Blood pressure estimation device, blood pressure estimation method, and program

Abstract

To provide a blood pressure estimation device allowing a user to easily measure a blood pressure at home, etc. and estimating the blood pressure without contact by acquiring a pulse wave from an image.SOLUTION: A distance acquisition part 501 acquires a first height difference representing a height difference between a heart and a hand when the hand of a subject is placed at a first position above the heart, and a second height difference representing a height difference when the hand is placed at a second position above the heart and different from the first position. A differential pressure acquisition part 502 acquires differential pressures between the blood pressure of the heart and the blood pressure of the hand, the differential pressure corresponding to the first height difference and the differential pressure corresponding to the second height difference respectively. A pulse wave acquisition part 503 acquires pulse waves detected from a plurality of points on the hand. A velocity calculation part 504 calculates a pulse wave velocity at the first position and a pulse wave velocity at the second position on the basis of the pulse waves. A blood pressure calculation part 505 calculates a blood pressure of the heart of the subject on the basis of the differential pressures acquired by the differential pressure acquisition part 502 and the respective pulse wave velocities calculated by the velocity calculation part 504.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a blood pressure estimation device, a blood pressure estimation method, and a program.

Background Art

[0002] In the measurement of blood pressure at home or in a hospital, the oscillometric method is mainly adopted. The oscillometric method is a method of measuring the maximum blood pressure (systolic blood pressure) and the minimum blood pressure (diastolic blood pressure) by compressing the upper arm using a cuff. The oscillometric method has the drawbacks of being cumbersome due to cuff wrapping, causing discomfort due to compression, and taking a long measurement time, so it is not suitable for easy measurement.

[0003] On the other hand, in recent years, several cuffless estimation methods have been announced. As a cuffless estimation method, for example, a wearable type that measures an electrocardiogram and a pulse at the wrist like a smartwatch is known. There is also a method of non-contact extraction of a pulse wave (video pulse wave) by photographing an exposed part of the skin such as the face or palm with a camera and analyzing a slight color change of the skin.

[0004] As a related technology, a device for estimating blood pressure based on the measurement positions of the high and low points of a specific part calculated from a video signal acquired by a video acquisition device and the ratio information of the pulse wave amplitudes of the high and low pulse wave information is disclosed (for example, see Patent Document 1). Among the cuffless estimation methods, those using the pulse wave velocity (PWV: Pulse Wave Velocity) and those using the correlation between the pulse wave propagation time and blood pressure are known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, conventional techniques have several drawbacks: the blood pressure estimation formula based on pulse wave propagation time varies from person to person, making it difficult to estimate absolute pressure; and the parameters of the estimation formula can fluctuate over time, leading to increased estimation errors during long-term measurements. Therefore, periodic calibration is necessary, which can be inconvenient. Thus, conventional techniques have the problem of not being able to easily measure blood pressure at home or in other settings.

[0007] This invention has been made in view of these circumstances, and its purpose is to provide a technology that allows for easy measurement of blood pressure at home, and further, to provide a technology that allows for non-contact estimation of blood pressure by obtaining pulse waves from video. [Means for solving the problem]

[0008] To solve the above-mentioned problems, a blood pressure estimation device according to one aspect of the present invention is a blood pressure estimation device comprising: an elevation difference acquisition unit that acquires a first elevation difference indicating the elevation difference between the heart and the part of the body when a part of the body of a subject that is displaceable relative to the heart is placed at a first position above the heart, and a second elevation difference indicating the elevation difference when the part of the body is placed at a second position above the heart but different from the first position; a differential pressure acquisition unit that acquires the differential pressure between the blood pressure of the heart and the blood pressure of the part of the body, wherein the differential pressure corresponds to the first elevation difference and the differential pressure corresponds to the second elevation difference; a pulse wave acquisition unit that acquires pulse waves detected from a plurality of locations in the part of the body; a velocity calculation unit that calculates the pulse wave propagation velocity at the first position and the pulse wave propagation velocity at the second position based on the pulse waves; a blood pressure calculation unit that calculates the blood pressure of the subject's heart based on the differential pressure acquired by the differential pressure acquisition unit and the pulse wave propagation velocity calculated by the velocity calculation unit; and an output unit that outputs the calculation result of the blood pressure calculation unit.

[0009] To solve the above-mentioned problems, another embodiment of the present invention is a blood pressure estimation device comprising: an elevation difference acquisition unit that acquires the elevation difference between the heart and a part of the subject's body that is displaceable relative to the heart, when the part is positioned at multiple locations above the heart; an estimated differential pressure acquisition unit that acquires an estimated differential pressure between the blood pressure of the heart and the blood pressure of the part, corresponding to each elevation difference; a pulse wave acquisition unit that acquires pulse waves detected from multiple locations on the part; a velocity calculation unit that calculates the pulse wave propagation time and pulse wave propagation velocity at the multiple locations based on the pulse waves at the multiple locations; a generation unit that generates an estimation formula showing the relationship between the pulse wave propagation velocity at the multiple locations and the corresponding estimated differential pressure corresponding to each elevation difference; a blood pressure calculation unit that calculates the blood pressure of the subject's heart based on the estimation formula; and an output unit that outputs the calculation result of the blood pressure calculation unit.

[0010] To solve the above-mentioned problems, another aspect of the present invention is a blood pressure estimation method which includes: an elevation difference acquisition step in which a computer of a blood pressure estimation device acquires a first elevation difference indicating the elevation difference between the heart and the part of the body when the part of the body that is displaceable relative to the heart is placed at a first position above the heart, and a second elevation difference indicating the elevation difference when the part of the body is placed at a second position above the heart but different from the first position; a differential pressure acquisition step which acquires a differential pressure between the blood pressure of the heart and the blood pressure of the part of the body, wherein the differential pressure corresponding to the first elevation difference and the differential pressure corresponding to the second elevation difference are acquired; a pulse wave acquisition step which acquires pulse waves detected from a plurality of locations in the part of the body; a velocity calculation step which calculates the pulse wave propagation velocity at the first position and the pulse wave propagation velocity at the second position based on the pulse waves; a blood pressure calculation step which calculates the blood pressure of the heart of the subject based on each differential pressure acquired in the differential pressure acquisition step and each pulse wave propagation velocity calculated in the velocity calculation step; and an output step which outputs the calculation result in the blood pressure calculation step.

[0011] To solve the above-mentioned problems, another aspect of the present invention is a blood pressure estimation method which includes processing the following steps: an elevation difference acquisition step in which the computer of a blood pressure estimation device acquires the elevation difference between the heart and a part of the subject's body that is displaceable relative to the heart, when the part of the body is positioned at a plurality of locations above the heart; an estimated differential pressure acquisition step in which an estimated differential pressure is obtained between the blood pressure of the heart and the blood pressure of the part, with the estimated differential pressure corresponding to each elevation difference; a pulse wave acquisition step in which a pulse wave is obtained from a plurality of locations on the part; a velocity calculation step in which the pulse wave propagation time and pulse wave propagation velocity at the plurality of locations are calculated based on the pulse waves at the plurality of locations; a generation step in which an estimation formula is generated that shows the relationship between the pulse wave propagation velocity at the plurality of locations and the corresponding estimated differential pressure corresponding to each elevation difference; a blood pressure calculation step in which the blood pressure of the subject's heart is calculated based on the estimation formula; and an output step in which the calculation result in the blood pressure calculation step is output.

[0012] To solve the above-mentioned problems, another aspect of the present invention is a program that causes a computer to function as a blood pressure estimation device, wherein the computer functions as: a height difference acquisition unit that acquires a first height difference indicating the height difference between the heart and a part of the subject's body that is displaceable relative to the heart when that part is placed at a first position above the heart, and a second height difference indicating the height difference when that part is placed at a second position above the heart but different from the first position; a differential pressure acquisition unit that acquires the differential pressure between the blood pressure of the heart and the blood pressure of the part, specifically the differential pressure corresponding to the first height difference and the differential pressure corresponding to the second height difference; a pulse wave acquisition unit that acquires pulse waves detected from multiple locations on the part; a velocity calculation unit that calculates the pulse wave propagation velocity at the first position and the pulse wave propagation velocity at the second position based on the pulse waves; a blood pressure calculation unit that calculates the blood pressure of the subject's heart based on the differential pressure acquired by the differential pressure acquisition unit and the pulse wave propagation velocity calculated by the velocity calculation unit; and an output unit that outputs the calculation result of the blood pressure calculation unit.

[0013] To solve the above-mentioned problems, another aspect of the present invention is a program that causes a computer to function as a blood pressure estimation device, wherein the computer is configured to function as: an elevation difference acquisition unit that acquires the elevation difference between the heart and a part of the subject's body that is displaceable relative to the heart, when the part of the body is positioned at multiple locations above the heart; an estimated differential pressure acquisition unit that acquires an estimated differential pressure between the blood pressure of the heart and the blood pressure of the part of the body, corresponding to each elevation difference; a pulse wave acquisition unit that acquires pulse waves detected from multiple locations on the part of the body; a velocity calculation unit that calculates the pulse wave propagation time and pulse wave propagation velocity at the multiple locations based on the pulse waves at the multiple locations; a generation unit that generates an estimation formula showing the relationship between the pulse wave propagation velocity at the multiple locations and the corresponding estimated differential pressure corresponding to each elevation difference; a blood pressure calculation unit that calculates the blood pressure of the subject's heart based on the estimation formula; and an output unit that outputs the calculation result of the blood pressure calculation unit. [Effects of the Invention]

[0014] According to the present invention, blood pressure can be easily measured at home or elsewhere, and furthermore, blood pressure can be estimated non-contact by obtaining pulse waves from video. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows an example configuration of the measurement system St according to the first embodiment. [Figure 2] This figure shows an example of the mounting position of the pulse wave sensor 10. [Figure 3] This figure shows an example of a subject's actions when estimating their blood pressure using the blood pressure estimation device 1. [Figure 4] This is a block diagram showing an example of the hardware configuration of blood pressure estimation device 1. [Figure 5] This is a block diagram showing an example of the functional configuration of blood pressure estimation device 1. [Figure 6] This flowchart shows an example of the blood pressure estimation process performed by the blood pressure estimation device 1. [Figure 7]This figure shows an example configuration of the measurement system St according to the second embodiment. [Figure 8] This is a schematic diagram showing an example of a measurement environment for verifying blood pressure estimation methods. [Figure 9] This figure shows the relationship between the height of the hand relative to the heart and the difference between the diastolic blood pressure of the heart and the diastolic blood pressure of the hand. [Figure 10] This figure shows the relationship between the height of the hand relative to the heart and the difference between the diastolic blood pressure of the heart and the diastolic blood pressure of the hand. [Figure 11] This figure shows the relationship between the height of the hand relative to the heart and the difference between the mean blood pressure of the heart and the mean blood pressure of the hand. [Figure 12] This diagram shows the relationship between the height of the hand relative to the heart and peripheral blood pressure. [Figure 13] This table shows individual differences in the relationship between height from the heart and peripheral blood pressure. [Figure 14] This is a schematic diagram of the measurement environment for Experiment 1, which used a contact-type sensor. [Figure 15] This diagram shows the mounting position of the photoelectric volume pulse wave sensor. [Figure 16] This figure shows the experimental protocol (for one set) for Experiment 1. [Figure 17] This figure shows the results of an electrocardiogram (ECG) and peripheral volume pulse wave measurements for a particular subject. [Figure 18] This figure shows the relationship between PWV2 and the estimated value ΔPd in ​​two measurements for a particular subject. [Figure 19] This figure shows the results of estimating diastolic blood pressure using the estimated value ΔPd calculated using formula (14). [Figure 20] This figure shows the results of comparing the estimated value P', which was corrected using the regression line in equation (15), with the actual measured value. [Figure 21] This table shows the estimated error (RMSE) of the estimated value compared to the measured value. [Figure 22] This is a schematic diagram of the measurement environment for Experiment 2, which was conducted completely without contact. [Figure 23] This figure shows the experimental protocol for Experiment 2. [Figure 24] This figure shows an example of setting up a Region of Interest (ROI) for extracting video pulse waves. [Figure 25] This figure shows the luminance values ​​of the G channel relative to the left and right positions within the ROI. [Figure 26] This figure shows the relationship between changes in hand height h and PTT (Point-to-Touch). [Figure 27] This figure shows the relationship between the intermediate parameter μ, which correlates with blood pressure, and the measured value of diastolic blood pressure (P). [Figure 28] This figure shows a comparison between the estimated diastolic blood pressure (PV) calculated using formula (16) and the measured value (P). [Figure 29] This figure shows the relationship between hand height and PTT when the ROI in the middle finger and carpal region of a particular subject is moved by 1 pixel. [Modes for carrying out the invention]

[0016] (Embodiment) The first, second, and third embodiments of the present invention will be described below.

[0017] (First Embodiment) (Example configuration of the measurement system St according to the first embodiment) Figure 1 shows an example of the configuration of the measurement system St according to the first embodiment. As shown in Figure 1, the measurement system St comprises a blood pressure estimation device 1, a pulse wave sensor 10, and a height detection unit 20. The blood pressure estimation device 1 is a device that estimates blood pressure without using a cuff. Specifically, the blood pressure estimation device 1 is a device that estimates blood pressure by utilizing the change in peripheral pulse waves caused by the change in the height of the hand from the heart as the subject's hand is raised and lowered.

[0018] The pulse wave sensor 10 detects pulse waves at two points on a part of the body. This part of the body is, for example, the hand. The detection results from the pulse wave sensor 10 are used to calculate pulse transmission times (PTT) and pulse wave velocity (PWV). The pulse wave sensor 10 is, for example, a photoplethysmogram (PPG) sensor.

[0019] The height detection unit 20 is a device capable of detecting the height of the subject's hand perpendicular to the ground from the heart (hereinafter sometimes referred to as "upward distance"). The height detection unit 20 may be a contact type that makes contact with the subject, or a non-contact type that does not make contact with the subject. Examples of contact types include wound linear encoders, ultrasonic rangefinders, and laser rangefinders. Examples of non-contact types use image data captured by imaging devices such as smartphones and digital cameras. Alternatively, instead of the height detection unit 20, the subject or the person taking the measurement may directly measure the height of their hand to obtain an actual measurement value, which can then be input into the blood pressure estimation device 1.

[0020] Before detecting the upward distance using the height detection unit 20, the position of the heart is determined. The position of the heart may be determined, for example, from the person's height or sitting height, or it may be determined based on image data of the subject. Furthermore, when detecting the upward distance, the part of the subject's hand to be detected may be a predetermined part of the hand, such as the fingertips or wrist.

[0021] The functions performed by the height detection unit 20 may also be provided in the blood pressure estimation device 1. For example, by inputting information about the position of the subject's raised hands or information about the position of the heart into the blood pressure estimation device 1, the blood pressure estimation device 1 may be configured to detect height.

[0022] Figure 2 shows an example of the mounting position of the pulse wave sensor 10. As shown in Figure 2, in this embodiment, two pulse wave sensors 10 are attached to the wrist 201 and fingertip 202 of one of the subject's hands 200 (for example, the left hand).

[0023] Figure 3 shows an example of a subject's movements when estimating their blood pressure using the blood pressure estimation device 1. As shown in Figure 3, subject Us assumes a seated position. Subject Us's heart height is set to 0 cm. Subject Us moves their hand 200 (for example, left hand) to an upper first position, and then moves it from the first position to a lower second position. The blood pressure estimation device 1 acquires pulse waves at the wrist 201 and fingertip 202 at the first and second positions. Based on these pulse waves and the displacement of the hand height, the blood pressure estimation device 1 can estimate subject Us's blood pressure. The blood pressure estimation method according to this embodiment will be described below.

[0024] (Regarding pulse wave propagation time (PTT)) Pulse wave propagation time is the time it takes for a pulse wave to travel between two points. The time when the pulse reaches the wrist 201 is T. A The time when the pulse reached fingertip 202 was recorded as T B Therefore, the pulse wave propagation time can be expressed by the following formula (1).

[0025]

number

[0026] (Regarding pulse wave velocity (PWV)) Pulse wave velocity is the speed at which a pulse wave propagates between two points, the wrist 201 and the fingertip 202. It is obtained by dividing the distance between the two measurement points by the pulse time (PTT). If the distance between the wrist 201 and the fingertip 202 is L, the pulse wave velocity can be expressed by the following formula (2).

[0027]

number

[0028] (Regarding Stiffness Parameter β) The stiffness parameter β is an index representing the intrinsic hardness of the local arterial wall. β is calculated from the change in the inner diameter (ΔD) of the blood vessel accompanying the heartbeat of the systolic blood pressure (P s ) and the diastolic blood pressure P d , and the blood pressure at the time of measurement. Since the relationship between the outer radius of the blood vessel and the internal pressure in the artery is not linear, by performing a logarithmic transformation on the change in internal pressure, a linear relationship is obtained with the blood vessel diameter expansion, which is expressed by the following formula (3).

[0029]

Equation

[0030] Here, ΔD is the difference D s between the blood vessel diameter D d in the systolic phase and the blood vessel diameter D d in the diastolic phase, which is D s -D

[0031]

Equation

[0032] PWV 2 is related to the change in blood pressure ΔP and is also related to the reciprocal of the volume change rate, which is the ratio of the blood vessel volume V and its change ΔV. ρ is the specific gravity of blood. Here, when expressing V / ΔV with the blood vessel diameter as the reference for measuring PWV, it is expressed by the following formula (5).

[0033]

Equation

[0034] Also, when rewriting formula (4) using formulas (3) and (5), it can be expressed as formula (6).

[0035]

number

[0036] Here, the ratio of pulse pressure on the right-hand side of equation (6) to the logarithm of the ratio of systolic blood pressure to diastolic blood pressure can be transformed into equation (7).

[0037]

number

[0038] Substituting this into equation (6), we obtain equation (8).

[0039]

number

[0040] This reveals that local pulse wave velocity (PWV) is related to vascular characteristics, blood viscosity, and diastolic blood pressure.

[0041] Here, the peripheral diastolic blood pressure (P) is affected by raising and lowering the hand. d Consider that ) changes. Peripheral diastolic blood pressure is the diastolic blood pressure of the heart (P) plus the hydrocephalus pressure (ΔP) due to the difference in height between the heart and the hand. d ) is the only difference. Therefore, when the hand is higher than the heart, P d This is expressed by formula (9).

[0042]

number

[0043] By substituting equation (9) into equation (8), which is the relationship between local pulse wave velocity (PWV) and stiffness parameter β, and rearranging the equation, we obtain equation (10).

[0044]

number

[0045] As shown in formula (10), PWV 2 ΔP d This relationship can be expressed as a linear equation. Therefore, when the height h of the hand from the heart is changed by raising and lowering the hand, ΔP d If you can obtain the pulse wave, then the PWV at different hand heights. 2 And, ΔP d By utilizing this, it is possible to estimate diastolic blood pressure in the heart.

[0046] Furthermore, it is possible to estimate diastolic blood pressure even when L is unknown when calculating pulse wave velocity. To elaborate on this, substituting the PWV from equation (2) into equation (10) yields equation (11).

number

[0047] Furthermore, both sides are L 2 Dividing by gives equation (12).

number

[0048] This makes it possible to estimate diastolic blood pressure using a similar method, even if L is unknown, or if PWV is calculated using an arbitrary L value.

[0049] (Hardware configuration of blood pressure estimation device) Figure 4 is a block diagram showing an example of the hardware configuration of the blood pressure estimation device 1. In Figure 4, the blood pressure estimation device 1 comprises a CPU 101, a memory 102, a communication interface 103, a display 104, and an input device 105. Each component is connected via a bus 120. The CPU 101 is a central processing unit that controls the operation of the blood pressure estimation device 1 by reading and executing programs stored in the memory 102.

[0050] Memory 102 includes, for example, ROM, RAM, and flash ROM. For example, flash ROM and ROM store various programs, such as the blood pressure estimation program according to this embodiment. RAM is used as the work area of ​​CPU 101. Programs stored in memory 102 are loaded into CPU 101, causing CPU 101 to execute the coded processes. Memory 102 also includes external memory such as USB memory and SD cards.

[0051] The communication interface 103 is connected to a network such as the internet via a communication line, and connects to other devices (such as smartphones) via the network. The communication interface 103 also manages the interface between the network and the inside of the device, and controls the input and output of data from other devices.

[0052] The display 104 is, for example, a liquid crystal display that displays images, and may be a touch panel type. In addition to the display 104, the blood pressure estimation device 1 may also be equipped with a speaker as an output device. The input device 105 is a device for inputting various types of information, and includes keyboards, mice, touch panels, microphones, and the like.

[0053] (An example of the functional configuration of blood pressure estimation device 1) Figure 5 is a block diagram showing an example of the functional configuration of the blood pressure estimation device 1. In Figure 5, the blood pressure estimation device 1 comprises a distance acquisition unit 501, a differential pressure acquisition unit 502, a pulse wave acquisition unit 503, a velocity calculation unit 504, a blood pressure calculation unit 505, and an output unit 506. Each unit is implemented by the CPU 101 of the blood pressure estimation device 1. That is, the CPU 101 implements the function of each unit by executing a blood pressure estimation program stored in the memory 102. The blood pressure estimation device 1 also includes a storage unit 510. The storage unit 510 is implemented by the memory 102.

[0054] (Regarding the acquisition and detection of upward distance) The distance acquisition unit 501 is an example of an elevation difference acquisition unit. The distance acquisition unit 501 acquires the upward distance (elevation difference: hereinafter referred to as "upward distance") between the heart and a part of the subject's body. The part can be any part that satisfies the following three conditions. • The location must be such that it can be positioned sufficiently high above the heart. • It must be a part of the body whose height relative to the heart can be changed. • The area must be capable of measuring pulse waves.

[0055] In this embodiment, one part is one hand. The hand is, for example, from the wrist to the fingertips. In this embodiment, one part is the hand because the accuracy of blood pressure estimation improves as the distance from the heart increases, but it is not limited to this. One part may be, for example, a part located in the forearm (from the elbow to the wrist) or a part located in the upper arm (from the shoulder to the elbow).

[0056] The distance acquisition unit 501 acquires the upward distance (first height difference; hereinafter sometimes referred to as "first upward distance") when the hand is placed in the first position. The first position is a position above the heart, and it is desirable that it be as high as possible above the heart. The first position is, for example, the position when the hand is extended straight upwards.

[0057] The first upward distance is detected by the height detection unit 20. In detecting the first upward distance, the height detection unit 20 considers the position where the detected hand height is within a first predetermined range and where the hand remains still for a predetermined time or longer as the first position, and detects the first upward distance. However, the detection of the first upward distance is not limited to this method. For example, the blood pressure estimation device 1 may be configured to accept an operation input indicating that the subject is in a state of extending their hand (first position), and in this case, the height detection unit 20 may consider the position at the time the operation input is received as the first position, and detect the first upward distance.

[0058] The distance acquisition unit 501 acquires the upward distance (second height difference; hereinafter sometimes referred to as "second upward distance") when the hand is placed in the second position. The second position is higher than the heart and lower than the first position. It is desirable that the second position is further away from the first position. However, if the elbow is bent too much, there is a risk of blood vessels being compressed, so the second position should be, for example, the position when the elbow angle is about 90°.

[0059] The second upward distance is detected by the height detection unit 20. In detecting the second upward distance, the height detection unit 20 considers the position where the detected height is within a second predetermined range and where the hand remains still for a predetermined time or longer as the second position, and detects the second upward distance. However, the detection of the second upward distance is not limited to this method. For example, the blood pressure estimation device 1 may be configured to accept an operation input indicating that the subject's elbow is bent at approximately 90° (second position), and in this case, the height detection unit 20 may consider the position at the time the operation input is received as the second position, and detect the second upward distance.

[0060] (Regarding obtaining differential pressure) The differential pressure acquisition unit 502 acquires the differential pressure between the blood pressure of the heart and the blood pressure of the hand. The differential pressure is a value obtained based on known data acquired in advance from the measured values ​​of multiple subjects. The differential pressure is expressed in relation to the upward distance using a linear equation. Therefore, the differential pressure acquisition unit 502 can acquire the differential pressure based on the upward distance acquired by the distance acquisition unit 501. The differential pressure acquisition unit 502 acquires the differential pressure corresponding to the first upward distance and the differential pressure corresponding to the second upward distance.

[0061] (Regarding using diastolic blood pressure as the blood pressure to be estimated) In particular, in this embodiment, the blood pressure to be estimated is the diastolic blood pressure, from the viewpoint of being able to accurately estimate the blood pressure of the heart. For this reason, the differential pressure acquisition unit 502 obtains the diastolic differential pressure (ΔP) which indicates the differential pressure between the diastolic blood pressure of the heart and the diastolic blood pressure of the hand. d The differential pressure acquired by the differential pressure acquisition unit 502 is the expanded differential pressure (ΔP) at the first upward distance. d1) and the differential pressure (ΔP) at the second upward distance. d2 ) Note that the blood pressure to be estimated is not limited to diastolic blood pressure; systolic blood pressure can also be used. However, the accuracy of blood pressure estimation is higher when using diastolic blood pressure than when using systolic blood pressure.

[0062] (Regarding pulse wave acquisition) The pulse wave acquisition unit 503 acquires pulse waves from multiple locations on the hand. These locations include, for example, the wrist 201 and the fingertips 202. The pulse wave acquisition unit 503 acquires pulse waves based on the measurement results of the pulse wave sensor 10. The pulse waves acquired by the pulse wave acquisition unit 503 include pulse waves when the hand is in a first position and pulse waves when the hand is in a second position.

[0063] (Regarding the subject's hand movements) Here, when raising the arm, peripheral blood pressure and blood flow decrease, making vascular reactions more likely to appear, while when lowering the arm, vascular reactions are relatively less likely to appear. For this reason, in this embodiment, the subject is instructed to perform an action of lowering their arm from above. The pulse wave acquisition unit 503 acquires pulse waves at a first upward distance and pulse waves at a second upward distance when the subject performs the action of lowering their arm.

[0064] Furthermore, the subject's hand movements are not limited to downward movements. For example, the subject may be instructed to raise their hand. In this case, the pulse wave acquisition unit 503 only needs to acquire the first upward distance and the second upward distance when the subject raises their hand. However, the accuracy of blood pressure estimation can be obtained more accurately when the hand is moved downward than when it is moved upward.

[0065] (Regarding the subject's breathing) Here, when estimating blood pressure, it is desirable to use a breathing pattern that eliminates disturbances caused by respiration. A predetermined breathing pattern is, for example, one in which the breath is held for about 15 seconds after exhaling. Specifically, before starting the measurement, the subject exhales lightly, holds their breath, and then starts the measurement, raising their hand to the height of the first position, and then lowering it to the second position and holding it for about 15 seconds. In this embodiment, the pulse wave acquisition unit 503 acquires the pulse wave at a first upward distance and the pulse wave at a second upward distance when the user adopts the predetermined breathing pattern.

[0066] (Regarding the calculation of pulse wave velocity) The velocity calculation unit 504 calculates the pulse wave velocity (PWV1) at the first position and the pulse wave velocity (PWV2) at the second position, respectively, based on the pulse wave acquired by the pulse wave acquisition unit 503. Specifically, the velocity calculation unit 504 calculates the pulse wave velocity (PWV1, PWV2) based on the difference in the time it takes for the pulse to reach the wrist 201 and the fingertip 202, respectively, and the distance between the wrist 201 and the fingertip 202. More specifically, the velocity calculation unit 504 calculates the pulse wave velocity (PWV1 and PWV2) using the formulas (1) and (2) described above.

[0067] (Regarding the estimation of the subject's cardiac blood pressure) The blood pressure calculation unit 505 calculates the blood pressure of the heart based on the differential pressure between the first upward distance and the second upward distance acquired by the differential pressure acquisition unit 502, and the pulse wave velocity (PWV) between the first upward distance and the second upward distance calculated by the velocity calculation unit 504. In this embodiment, the blood pressure calculation unit 505 calculates the diastolic differential pressure (ΔP d Based on the pulse wave velocity (PWV) and the blood pressure calculation unit 505 calculates the diastolic blood pressure (P) of the heart using the formula (10) described above.

[0068] More specifically, the blood pressure calculation unit 505 adds the diastolic differential pressure (ΔP) at the first upward distance to the formula (10) described above. d1The blood pressure calculation unit 505 then generates a first equation by substituting the pulse wave velocity (PWV1) at the first upward distance into equation (10). d2 A second equation is generated by substituting the pulse wave velocity (PWV2) at the second upward distance into the first equation. The blood pressure calculation unit 505 calculates the unknown "β / 2ρ" and the cardiac diastolic blood pressure "P" from the simultaneous equations of the first and second equations. This derives the estimated cardiac diastolic blood pressure "P" of the subject.

[0069] (Regarding the output of calculation results) The output unit 506 outputs the calculation result of the blood pressure calculation unit 505 to the display 104. If the blood pressure estimation device 1 is equipped with a speaker, the output unit 506 may output the calculation result as audio via the speaker. The output unit 506 can also control the communication interface 103 to output the calculation result to an external device, or it can output the calculation result to the memory 102 and store the calculation result in the memory 102.

[0070] (Processing related to blood pressure estimation performed by blood pressure estimation device 1) Figure 6 is a flowchart illustrating an example of the blood pressure estimation process performed by the blood pressure estimation device 1. In Figure 6, the blood pressure estimation device 1 determines whether measurement has started or not by receiving an operation related to the start of measurement (step S601). During measurement, the subject breathes in a predetermined breathing pattern.

[0071] The blood pressure estimation device 1 waits until measurement begins (step S601: NO), and when measurement begins (step S601: YES), it determines whether or not the first upper distance has been acquired (step S602). The blood pressure estimation device 1 waits until the first upper distance has been acquired (step S602: NO), and when the first upper distance has been acquired (step S603: YES), it acquires the pulse wave at the first upper distance (step S603).

[0072] Then, the blood pressure estimation device 1 calculates the pulse wave velocity (PWV1) at the first upward distance using the formulas (1) and (2) described above, based on the acquired pulse wave (step S604). Next, the blood pressure estimation device 1 calculates the differential pressure (ΔP) corresponding to the first upward distance (height h1). d1 ) obtains (step S605). Then, the blood pressure estimation device 1 adds the differential pressure (ΔP) corresponding to the first upward distance to formula (10). d1 Substituting the pulse wave velocity (PWV1) at the first upward distance into the given equation generates a first equation (step S606).

[0073] Next, the blood pressure estimation device 1 determines whether or not the second upper distance has been acquired (step S607). The blood pressure estimation device 1 waits until the second upper distance has been acquired (step S607: NO), and once the second upper distance has been acquired (step S607: YES), it acquires the pulse wave at the second upper distance (step S608).

[0074] Then, the blood pressure estimation device 1 calculates the pulse wave velocity (PWV2) at the second upward distance using the formulas (1) and (2) described above, based on the acquired pulse wave (step S609). Next, the blood pressure estimation device 1 calculates the differential pressure (ΔP) corresponding to the second upward distance (height h2). d2 ) is obtained (step S610). Then, the blood pressure estimation device 1 adds the differential pressure (ΔP) corresponding to the second upward distance to formula (10). d2 Substituting the pulse wave velocity (PWV2) at the second upward distance into the given equation generates a second equation (step S611).

[0075] Next, the blood pressure estimation device 1 calculates the diastolic blood pressure (P) of the subject's heart from the simultaneous equations of the first and second equations (step S612). Then, the blood pressure estimation device 1 outputs the calculated diastolic blood pressure (P) (step S613) and completes the series of processes.

[0076] In addition, in the process described above, the pulse wave at each position may be acquired before acquiring the upward distance (for example, step S602 may be performed after step S603), or the generation of the first equation and the second equation may be performed together after acquiring the second upward distance. Specifically, the processes related to steps S604 to S706 may be performed, for example, after the process related to step S608.

[0077] As described above, the blood pressure estimation device 1 according to this embodiment measures the differential pressure (ΔP) between the first position, where the subject's hand is higher than the heart, and the second position. d The blood pressure of the subject's heart is calculated based on the pulse wave velocity at both positions. This allows blood pressure to be measured by the subject performing a simple action, such as lowering their hand from above to below. Furthermore, the blood pressure estimation device 1 according to this embodiment can suppress estimation errors that occur during prolonged use. Therefore, blood pressure can be easily measured at home or elsewhere.

[0078] Furthermore, the blood pressure estimation device 1 according to this embodiment uses diastolic blood pressure as the blood pressure to be estimated and calculates the diastolic blood pressure of the subject's heart. This allows for blood pressure measurement to be performed using the diastolic blood pressure that can be estimated with high accuracy.

[0079] Furthermore, the blood pressure estimation device 1 according to this embodiment acquires pulse waves at a first upward distance and pulse waves at a second upward distance while the user is in a predetermined breathing pattern. This eliminates disturbances caused by breathing when measuring cardiac blood pressure, thereby improving the accuracy of blood pressure estimation.

[0080] Furthermore, in this embodiment, the part of the subject that is raised or lowered is the hand. This allows the subject to have their blood pressure measured with a simple motion, and to have their blood pressure estimated with high accuracy.

[0081] Furthermore, in this embodiment, the first position is set higher than the second position, and the blood pressure estimation device 1 acquires pulse waves at the first upward distance and the second upward distance when the subject lowers their hand. This makes it possible to estimate blood pressure when vascular reactions are less likely to appear, thereby improving the accuracy of blood pressure estimation.

[0082] (Other embodiments) Other embodiments will be described below. In the other embodiments, explanations of the contents described in the first embodiment described above will be omitted as appropriate. It is also possible to combine the configurations shown in the first embodiment and the other embodiments. Specifically, a configuration may include all of the first embodiment and the other embodiments, or a configuration may be a combination of any of them.

[0083] (Second Embodiment) In the first embodiment described above, an example was described in which a pulse wave sensor 10 is provided to detect the pulse wave and its height. In the second embodiment, an example will be described in which the pulse wave is detected based on image data captured by an imaging device. In the second embodiment, the height of the hand from the heart will also be acquired based on the image data.

[0084] (Example configuration of the measurement system St according to the second embodiment) Figure 7 shows an example configuration of the measurement system St according to the second embodiment. As shown in Figure 7, the measurement system St comprises a blood pressure estimation device 1 and an imaging device 700. The blood pressure estimation device 1 and the imaging device 700 are connected by wire or wireless, for example, via a network.

[0085] The imaging device 700 is a terminal device equipped with a common imaging function (visible light camera), such as a smartphone, camera-equipped mobile phone, digital camera, video camera, or webcam. The imaging device 700 comprises a photographic lens and a visible light image sensor (e.g., a CCD sensor or CMOS sensor) that receives visible light, and outputs image data obtained by converting the subject image formed on the image sensor by the photographic lens into an electrical signal. The image data is, for example, video data consisting of multiple frame images. However, the image data is not limited to video data, but may also consist of multiple still image data.

[0086] The imaging device 700 performs signal processing on the image data, including noise reduction, black level subtraction, color mixing correction, shading correction, white balance correction, gamma correction, simultaneous processing, and RGB / YC conversion. In this embodiment, the imaging device 700 outputs image data in RGB format.

[0087] The imaging device 700 non-contact imaging of two different locations on the human body (hereinafter also referred to as "measurement sites") and outputs a series of continuous image data (RGB format image data). Examples of measurement sites include the palm area, more specifically, the subject's wrist 201 and fingertips 202. Blood flow in the skin area of ​​the human body changes in accordance with the pulse wave (pulsation). The imaging device 700 outputs the image data to the blood pressure estimation device 1.

[0088] The blood pressure estimation device 1 acquires pulse waves based on image data obtained from the imaging device 700. Specifically, the pulse wave acquisition unit 503 according to the second embodiment acquires pulse waves by detecting temporal changes in pixel values ​​(changes in skin color) in the skin region. The palm region has a larger skin area compared to other regions, and is a region where changes in skin color can be detected while minimizing the influence of noise.

[0089] Specifically, the pulse wave acquisition unit 503 extracts each measurement area from each frame image obtained from the imaging device 700 and detects the change in pixel value at each measurement area. Specifically, in each frame image, it calculates the average pixel value of each pixel belonging to the wrist 201 (first measurement area) and the average pixel value of each pixel belonging to the fingertip 202 (second measurement area). As a result, the pulse wave acquisition unit 503 obtains a waveform showing the change in pixel value and can further obtain a pulse wave (pulse wave signal) having an amplitude corresponding to the pulse wave. The pulse wave acquisition unit 503 outputs the acquired pulse wave to the velocity calculation unit 504.

[0090] The velocity calculation unit 504 calculates the pulse wave propagation velocity from the time difference of pulse changes obtained based on the pixel value changes between the wrist 201 and the fingertip 202. Specifically, the velocity calculation unit 504 calculates the pulse wave propagation velocity from the time difference (pulse wave propagation time) of the reference point (e.g., rising point) of the pulse wave signal at each measurement site. B -T A If we determine the value of '[value]' using formula (1) and let L be the distance between each measurement site, then the pulse wave velocity (PWV) can be calculated using formula (2).

[0091] (Regarding the detection of upward distance from image data) The imaging device 700 detects a first upward distance and a second upward distance based on the captured image data. The imaging device 700 detects the first upward distance and the second upward distance by tracking the movement of the hand (subject) with the position of the heart as a reference. The imaging device 700 may also acquire each upward distance using, for example, a pre-stored measurement program (measurement application). The distance acquisition unit 501 acquires each upward distance detected by the imaging device 700.

[0092] Furthermore, the measurement system St according to the second embodiment may include a display that shows guidance images related to posture during shooting. The display may, for example, superimpose a shooting guide frame onto the captured image on the screen. When video recording is started by the imaging device 700, the display may show a hand guide frame and also display a notification message, for example, "Shoot your hand within the frame, extend it upwards, and slowly lower it."

[0093] As described above, the blood pressure estimation device 1 according to the second embodiment acquires pulse waves based on hand image data captured by the imaging device 700. This makes it possible to measure blood pressure without having the subject wear a pulse wave sensor 10. Therefore, the burden on the subject involved in blood pressure measurement can be reduced.

[0094] Furthermore, the blood pressure estimation device 1 according to the second embodiment acquires a first upward distance and a second upward distance based on hand image data captured by the imaging device 700. In other words, the blood pressure estimation device 1 according to the second embodiment acquires both pulse wave data and hand upward distance based on image data. This makes it possible to measure blood pressure in a completely non-contact manner. Therefore, the burden on the subject in relation to blood pressure measurement can be further reduced, making it easier for the subject to measure their blood pressure.

[0095] (Third embodiment) In the first embodiment described above, blood pressure was calculated by deriving the equation of a straight line from the values ​​of two points. In the third embodiment, when the height of the hand can be measured while the hand is moving, an example is described in which the height of the hand from the heart and the pulse wave propagation velocity are measured continuously at multiple positions, and the equation of a straight line is derived from the data of multiple points using the least squares method or similar.

[0096] In the third embodiment, the subject is instructed to lower their hand from above to below. In the third embodiment, the measurement of height and detection of pulse waves are the same as in the first or second embodiment. In the third embodiment, the estimation unit of the blood pressure estimation device 1 estimates the value ΔP d and PWV 2 An estimation formula corresponding to equation (10), which is the regression line between the two points, is generated using the least squares method.

[0097] The blood pressure calculation unit 505 calculates the subject's blood pressure from the coefficient values ​​of the estimation formula estimated by the generation unit. Specifically, the blood pressure calculation unit 505 calculates an estimated value of diastolic blood pressure P by dividing the intercept of the estimation formula by the slope multiplied by "-1". The output unit 506 outputs the calculation result of the blood pressure calculation unit 505.

[0098] As explained above, even with the configuration of the third embodiment, blood pressure can be measured by the subject performing a simple action such as lowering their hand from above to below. Furthermore, as mentioned above, in the third embodiment as well, the hand movement is not limited to lowering; raising the hand is also possible.

[0099] (Modified examples of the embodiment) Modifications of the first and second embodiments are described below. It is also possible to combine the configurations shown in the first embodiment, the second embodiment, and the modifications described above. Specifically, a configuration may include all of the first embodiment, the second embodiment, and the modifications, or it may be a combination of any of them.

[0100] (Variation 1) Modification 1 is a modification of the second embodiment. Modification 1 describes measuring the blood pressure of multiple subjects at once. In Modification 1, multiple subjects are imaged so that they fit within the frame of the imaging device 700. The blood pressure estimation device 1 detects the pulse wave and the upward distance of each of the multiple subjects based on the image data captured by the imaging device 700. As a result, the blood pressure estimation device 1 can calculate the blood pressure of each subject and output them together.

[0101] According to Modification 1, by having users of nursing care facilities, etc., perform actions such as raising and lowering their arms during exercise, the blood pressure of multiple subjects can be measured simultaneously. Therefore, blood pressure can be measured easily and quickly without causing stress to multiple subjects.

[0102] (Modification 2) In the embodiment described above, the part of the body targeted for height detection by the height detection unit 20 was the hand, but it is not limited to this. The part of the body targeted for detection can be any part of the body where β / 2ρ (slope) is considered not to change significantly with elevation, for example, the foot. The foot is, for example, the part from the ankle to the toes. The area where the pulse wave is acquired is, for example, the heel and the tips of the toes on the sole of the foot. The imaging device 700 is designed to image the sole of the foot.

[0103] The subject will be positioned so that their feet are higher than their heart, for example, while their blood pressure is measured. The height detection unit 20 detects the upward distance, which is the distance between the heart and the feet. In detecting the upward distance, the part of the subject's foot to be detected may be a predetermined part of the foot, such as the toes or heel.

[0104] The first position should preferably be as high as possible, for example, the position when the legs are extended straight upwards. The second position should be higher than the heart and lower than the first position. The subject should be instructed to perform a movement in the direction of lowering their legs from above, and the height detection unit 20 should detect the first and second upward distances based on this movement.

[0105] According to Modification 2, blood pressure can be measured while the subject is lying down. This makes it easy to measure blood pressure even for subjects who have difficulty sitting upright.

[0106] Furthermore, in the embodiment described above, the part of the body targeted for height detection by the height detection unit 20 was one hand, but it is not limited to this and may be both hands. However, since it is necessary that the part of the body be considered to have the same β / 2ρ (magnitude of the slope in equation (10)) on both the left and right sides, the part of the body targeted for detection can be the same on both the left and right sides. For this reason, for example, it is possible to detect the first upward distance with the right hand and the second upward distance with the left hand.

[0107] (Regarding the apparatus equipped with each functional part according to the embodiment and modified example) Furthermore, all or part of the functions (input / output, memory, processing (including judgment)) of the blood pressure estimation device 1 described above may be implemented in a device other than the one described as the main entity executing the function. Specifically, the above description described a configuration in which the blood pressure estimation device 1 comprises a distance acquisition unit 501, a differential pressure acquisition unit 502, a pulse wave acquisition unit 503, a velocity calculation unit 504, a blood pressure calculation unit 505, and an output unit 506. All or part of each functional unit may be provided in another computer device, such as an external server device. In addition, there may be multiple other computer devices or just one other computer device.

[0108] In relation to the above, the blood pressure estimation device 1 calculates the differential pressure (ΔP) at both the first position, where the subject's hand is higher than the heart, and the second position. d With regard to calculating the blood pressure of the subject's heart based on the pulse wave velocity at both locations, it may function as a so-called thin client specializing in the input / output interface portion. In other words, the blood pressure estimation device 1 may receive various inputs (operation by the operator, as well as detection by devices such as the pulse wave sensor 10, height detection unit 20, and imaging device 700), transmit input information (operation information, etc.) to other external devices, receive processing results from other devices based on said input information (blood pressure calculation results, etc.), and perform various outputs.

[0109] Furthermore, the program for realizing the blood pressure estimation device 1 described above may be recorded on a computer-readable storage medium, and the program may be loaded into a computer system and executed. Here, "computer system" includes hardware such as the OS and peripheral devices. "Computer-readable storage medium" refers to portable media such as USB (Universal Serial Bus) flash memory, SSD (Solid State Drive), flexible disk, magneto-optical disk, ROM, CD-ROM, and storage devices such as hard disks built into a computer system. Moreover, "computer-readable storage medium" also includes volatile memory (RAM) inside a computer system that acts as a server or client when the program is transmitted via a network such as the Internet or a communication line such as a telephone line, which retains the program for a certain period of time. Furthermore, the above program may be transmitted from the computer system that stores the program in a storage device, etc., to another computer system via a transmission medium or by transmission waves in the transmission medium. Here, the "transmission medium" for transmitting the program refers to a medium that has the function of transmitting information, such as a network such as the Internet or a communication line such as a telephone line. Furthermore, the above program may be for realizing only a part of the functions described above. Furthermore, the aforementioned functions may be implemented in combination with programs already recorded in the computer system, such as so-called differential files (differential programs).

[0110] (Regarding verification) Next, the verification conducted by the inventors will be described. The blood pressure estimation algorithm in this embodiment will be described. The conditions for the above-described blood pressure estimation method to be valid are h and ΔP d The relationship between these factors requires that there is little individual variation and that it is constant over time. We examined these conditions.

[0111] The blood pressure estimation method used in this verification generally measures the lowest blood pressure measured in the upper arm, that is, it is a method for estimating the diastolic blood pressure P in the heart. Formula (10) includes the diastolic differential pressure (ΔP) from the height of the hand h (upward distance). d It is necessary to be able to calculate ΔP. If we simplify blood vessels to be rigid tubes with open tops, then ΔP d Since it is expressed as the hydrocephalus due to blood, it should be equal to ρgh. ρ represents the specific gravity of blood, and g represents the acceleration due to gravity. Therefore, the actual ΔP d It is expected that this can also be expressed as a simple function of h.

[0112] Therefore, in order to confirm this, we checked the relationship between the two beforehand. Figure 8 is a schematic diagram showing an example of a measurement environment for verifying a blood pressure estimation method. As shown in Figure 8, for the right hand, a tonometry-type continuous blood pressure monitor 801 was attached to the wrist, positioned at approximately the same height as the heart, and a finapres-type continuous blood pressure monitor cuff 802 was attached to the right arm. For the left hand, a finapres-type continuous blood pressure monitor 811 was attached to the middle and ring fingers, and a photoelectric volume pulse wave sensor 812 was attached to the index finger. Electrodes 820 for electrocardiogram were attached to the chest. The left hand was then raised and lowered at a constant speed within a range of -40 cm to +60 cm relative to the height of the heart, and the systolic blood pressure, diastolic blood pressure, and mean blood pressure were measured. The relationship between the difference between these blood pressures at the heart and the height of the hand was then investigated.

[0113] Figure 9 shows the relationship between the height of the hand relative to the heart and the difference between the cardiac systolic blood pressure and the hand systolic blood pressure. Figure 10 shows the relationship between the height of the hand relative to the heart and the difference between the cardiac diastolic blood pressure and the hand diastolic blood pressure. Figure 11 shows the relationship between the height of the hand relative to the heart and the difference between the cardiac mean blood pressure and the hand mean blood pressure.

[0114] As shown in Figures 9 to 11, the blood pressure of the raised and lowered hands changes differently depending on whether they are at a position lower or higher than the heart. In other words, when the hands are raised at a position lower than the heart, there are large individual differences in systolic blood pressure, diastolic blood pressure, and mean blood pressure, and the slopes of each also differ.

[0115] Figure 12 shows the relationship between the height of the hand relative to the heart and peripheral blood pressure. The figures in Figure 12 summarize the results for systolic blood pressure, diastolic blood pressure, and mean blood pressure when the hand is higher than the heart. The error bars in the figure indicate the standard deviation. These results show that peripheral diastolic blood pressure at a position higher than the heart exhibits particularly small variability.

[0116] Figure 13 is a table showing individual differences in the relationship between height from the heart and peripheral blood pressure. The diagram in Figure 13 is divided into two cases: when the arm is raised from a position lower than the heart, and when the arm is raised from heart height. For each subject, the relationship between the blood pressure difference and height is approximated by a linear function, and the mean value and variance of the slope of the approximation line are shown. As shown in Figure 13, at a position higher than the heart, the difference ΔP between the height of the hand from the heart h and the diastolic blood pressure of the heart and the diastolic blood pressure of the hand is shown. d The relationship between these two factors shows little individual variation.

[0117] One reason why there is little individual variation in diastolic blood pressure is thought to be that blood flow is extremely low during diastole, and blood pressure changes due to differences in hand height mainly depend on differences in hydrocephalus pressure. Therefore, if the hand is higher than the heart, it can be inferred that the pressure difference between the diastolic blood pressure in the heart and the diastolic blood pressure in the hand is determined by the height from the heart.

[0118] Therefore, the height h of the hand from the heart and the difference ΔP between the diastolic blood pressure of the hand and the diastolic blood pressure of the heart are considered. d The relationship between ΔP d Expressed as =f(h), the results of this verification are shown in equation (13). Furthermore, the change in blood pressure due to hydrocephalus pressure, assuming a specific gravity of 1.06 for blood, is given by equation (14), and the slope is significantly different from that of hydrocephalus pressure. This is thought to be due to factors such as the fact that equation (14), which shows the change in blood pressure due to hydrocephalus pressure, does not include parameters indicating blood viscosity or vascular resistance, as well as the characteristics of the continuous blood pressure monitor used.

[0119]

number

[0120]

number

[0121] This verification involves h and ΔP d Assuming that there is almost no individual difference and that this relationship remains constant, we will estimate blood pressure.

[0122] Based on the above, in the blood pressure estimation method used in this verification, the hand should be raised and lowered at a position sufficiently higher than the heart, and measurements should be taken within the range of height where the total amplitude of the pulse wave decreases. Furthermore, in order to minimize the influence of respiration, it is desirable to measure the pulse wave while holding your breath.

[0123] (Verification results) As described above, the conditions for estimating blood pressure are (1) the hand position being sufficiently higher than the heart, and (2) the effect of respiration being excluded. By doing so, the change in peripheral blood pressure P can be estimated from the change in hand height. d It is possible to calculate the change in peripheral diastolic blood pressure and peripheral PWV 2 The relationship between the two can be expressed as a linear function. Using this, the diastolic blood pressure at heart level can be estimated by dividing the intercept of the regression line obtained from the relationship between the two by the slope.

[0124] Pulse waves can be obtained not only by contact-type photoelectric volumetric pulse wave analysis but also by non-contact measurement using video pulse wave analysis. In Experiment 1, the blood pressure estimation method was verified using a contact-type sensor, and the estimation accuracy was considered. Subsequently, in Experiment 2, described later, we attempted completely non-contact blood pressure estimation using video pulse wave analysis.

[0125] (Experiment 1: Blood pressure estimation using a volume pulse wave sensor) To verify this blood pressure estimation method, we first investigated a blood pressure estimation method using a contact-type volume pulse wave sensor. Figure 14 is a schematic diagram of the measurement environment for Experiment 1, which used a contact-type sensor. Figure 15 shows the mounting position of the photoelectric volume pulse wave sensor. In Experiment 1, the subjects were 18 healthy individuals (average age: 20.6 ± 0.8 years). At the start and end of the experiment, the subjects measured their blood pressure using a commercially available home blood pressure monitor. Then, as shown in Figure 14, the subjects sat in a chair and had electrocardiogram (ECG) electrodes 1603 attached to their chest, a photoelectric volume plethysmography (PPG) sensor 1611 and a finapres continuous blood pressure monitor cuff 1602 attached to their left arm, which was used to raise and lower the arm.

[0126] As shown in Figure 15, the photoelectric volume pulse wave sensors 1611 were attached to four locations (wrist 1701, fingertip ball 1702, proximal phalanges 1703, and fingertips 1704), starting from the area closest to the heart and extending towards the fingertips. To measure the height of the hand, a wound-type linear encoder 1620 was used, with its tip attached to the thumb of the left hand, which was being raised and lowered. Because the wound-type linear encoder 1620 measures the length of the wound-up thread, the hand needed to be raised and lowered vertically. A Finapress-type continuous blood pressure monitor 1601 was attached to the middle and ring fingers of the right hand, fixed at approximately heart height. All measurements were recorded with a sampling period of 1 ms.

[0127] Figure 16 shows the experimental protocol (for one set) for Experiment 1. As shown in Figure 16, (0) various sensors are attached, and (1) the left hand is raised 60 cm above the heart. Next, to eliminate the influence of breathing, (2) exhale for 3 seconds at the signal to start measurement. (3) Then, while holding your breath, lower your left hand to heart level over 15 seconds. At this time, if the tilt angle of the hand (wrist) changes, the height difference between the photoelectric volume pulse wave sensors will change, so the hand was lowered without changing the angle of the hand. A total of 5 sets of measurements (1) to (3) in the experimental protocol were performed in Figure 16.

[0128] Of the 18 subjects, peripheral pulse waves could not be measured correctly for 2 subjects, and the sensors were improperly attached for 2 subjects. Therefore, data from a total of 14 subjects were analyzed, excluding these 4 individuals.

[0129] Figure 17 shows the electrocardiogram (ECG) and peripheral pulse wave measurement results for a subject. First, all measurement data is extracted into a 3-beat data window based on the R wave of the ECG. PWV is calculated for all combinations (6 types) of pulse waves at four peripheral locations (wrist 1701, fingertip 1702, proximal 1703, fingertip 1704). Calculating peripheral PWV requires a time resolution higher than the sampling period of 1 ms. Therefore, the peripheral PWV was calculated by approximating the cross-correlation function. At this time, beats with a correlation coefficient below 0.85 or data exceeding three times the central absolute deviation were excluded as outliers.

[0130] Figure 18 shows the PWV of a particular subject over two measurements. 2 and estimated value ΔP d This figure shows the relationship with [the given value]. Note that the estimated value is ΔP. d This is ΔP shown in Figure 18. d (Hat) is shown. The figure in Figure 18 shows the difference ΔP between the diastolic blood pressure in the heart and the diastolic blood pressure in the periphery of a subject. d The estimated value ΔP was obtained by estimating the height h of the hand from the heart using formula (13). d and PWV 2 The relationship is shown. There is a strong linear correlation between the two (R=-0.95, R=-0.97), and the relationship is almost exactly as predicted by the theoretical formula. Estimated value ΔP d The height h is determined from the hand height, but in this experiment, since the hand was lowered continuously, the hand height at the time of the R wave in the middle beat of the 3-beat data window was used as the height in that data.

[0131] The estimated value ΔP shown in Figure 18 d and PWV 2 The regression line between and is given by equation (10), which was estimated using the least squares method. The estimated value of diastolic blood pressure P was calculated by dividing its intercept by the slope. At this time, the estimated value ΔP dThe estimated value P, calculated using formula (14), was compared with the measured diastolic blood pressure of the heart obtained from arterial pressure at the wrist (radial artery pressure). Furthermore, a new correction parameter was set based on the relationship between the estimated and measured values, and the resulting estimated value P' was used to examine the estimation accuracy using the root mean square error (RMSE).

[0132] (Results of Experiment 1) In Experiment 1, six types of PWV were calculated using pulse waves obtained from sensors attached to four peripheral points on the hand (wrist 1701, fingertip ball 1702, proximal phalanx 1703, fingertip 1704). The pair of wrist 1701 and fingertip 1704, which had the longest distance between the two points, was selected. For each individual, the data used for estimation was selected from five sets of data to determine the estimated value ΔP d and PWV 2 The correlation coefficient (R) of the regression line with 2 The set with the highest value was used. PWV across all subjects 2 and estimated value ΔP d The mean correlation coefficient between the two points was R = -0.89 ± 0.09, confirming sufficient linearity for all data.

[0133] Figure 19 shows the estimated value ΔP calculated using formula (14). d This figure shows the results of estimating diastolic blood pressure using R. The estimated values ​​showed a positive correlation with the average diastolic blood pressure measured with an upper arm blood pressure monitor before and after the experiment (R). 2 (=0.48). The RMSE value was 26.5 mmHg. From this result, height and PWV 2 A linear relationship is observed between the two, suggesting that it is possible to perform a new correction based on actual blood pressure measurements. The regression line in Figure 19 is shown by equation (15).

[0134]

number

[0135] Figure 20 shows the results of comparing the estimated value P', which was corrected using the regression line of equation (15), with the actual measured value. Figure 21 is a table showing the root mean square error (RMSE) of the estimated values ​​compared to the measured values. To evaluate the estimation accuracy, the root mean square error (RMSE) was calculated, and the estimation error for the estimated value P' was 10.4 mmHg. Home blood pressure monitors generally allow a measurement error of 5.0 mmHg. In this experiment, it was possible to estimate diastolic blood pressure with an accuracy of 10.4 mmHg without applying cuff compression.

[0136] (Regarding the practical application of this blood pressure estimation method) Next, we will explain the verification results of Experiment 1, which used a contact-type sensor. By raising and lowering the hand at a sufficiently high position above the heart, the relationship between hand height and PWV change showed results consistent with the theoretical formula. Therefore, estimation was performed using formula (14), which represents the relationship between hand height and diastolic blood pressure derived from hydrocephalus pressure. The estimation error with the diastolic blood pressure measured in the upper arm was 26.5 mmHg. Furthermore, when the estimated value was corrected using a regression equation obtained from the estimated and measured values, the estimation error became 10.4 mmHg. Considering the ease of multiple measurements, this estimation error may be useful in daily health monitoring. In addition, these results were obtained for multiple subjects using the same algorithm and parameters, and this estimation method is not affected by individual differences. 2 Since the relationship exhibited sufficient linearity, this relationship can be used to obtain a correction parameter related to the difference between cardiac diastolic blood pressure and peripheral diastolic blood pressure.

[0137] (Experiment 2: Completely Non-Contact Blood Pressure Estimation) The validity of the blood pressure estimation method was demonstrated in Experiment 1 described above. In Experiment 1, a contact sensor and height measurement were required to obtain peripheral pulse wave propagation velocity. On the other hand, if the pulse wave (video pulse wave) and the height of the hand from the heart can be obtained from video footage capturing the raising and lowering of the hand, completely non-contact blood pressure measurement can be achieved. The inventors attempted to estimate blood pressure completely non-contact by using video pulse wave extraction technology to replace the sensors attached to the left hand during raising and lowering with only a single video camera, and extracting the pulse wave from the video footage captured by the video camera.

[0138] Figure 22 is a schematic diagram of the measurement environment for Experiment 2, which was completely non-contact. The subjects of Experiment 2 were a total of 9 people (average age 20.4 ± 0.9 years), consisting of 8 healthy men and 1 healthy woman. The measured items were an electrocardiogram using electrodes 2501 attached to the chest and blood pressure using a Finapres continuous blood pressure monitor 2502 attached to the right hand. The height of the right hand was fixed at the height of the heart. A tracking marker 2503 and a photoelectric volume plethysmography sensor 2504 were attached to the middle finger of the left hand. The sampling period for the electrocardiogram, continuous blood pressure, and volume plethysmography was set to 1 ms.

[0139] Furthermore, the video camera 2510 used to film the left hand recorded at a frame rate of 250fps. LED lighting 2511 was positioned to ensure that the light was distributed as evenly as possible when the hand was raised and lowered. Polarizing filters were attached to the lenses of both the lighting and the video camera 2510 to suppress surface reflections from the lighting on the palm. The measurement environment was enclosed with blackout curtains to eliminate the influence of ambient light from outside. The hand height conditions were set with the height of the heart as the baseline (0cm), and the hand's raising and lowering range was defined as 0-60cm above that. In this experiment, in order to extract the pulse wave with the highest possible accuracy, the height of the left hand was set to approximately 20cm (h0) and 40cm (h0). L ), 60cm(h H Measurements were taken with the hands held still at three locations. Participants were instructed to hold their hands still at an approximate height, and the actual height was measured from the video footage of the 2510 video camera.

[0140] Figure 23 shows the experimental protocol for Experiment 2. As shown in Figure 23, first, blood pressure was measured with a Finapres continuous blood pressure monitor 2502 before attaching the photoelectric volume pulse wave sensor 2504, (0) then the sensors were attached. (1) Before starting the measurement, the right hand was raised to heart level, and the left hand was raised to the initial height h H Set it to (2) exhale for 2 seconds, then (3) hold your breath for 5 seconds. After that, (4) breathe for 2 seconds while h L(5) Lower your hands to the desired height, hold your breath for 5 seconds, and (6) lower them to the height of your heart (h0) over 2 seconds while breathing, hold your breath for 5 seconds, and (7) hold your hands still. Perform two sets of measurements (1) to (7) of the experimental protocol.

[0141] Figure 24 shows an example of setting up a Region of Interest (ROI) for extracting video pulse waves. The ROI size is 8 x 8 pixels (approximately 1.0 cm x 1.0 cm). Furthermore, four sub-ROIs (4 x 4 pixels (approximately 0.5 cm x 0.5 cm)) were created by dividing the ROI into four sections. ROIs were set up in two locations: the fingertips and the carpal region. At the fingertips, three ROIs were set up approximately vertically on each of the fingertips of the left hand (index finger, middle finger, and ring finger). The vertical position of the fingertips ROI was determined based on the center coordinates of the tracking marker 2503, and the center coordinates of the finger ROIs were set from the actual finger positions. To obtain the left-right position of the fingers, we first focused on the G component of a horizontally elongated area from the index finger to the ring finger.

[0142] Figure 25 shows the brightness value of the G channel among RGB for left-right positions within the ROI. As shown in Figure 25, a threshold was set for the magnitude of the G component, the range of each finger was calculated, and the center coordinates of the fingers were calculated for each frame. This makes it possible to set the ROI and extract pulse waves while tracking slight body movements. For the carpal region, the ROI was set 100 pixels (approximately 12.5 cm) below the fingertip ROI. Next, the power spectral density of the electrocardiogram was determined, and the average frequency of the heart rate estimated from its peak frequency was set as f0 [Hz]. A bandpass filter (BPF) with a passband of 0.5f0 to 3f0 [Hz] was used to extract the pulse wave, and a total of 8 channels, including the RR interval obtained from the time-series data of the electrocardiogram and the G and B components extracted from the subROI, were used to extract pulse waves with strong periodicity using PiCA (Periodic Component Analysis).

[0143] The extracted pulse waves were segmented every second within a 3-second data window, and the PWV of the fingertip and wrist pulse waves was calculated. Similar to Experiment 1, the PWV was calculated using the PTT calculated using the cross-correlation function between pulse waves. Beats with a correlation coefficient below 0.85 were excluded as outliers. In this experiment, the electrocardiogram waveform obtained from the body surface by attaching electrode 2501 was used, achieved by setting the BPF passband and incorporating RR interval information into PiCA. However, since it is known that pulse wave components can be extracted by applying an appropriate frequency filter to the G channel extracted from the video, it is also possible to set the BPF passband and extract pulse waves using PiCA without using an electrocardiogram.

[0144] In the blood pressure estimation method used in this experiment, the relationship between hand height and peripheral diastolic blood pressure was estimated using equation (12), which was derived from the change in blood pressure due to hydrocephalus pressure when the specific gravity of blood was assumed to be 1.06. However, based on the results of Experiment 1 using a contact sensor, equation (12) was not used, and the blood pressure was estimated at a sufficient distance from the heart. H and h L In this context, hand height (h) and PWV 2 From the relationship, the relative value of blood pressure, μ, is calculated. Using the estimated parameter obtained from the relationship between the calculated μ and the measured diastolic blood pressure (P), the estimated diastolic blood pressure (P v Calculate the estimated diastolic blood pressure (P). v We compared the estimated values ​​with the measured values, calculated the root mean square error (RMSE), and considered the estimation accuracy.

[0145] (Experimental results) Figure 26 shows the relationship between changes in hand height h and PTT. For most subjects, lowering the hand resulted in a decrease in PTT. Note that the analysis focused on data where PTT was positive, i.e., pulse propagation towards the fingertips. PWV was calculated from the measured PTT, and in this experiment, the relationship between hand height (h) and PWV was analyzed. 2 From this relationship, the relative value of blood pressure, μ, was calculated.

[0146] Figure 27 shows the relationship between an intermediate parameter μ correlated with blood pressure and the measured diastolic blood pressure (P). There is a positive correlation (R=0.79) between the intermediate parameter μ and the measured diastolic blood pressure (P). The regression equation obtained from this result is shown in equation (16). This equation shows that the estimated value of cardiac diastolic blood pressure (P) can be estimated using the intermediate parameter μ.

[0147]

number

[0148] Figure 28 shows the estimated diastolic blood pressure (P) calculated using formula (16). V This figure shows the results of comparing the estimated value (P) with the measured value (P). V ) is shown in Figure 18 P V (Hat) is shown. Estimated value (P) relative to the measured value. V The estimation error was 7.69 mmHg. Although the amount of data used was different, the estimation error was smaller than that obtained with the contact-type sensor, indicating that blood pressure can be estimated using the same method as when using the contact-type sensor, even when using video pulse waves.

[0149] I would like to add a note about the possibility of the PTT reading being negative. Figure 29 shows the relationship between hand height and PTT when the ROI at the middle finger and wrist of a subject was moved by 1 pixel. ROI placement in the analysis of this experimental data was based on tracking marker 2503. It was found that by finely adjusting the ROI, it was possible to select an ROI where pulse propagation is directed from the wrist to the fingertips. As a result, an intermediate parameter μ was calculated for the data where the relationship between hand height and PTT matched the theoretical pattern. Using equation (16), diastolic blood pressure was estimated, resulting in an estimation error of 8.72 mmHg. When this result was added to the data used in this experiment, the estimation error became 7.81 mmHg. A positive correlation (R=0.77) remained between the intermediate parameter μ after adding the data and the measured diastolic blood pressure (P). From these results, it is possible to estimate blood pressure using the intermediate parameter μ calculated from PWV measured on the surface of the hand.

[0150] The estimated value calculated by correcting for ROI and the estimated diastolic blood pressure in this experiment (P V Based on the comparison results, it may be possible to suppress the effects of the time lag between blood propagation reaching the surface by making the distance between the two points where PTT is measured sufficiently long, and by using a near-infrared camera or R (red) channel that can measure the propagation of blood in deep tissues. Furthermore, as shown in Figure 29, when measuring pulse wave velocity from video, it is possible to set an infinite number of ROI pairs, so by measuring multiple pairs of PTT across the entire palm and creating an algorithm that selects the most reliable PTT, the estimation accuracy can be further improved.

[0151] In Experiment 2, a non-contact verification of the blood pressure estimation method was performed using video pulse waves. As a result, the measured value (P) and estimated value (P) of diastolic blood pressure were compared. V The RMSE, which indicates the estimation error, was 7.69 mmHg. Further improvements in estimation accuracy are possible by incorporating data from hypertensive patients and improving the analysis method.

[0152] In Experiment 2, a tracking marker 2503 was used to detect the hand, and the hand was kept still at the measurement point. However, depending on the performance of the video camera or smartphone camera, it may be possible to continuously track the palm without using the marker 2503. This makes it possible to extract pulse waves without keeping the hand still. Therefore, this leads to a reduction in measurement time and allows for measurement without causing stress. Furthermore, it is possible to perform remote blood pressure measurement using a webcam.

[0153] As described above, the results of this experiment suggest that it is useful for daily health monitoring. Furthermore, it can eliminate the complexity of measurement that has been a challenge in daily health monitoring. In particular, since there are many hypertensive patients who are unaware of their condition, accumulating daily measurement data will allow them to quickly notice changes in their blood pressure, enabling early treatment before the condition becomes severe. [Explanation of symbols]

[0154] 1...Blood pressure estimation device, 10...Pulse wave sensor, 20...Height detection unit, 101...CPU, 102...Memory, 104...Display, 501...Distance acquisition unit, 502...Differential pressure acquisition unit, 503...Pulse wave acquisition unit, 504...Velocity calculation unit, 505...Blood pressure calculation unit, 506...Output unit, 700...Imaging device

Claims

1. A blood pressure estimation device for estimating blood pressure using a cuffless system, An elevation difference acquisition unit that acquires a first elevation difference indicating the elevation difference between the heart and a part of the subject's body that is displaceable relative to the heart when that part is placed in a first position above the heart, and a second elevation difference indicating the elevation difference when that part is placed in a second position above the heart but different from the first position, A differential pressure acquisition unit that acquires a differential pressure corresponding to a first high-low difference and a differential pressure corresponding to a second high-low difference, based on known data obtained in advance from actual measurements of multiple subjects, which is the differential pressure between the blood pressure of the heart and the blood pressure of the aforementioned one site. A pulse wave acquisition unit that acquires pulse waves detected from multiple locations in the aforementioned one body part, A velocity calculation unit that calculates the pulse wave propagation velocity at the first position and the pulse wave propagation velocity at the second position based on the pulse wave, A blood pressure calculation unit calculates the blood pressure of the subject's heart based on the differential pressures obtained by the differential pressure acquisition unit and the pulse wave propagation velocities calculated by the velocity calculation unit. An output unit that outputs the calculation result of the blood pressure calculation unit, A blood pressure estimation device equipped with the following features.

2. The differential pressure acquisition unit acquires the diastolic differential pressure between the diastolic blood pressure of the heart and the diastolic blood pressure of the aforementioned site, specifically the diastolic differential pressure at the first pressure difference and the diastolic differential pressure at the second pressure difference. The blood pressure calculation unit calculates the diastolic blood pressure of the subject's heart based on the diastolic differential pressures obtained by the differential pressure acquisition unit and the pulse wave velocity. The blood pressure estimation device according to claim 1.

3. The pulse wave acquisition unit acquires the pulse wave at the first height difference and the pulse wave at the second height difference when the user adopts a predetermined breathing pattern. The blood pressure estimation device according to claim 1 or 2.

4. The pulse wave acquisition unit acquires the pulse wave obtained based on the image data of the one area captured by the imaging unit. The blood pressure estimation device according to claim 1 or 2.

5. The aforementioned body part is one of the subject's hands. The blood pressure estimation device according to claim 1 or 2.

6. The first position is a position above the second position. The pulse wave acquisition unit detects the pulse wave at the first height difference and the pulse wave at the second height difference when the subject performs the action of lowering one part of the body. The blood pressure estimation device according to claim 1 or 2.

7. A blood pressure estimation device for estimating blood pressure using a cuffless system, A height difference acquisition unit that acquires the height difference between the heart and a part of the subject's body that is displaceable relative to the heart, when the part is positioned at multiple locations above the heart, An estimated differential pressure acquisition unit that acquires an estimated differential pressure corresponding to each of the above-mentioned differences, which is obtained based on known data obtained in advance from actual measurements of multiple subjects, between the blood pressure of the heart and the blood pressure of the aforementioned one site. A pulse wave acquisition unit that acquires pulse waves detected from multiple locations in the aforementioned one body part, A velocity calculation unit that calculates the pulse wave propagation time and pulse wave propagation velocity at the plurality of locations based on the pulse waves at the plurality of locations, A generation unit that generates an estimation formula showing the relationship between the pulse wave propagation velocity at the plurality of locations and the estimated differential pressure corresponding to each of the height differences, A blood pressure calculation unit that calculates the blood pressure of the subject's heart based on the estimation formula, An output unit that outputs the calculation result of the blood pressure calculation unit, A blood pressure estimation device equipped with the following features.

8. A computer for a blood pressure estimation device that estimates blood pressure using a cuffless system, A height difference acquisition step that acquires a first height difference indicating the height difference between the heart and a part of the subject's body that is displaceable relative to the heart when that part is placed in a first position above the heart, and a second height difference indicating the height difference when that part is placed in a second position above the heart but different from the first position, A differential pressure acquisition step is to acquire a differential pressure corresponding to a first high-low difference and a differential pressure corresponding to a second high-low difference, based on known data obtained in advance from actual measurements of multiple subjects, which is the differential pressure between the blood pressure of the heart and the blood pressure of the aforementioned one site. A pulse wave acquisition step of acquiring pulse waves detected from multiple locations in the aforementioned one body part, A velocity calculation step that calculates the pulse wave propagation velocity at the first position and the pulse wave propagation velocity at the second position based on the pulse wave, A blood pressure calculation step which calculates the blood pressure of the subject's heart based on each differential pressure obtained in the differential pressure acquisition step and each pulse wave propagation velocity calculated in the velocity calculation step, An output step which outputs the calculation result in the blood pressure calculation step, A blood pressure estimation method that includes processing.

9. A computer for a blood pressure estimation device that estimates blood pressure using a cuffless system, A step to acquire elevation difference, in which a part of the subject's body that is displaceable relative to the heart is placed at multiple positions above the heart, and the elevation difference between the heart and the part is acquired for each of these positions, An estimated differential pressure acquisition step is to obtain an estimated differential pressure corresponding to each of the above-mentioned differences in pressure, which is obtained based on known data obtained in advance from actual measurements of multiple subjects, between the blood pressure of the heart and the blood pressure of the aforementioned one site. A pulse wave acquisition step of acquiring pulse waves detected from multiple locations in the aforementioned one body part, A velocity calculation step that calculates the pulse wave propagation time and pulse wave propagation velocity at the plurality of locations based on the pulse waves at the plurality of locations, A generation step of generating an estimation formula that shows the relationship between the pulse wave propagation velocity at the plurality of locations and the estimated differential pressure corresponding to each of the height differences, A blood pressure calculation step of calculating the blood pressure of the subject's heart based on the estimation formula, An output step which outputs the calculation result in the blood pressure calculation step, A blood pressure estimation method that includes processing.

10. A program that makes a computer function as a blood pressure estimator that estimates blood pressure without cuffs, The aforementioned computer, An elevation difference acquisition unit that acquires a first elevation difference indicating the elevation difference between the heart and a part of the subject's body that is displaceable relative to the heart when that part is placed in a first position above the heart, and a second elevation difference indicating the elevation difference when that part is placed in a second position above the heart but different from the first position. A differential pressure acquisition unit that acquires a differential pressure corresponding to a first high-low difference and a differential pressure corresponding to a second high-low difference, based on known data obtained in advance from actual measurements of multiple subjects, which is the differential pressure between the blood pressure of the heart and the blood pressure of the aforementioned one site. A pulse wave acquisition unit that acquires pulse waves detected from multiple locations in the aforementioned one body part. A velocity calculation unit that calculates the pulse wave propagation velocity at the first position and the pulse wave propagation velocity at the second position based on the pulse wave. A blood pressure calculation unit calculates the blood pressure of the subject's heart based on the differential pressures obtained by the differential pressure acquisition unit and the pulse wave propagation velocities calculated by the velocity calculation unit. An output unit that outputs the calculation result of the blood pressure calculation unit, A program that makes it function as such.

11. A program that makes a computer function as a blood pressure estimator that estimates blood pressure without cuffs, The aforementioned computer, A height difference acquisition unit that acquires the height difference between the heart and a part of a subject's body that is displaceable relative to the heart, when the part is positioned at multiple locations above the heart. An estimated differential pressure acquisition unit that acquires an estimated differential pressure corresponding to each of the above-mentioned differences, which is obtained based on known data obtained in advance from actual measurements of multiple subjects, between the blood pressure of the heart and the blood pressure of the aforementioned one site. A pulse wave acquisition unit that acquires pulse waves detected from multiple locations in the aforementioned one body part. A velocity calculation unit calculates the pulse wave propagation time and pulse wave propagation velocity at the plurality of locations based on the pulse waves at the plurality of locations. A generation unit that generates an estimation formula showing the relationship between the pulse wave propagation velocity at the plurality of locations and the estimated differential pressure corresponding to each of the height differences. A blood pressure calculation unit calculates the blood pressure of the subject's heart based on the estimation formula. An output unit that outputs the calculation result of the blood pressure calculation unit, A program that makes it function as such.

Images