JP2020189077A - Blood pressure measuring device and blood pressure measuring method - Google Patents

Abstract

To provide a blood pressure measuring device and blood pressure measuring method capable of easily and accurately measuring blood pressure of a subject.SOLUTION: According to an embodiment, a blood pressure measuring device includes a measurement section and a blood pressure acquisition section. The measurement section measures a pulse wave of a subject based on a light reception signal scattered inside a body of a subject when radiating an optical signal having a predetermined frequency band. The blood pressure acquisition section acquires diastolic blood pressure based on a first value corresponding to a blood flow rate of a subject in a first period within a first period ranging from a first reference time point where a value obtained by performing first-order differentiation on a pulse wave by time becomes maximum to a second reference time point where a next pulse wave rises, and a second value corresponding to a blood flow resistance of a subject.SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to a blood pressure measuring device and a blood pressure measuring method.

A photoelectric volume plethysmogram (PPG) sensor that detects a pulse wave accompanying a heartbeat by measuring a change in blood volume of an artery and a capillary vessel corresponding to a change in heart rate is known. A method of detecting a heart rate based on the amount of blood passing through a tissue for each pulse using a PPG sensor is called a volume pulse wave (BVP: Volume Volume) measurement.

A method of estimating blood pressure based on the characteristic points of the volume pulse wave shape is generally known. However, the waveform of the volume pulse wave fluctuates depending on the active state and the mental state of the subject, and the volume pulse wave is disturbed. If the volume pulse wave is disturbed, the feature points and the like cannot be measured accurately, and the blood pressure measurement accuracy deteriorates.

Japanese Unexamined Patent Publication No. 2000-217996

An object to be solved by the present invention is to provide a blood pressure measuring device and a blood pressure measuring method capable of easily and accurately obtaining the blood pressure of a subject.

According to the present embodiment, the blood pressure measuring device includes a measuring unit and a blood pressure acquiring unit. The measuring unit measures the pulse wave of the subject based on the received light signal scattered in the body of the subject when the optical signal of a predetermined frequency band is irradiated. The blood pressure acquisition unit is the blood flow rate of the subject in the first period within the period from the first reference time when the first-order differential value of the pulse wave is maximized to the second reference time when the next pulse wave rises. The diastolic blood pressure is obtained based on the first value corresponding to and the second value corresponding to the blood flow resistance of the subject.

The block diagram which shows the schematic structure of the blood pressure measuring apparatus according to 1st Embodiment. The figure which shows an example of the wristwatch type blood pressure measuring apparatus. The figure which shows an example of the volumetric pulse wave measured by the measuring part. The figure which shows the blood vessel approximated by a cylindrical tube. The figure which shows an example of the waveform of the pulse wave which concerns on 1st Embodiment, and the radius of the modeled cylindrical tube. The figure which shows typically the change of the radius of the cylindrical tube with the volume change of the blood vessel which concerns on 1st Embodiment. Schematically shows a flow when reaching from point P _S to point P _E. Schematically shows a flow when reaching from point P _E to the point P _H. The figure which shows the example of the information acquired by the feature point processing part which concerns on 1st Embodiment. The figure which shows the measurement data of the subject with high blood pressure. The figure which shows the measurement data of the subject with low blood pressure. The flowchart which shows the processing of the blood pressure measuring apparatus. The figure which shows the relationship between the example of the waveform of the pulse wave which concerns on 2nd Embodiment, and the radius of the modeled cylindrical tube. The figure which shows typically the change of the radius of the cylindrical tube with the volume change of the blood vessel which concerns on 2nd Embodiment. Schematically shows a flow when reaching through the point P _E from the point P _S to the point P _H. Schematically shows a flow when reaching from point P _H to the point P _D. The figure which shows the example of the information acquired by the feature point processing part which concerns on 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the characteristic configurations and operations in the blood pressure measuring device will be mainly described, but the blood pressure measuring device may have configurations and operations omitted in the following description.

(First Embodiment)
FIG. 1 is a block diagram showing a schematic configuration of the blood pressure measuring device 1 according to the first embodiment. The blood pressure measuring device 1 includes a measuring unit 2 and a blood pressure acquiring unit 4. The blood pressure measuring device 1 can be incorporated into, for example, a wristwatch-type biometric measuring device 6 as shown in FIG. The biometric device 6 may be arranged on the upper arm, chest, or the like.

The measuring unit 2 acquires information on the volume pulse wave associated with the heartbeat by measuring the change in the blood volume of the arteries and capillaries accompanying the change in the heart rate of the subject. In the following, the volume pulse wave may be simply referred to as a pulse wave.

The measuring unit 2 includes a light emitting unit 22, a light receiving unit 24, and a pulse wave generating unit 26. The light emitting unit 22 has, for example, an LED (Light Emitting Device) that emits an optical signal in a specific wavelength band (green, near infrared band, etc.). The light receiving unit 24 receives the signal after the light signal from the light emitting unit 22 is absorbed, reflected, and scattered in the body of the subject. The pulse wave generation unit 26 generates a pulse wave for each beat of the heartbeat based on the received signal.

When the light emission amount of the optical signal fluctuates, the light reception amount of the light reception signal also fluctuates. Therefore, the pulse wave generation unit 26 separates the DC component and the AC component of the received signal and generates a pulse wave based on the AC / DC ratio. Therefore, the generated pulse wave is dimensionless data.

FIG. 3 is a diagram showing an example of a volumetric pulse wave measured by the measuring unit 2. The vertical axis shows the value of the pulse wave, and the horizontal axis shows the time. As shown in FIG. 3, the pulse wave repeats fluctuation with each heartbeat. The pulse wave y _i of the i-beat is an AC component and a DC component that fluctuate periodically.
Consists of.

The blood pressure acquisition unit 4 acquires the blood pressure of the subject based on the pulse wave. The blood pressure acquisition unit 4 has a feature point processing unit 42 and a blood pressure calculation unit 44.

First, the model used in the blood pressure acquisition unit 4 will be described with reference to FIGS. 4 to 7B. FIG. 4 is a diagram showing a modeled blood vessel. The blood vessel model shown in FIG. 4 _is approximated by a cylindrical tube having a radius of _ris and a length of L. Blood pressure fluctuations are fluctuations in the pressure exerted on the walls of blood vessels by the blood pumped from the heart. This blood pressure fluctuation is linked to the pulse wave _yi .

The relationship between the pressure difference ΔP, the flow rate Q, and the resistance R of the cylindrical tube is derived from the Navier-Stokes equation and is shown by the equation (1).
The blood pressure acquisition unit 4 calculates the values corresponding to the flow rate Q and the resistance R using the pulse wave _yi based on the model of the cylindrical tube, and acquires the blood pressure of the subject. In general, human blood pressure is the systolic blood pressure SBP (Systemolic Blood Pressure), which is the maximum pressure in blood vessels during the contractile phase of the heart, and the diastolic blood pressure DBP (Diastolic Blood Pressure), which is the minimum pressure in the blood vessels during the diastolic phase of the heart. ), The pulse pressure PP (Pulse pressure) obtained by subtracting the systolic blood pressure from the diastolic blood pressure is used for evaluation.

FIG. 5 is a diagram showing the relationship between an example of the pulse wave waveform according to the first embodiment and the radius of the modeled cylindrical tube. The figure on the left shows an example of a waveform of a normal pulse wave for one beat. The vertical axis shows the value of the pulse wave, and the horizontal axis shows the time. The figure on the right shows the radius of the modeled cylindrical tube. The volume change of the blood vessel, is shown by Δr _id is a change in the radius _{r is.} That is, the radius _{r IS} is the radius of the vessel at the point _{P E,} [Delta] r _id is the radius of the increment of the increase in volume from the point _{P E} to the point _{P H.}

A normal pulse wave y _i starts at the bottom position (t ₀ ) in amplitude, increases almost monotonously to reach the maximum peak (t ₂ ), and then monotonically decreases in amplitude to the bottom position. The value (t ₃ ) is reached and the process ends. Here, the subscript i is a number that identifies each one pulse in the volume pulse wave data. That is, it means the data corresponding to the pulse wave of the i-beat. In the calculation according to the present embodiment, the calculation is performed for each beat, but the calculation is not limited to this, and the data for several beats may be averaged and calculated.

t ₁ is the time between t ₀ and t ₂ at which the value obtained by first-derivating the pulse wave y _i with respect to time becomes maximum. This t ₁ corresponds to the equilibrium point of the displacement r (t) of the viscoelastic equation of motion shown by the equation (4) described later.

As shown by Eq. (2), t _s is a DC component from the value y _is of the pulse wave y _i at time t _1.
The first difference value obtained by subtracting is the first derivative value that maximizes
It is the time based on the value divided by. Here, the first derivative value
Is calculated by, for example, equation (15) described later.
Line Ls is a tangent to the point _{P E.} That is, tan θ calculated by the angle θ between the line Ls and the horizontal axis and the horizontal line is the first derivative value.
Corresponds to. P _S , P _E , P _H , and P _L correspond to the times t _s , t ₁ , t ₂ , and t ₃ , respectively. The time t _{1 according} to the present embodiment corresponds to the first time, the time t ₂ corresponds to the second time, and the time t ₀ or t _s corresponds to the third time.

Figure 6 is a diagram schematically showing the change in radius of the cylindrical tube with the point P _S to the volume change of the blood vessels into the point P _L. The vertical axis represents time and the horizontal axis represents the radius variation of the point P _S. According lapse of radius time, from the point P _S to the point P _H increases and then decreases.

The blood flow rate is measured as the volumetric flow rate Q based on the radius r according to the volume change of the modeled blood vessel. Therefore, the flow rate Q can be defined by using the average rate of change (Δr / Δt) of the radius per unit time. Δt indicates the amount of change in t with time, and Δr indicates the amount of change in radius r at Δt.

Figure 7A is a diagram schematically showing the flow rate _{Q SE} when, from the point _{P S} to point _{P E.} Figure 7B is a diagram schematically showing the flow rate _{Q EH} when, from the point _{P E} to the point _{P H.} The horizontal axis represents the square of the average rate of change (Δr / Δt), and the vertical axis is the multiplication value of the length L and π. The average rate of change mis _is represented by the equation (8) described later. Average rate _{m IS} of FIG. 7A is a value obtained by dividing the value obtained by subtracting a radius _r times the _is from time _{t 1 t s} when, from the point _{P S} to point _{P E.} Average rate _{m id} in FIG. 7B is a value obtained by dividing the value obtained by subtracting the time _{t 1} a [Delta] r _id from time _{t 2.} Furthermore, (not shown) the flow rate _{Q EL} when, from the point _{P H} to the point _{P L,} using the the time _{T id2} extending from the point _{P H} to the point _{P L} resistor R and vascular compliance C and the flow rate _{Q EH} of , (3) can be obtained. In equation (3), the Napier number term is known as a method of expressing the pressure drop after systole in a two-factor Windkessel model.

The displacement r (t) of the blood vessel wall, that is, the displacement of the radius r (t) is linked to the value of the pulse wave _yi . Further, the pressure can be approximated by the displacement r (t) of the blood vessel wall, and the displacement of the radius r (t) is equivalent to the viscoelastic equation of motion shown in Eq. (4). That is, when the blood vessel is approximated by a cylindrical tube, the blood pressure can be calculated based on the information of the pulse wave _yi .

Here, b is a viscosity constant and k is an elastic constant, which reflects the elasticity of the blood vessel. In equation (4), the left side shows the total force in Newton's second law of motion. The first term on the right side shows the damping force, the second term shows the restoring force, and the third term shows the force due to the Windkessel effect. Equilibrium position of the displacement r (t) is corresponding to the point _{P E.}

During contraction period of the heart, to the point P _E from the rising of the pulse wave yi is mainly vascular wall is displaced by Windkessel effect. On the other hand, from the point P _E to the point P _H, it is displaced by the damping force and restoring force. In the point P _H, Windkessel effects and damping force can be ignored.

For this reason, during the contraction period of the heart, expansion of radius _r is to the point P _E occurs primarily in the window Kessel effect. Therefore, the force generated during systole of the heart, namely, systolic blood pressure SBP is reflected in the flow rate Q _SE. On the other hand, the diastolic blood pressure DBP is reflected in the flow rate _{Q EL.} Flow rate _{Q EL,} since the lower limit of force by Windkessel effect, resulting from the flow _{Q EH} when, from the point _{P E} to the point _{P H.} The flow rate Q _{EH according} to the present embodiment corresponds to the first value, the resistor R corresponds to the second value, and the flow rate Q _SE corresponds to the third value.

Therefore, in the present embodiment, the systolic blood pressure SBP _i in the heartbeat i is modeled by the equation (5). R _i is a value that reflects the circulation resistance of the peripheral at the time of observation of the flow rate _{Q SEi} and _{Q ELi.} Here, a and α are constants.

In addition, the diastolic blood pressure DBP _i is modeled by Eq. (6).
Here, b and β are constants. For the constants a, α, b, β, etc., for example, the least squares method so that the values measured by the blood pressure measuring device 1 and the data measured by the medical device (for example, wrist cuff type) measured at the same time as the blood pressure measuring device 1 match. It is possible to calculate with. Once the constants a, α, b, β are determined, the calculation of the constants a, α, b, β is unnecessary in the later measurement. The pulse pressure PP _i is a value obtained by subtracting the diastolic blood pressure DBP _i from the systolic blood pressure SBP _i .

The above is the description of the model used by the blood pressure acquisition unit 4 according to the present embodiment, but the detailed configuration of the blood pressure acquisition unit 4 will be described below. FIG. 8 is a diagram showing an example of information acquired by the feature point processing unit 42 from the pulse wave _yi . The vertical axis shows the value of the pulse wave, and the horizontal axis shows the time.

The feature point processing unit 42 detects t ₀ as the rise time and t ₂ as the time when the maximum peak occurs. Further, the feature point processing unit 42 calculates t _{1 in} which the value obtained by first-derivating the pulse wave with respect to time becomes the maximum between t ₀ and t ₂ .

Further, the feature point processing unit 42, the DC component from the value of the pulse wave y _i at time t ₁
A first difference value [Delta] y _IS obtained by subtracting the DC component from the value of the pulse wave _{y i} at time _{t 2}
The second difference value Δy _ih obtained by subtracting is calculated.

Feature point processing unit 42 calculates the time _{T IS} using equation (7). _T is is the time obtained by dividing the first difference value _Δy is in tanθ which corresponds to the differential value of the time _{t 1.} Then, the second rise time t _s obtained by subtracting T _is from t _{1 is} calculated. T _id1 is the time obtained by subtracting _{t 1} from the time _{t 2, T id2} is the time obtained by subtracting _{t 4} from time _{t 3.}
The shape of the pulse wave _{yi at} the rise time t ₀ varies greatly among individuals, and there are those who change gently and those who change sharply. Therefore, the difference value between the rise time t ₀ and the time t ₁ tends to fluctuate due to individual differences. On the other hand, the time difference _Tis between the second rise time t _s and the time t ₁ shows a stable value with reduced fluctuation due to individual differences. Therefore, this time difference Tis _is used in the calculation of the flow rate. Depending on the shape of the pulse wave y _i , the time _Tis may be calculated as the time difference between the time t ₀ and the time t ₁ . As a result, the calculation can be simplified.

Blood pressure calculation section 44, (3), (6) as shown in the equation, the second largest peak of the pulse wave from the first time t ₁ to 1 derivative value of the pulse wave y _i at time is maximum flow rate corresponding to the blood flow of a subject until time t ₂ Q _{EH (first} value), based on a resistance R corresponding to the blood flow resistance of the subject (second value), the diastolic blood pressure DBP get. That is, the blood pressure calculation unit 44 calculates a value obtained by multiplying the multiplication of the flow rate Q _EL based on the flow rate Q _EH and the resistance R by a predetermined coefficient b and further adding a predetermined constant β as the diastolic blood pressure DBP. The resistance R is calculated based on the equations (14) and (15) described later. Further, the blood pressure calculation unit 44 further uses the equation (5) based on the flow rate Q _SE (third value) corresponding to the blood flow rate from the third time t _s or t ₀ to the time t ₁ of the rise of the pulse wave. , Obtain systolic blood pressure SBP. The first time according to the present embodiment corresponds to the first reference time, the second time corresponds to the fourth reference time, and the third time corresponds to the third reference time.

More specifically, the blood pressure calculation unit 44 calculates _ris based on the equation (8), and calculates the average rate of change _mis based on the equation (9). The flow rate Q _SE is calculated based on the equation (10). here,
It is proportional to the blood vessel volume of point P _E. In this way, the blood pressure calculation unit 44 acquires the systolic blood pressure SBP _i based on the equations (5) and (10). The first difference value Δy _is of the pulse wave y _i calculated at this time, the DC component
, Time T _IS is stably and possible operations easily even to variations of the pulse wave y _i. Therefore, the systolic blood pressure SBP _i can be obtained easily and accurately. G is a constant.

The blood pressure calculation unit 44 calculates the Δrid _id based on the equation (11), and calculates the average rate of change _mid based on the equation (12). Then, blood pressure calculation unit 44 further calculates based flow _{Q EL} when, from the point _{P H} to the point _{P L} (2) below. In this way, the blood pressure calculation unit 44 acquires the diastolic blood pressure DBP _i based on the equations (6) and (13). The first difference value Δy _is , the second difference value Δy _ih , and the DC component to be calculated at this time.
, Time T _is , T _id can be calculated stably and easily with respect to the fluctuation of the pulse wave y _i . Therefore, the systolic blood pressure SBP _i can be obtained easily and accurately.

Thus, the first value _{Q EL} and the third value _{Q SE} corresponds to the vascular volume of the subject at a time _{t s}
It is a value based on. In addition, the blood vessel volume has the first difference value Δy _is as a DC component.
It is a value based on the value divided by. That is, the first value Q _EL corresponds to the value obtained by subtracting the first difference value Δy _is from the second difference value Δy _ih and dividing by the first difference value Δy _is , and the blood vessel volume.
It is a value based on the square root of and the multiplication of.

Blood pressure calculating unit 44 (14), (15) based on the equation for calculating the _{R i} corresponding to the blood flow resistance of the subject.
Here, f _s is the sampling frequency of the pulse wave y _i .

FIG. 9A is a diagram showing measurement data of a subject with high blood pressure. FIG. 9B is a diagram showing measurement data of a subject having a low blood pressure. The vertical axis shows blood pressure and the horizontal axis shows time. The diamond-shaped mark indicates the value measured by the blood pressure measuring device 1, and the solid line indicates the data of the medical device (wrist cuff type) measured for comparison. In both cases, the values measured by the blood pressure measuring device 1 of the present embodiment are in good agreement with the data measured for comparison.

FIG. 10 is a flowchart showing the processing of the blood pressure measuring device 1. First, the measuring unit 2 acquires the pulse wave of the subject (step S100). Subsequently, the feature point processing unit 42 performs processing based on the pulse wave _yi .

Then the blood pressure calculation section 44, first derivative value of the pulse wave y _i at time corresponds to the blood flow rate of the pulse wave y _i subject from the time of maximum until the time of the maximum peak of the pulse wave y _i The flow rate Q _EL , the resistance R corresponding to the blood pressure resistance of the subject, and the flow rate Q _SE corresponding to the blood flow rate from the rise time of the pulse wave to the time when the value obtained by first-order differentiation of the pulse wave with time becomes maximum. Calculate (step S102).

Next, the blood pressure calculation unit 44 calculates the diastolic blood pressure DBP, the systolic blood pressure SBP, and the pulse pressure PP based on the flow rate Q _EL , the resistance R, and the flow rate Q _SE . (Step S104). The blood pressure calculation unit 44 determines whether or not to end the overall processing (step S106), ends the overall processing (step S106: YES), ends the overall processing, and does not end the overall processing (step S106). : NO), the process from step S100 is repeated.

As described above, in the present embodiment, the systolic blood pressure SBP _i is acquired based on the equations (5) and (10), and the diastolic blood pressure DBP _i is acquired based on the equations (6) and (13). Therefore, blood pressure can be detected easily and accurately.

(Second Embodiment)
In the first embodiment, the blood pressure measuring device 1 calculates the systolic blood pressure SBP based on the flow rate Q _SE (FIG. 6), whereas in the second embodiment, the systolic blood pressure SBP is calculated based on the flow rate Q _EH. , The difference is in the calculation. Further, the blood pressure measuring apparatus 1 in the first embodiment based on the diastolic blood pressure DBP flow rate Q _{EH (Fig.} 6), whereas I want to calculate, in the second embodiment, the diastolic blood pressure DBP flow rate Q _HD Based on this, it differs in that it is calculated. Hereinafter, the points different from the first embodiment will be described.

The blood pressure measured by the blood pressure measuring device 1 according to the first embodiment is in good agreement with the systolic blood pressure SBP and the diastolic blood pressure DBP of a general person. However, it has become clear that some subjects have different pulse wave characteristics from those of ordinary people. The blood pressure measuring device 1 according to the second embodiment can handle such a person.

FIG. 11 is a diagram showing the relationship between an example of the pulse wave waveform according to the second embodiment and the radius of the modeled cylindrical tube. Similar to FIG. 5, the left figure is a diagram showing an example of a waveform of a normal pulse wave for one beat. The vertical axis shows the value of the pulse wave, and the horizontal axis shows the time. The figure on the right shows the radius of the modeled cylindrical tube. The change in the volume of the blood vessel is indicated by the radius r _si and the change amount Δr _di . Point P _D is a point showing the same value of the volume pulse wave and the point P _E between the point P _H and the point P _L. I _dc is a DC component of the volume pulse wave. Here, the subscript i is a number that identifies each one pulse in the volume pulse wave data. That is, it means the data corresponding to the pulse wave of the i-beat. The time of the point P _D corresponding to the time of the fifth reference.

Figure 12 is a diagram schematically showing the change in radius of the cylindrical tube with the point P _S to the volume change of the blood vessels into the point P _L. That is, FIG. 12 shows the change in the radius of the cylindrical tube with respect to the pulse wave for one beat. The vertical axis represents time and the horizontal axis represents the radius variation of the point P _S. According lapse of radius time, from the point P _S to the point P _H increases and then decreases.

13A is a diagram schematically showing the flow rate _{Q S} at the time of reaching through the point _{P E} from the point _{P S} to the point _{P H.} 13B is a diagram schematically showing the flow rate _{Q HD} when, from the point _{P H} to the point _{P D.} The horizontal axis represents the square of the average rate of change (Δr / Δt) of the blood vessel radius r, and the vertical axis is the multiplication value of the length L and π. _{M si} in Figure 13A is the average rate of change of the radius when extending from the point _{P S} to point _{P E, m d1i} is the average rate of change of the radius when extending from the point _{P E} to the point _{P H. M d2i} in FIG. 13B, the average rate of change of the radius when extending from the point _{P D} to the point _{P H.} The flow rate Q _HD according to the present embodiment corresponds to the first value, the resistance R corresponds to the second value, the flow rate Q _S corresponds to the third value.

In the present embodiment, the systolic blood pressure SBP is calculated by the flow rate Q _S. Expansion vessel diameter up to P _E point in contraction period of the heart occurs predominantly in Windkessel effect. Then, gradually restoring force and the damping force becomes dominant from point P _E after. That is, in this embodiment, is modeled extends from P _E that restoring force is applied to the Windkessel effect until the flow rate Q _SE to the point P _H, the range of the forces generated during systole. Depending on the subject, also in the range of from the point P _E to the point P _H is considered that there are more strongly out people wind Kessel effect. When the measurement including such person, the use of flow rate Q _S, the measurement accuracy of the systolic blood pressure SBP is further improved. Even with a flow rate Q _S, the accuracy of the common human systolic blood pressure SBP may not decrease has been verified experimentally.

On the other hand, in the case of a person who Windkessel effect comes out more strongly in the range from point P _E to the point P _H, the point Windkessel effect is weakened, it is considered that offset the point P _L side. Diastolic blood pressure, since it is the lower limit of force by Windkessel effect, wind shifting Kessel points effect weakens to the point P _H, the point P flow rate range of from _H to point P _D Q _D diastolic blood pressure DBP using Is modeled. In particular, based on the flow rate _{Q D} on the flow rate _{Q HD,} calculates. It has been experimentally verified that the accuracy of diastolic blood pressure DBP in general people does not decrease even if the flow rate _QHD is used.

The above is a description of the model used by the blood pressure acquisition unit 4 according to the present embodiment, but a detailed processing example of the blood pressure acquisition unit 4 will be described below.
FIG. 14 is a diagram showing an example of information acquired from the pulse wave _{yi by the} feature point processing unit 42 according to the second embodiment. The vertical axis shows the value of the pulse wave, and the horizontal axis shows the time. The figure on the right shows the radius of the modeled cylindrical tube. The change in the volume of the blood vessel is indicated by the radius r _si and the change amount Δr _di .

Feature point processing unit 42 subtracts the first difference value [Delta] y _si obtained by subtracting the DC component _{I dc} from the value of the pulse wave _{y i} at time _{t 1,} the DC component _{I dc} from the value of the pulse wave _{y i} at time _{t 2} The second difference value Δy _hi is calculated.
Further, the feature point processing unit 42 calculates the time T _d2i using the equation (16). T _d2i is the time between points _{P D} and the point _{P H.} T _si is the time obtained by subtracting t ₀ from the time t ₁ , T _{d 1i} is the time obtained by subtracting t ₁ from the time t ₂ , and T _{d 3i} is the time obtained by subtracting t ₂ from the time t _3. .. That is, the feature point processing unit 42, when the time the fifth reference of P _D point indicating the value equivalent to the pulse wave y _i at time t ₁ in the period from time t ₂ of the pulse wave y _i to time t ₃ And the time between the time t ₂ and the fifth reference time is calculated as the time T _d2i .

If a reference volume corresponding to the point _{P L,} Δy _si / _{I dc} is the point _P E, proportional to the volume at _{P D,} similarly Δy _hi / _{I dc} is proportional to the volume at the point _{P H.} G is a constant of proportionality, and I _dc is the value of the DC component of the pulse wave.
If the radius of the cylindrical tube is changed from _{r si} to _{r si} + Δr _di, the [Delta] r _di with radius _{r si} at the point _{P E,} it can be calculated by (17) - (19).
Here, the radius r _si of the equation (19) can be transformed into the following equations (20) and (21) by rearranging the radius r _si using the equation (17). The blood pressure calculation unit 44 calculates the radii r _si and Δ r _di using the equations (20) and (21). L is the length of the model cylindrical tube.

The blood pressure calculation unit 44 calculates the average rate of change _msi using the equation (22).
Further, the blood pressure calculating unit 44, respectively an average rate of change _{m d1i} and _Md2i, is calculated by using (23), (24).

The blood pressure calculation unit 44 calculates the flow rate Q _Si using the equation (25) based on the average rate of change _md1i and _md2i .

Blood pressure calculating unit 44 calculates by using a resistor _{R i} (26) below. Here, _{V i} is the volume of the model cylindrical _tube, V i _{(t 1)} is the volume of the model cylindrical tube at time _{t 1.} That is, I _dc is the first embodiment.
Corresponds to. Therefore, the equation (26) has the same value as the equation (16).
Blood pressure calculating unit 44, the resistor with _{R i} and the compliance C, and calculated based flow _{Q Di} when, from the point _{P H} to the point _{P L} in (27).
The resistance Rdi is obtained by the equations (28) and (29).

The blood pressure calculation unit 44 calculates the diastolic blood pressure DBP and the systolic blood pressure SBP for each i-beat based on the equations (30) and (31).
Here, a ₁ , a ₂ , b ₁ , b ₂ , α, and β are constants.

In this way, the blood pressure calculation unit 44 has a period T within the period from the first time t ₁ at which the value obtained by first-order differentiation of the pulse wave y _i with time becomes maximum to the fourth time t _{3 at} which the next pulse wave rises. _d2i flow Q _HD corresponding to the blood flow rate _(first period) of the subject _(the first value), based on the R (second value) corresponding to the blood flow resistance of the subject, diastolic blood pressure DBP To get. In addition, the blood pressure calculation unit 44 is a subject in a period (T _si + T _d1i ) (second period) within the period from the third time t ₀ when the pulse wave rises to the second time t ₂ of the maximum peak of the pulse wave. Furthermore, based acquires systolic blood pressure to the flow rate Q _S corresponding to the blood flow rate _(the third value). The first time according to the present embodiment corresponds to the first reference time, the second time corresponds to the fourth reference time, the third time corresponds to the third reference time, and the fourth time corresponds to the second reference time. ..

As described above, in the present embodiment, the diastolic blood pressure DBP _i is acquired based on the equations (27) and (30), and the systolic blood pressure SBP _i is acquired based on the equations (25) and (31). Therefore, blood pressure can be detected easily and accurately.

At least a part of the blood pressure measuring device 1 may be configured by hardware or software. When configured by software, a program that realizes at least a part of the functions of the blood pressure measuring device 1 may be stored in a recording medium such as a flexible disk or a CD-ROM, read by a computer, and executed. The recording medium is not limited to a removable one such as a magnetic disk or an optical disk, and may be a fixed recording medium such as a hard disk device or a memory.

Further, a program that realizes at least a part of the functions of the blood pressure measuring device 1 may be distributed via a communication line (including wireless communication) such as the Internet. Further, the program may be encrypted, modulated, compressed, and distributed via a wired line or wireless line such as the Internet, or stored in a recording medium.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

1: Blood pressure measuring device, 2: Measuring unit, 4: Blood pressure acquisition unit, 6: Biometric measuring device.

Claims (7)

A measuring unit that measures the pulse wave of the subject based on the received signal scattered in the subject's body when irradiating an optical signal in a predetermined frequency band.
The first period corresponding to the blood flow rate of the subject in the first period within the period from the first reference time at which the value obtained by first-order differentiation of the pulse wave with time becomes maximum to the second reference time at which the next pulse wave rises. A blood pressure acquisition unit that acquires diastolic blood pressure based on one value and a second value corresponding to the blood flow resistance of the subject, and
A blood pressure measuring device. The blood pressure acquisition unit has a third value corresponding to the blood flow rate of the subject in the second period within the period from the third reference time when the pulse wave rises to the fourth reference time of the maximum peak of the pulse wave. The blood pressure measuring device according to claim 1, further based on which the systolic blood pressure is acquired. The blood pressure according to claim 2, wherein the first period is between the first reference time and the fourth reference time, and the second period is a period from the third reference time to the first reference time. measuring device. The blood pressure acquisition unit obtains a fifth reference time showing a value equivalent to that of the pulse wave at the first reference time within the period from the fourth reference time to the second reference time of the pulse wave.
The blood pressure measuring device according to claim 2, wherein the first period and the second period are a period from the fourth reference time to the fifth reference time. The blood pressure acquisition unit is based on a value obtained by dividing the first difference value obtained by subtracting the DC component of the pulse wave from the value of the pulse wave at the time of the first reference by the value of the first derivative that becomes the maximum. The blood pressure measuring device according to claim 2, which acquires the third reference time. The blood pressure measurement according to claim 2, wherein the blood pressure acquisition unit acquires at least one of the first value and the third value based on the value corresponding to the blood vessel volume of the subject at the time of the first reference time. apparatus. A measurement step of measuring the pulse wave of the subject based on the received signal scattered and received in the body of the subject when the subject is irradiated with an optical signal in a predetermined frequency band.
The first period corresponding to the blood flow rate of the subject in the first period within the period from the first reference time at which the value obtained by first-order differentiation of the pulse wave with time becomes maximum to the second reference time at which the next pulse wave rises. A blood pressure acquisition step of acquiring diastolic blood pressure based on one value and a second value corresponding to the blood flow resistance of the subject, and
A blood pressure measurement method.