JP2011239972A - Blood pressure measuring device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a constantly attachable blood pressure measuring apparatus that achieves easy correction without using a cuff blood pressure measurement device when a subject is constantly measured under free actions.SOLUTION: The blood pressure measuring device includes: a blood flow sensor part 18 for detecting the flow of flood flow in a living body; a blood speed sensor driving part 20 for driving the blood flow sensor part 18; a blood speed sensor signal calculation part 22 for controlling the blood speed sensor driving part 20 and the blood speed sensor part 18, and calculating the blood speed in the living body; a blood vessel diameter sensor part 27 for detecting differences in a reflection arrival time of a blood wall of the living body; a blood vessel diameter sensor driving part 28 for driving the blood vessel diameter sensor part 27; a blood vessel sensor signal calculation part 30 for controlling the blood vessel diameter sensor driving part 28 and the blood vessel diameter sensor 27, and calculates a blood vessel diameter in the living body; and a blood pressure signal calculation part 32 for calculating a blood pressure of the person to be measured using calculation results of the blood speed sensor signal calculation part 22 and the blood vessel diameter sensor signal calculation part 30.

Description

  The present invention relates to a blood pressure measurement device and a blood pressure measurement method.

  Today, as a method for measuring blood pressure, a method using ultrasonic waves has been proposed. For example, in the local region of the artery, the maximum diameter and the minimum diameter are obtained, the parameter values thereof are given to the nonlinear function, and the diameter at each input time is converted by the nonlinear function, so that The pressure at the time is calculated (for example, see Patent Document 1).

  Further, a method has been proposed in which blood flow velocity, flow rate, volume, or the like is detected by ultrasonic waves and pulse wave velocity is detected by light waves, and the blood pressure and the amount of change thereof are calculated by associating both of these amounts (for example, Patent Documents). 2 and 3).

Japanese Patent Laid-Open No. 2004-041382 JP-A-4-250135 JP 2004-154231 A

  However, as disclosed in Patent Documents 1 to 3, the calculation of blood pressure values using conventional ultrasonic waves requires calibration with a cuff type sphygmomanometer. This is a 24 hour free action, considering blood pressure measurement (24hABPM) and continuous blood pressure measurement every beat, there are inconveniences such as wearing a cuff all the time or carrying it around and use it regularly. Therefore, there is a possibility that the practical use becomes difficult.

  Moreover, in addition to the need for calibration with a cuff type sphygmomanometer, there is a possibility that the calibration is required regularly (about 30 minutes to 1 hour). In general, it is known that when the blood pressure value is estimated from the pulse wave velocity, the error probability increases as the calibration interval increases. This is because the vascular elasticity characteristic (E0: vascular elasticity at no pressure, γ: constant in a specific blood vessel) can be considered constant within a short time, but the error increases after a certain time. In Patent Document 1, the stiffness parameter β is calculated from the systolic blood pressure Ps and the systolic blood pressure Pd obtained by the cuff type sphygmomanometer. However, since this correlates with the vascular elastic modulus, the value naturally changes after a certain time. Come on. That is, in order to obtain a correct blood pressure value continuously and continuously, it is not necessary to perform calibration once, but it is necessary to perform it at a certain interval, for example, about every hour.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 A blood flow velocity sensor unit that detects a flow of blood inside a living body by transmitting and receiving waves from the surface of the subject's living body to the blood inside the living body, and blood that drives the blood flow velocity sensor unit A blood flow velocity sensor driving unit; a blood flow velocity sensor driving unit that controls the blood flow velocity sensor driving unit and the blood flow velocity sensor unit to obtain a blood flow velocity inside the living body; A blood vessel diameter sensor unit that transmits and receives sound waves to detect a difference in reflection arrival time of a blood vessel wall inside the living body, a blood vessel diameter sensor drive unit that drives the blood vessel diameter sensor unit, the blood vessel diameter sensor drive unit, and the blood vessel diameter A blood vessel diameter sensor signal calculation unit for controlling a sensor unit to obtain a blood vessel diameter inside the living body, and the measurement subject using calculation results of the blood flow velocity sensor signal calculation unit and the blood vessel diameter sensor signal calculation unit Blood pressure measuring apparatus characterized by comprising: a blood pressure signal operation unit for obtaining the blood pressure, the.

  According to this, it is possible to measure blood pressure with high accuracy without using a cuff sphygmomanometer after that, only by obtaining a correction coefficient based on the blood pressure value first measured using a cuff sphygmomanometer. When a measurer constantly measures blood pressure under free action, a blood pressure measuring device that can be always worn can be provided that can be easily calibrated without using a cuff sphygmomanometer.

  Application Example 2 In the blood pressure measurement device, the blood pressure signal calculation unit performs a calculation to obtain the blood pressure by converting the blood vessel diameter into a head pressure.

  According to this, since it can be considered that the blood vessel diameter and the blood pressure change substantially linearly, a value correlated with the time change of the blood pressure can be obtained by measuring the time change of the blood vessel diameter.

  [Application Example 3] In the blood pressure measurement device, the first state and the predetermined part of the measured person are in the first state in which the predetermined part of the measured person is positioned at a predetermined height. A height position sensor unit that obtains a height difference of the predetermined part from the second state positioned at the height of the heart, and the hydraulic head pressure is obtained by calculating the height difference measured by the height position sensor unit. A blood pressure measurement apparatus characterized by being obtained by using.

  According to this, the height difference which is one element at the time of calculating | requiring water head pressure can be measured easily.

  Application Example 4 In the blood pressure measurement device, the blood flow velocity sensor unit includes a transmission element and a reception element, and there are a plurality of pairs of the transmission element and the reception element. The blood pressure measuring device, wherein the angle formed by the traveling direction of the wave to be transmitted / received and the direction of blood flow is different for each pair.

  According to this, the blood flow velocity can be obtained even when the angle formed between the blood vessel and the wave is unknown.

  Application Example 5 In the blood pressure measurement device, the blood flow velocity sensor unit is configured using a piezoelectric element.

  According to this, since the piezoelectric element has a simple structure, the blood flow velocity sensor can be reduced in size.

  Application Example 6 In a first state in which a predetermined part of the measurement subject is positioned at a predetermined height, the blood flow velocity of the predetermined part is divided by the square of the blood vessel diameter of the predetermined part. The blood pressure of the measurement subject that is proportional to a predetermined proportionality constant, and the blood vessel diameter and the blood flow velocity at the predetermined portion are measured in the calibration step for obtaining the proportionality constant and in the first state, respectively. Determining the blood pressure using the blood vessel diameter, the blood flow velocity, and the proportional constant, displaying the blood pressure, and determining whether the proportional constant needs to be calibrated, A blood pressure measurement method characterized by comprising:

  According to this, it is possible to measure blood pressure with high accuracy without using a cuff sphygmomanometer after that, only by obtaining a correction coefficient based on the blood pressure value first measured using a cuff sphygmomanometer. When a measurer constantly measures blood pressure under free action, a blood pressure measuring method that can be always worn and can be easily calibrated without using a cuff type sphygmomanometer can be provided.

  Application Example 7 In the blood pressure measurement method, the calibration step includes a second state in which the predetermined part is positioned at a height of the heart of the measurement subject, a blood vessel diameter of the predetermined part, and Measuring the first and second systolic blood vessel diameters, the first systolic blood vessel diameter, and the average diastolic blood vessel diameter, respectively, in the first state; A height difference measuring step of measuring a height difference of the predetermined portion between the state and the second state, a step of obtaining a hydraulic head pressure between the first state and the second state using the height difference; In the first state, the blood vessel diameter of the predetermined part, and the blood flow velocity and blood vessel diameter of the predetermined part of the systole and the diastole are measured, respectively, the second average blood vessel diameter, the systolic blood flow velocity, A step of obtaining a systolic blood vessel diameter, a diastolic blood flow velocity, and a diastolic blood vessel diameter, and the first average blood vessel And calculating the average blood vessel diameter change using the second average blood vessel diameter, and the hydrostatic pressure, the average blood vessel diameter change, the average systolic blood vessel diameter, and the systolic blood pressure using the average diastolic blood vessel diameter. Determining the blood pressure difference between the blood pressure and the diastolic blood pressure, and the proportionality using the blood pressure difference, the systolic blood flow velocity, the systolic blood vessel diameter, the diastolic blood flow velocity, and the diastolic blood vessel diameter And a step of determining a constant.

  According to this, the proportionality constant can be easily calibrated.

  Application Example 8 In the blood pressure measurement method, the height difference measurement step is measured by a height position sensor unit that measures the height difference of the predetermined part between the first state and the second state. A blood pressure measurement method characterized by comprising:

  According to this, the height difference which is one element at the time of calculating | requiring water head pressure can be measured easily.

The external view which shows the state with which the blood-pressure measuring apparatus which concerns on this embodiment was mounted | worn. The figure which shows the blood flow velocity sensor and blood vessel diameter sensor which concern on this embodiment. The figure which shows the circuit block which concerns on this embodiment. The figure which shows the measurement position of the blood-pressure measurement apparatus which concerns on this embodiment. The figure which shows the blood vessel diameter to which the hydraulic head pressure part which concerns on this embodiment was added. The figure which shows the relationship between the blood vessel wall pressure which concerns on this embodiment, and the blood vessel diameter (volume). The figure which shows the cuff pressurization measurement value which concerns on this embodiment. The figure which shows the blood flow velocity sensor which concerns on this embodiment. The figure which shows the measuring method which concerns on this embodiment. The figure which shows the calibration routine which concerns on this embodiment.

  Hereinafter, the present embodiment will be described with reference to the drawings. Note that the drawings to be used are appropriately enlarged or reduced so that the part to be described can be recognized.

  FIG. 1 is an external view showing a state in which the blood pressure measurement device according to the present embodiment is mounted. FIG. 2 is a diagram showing a blood flow velocity sensor and a blood vessel diameter sensor according to the present embodiment. FIG. 3 is a diagram illustrating a circuit block according to the present embodiment. The blood pressure measurement device 2 according to this embodiment includes a blood flow velocity sensor 10 and a blood vessel diameter sensor 12. The blood pressure measurement device 2 is attached to the wrist 16 of the person to be measured 4 (see FIG. 4) and measures the blood flow velocity v and the blood vessel diameter d of the radial artery (blood vessel) 14 to obtain the blood pressure P.

  The blood flow velocity sensor 10 is attached at a position where ultrasonic waves can be applied to the radial artery 14 inside the wrist 16. The blood flow velocity sensor 10 mixes the fundamental wave f and the received wave f ′ output from the blood flow velocity sensor 10. The mixed wave is detected by a blood flow velocity sensor signal calculation unit (signal calculation unit) 22 so that only the frequency component of Doppler shift is extracted. In the signal calculation unit 22, the blood flow velocity v is calculated from the Doppler frequency component Δf (= f−f ′), the angle θ formed by the waves f and f ′ and the radial artery 14.

  The blood flow velocity sensor 10 includes a blood flow velocity sensor unit 18, a blood flow velocity sensor drive unit (drive unit) 20, and a signal calculation unit 22. The blood flow velocity sensor unit 18 transmits and receives waves from the surface of the living body of the measurement subject 4 to the blood inside the living body, and detects the flow of blood inside the living body. The blood flow velocity sensor unit 18 includes a transmission unit (transmission element) 24 and a reception unit (reception element) 26. There are a plurality of pairs of the transmitting unit 24 and the receiving unit 26, and the angle formed between the traveling direction of the wave to be transmitted and received and the radial artery 14 is different for each pair. The drive unit 20 drives the blood flow velocity sensor unit 18. The signal calculation unit 22 controls the drive unit 20 and the blood flow velocity sensor unit 18 to obtain the blood flow velocity v inside the living body. The blood flow velocity sensor unit 18 is configured using a piezoelectric element. Thereby, since the piezoelectric element has a simple structure, the blood flow velocity sensor can be reduced in size.

  The blood vessel diameter sensor 12 is attached at a position where ultrasonic waves can be applied to the radial artery 14 inside the wrist portion 16. The blood vessel diameter sensor 12 transmits a pulse signal or burst signal of several M to several tens of MHz, and measures the arrival time of the reflected wave from the radial artery 14 wall from the transmitted wave and the received wave. The blood vessel diameter sensor unit 27 transmits / receives ultrasonic waves to / from the radial artery 14 inside the living body, and detects the reflection arrival time difference of the radial artery 14 wall inside the living body.

  The blood vessel diameter sensor 12 includes a blood vessel diameter sensor unit 27, a blood vessel diameter sensor drive unit (drive unit) 28, and a blood vessel diameter sensor signal calculation unit (signal calculation unit) 30. The blood vessel diameter sensor unit 27 includes a transmission unit 29 and a reception unit 31. The blood vessel diameter sensor unit 27 transmits / receives ultrasonic waves to / from the radial artery 14 inside the living body, and detects the reflection arrival time difference of the radial artery 14 wall inside the living body. The drive unit 28 drives the blood vessel diameter sensor unit 27. The signal calculation unit 30 controls the driving unit 28 and the blood vessel diameter sensor unit 27 to obtain the blood vessel diameter d inside the living body.

  The blood pressure measurement device 2 according to the present embodiment includes a blood pressure signal calculation unit 32, a display unit 34, an atmospheric pressure sensor (height position sensor unit) 36, a switch 37, and a power supply unit 40. The blood pressure signal calculation unit 32 obtains the blood pressure P of the measurement subject 4 using the calculation results of the signal calculation unit 22 and the signal calculation unit 30. The display unit 34 displays the blood pressure P of the person 4 to be measured. It can also be visualized and displayed on a graph or the like. Further, the pulse may be displayed in the same manner. Furthermore, it is displayed that calibration is necessary. The atmospheric pressure sensor 36 measures the height position of the blood pressure measurement device 2. The switch 37 switches supply / cut-off of power from the power supply unit 40 to each functional unit of the blood pressure measurement device 2. The power supply unit 40 supplies power to each functional unit of the blood pressure measurement device 2. In the present embodiment, for example, a rechargeable secondary battery is assumed.

  FIG. 4 is a diagram illustrating measurement positions of the blood pressure measurement device 2 according to the present embodiment. FIG. 5 is a view showing the blood vessel diameter d to which the hydraulic head pressure component is applied according to the present embodiment. Here, a method of calculating blood pressure P by measuring blood flow velocity v and blood vessel diameter d without using a cuff (compression band) for non-invasive blood pressure measurement will be described. The blood pressure P is obtained by the product of the blood flow rate Q and the vascular resistance R.

P = Q · R (1)
Among these, the blood flow rate Q is obtained by the product of the blood vessel diameter d and the blood flow velocity v as expressed in the equation (2).

Q = (π · d ² · v) / 8 (2)
The vascular resistance R is determined by the ratio of the viscosity η of blood flowing in the radial artery 14 and the vascular diameter d, and the relationship that the vascular resistance R decreases as the vascular diameter d increases. Consider C as a constant.

R = η · C / d ⁴ (3)
When trying to derive the blood pressure P in consideration of these relational expressions, the intensity change of the volume pulse wave called a pulse wave is actually captured as a change in volume of the blood vessel diameter d when blood pulsates. By measuring the volume pulse wave, a value correlated with the blood vessel diameter d can be measured, and a value correlated with the vascular resistance R can be measured. Then, by measuring the blood flow velocity v in the blood vessel, a value correlating with the blood flow rate Q can also be obtained, and therefore the blood pressure P can be measured.

  Next, calculation of the systolic blood pressure Psys and the diastolic blood pressure Pdia will be described. The systolic blood pressure Psys and the diastolic blood pressure Pdia can be obtained as in equations (4) and (5) by using equations (1) to (3).

Psys = π / 8 · η · C · vsys / dsys ² (4)
Pdia = π / 8 · η · C · vdia / ddia ² (5)
Thereby, the blood pressure difference (Psys−Pdia) between the systolic blood pressure Psys and the diastolic blood pressure Pdia can be obtained as shown in Expression (6).

Psys−Pdia = π / 8 · η · C · (vsys / dsys ² −vdia / ddia ² ) (6)
Here, vsys is a systolic blood flow velocity, dsys is a systolic blood vessel diameter, vdia is a diastolic blood flow velocity, and ddia is a diastolic blood vessel diameter.

  FIG. 6 is a diagram showing a relationship between the blood vessel wall pressure and the blood vessel diameter (volume) according to the present embodiment. FIG. 6 is a diagram showing a blood vessel law. Conventional blood pressure measurement by cuff pressurization uses a non-linear region of tube law to obtain an oscillometric waveform. In contrast, in the present embodiment, a substantially linear approximation region shown in FIG. 6 is used. In this portion, the blood vessel diameter d and the blood vessel wall pressure (blood pressure P) can be considered to change substantially linearly. Therefore, by measuring the time change of the blood vessel diameter d, a value correlated with the time change of the blood pressure P can be obtained.

  Next, a method for calculating the systolic blood pressure Psys and the diastolic blood pressure Pdia using the above equations will be described. First, the systolic blood flow velocity vsys, the systolic blood vessel diameter dsys, the diastolic blood flow velocity vdia, and the diastolic blood vessel diameter ddia are set at the same height H as the position of the heart 38, that is, in a state where correction of the hydrocephalic pressure is not necessary. Ask. Waves are transmitted / received to / from the blood vessel inside the living body, the systolic blood flow velocity vsys and the diastolic blood flow velocity vdia are calculated from the Doppler shift amount of the blood flow scattered wave, and the systolic blood vessel diameter dsys and the diastole are calculated from the reflection arrival time difference between the blood vessels. The blood vessel diameter ddia is calculated. At the same time, the time change of the blood vessel diameter d is measured. From the blood vessel law, the blood vessel diameter d and the blood vessel wall pressure (blood pressure P) can be approximately linearly approximated when there is no pressure or slight pressure. At that time, the time change of the blood vessel diameter d is similar to the time change of the blood pressure P (see FIG. 6).

  Subsequently, the blood vessel diameter d is similarly measured at the position L of the heart 38 and the position L lowered by the height h. In that case, assuming that the person to be measured 4 is in a stable state, an extra pressure corresponding to the head pressure is applied to the blood vessel as compared with the position of the heart 38. That is, when the time change of the blood vessel diameter d is measured again in this state, the time change of the blood pressure P to which the hydraulic head pressure is added is obtained (see FIG. 5). From this, the change Δd of the blood vessel diameter d corresponding to the hydrocephalic pressure (ρ · g · h), (ρ: density of blood, g: gravitational acceleration) is known. The change of the blood vessel diameter d in the systole and the diastole is obtained by measurement, and the blood pressure difference ΔP (= Psys−Pdia) between the systolic blood pressure Psys and the diastole blood pressure Pdia can also be calculated. When this value is applied to the equation (6), the proportionality constant (π / 8 · η · C) is obtained, so that the systolic actual blood pressure Prsys and the diastolic actual blood pressure Prdia can be calculated from the equations (4) and (5).

Since the blood density ρ is about 1.055 ± 0.005 g / cm ² depending on the individual, the influence on the blood pressure value is ± 0.00. Since it is several mmHg, it can be considered constant. It can be seen that the correct value of the water head pressure (ρ · g · h) can be obtained if the height is accurately measured. According to the present embodiment, calibration by another sphygmomanometer such as a cuff sphygmomanometer is unnecessary, and calibration can be performed very simply by using the hydraulic head pressure. Further, it is not necessary to measure the volume pulse wave, and blood pressure can always be measured only by measuring the blood flow velocity and blood vessel diameter by wave motion.

(Method of converting hydrocephalic pressure (ρ · g · h) into vessel diameter d)
As shown in FIG. 4, the blood pressure measurement device according to the present embodiment is measured with respect to the time variation of the blood vessel diameter d at the position of the same height H as the heart 38 in the state where the blood pressure measurement device is worn on the wrist 16, and the cuff pressurization type. The systolic actual blood pressure Prsys and the diastolic actual blood pressure Prdia are measured by the sphygmomanometer 42. Subsequently, the arm is lowered to the position of the height L, and the time change of the blood vessel diameter d is measured. As a result, it is possible to calculate how much the pressure value due to the hydraulic head pressure corresponds to the change in the blood vessel diameter d (see FIG. 5).

FIG. 7 is a diagram showing cuff pressurization measurement values according to the present embodiment. There are the following methods (a) to (c) for calculating how much the pressure value due to the water head pressure corresponds to the change in the blood vessel diameter d.
(A) The change in blood vessel diameter d is measured for about 10 seconds, and the average blood vessel diameters (dm1 and dm2) at the heights H and L in FIG. 4 are calculated. Subsequently, a change Δdm in the average blood vessel diameter (dm1, dm2) is obtained from the equation (7).

Δdm = dm2-dm1 (7)
The blood vessel diameter change Δd corresponding to the hydraulic head pressure is obtained from the equation (8).

Δd = Δdm (8)
Accordingly, when the average systolic blood vessel diameter dmsys1 and the average diastolic blood vessel diameter dmdia1 at the position of the height H in FIG. 4 are used, Equation (9) is established when the relationship between the pressure and the blood vessel diameter is considered.

(Prsys−Prdia): ρ · g · h = (dmsys1−dmdia1): Δdm (9)
Therefore, the water head pressure (ρ · g · h) is obtained from the equation (10) (see FIG. 7A).

  ρ · g · h = (Prsys−Prdia) · Δdm / (dmsys1−dmdia1) (10)

  (B) The change in blood vessel diameter d is measured for about 10 seconds, and the average systolic blood vessel diameter (dmsys1, dmsys2) and average diastolic blood vessel diameter (dmdia1, dmdia2) at the positions of heights H and L in FIG. 4 are calculated. . Subsequently, the change (Δdmsys, Δdmdia) of the average blood vessel diameter (dm1 and dm2) is obtained from the equations (11) and (12).

Δdmsys = dmsys2-dmsys1 (11)
Δdmdia = dmdia2-dmdia1 (12)
Further, taking the average from the above, the blood vessel diameter change Δd corresponding to the hydraulic head pressure is obtained from the equation (13).

Δd = (Δdmsys + Δdmdia) / 2 (13)
Thereby, when the relationship between the pressure and the blood vessel diameter is considered, Expression (14) is established.

(Prsys−Prdia): ρ · g · h = (dmsys1−dmdia1): (Δdmsys + Δdmdia) / 2 (14)
Therefore, the water head pressure (ρ · g · h) is obtained from the equation (15) (see FIG. 7B).

  ρ · g · h = (Prsys−Prdia) · (Δdmsys + Δdmdia) / 2 · (dmsys1−dmdia1) (15)

(C) In the above methods (a) and (b), the calculation was made based on the idea of using the substantially linear approximation region of FIG. 6, but here, a method of measuring more strictly is shown. First, the time change of the blood vessel volume V is calculated from the time change of the blood vessel diameter d at the position of the height H in FIG. In general, the relationship between the blood vessel volume V and the pressure difference Pt between the intravascular pressure and the cuff pressure can be expressed by equation (16). Therefore, when b = 0.03 mmHg ⁻¹ is used, the systolic actual blood pressure Prsys and the diastolic actual blood pressure Prdia V0 and Vmax are obtained from the relationship of the blood vessel volume (Vrsys, Vrdia). Thereby, from the time change of the blood vessel volume V, the time change of the pressure difference Pt between the blood vessel pressure and the cuff pressure at the position of the height H can be calculated.

V = Vmax + (V0−Vmax) · e ^b · Pt (16)
Next, the time change of the blood vessel volume (Vrsys, Vrdia) is calculated from the time change of the blood vessel diameter d at the position of the height L, and the time change of the pressure difference Pt between the intravascular pressure and the cuff pressure is calculated using the equation (16). Ask for. From the time change of the pressure difference Pt between the intravascular pressure and the cuff pressure at the positions of heights H and L, the difference between the average values of the intravascular pressure and the cuff pressure difference Pt at each position is obtained, and the value is obtained as the hydraulic head pressure. (Ρ · g · h). Alternatively, the difference between each of the average systolic blood pressure and the average diastolic blood pressure is obtained, and the average value of the differences is set as the hydraulic head pressure. If the hydrocephalic pressure (ρ · g · h) and the blood vessel diameter d (blood vessel volume) can be converted, the blood pressure difference (Prsys−Prdia) between the systolic actual blood pressure Prsys and the diastolic actual blood pressure Prdia can be expressed by equation (17). I want.

Prsys−Prdia = 1 / b · log {(Vsys−Vmax) / (Vdia−Vmax)} (17)
Here, Vsys is a systolic blood vessel volume, and Vdia is a diastolic blood vessel volume.

  If the hydrocephalic pressure (ρ · g · h) can be calculated, the blood pressure difference (Prsys−Prdia) between the systolic actual blood pressure Prsys and the diastolic actual blood pressure Prdia can be determined from the above-described relationship only by measuring the blood vessel diameter d. The calculation of the water head pressure (ρ · g · h) is always performed before the start of continuous measurement, that is, once at the beginning of the day, etc., so that more accurate measurement can be performed. In addition, the height difference h between the measurement position heights H and L is an important parameter related to accuracy, and is therefore performed at the same position for each measurement. For example, the height H is determined to be the position of the heart 38, the height L is determined to be a position where the arm is lowered straight, and the height difference h is measured. Alternatively, the height may be calculated using a highly accurate barometric sensor 36 or the like. Thereby, the height difference which is one element at the time of calculating | requiring a hydraulic head pressure can be measured easily.

(Measurement method of blood vessel diameter)
In the case of measuring the blood vessel diameter d, the drive unit 28 of the blood vessel diameter sensor 12 shown in FIG. 3 transmits a pulse signal or burst signal of several M to several tens of MHz as shown in FIG. The arrival time of the reflected wave from the blood vessel wall is measured from the received wave. If the reflected wave arrival time is 1.73 μs and the sound velocity inside the living body is 1500 m / s, the blood vessel diameter d can be calculated as 2.6 mm. For example, a piezoelectric element may be used for transmitting and receiving ultrasonic waves. Furthermore, as a method for measuring the blood vessel diameter d, an echo tracking method for tracking a blood vessel wall or the like based on an echo signal obtained from an ultrasonic beam is known. By the echo tracking method, the displacement of the blood vessel wall or the like can be measured with an accuracy of about several μm below the wavelength of the ultrasonic wave.

(Measurement method of blood flow velocity)
FIG. 8 is a diagram showing a blood flow velocity sensor according to the present embodiment. When measuring the blood flow velocity v, the fundamental wave f output from the drive unit 20 of the blood flow velocity sensor 10 shown in FIG. 3 and the received wave f ′ (see FIG. 2) of the reception unit 26 are mixed and the signal calculation unit 22 is mixed. Only the frequency component of the Doppler shift is extracted by performing detection at. The signal calculation unit 22 calculates the blood flow velocity v from the Doppler frequency component Δf (= f−f ′), the wave and the angle θ formed by the radial artery 14 using the equation (18).

v = ε · Δf / (2 · f · cos θ) (18)
Here, ε is the speed of sound inside the living body, f is the frequency of the input wave, v is the blood flow velocity, and θ is the angle between the radial artery 14 and the wave. Actually, since it is difficult to obtain the angle θ formed by the wave and the radial artery 14, the angle θ formed by the wave and the radial artery 14 is unknown using a plurality of blood flow velocity sensors as shown in FIG. In order to obtain the blood flow velocity v, a sensor capable of transmitting and receiving two ultrasonic waves of an angle θ and an angle θ-α with respect to the direction of blood flow measured using two blood flow velocity sensors is used. If the angle formed by the two blood flow velocity sensors is α, the angle θ formed by the wave and the radial artery 14 can be obtained. That is, a pair of blood flow velocity sensors 10 that transmit and receive waves from the surface of the living body to the inside. If the Doppler frequency components Δf0 and Δf1 received by the blood flow velocity sensors and the angle formed by the two blood flow velocity sensors are α, θ is obtained using equation (19).

θ = Tan ⁻¹ (Δf1 / Δf0−cos α) / sin α (19)
And the blood flow velocity v is calculated | required by substituting the angle (theta) and Doppler frequency component (DELTA) f0 which the wave and the radial artery 14 which were calculated | required here calculated | required into (18) as (DELTA) f = (DELTA) f0.

  For example, in order to obtain the blood flow velocity v, a 1 MHz pulse signal is transmitted, and the Doppler frequency component Δf of the received wave is calculated. When the Doppler frequency component Δf is 0.33 kHz and the angle θ between the radial artery 14 and the wave is 45 degrees, the blood flow velocity v can be calculated as approximately 50 cm / s. The blood pressure P for each beat is calculated from the blood vessel diameter d and the blood flow velocity v obtained above. That is, the blood pressure P is determined by measuring the blood vessel diameter d and the blood flow velocity v with a wave such as an ultrasonic wave as shown in the equations (4) and (5) for each beat. The proportionality constant (π / 8 · η · C) in the equations (4) and (5) is obtained from the equation (20) obtained by modifying the equation (6).

π / 8 · η · C = (Psys−Pdia) / (vsys / dsys ² −vdia / ddia ² ) (20)
Therefore, stable blood pressure measurement can be performed under no pressure by calculating the blood pressure P for each sample rate or at regular intervals from the relationship of equations (4) and (5).

(Simple calibration method)
Since the proportionality constant (π / 8 · η · C) largely reflects biological information, it is necessary to calibrate the value at a certain interval. In that case, as shown in FIG. 4, the position of the height H and the position of the height L, the blood vessel diameter d and the blood flow velocity v at the respective positions are obtained as described above by waves such as ultrasonic waves, and the systolic blood pressure Psys and the diastole. The blood pressure difference (Psys-Pdia) of the blood pressure Pdia is obtained by conversion of the hydrocephalic pressure (ρ · g · h) and the blood vessel diameter d. From the above, calibration can be performed in a timely manner without cuff pressurization.

(Blood pressure measurement method and calibration value calculation)
FIG. 9 is a diagram illustrating a blood pressure measurement method according to the present embodiment. First, after the switch 37 is turned on, calibration for calculating a proportionality constant (π / 8 · η · C) is performed as shown in step S10. Details of step S10 will be described later.

  Subsequently, as shown in step S20, the blood vessel diameter d and the blood flow velocity v are measured. As the measurement method, the above-described ultrasonic reflection arrival time is measured to measure the blood vessel diameter d, or the blood flow velocity v is measured by the Doppler method.

  Next, as shown in step S30, the blood pressure P is calculated using the proportionality constant obtained by the calibration routine of step S10. The temporal change in blood pressure P can also be calculated by obtaining temporal changes in the blood vessel diameter d and blood flow velocity v at the same location and at the same time.

  Next, as shown in step S <b> 40, the blood pressure P is displayed on the display unit 34. Further, it can be visualized by a graph or the like and displayed on the display unit 34. Further, the pulse may be displayed in the same manner.

  Next, as shown in step S50, it is determined whether calibration is necessary again. If necessary, return to step S10 and perform calibration. If not necessary, the process proceeds to step S60. The case where calibration is necessary is, for example, a case where the blood pressure changes by ± 15 mmHg or more compared to normal. In this case, a recalibration instruction is displayed on the display unit 34.

  Next, as shown in step S60, it is determined whether it is necessary to continue the measurement. If necessary, the process returns to step S20 to measure the blood vessel diameter d and the blood flow velocity v. Exit if not needed. As a result, it is possible to measure the blood pressure accurately without using a cuff sphygmomanometer after that, only by obtaining the correction coefficient based on the blood pressure value first measured using the cuff sphygmomanometer. Can calibrate easily without using a cuff sphygmomanometer when measuring blood pressure constantly under free action.

FIG. 10 is a diagram showing a calibration routine according to the present embodiment.
A flow showing details of the calibration routine in step S10 is shown in FIG. The procedure according to (a) of the water head pressure conversion method is as follows. First, as shown in step S110, the blood vessel diameter d at the height H in FIG. 4 is measured, and at the same time, the average blood vessel diameter dm1 is calculated. The blood vessel diameter change is measured for about 10 seconds.

  Next, as shown in step S120, the arm is moved to the position of the height L. At that time, the height difference h between the positions of the heights H and L is measured. Note that the height may be calculated using a high-precision atmospheric pressure sensor 36 (see FIG. 3) as the height position sensor unit. Thereby, the height difference which is one element at the time of calculating | requiring a hydraulic head pressure can be measured easily.

  Next, as shown in step S130, the hydraulic head pressure (ρ · g · h) is calculated.

  Subsequently, as shown in step S140, the blood vessel diameter d and the blood flow velocity v are measured, and at the same time, the average blood vessel diameter dm2 is obtained.

  Next, as shown in step S150, an average blood vessel diameter change Δdm (= dm1-dm2) at the positions of heights H and L is calculated.

  Next, as shown in step S160, a blood pressure difference (Psys−Pdia) between the diastolic blood pressure Pdia and the systolic blood pressure Psys is calculated. When the average systolic blood vessel diameter dmsys1 and the average diastolic blood vessel diameter dmdia1 at the position of the height H in FIG. 4 are used, the equation (9) is transformed and the diastolic blood pressure Pdia and the systolic blood pressure Psys are obtained from the equation (21). Blood pressure difference (Psys−Pdia).

Psys−Pdia = ρ · g · h · (dmsys1−dmdia1) / Δdm (21)
In this case, the blood pressure difference (Prsys−Prdia) between the diastolic actual blood pressure Prdia and the systolic blood pressure Prsys is calculated as being equal to the blood pressure difference (Psys−Pdia) between the diastolic blood pressure Pdia and the systolic blood pressure Psys.

  Next, as shown in step S170, a proportionality constant (π / 8 · η · C) is calculated from the following equation. The proportionality constant (π / 8 · η · C) is calculated from the equation (20). In this case, the blood pressure difference (Psys−Pdia) between the diastolic blood pressure Pdia and the systolic blood pressure Psys is calculated as being equal to the blood pressure difference (Prsys−Prdia) between the diastolic actual blood pressure Prdia and the systolic blood pressure Prsys. Further, since the relationship between the hydrocephalic pressure and the blood vessel diameter change does not change, the blood pressure difference (Psys-Pdia) between the diastolic blood pressure Pdia and the systolic blood pressure Psys can be calculated without cuff pressure. Thereby, the proportionality constant can be easily calibrated.

  According to the blood pressure measurement device and the blood pressure measurement method of the present embodiment, timely calibration can be simplified without using a cuff, and the blood pressure P can be measured with high accuracy. Further, it is possible to provide a blood pressure measuring device and a blood pressure measuring method that are wearable and can always be measured.

  DESCRIPTION OF SYMBOLS 2 ... Blood pressure measuring apparatus 4 ... Person to be measured 10 ... Blood flow velocity sensor 12 ... Blood vessel diameter sensor 14 ... Radial artery (blood vessel) 16 ... Wrist 18 ... Blood flow velocity sensor unit 20 ... Drive unit (blood flow velocity sensor drive unit) 22 ... Signal calculation unit (blood flow velocity sensor signal calculation unit) 24 ... Transmission unit (transmission element) 26 ... Reception unit (reception element) 27 ... Blood vessel diameter sensor unit 28 ... Drive unit (blood vessel diameter sensor drive unit) DESCRIPTION OF SYMBOLS 29 ... Transmitting part 30 ... Signal calculating part (blood vessel diameter sensor signal calculating part) 31 ... Receiving part 32 ... Blood pressure signal calculating part 34 ... Display part 36 ... Barometric pressure sensor (height position sensor part) 37 ... Switch 38 ... Heart 40 ... Power source 42 ... Cuff pressurization type blood pressure monitor.

Claims (8)

A blood flow velocity sensor that detects the flow of blood inside the living body by transmitting and receiving waves from the surface of the living body of the subject to the blood inside the living body;
A blood flow velocity sensor driving unit for driving the blood flow velocity sensor unit;
A blood flow velocity sensor signal calculation unit for controlling the blood flow velocity sensor driving unit and the blood flow velocity sensor unit to obtain a blood flow velocity inside the living body;
A blood vessel diameter sensor unit that transmits and receives ultrasonic waves to and from the blood vessel inside the living body, and detects a reflection arrival time difference of the blood vessel wall inside the living body; and
A blood vessel diameter sensor driving unit for driving the blood vessel diameter sensor unit;
A blood vessel diameter sensor signal calculating unit for controlling the blood vessel diameter sensor driving unit and the blood vessel diameter sensor unit to obtain a blood vessel diameter inside the living body;
A blood pressure signal calculation unit for obtaining the blood pressure of the measurement subject using calculation results of the blood flow velocity sensor signal calculation unit and the blood vessel diameter sensor signal calculation unit;
A blood pressure measurement device comprising: The blood pressure measurement device according to claim 1,
The blood pressure measurement device, wherein the blood pressure signal calculation unit performs a calculation for obtaining the blood pressure by converting the blood vessel diameter into a hydrocephalic pressure. The blood pressure measurement device according to claim 1 or 2,
A first state in which the predetermined part of the subject is positioned at a predetermined height, and the first state and a second state in which the predetermined part is positioned at the height of the heart of the subject A height position sensor unit for obtaining a height difference of the predetermined part;
The blood pressure measuring device, wherein the water head pressure is obtained using the height difference measured by the height position sensor unit. The blood pressure measurement device according to any one of claims 1 to 3,
The blood flow velocity sensor unit is composed of a transmitting element and a receiving element, and there are a plurality of pairs of the transmitting element and the receiving element, and the traveling direction of waves to be transmitted and received and the direction of blood flow The blood pressure measuring device is characterized in that the angle formed by the pair is different for each pair. The blood pressure measurement device according to any one of claims 1 to 3,
The blood flow rate sensor unit is configured by using a piezoelectric element. In a first state where a predetermined part of the measurement subject is positioned at a predetermined height, a predetermined proportionality to a value obtained by dividing the blood flow velocity of the predetermined part by the square of the blood vessel diameter of the predetermined part A blood pressure of the measurement subject proportional to a constant, and a calibration step for obtaining the proportionality constant;
Measuring the blood vessel diameter and the blood flow velocity at the predetermined site in the first state,
Determining the blood pressure using the blood vessel diameter, the blood flow velocity, and the proportionality constant;
Displaying the blood pressure; and
Determining whether calibration of the proportionality constant is necessary;
A blood pressure measurement method characterized by comprising: The blood pressure measurement method according to claim 6,
The calibration process includes
In the second state where the predetermined portion is positioned at the height of the heart of the measurement subject, the blood vessel diameter of the predetermined portion, and the blood vessel diameter of the predetermined portion and the systolic and diastolic phases are respectively measured. Obtaining a first average vessel diameter, an average systolic vessel diameter, and an average diastolic vessel diameter;
A height difference measuring step for measuring a height difference of the predetermined portion between the first state and the second state in the first state;
Obtaining a hydraulic head pressure between the first state and the second state using the height difference;
In the first state, the blood vessel diameter of the predetermined part, and the blood flow velocity and blood vessel diameter of the predetermined part of the systole and the diastole are measured, respectively, the second average blood vessel diameter, the systolic blood flow velocity, Obtaining a systolic blood vessel diameter, a diastolic blood flow velocity, and a diastolic blood vessel diameter;
Obtaining an average blood vessel diameter change using the first average blood vessel diameter and the second average blood vessel diameter;
Determining a blood pressure difference between systolic blood pressure and diastolic blood pressure using the hydrocephalic pressure, the mean blood vessel diameter change, the mean systolic blood vessel diameter, and the mean diastolic blood vessel diameter; and
Obtaining the proportionality constant using the blood pressure difference, the systolic blood flow velocity, the systolic blood vessel diameter, the diastolic blood flow velocity, and the diastolic blood vessel diameter;
A blood pressure measurement method characterized by comprising: The blood pressure measurement method according to claim 7,
The height difference measuring step includes
A blood pressure measurement method characterized by being measured by a height position sensor unit that measures the height difference of the predetermined part between the first state and the second state.