in accordance with the following calculation processing equation (3).
 
Δτ Vh ( n )=τ V ( n )−τ h ( n )  Calculation processing equation (3)
 
Moreover, there is detected a phase difference δ between the blood flow rate waveform  65  and the pulsatile displacement waveform  66  in accordance with the following calculation processing equation (4) by use of an average value of time differences Δτ Vh (n) and the heartbeat frequency F detected by the waveform information calculation processing unit  19 .
 
     
       
         
           
             
               
                 
                   δ 
                   = 
                   
                     2 
                     ⁢ 
                     π 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     F 
                     ⁢ 
                     
                       
                         
                           ∑ 
                           
                             n 
                             = 
                             1 
                           
                           N 
                         
                         ⁢ 
                         
                           
                             Δτ 
                             Vh 
                           
                           ⁡ 
                           
                             ( 
                             n 
                             ) 
                           
                         
                       
                       N 
                     
                   
                 
               
               
                 
                   Calculation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   processing 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     4 
                     ) 
                   
                 
               
             
           
         
       
     
     Moreover, an amplitude ratio μ is detected as an average value of a ratio V p (n)/ξ p (n) of the peak values of the N blood flow rate waveforms  65  and pulsatile displacement waveforms  66  shown in Table 2. That is, the ratio is detected as follows: 
                   μ   =       1   N     ⁢       ∑     n   =   1     N     ⁢         V   p     ⁡     (   n   )           ξ   p     ⁡     (   n   )                     Calculation   ⁢           ⁢   processing   ⁢           ⁢   equation   ⁢           ⁢     (   5   )                 
In the above-described calculation processing, the calculation processing concerning the phase difference is a calculation processing method on the basis of the peak value, but may be based on minimum values of the blood flow rate waveform  65  and the pulsatile displacement waveform  66  shown in  FIG. 10  without any essential problem.
 
     Furthermore, in the waveform information calculation processing unit  19  of the present embodiment, a general calculation processing method such as the Fourier analysis method or a phased locked loop (PLL) method is adopted as calculation processing means of waveform information. Accordingly, the heartbeat frequency F and the phase difference δ may be detected directly on the basis of the blood flow rate waveform  65  and the pulsatile displacement waveform  66  without any problem, and can be appropriately changed. 
     In the rheology index calculation processing unit  22  which is a fourth calculation processing device built in the rheology calculation processing unit  18  of the present invention, the kinematic viscosity υ is detected from blood vessel information such as the artery radius R detected by the blood vessel information calculation processing unit  17 , the heartbeat frequency F detected by the heartbeat frequency calculation processing unit  20 , and the phase difference δ or the amplitude ratio μ between the blood flow rate waveform  65  and the pulsatile displacement waveform  66 , detected by the parameter calculation processing unit  21 . 
     There will be described a case where the kinematic viscosity υ of the blood is determined by the phase difference δ between the blood flow rate waveform  65  and the pulsatile displacement waveform  66 . In this case, the blood kinematic viscosity υ is determined from the characteristic curve  34 -A stored in the rheology index calculation processing unit  22  and shown in  FIG. 4 , the phase difference δ detected by the parameter calculation processing unit  21  (calculation processing equation (4)), the heartbeat frequency F detected by the heartbeat frequency calculation processing unit  20  (calculation processing equation (2)), and the artery radius R detected by the blood vessel information calculation processing unit  17  (equation (14)). First, the value of α is detected from the stored characteristic curve  34 -A and the phase difference δ detected by the parameter calculation processing unit  21 . Assuming that the detected value of α is α 1 , the kinematic viscosity υ of the blood to be obtained is determined in accordance with the following calculation processing equation (6) from the heartbeat frequency F and the artery radius R. 
                   v   =       2   ⁢   π   ⁢           ⁢     FR   2           (     α   1     )     2               Calculation   ⁢           ⁢   processing   ⁢           ⁢   equation   ⁢           ⁢     (   6   )                   FIG. 11  is a characteristic diagram showing a correlation between the kinematic viscosity υ detected using this calculation processing equation (6) and the whole blood passing time T which is an index of the blood rheology by a blood sampling system using a micro channel array. As described above, it is found that the kinematic viscosity υ of the blood detected by the blood rheology measurement device of the present invention and the whole blood passing time T have a high degree of correlation.
 
     Next, there will be described a case where the kinematic viscosity υ of the blood is determined by the amplitude ratio μ between the blood flow rate waveform  65  and the pulsatile displacement waveform  66 . In this case, the characteristic curve  34 -B shown in  FIG. 5 , the blood density ρ, and the blood vessel Young&#39;s modulus E are stored in the rheology index calculation processing unit  22 . Furthermore, the blood kinematic viscosity υ is determined by the amplitude ratio μ detected by the parameter calculation processing unit  21  (calculation processing equation (5)), the heartbeat frequency F detected by the heartbeat frequency calculation processing unit  20  (calculation processing equation (2)), and the artery radius R and h/R detected by the blood vessel information calculation processing unit  17  (equations (14) and (20)). 
     First, there is detected the standardized amplitude ratio Γ defined in accordance with the equations (10) and (11) from the detected amplitude ratio μ, the artery radius R and h/R, further recorded blood density ρ, and the blood vessel Young&#39;s modulus E. 
     Assuming that this detected standardized amplitude ratio is Γ 0 , Γ 0  is obtained as follows. 
     
       
         
           
             
               
                 
                   
                     Γ 
                     0 
                   
                   = 
                   
                     
                       R 
                       
                         
                           
                             E 
                             ρ 
                           
                           ⁢ 
                           
                             ( 
                             
                               h 
                               R 
                             
                             ) 
                           
                         
                       
                     
                     ⁢ 
                     μ 
                   
                 
               
               
                 
                   Calculation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   processing 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     7 
                     ) 
                   
                 
               
             
           
         
       
     
     Furthermore, the value of α is detected using Γ 0  and the characteristic curve  34 -B. Assuming that the detected value of α is α 2 , the kinematic viscosity υ of the blood to be obtained is determined using the following calculation processing equation (8) from the heartbeat frequency F and the artery radius R. 
     
       
         
           
             
               
                 
                   v 
                   = 
                   
                     
                       2 
                       ⁢ 
                       π 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         FR 
                         2 
                       
                     
                     
                       
                         ( 
                         
                           α 
                           2 
                         
                         ) 
                       
                       2 
                     
                   
                 
               
               
                 
                   Calculation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   processing 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     8 
                     ) 
                   
                 
               
             
           
         
       
     
     Incidentally, it is found that since the kinematic viscosity υ is calculated from the amplitude ratio, there is hardly an individual difference of the living body in the values of the stored blood density ρ and the blood vessel Young&#39;s modulus E, and a detection precision equal to that of the characteristic diagram of  FIG. 11  is obtained. 
     In the present invention, it is possible to measure the blood flow rate in the living body, which has a strong correlation with the blood rheology as the index indicating the fluidity of the body fluid for the medical purpose of maintaining and enhancing the health. In addition, the present invention is usable in measurement to know the activity situation of the living body (human body) and the blood flow condition in each part of the living body.