Peripheral blood pressure estimation method and biological information measurement system

Abstract

Provided are a peripheral blood pressure estimation method and a biological information measurement system with which it is possible to non-invasively and conveniently estimate the magnitude of the blood pressure in peripheral capillaries or arterioles. The biological information measurement system 10 executes: a step for acquiring, by means of a photoelectric pulse wave sensor 211, a photoelectric pulse wave signal 53 for the peripheral capillaries or arterioles of a user who is a subject; and a step for calculating, on the basis of the steepness by which the photoelectric pulse wave signal 53 rises, a peripheral blood pressure index serving as an index for the magnitude of the blood pressure in the peripheral capillaries or arterioles. The magnitude of the blood pressure in the peripheral capillaries or arterioles is estimated on the basis of the peripheral blood pressure index.

Description

Technical Field

[0001] The present invention relates to a peripheral blood pressure estimation method and a biological information measurement system for estimating the blood pressure of capillaries or arterioles in the periphery of a subject (user).

Background Art

[0002] A pulse wave propagating in a user's artery is used as an index for estimating the user's health condition. The pulse wave changes according to the change in the user's blood pressure at the measurement location. Patent Document 1 shows a pulse wave measurement device for measuring blood pressure with a small burden on the living body. In the pulse wave measurement device described in Patent Document 1, the blood pressure information of the living body is estimated based on the pulse rate of the living body and the time information of the pulse wave of the living body.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the estimation of blood pressure information in the pulse wave measurement device described in Patent Document 1 is performed for arterial blood pressure information, and no blood pressure information about capillaries or arterioles in the periphery of the user is performed.

[0005] An object of the present invention is to provide a peripheral blood pressure estimation method and a biological information measurement system capable of non-invasively estimating such peripheral blood pressure information.

Means for Solving the Problems

[0006] For this purpose, the present invention acquiring a photoelectric pulse wave signal of capillaries or arterioles in the periphery of a subject with a photoelectric pulse wave sensor; Information including the width of the first peak that appears within one beat of the waveform of the velocity pulse wave signal obtained by first-order differentiating the photoelectric pulse wave signal, or information regarding the peak differences (a - b) and (a - d) when the peak values of the a-wave, b-wave, c-wave, and d-wave of the acceleration pulse wave signal obtained by second-order differentiating the photoelectric pulse wave signal are respectively denoted as a, b, c, and d. A step of calculating a peripheral blood pressure index that serves as an index of the magnitude of blood pressure in peripheral capillaries or arterioles based on the steepness of the rise of the photoelectric pulse wave signal This was executed by a biological information measurement system to constitute a peripheral blood pressure estimation method for estimating the magnitude of blood pressure in peripheral capillaries or arterioles based on the peripheral blood pressure index. Also, a sensing device having a photoelectric pulse wave sensor for acquiring a photoelectric pulse wave signal of a subject's peripheral capillaries or arterioles, Information including the width of the first peak that appears within one beat of the waveform of the velocity pulse wave signal obtained by first-order differentiating the photoelectric pulse wave signal, or information regarding the peak differences (a - b) and (a - d) when the peak values of the a-wave, b-wave, c-wave, and d-wave of the acceleration pulse wave signal obtained by second-order differentiating the photoelectric pulse wave signal are respectively denoted as a, b, c, and d. A computer having a signal processing device for calculating a peripheral blood pressure index that serves as an index of the magnitude of blood pressure in peripheral capillaries or arterioles based on the steepness of the rise of the photoelectric pulse wave signal A biological information measurement system including these was constituted.

[0007] According to this configuration, a photoelectric pulse wave signal of a subject's peripheral capillaries or arterioles is acquired by the photoelectric pulse wave sensor, and based on the steepness of the rise of the acquired photoelectric pulse wave signal, a peripheral blood pressure index that serves as an index of the magnitude of blood pressure in the subject's peripheral capillaries or arterioles is calculated. The magnitude of blood pressure in the subject's peripheral capillaries or arterioles is estimated based on the calculated peripheral blood pressure index.

Advantages of the Invention

[0008] Therefore, according to the present invention, it is possible to provide a peripheral blood pressure estimation method and a biological information measurement system that can non-invasively and simply estimate the magnitude of blood pressure in peripheral capillaries or arterioles without burdening the subject.

Brief Description of the Drawings

[0009]

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Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the respective drawings. Here, the same reference numerals indicate the same components, and redundant explanations will be omitted.

[0011] FIG. 1 is an explanatory diagram showing the configuration of a biological information measurement system 10 according to an embodiment of the present invention. The biological information measurement system 10 includes a sensing device 20 that measures biological information of a user who is a subject, and a computer 30 that is configured to be communicable with the sensing device 20.

[0012] The sensing device 20 is, for example, a wearable device having a structure that can be worn on a peripheral part (e.g., finger) of a user. The sensing device 20 includes a biosensor 21 that measures biological information from a peripheral part (e.g., finger) of the user, a control circuit 22 that controls the operation of the biosensor 21, a communication module 23 that transmits the measurement result of the sensing device 20 to a computer 30 through a wireless line or a wired line, and an acceleration sensor 24 that measures the movement acceleration of the sensing device 20.

[0013] The biosensor 21 includes, for example, a photoelectric plethysmogram sensor 211 that measures an index value indicating the peripheral blood pressure of the user. The peripheral blood pressure in the present invention is defined as the blood pressure of peripheral capillaries and arterioles. In the present invention, an index indicating the blood pressure in arterioles, capillaries, particularly capillaries, is called a peripheral blood pressure index. Here, an arteriole is, for example, a thin artery having a diameter of about 20 to 200 μm and is a blood vessel existing between an artery and a capillary. A capillary is, for example, a thin blood vessel having a diameter of about 10 μm and is a blood vessel connecting an artery and a vein.

[0014] Peripheral blood pressure may be used in the sense of the blood pressure of the wrist and ankle measured by a cuff-type blood pressure monitor. In that case, it is a measured value in a thick artery (such as the radial artery), which is different from the blood pressure in arterioles and capillaries in the present invention. The blood pressure in a thick artery is generally the blood pressure measured by a cuff-type blood pressure monitor, and the blood pressure in the blood vessel decreases as it progresses from an artery to an arteriole and a capillary. The degree of the blood pressure drop varies depending on the measurement site, the vascular condition of an individual (such as arteriosclerosis), the mental state (such as the autonomic nerve state), the environment (such as temperature and noise), and clothing.

[0015] As characteristics of the peripheral blood pressure index, the following two points (1) and (2) are assumed. (1) When the blood vessels are healthy and the vascular resistance does not change, the peripheral blood pressure index is almost proportional to the blood pressure (of the upper arm or wrist). (2) When the blood vessels are constricted by cooling the vicinity of the measurement site, the peripheral blood pressure index decreases. This means that the peripheral vascular resistance increases, so the blood pressure of the upper arm or wrist may increase.

[0016] The photoelectric pulse wave sensor 211 is equipped with three LEDs as light sources and measures photoelectric pulse wave signals at three wavelengths (green, red, near-infrared). Since oxyhemoglobin exists in the blood of arteries and has the characteristic of absorbing incident light, the blood flow volume (vascular volume change) that changes with the heartbeat of the heart is sensed in time series, and thus the photoelectric pulse wave signal can be measured. The red LED is installed for calculating oxygen saturation and is not essential for extracting peripheral blood pressure indicators. The photoelectric pulse wave sensor 211 is equipped with a photodiode (PD) as a light-receiving element, sequentially emits light from the three LEDs in a time-division manner to irradiate the skin of the finger, and receives the light that is reflected and scattered back with the PD.

[0017] The communication module 23 transmits the measurement results of the sensing device 20 (for example, the photoelectric pulse wave signal measured by the photoelectric pulse wave sensor 211 and the acceleration of the sensing device 20 measured by the acceleration sensor 24, etc.) to the computer 30 through a wireless line or a wired line.

[0018] The acceleration sensor 24 measures the movement acceleration of the sensing device 20 when the user changes the posture to measure the pulse wave signal. The acceleration sensor 24 is a three-axis acceleration sensor that detects the direction of the gravitational acceleration, and its detection signal is used for estimating the height at which the user attaches the sensing device 20, and estimating the position where the user attaches the sensing device 20 (for example, the position of the user's heart), and estimating the posture of the user, such as the standing posture (standing position), sitting posture (sitting position), or lying on the back posture (supine position).

[0019] The computer 30 is, for example, a multifunctional mobile phone called a smartphone, or a general-purpose computer (e.g., a notebook computer, a desktop computer, a tablet terminal, a server computer, etc.). The computer 30 includes a communication module 31 that receives the measurement results of the biological sensor 21 from the sensing device 20 through a wireless line or a wired line, and a signal processing device 32 that performs a process of estimating the user's biological information from the measurement results of the biological sensor 21. The signal processing device 32 includes a processor 321, a memory 322, and an input / output interface 323.

[0020] The signal processing device 32 differentiates the two photoplethysmograms (volume plethysmograms) measured by the green LED and the near-infrared LED into the first derivative (velocity plethysmogram) and the second derivative (acceleration plethysmogram), respectively, and calculates the pulse feature quantities by slicing each of them every heartbeat. Then, based on the pulse feature quantities, a peripheral blood pressure index is calculated. In addition, the signal processing device 32 estimates the height of the part where the user attaches the sensing device 20 and the user's posture based on the signal from the acceleration sensor 24.

[0021] FIG. 2 is an explanatory diagram showing the external configuration of the sensing device 20 according to an embodiment of the present invention. As the measurement site of the photoplethysmogram, there are the wrist, the neck, the face, the ear, etc., but the finger is preferable. The finger is preferably used because the epidermis is relatively thin and it is easy to measure the photoplethysmogram, and the path of the capillary is not as complex as that of the face, etc., so the values of each feature quantity are likely to be stable. As a device for measuring the photoplethysmogram, a ring-type wearable device attached to a finger equipped with an optical sensor is preferable. This is because when measuring continuously or intermittently, there is little discomfort or unpleasant feeling even when worn for a long time. However, it is not limited to the finger, and as the wearable device, a wristband type, a wristwatch type, an earphone type attached to the ear, a patch type attached to the skin, or a neckband type attached to the neck may be used. Also, it does not have to be a wearable device, and a portable or installed type such as a smartphone, with a configuration in which the finger is placed on the sensor for measurement, may be used.

[0022] In this embodiment, the sensing device 20 includes an annular housing 25 configured to be wearable on a user's finger. For example, in the example shown in FIG. 2, the housing 25 has a hollow cylindrical shape. When the sensing device 20 is worn on the user's finger, the biological sensor 21 is attached to the inner peripheral surface (the inner surface of the hollow cylinder) of the housing 25 so that the pad of the user's finger faces the biological sensor 21. Note that the shape of the housing 25 is not limited to a hollow cylindrical shape, and may be, for example, a cylindrical shape (e.g., the shape of a finger sack) that fits on the user's finger, and the bottom of the cylinder (the portion where the fingertip abuts) may or may not be present.

[0023] FIG. 3 is an example of the posture of the user 40 when measuring biological information. In this example, the user 40 is in a state where the finger wearing the sensing device 20 is stationary at the position of the heart 41, and the sensing device 20 is measuring biological information from the finger of the user 40. Note that the position (measurement position) of the sensing device 20 when measuring biological information is not limited to the position of the chest (heart) 41 of the user 40, and may also be the position of the face (forehead) or the abdomen (navel) of the user 40. Also, the posture of the user 40 when measuring biological information may be a sitting posture or a supine posture.

[0024] With reference to FIG. 4, acquisition of a photoplethysmogram signal by the biological sensor 21 will be described. FIG. 4 is a schematic cross-sectional view of a state where the biological sensor 21 is attached close to the body surface S of the user.

[0025] The biological sensor 21 includes light-emitting elements 211a, 211b and a light-receiving element 211c. The biological sensor 21 irradiates light onto the body surface S and receives the light absorbed or reflected by the epidermal region EP of the user, a plurality of capillaries CA, and the arteriole AR that is the branch point of each capillary CA. In this embodiment, the case where one light-receiving element 211c is provided for the light-emitting elements 211a, 211b serving as light sources will be described. Note that a light-receiving element may be provided for each of the light-emitting elements 211a, 211b.

[0026] The light-emitting element 211a is preferably an LED or a laser having a wavelength in the vicinity of blue to yellow-green (preferably a wavelength in the vicinity of 500 to 550 nm), and in this embodiment, it is a green LED. The light-emitting element 211b is preferably an LED or a laser having a wavelength in the vicinity of red to near-infrared (preferably a wavelength in the vicinity of 750 to 950 nm), and in this embodiment, it is a near-infrared LED. The light-emitting element 211a irradiates light in a wavelength range that is strongly absorbed by the living body, and the light-emitting element 211b irradiates light in a wavelength range that is relatively weakly absorbed by the living body. Hereinafter, the light-emitting element 211a will be described as the green LED 211a, and the light-emitting element 211b will be described as the near-infrared LED 211b. The light-receiving element 211c uses a photodiode (PD) or a phototransistor. An Si photodiode is preferable.

[0027] The green LED 211a is provided at a position closer to the light-receiving element 211c than the near-infrared LED 211b. For example, it is preferable that the distance between the green LED 211a and the light-receiving element 211c is about 1 to 3 mm, and the distance between the near-infrared LED 211b and the light-receiving element 211c is about 5 to 20 mm. By providing the green LED 211a at a position closer to the light-receiving element 211c than the near-infrared LED 211b, the light-receiving signal based on the light from the green LED 211a can contain more information on the shallow region of the skin than the light-receiving signal based on the light from the near-infrared LED 211b.

[0028] The light emitted from the green LED 211a is absorbed by the user's epidermal region EP and the capillaries CA on the epidermal region EP side, and the transmitted light or reflected light is detected by the light-receiving element 211c. The light emitted from the near-infrared LED 211b is absorbed by the user's epidermal region EP, capillaries CA, and arterioles AR inside the body from the epidermal region EP, and is detected by the light-receiving element 211c. In FIG. 4, the light from the green LED 211a is schematically shown as the light along the optical path P1, and the light from the near-infrared LED 211b is shown as the light along the optical path P2.

[0029] The characteristic quantities of the pulse wave showing the characteristics (1) and (2) of the peripheral blood pressure index were extracted by the following method. That is, a finger-mounted sensing device 20 shown in FIG. 2 equipped with a photoelectric pulse wave sensor 211 was prepared. A wrist-type cuff blood pressure monitor was attached to the left wrist (or right wrist) of the user 40, and this sensing device 20 was attached to the index finger of the same left hand (or other finger). Then, in a sitting position at rest, the left hand with the sensing device 20 attached was held at the height of the abdomen (navel), the height of the chest, and the height of the face (forehead), respectively, and the photoelectric pulse and blood pressure were measured. Since the blood flow in the finger is inhibited by the cuff when the photoelectric pulse and blood pressure are measured simultaneously, the blood pressure was measured after the measurement of the photoelectric pulse wave was completed. Next, with the left hand held at the height of the chest, the left elbow was cooled with a coolant. After cooling for several minutes, the photoelectric pulse wave and blood pressure were measured. From the photoelectric pulse wave measured in this way, the characteristic quantities of the pulse wave showing the characteristics (1) and (2) of the peripheral blood pressure index were calculated as follows.

[0030] The graph of FIG. 5 shows an acceleration pulse wave signal 52 obtained by second-order differentiating a photoelectric pulse wave (photoelectric volume pulse wave) signal 53. The horizontal axis of the graph represents time [sec], and the vertical axis represents the signal intensities of the acceleration pulse wave signal 52 and the photoelectric pulse wave signal 53. As shown in the figure, for the photoelectric pulse wave signal 53, the height of the maximum point after connecting the minimum points with a straight line and performing slope correction so that the slope of the straight line becomes 0 is defined as the pulse wave height (maximum amplitude value) S.

[0031] Also, as shown in the graph of FIG. 6, the waveform width at the half-value of the maximum peak value of the velocity pulse wave signal 51 obtained by first-order differentiating the photoelectric pulse wave signal 53 is referred to as VE0.5. The horizontal axis of the graph represents time [sec], and the vertical axis represents the signal intensities of the velocity pulse wave signal 51, the acceleration pulse wave signal 52, and the photoelectric pulse wave signal 53. The velocity pulse wave signal 51 and the acceleration pulse wave signal 52 are each subjected to a normalization process with their respective maximum values set to 1. The peaks (maximum peak and minimum peak) of the acceleration pulse wave signal 52 are respectively referred to as the a wave, b wave, c wave, d wave, and e wave, as shown in the figure. The a wave, c wave, and e wave are peaks convex on the positive side, and the b wave and d wave have waveforms with peaks convex on the negative side. Also, the difference between the a wave peak time and the b wave peak time is referred to as the ab time. Also, the signal intensities at the peak vertices of the a wave, b wave, c wave, d wave, and e wave are denoted as a, b, c, d, and e, respectively. Also, as shown in the graph of FIG. 7, the peak difference between the a wave and the b wave of the acceleration pulse wave signal 52 is denoted as a - b, and the peak difference between the a wave and the d wave is denoted as a - d. The horizontal axis and the vertical axis of the graph are the same as those of the graph of FIG. 6.

[0032] As pulse characteristics indicating the feature described in (1) above that the peripheral blood pressure index is approximately proportional to the blood pressure in the upper arm and wrist, the following three were extracted. ·1 / VE0.5 ·a / S ·(a - b) / (a - d)

[0033] These pulse characteristics are related to the steepness of the rise of the waveform of the photoelectric pulse wave signal 53, as shown in FIG. 8. FIG. 8(a) is a graph showing two photoelectric pulse wave signals 53a and 53b with different steepnesses of the rise of the photoelectric pulse waveform. The horizontal axis of the graph represents time [sec], and the vertical axis represents the signal intensity of the photoelectric pulse wave signal 53. Among these two photoelectric pulse wave signals 53a and 53b, it can be seen that the photoelectric pulse wave signal 53a indicated by the solid line has a steeper rise (larger slope) than the photoelectric pulse wave signal 53b indicated by the broken line.

[0034] The graph shown in Fig. 8(b) shows the changes in the values of the pulse characteristic quantity 1 / VE0.5 and the pulse characteristic quantity a / S due to the difference in the slopes of the photoelectric pulse wave signals 53a and 53b. The vertical axis of the graph represents the values of the pulse characteristic quantity 1 / VE0.5 and the pulse characteristic quantity a / S, and the horizontal axis is divided into the photoelectric pulse wave signal 53b with a small slope and the photoelectric pulse wave signal 53a with a large slope. From the graph, it can be seen that for both the pulse characteristic quantity 1 / VE0.5 and the pulse characteristic quantity a / S, each pulse characteristic quantity for the photoelectric pulse wave signal 53a with a large slope is larger than each pulse characteristic quantity for the photoelectric pulse wave signal 53b with a small slope.

[0035] The graph shown in Fig. 8(c) shows the changes in the values of the pulse characteristic quantity (a - b) / (a - d) and the pulse characteristic quantity 1 / ab time due to the difference in the slopes of the photoelectric pulse wave signals 53a and 53b. The vertical axis of the graph represents the values of the pulse characteristic quantity (a - b) / (a - d) and the pulse characteristic quantity 1 / ab time, and the horizontal axis is divided into the photoelectric pulse wave signal 53b with a small slope and the photoelectric pulse wave signal 53a with a large slope. From the graph, it can be seen that for both the pulse characteristic quantity (a - b) / (a - d) and the pulse characteristic quantity 1 / ab time, each pulse characteristic quantity for the photoelectric pulse wave signal 53a with a large slope is larger than each pulse characteristic quantity for the photoelectric pulse wave signal 53b with a small slope.

[0036] Therefore, it can be confirmed that the above-mentioned three pulse characteristic quantities 1 / VE0.5, a / S, and (a - b) / (a - d) are related to the steepness of the rise of the photoelectric pulse wave form. That is, the steepness of the rise of the photoelectric pulse wave form can be represented by these pulse characteristic quantities, and these pulse characteristic quantities are assumed to be the pulse characteristic quantities showing the characteristics of (1) above. In addition, as other characteristic quantities related to the steepness of the rise of the photoelectric pulse wave form, the pulse characteristic quantity 1 / ab time is added for comparison.

[0037] Figures 9 and 10 show the systolic blood pressure and each pulse wave characteristic quantity when the height of the measurement site (finger) from the heart is changed as measured by the above-described measurement method, and the relationship between the systolic blood pressure and each pulse wave characteristic quantity when the vicinity of the elbow of the arm on the side where the finger, which is the measurement site, is located is cooled at the height of the chest. Also, FIGS. 9(a), (b), (c) and (d) show the results calculated from the photoelectric pulse wave signals measured with the green light emitted from the green LED 211a for the pulse wave characteristic quantities 1 / VE0.5, a / S, (a - b) / (a - d) and 1 / ab time, respectively. Further, FIGS. 10(a), (b), (c) and (d) show the results calculated from the photoelectric pulse wave signals measured with the near-infrared light emitted from the near-infrared LED 211b for the pulse wave characteristic quantities 1 / VE0.5, a / S, (a - b) / (a - d) and 1 / ab time, respectively.

[0038] The horizontal axis of each of these graphs is the systolic blood pressure [mmHg] measured at the wrist, and the vertical axis is the magnitude of each pulse wave characteristic quantity. Also, the measurement was performed for three users A, B, and C. The characteristic line A obtained by connecting the triangular plots is for user A, the characteristic line B obtained by connecting the circular plots is for user B, and the characteristic line C obtained by connecting the square plots shows the measurement results when the height of the measurement site (finger) from the heart is changed for user C. Also, each plot shown by the dashed line indicates the measurement results when the vicinity of the elbow of the arm on the side where the finger, which is the measurement site, is located is cooled at the height of the chest.

[0039] It can be seen from each of the characteristic lines A, B, and C that the pulse wave characteristic quantities shown in FIGS. 9(a), (b), and (c) calculated from the photoelectric pulse wave signals measured with green light show a tendency that the systolic blood pressure and each pulse wave characteristic quantity are nearly proportional when the height of the measurement site (finger) from the heart is changed. The systolic blood pressure decreases almost proportionally as the height of the measurement site (finger) from the heart increases to the abdomen, chest, and face and each pulse wave characteristic quantity decreases. Also, when the vicinity of the measurement site is cooled, it can be confirmed from each plot shown by the dashed line that the magnitude of each pulse wave characteristic quantity decreases and the systolic blood pressure increases. This is consistent with the above-described characteristics (1) and (2) of the assumed peripheral blood pressure index.

[0040] On the other hand, the pulse wave characteristic amounts at 1 / ab time shown in Fig. 9(d) are not as clear as those of the respective pulse wave characteristic amounts shown in Figs. 9(a), (b), and (c). Also, the calculation results of the respective pulse wave characteristic amounts shown in Figs. 10(a), (b), (c), and (d), which are calculated from the photoelectric pulse wave signals measured almost simultaneously with green light in near-infrared light, are found to have unclear above-mentioned tendencies when compared with the results calculated from green light.

[0041] That is, what conforms to the characteristics (1) and (2) of the peripheral blood pressure index is each pulse wave characteristic amount obtained with green light. This is due to the fact that the biological absorbance of green light is high and it is absorbed before reaching the deep region of the skin, so it only contains information on the shallow region of the skin. Since the information to be measured is only that of the shallow region of the skin, the information contained in the photoelectric pulse wave signal of green light mainly comes from capillaries. Therefore, it is considered that the reason why each pulse wave characteristic amount shown in Figs. 9(a), (b), and (c) shows the characteristics (1) and (2) of the peripheral blood pressure index is that there is a lot of capillary information. In order to obtain information on the shallow region of the skin, as described above, an LED or laser having a wavelength in the vicinity of blue to yellow-green (preferably around 500 to 550 nm) with high biological absorption is used as the light source of the photoelectric pulse wave sensor 211, and further, the distance between the light source and the light receiver is preferably short, specifically, 1 to 3 mm is suitable.

[0042] In order to accurately obtain each pulse wave characteristic amount serving as the peripheral blood pressure index, it is necessary to pay attention to the following points.

[0043] First, it is the height from the heart of the measurement site. As shown in Figs. 9 and 10, the peripheral blood pressure index changes depending on the height from the heart. When observing daily fluctuations, weekly fluctuations, and monthly fluctuations, it is necessary to align the measurement conditions. Although it is desirable to measure at the height of the heart (chest), if the height from the heart is constant, it does not have to be at the height of the heart. For example, The posture in which the user holds the biological sensor 21 at the height of the chest with the hand in the sitting position, The posture in which the user holds the biological sensor 21 at the height of the face with the hand in the sitting position, The posture in which the user holds the biological sensor 21 at the height of the abdomen with the hand in the sitting position, The posture in which the user holds the biosensor 21 at chest height in a supine position on a flat surface, and the posture in which the user holds the biosensor 21 at the height of the flat surface in a supine position on the flat surface are postures that anyone can easily assume and have high repeatability among individuals. Furthermore, for example, if "abdomen" is limited to "navel" and "face" is limited to "forehead", the repeatability becomes even higher, and the measurement variation of the photoelectric pulse wave signal can be reduced.

[0044] Second, it is the resting state of the user. If each pulse wave characteristic quantity serving as a peripheral blood pressure index is not measured in the resting state, the peripheral blood pressure index will not be stable. As a physiological reaction, there are two main reasons: after movement, the pulse rate and blood pressure do not stabilize for 10 to several tens of seconds or more, and the relative position between the biosensor 21 and the skin shifts. The former is that, for example, even a slight movement such as sitting up straight in a seated position causes the heart rate to increase for 10 to several tens of seconds. In some cases, it may take several tens of minutes to return to the resting state after exercise. The latter is what is called body movement noise, which is an unavoidable noise when moving violently, but it subsides immediately when the movement stops. It is desirable to provide an acceleration sensor 24 and a gyro sensor in the sensing device 20 and make a determination such as when the state where the acceleration is smaller than the threshold value continues for a certain period of time, it is considered the resting state, and use the photoelectric pulse wave signal when the resting state is maintained.

[0045] Third, it is excessive pressure of the biosensor 21 on the skin. When the pressure of the biosensor 21 on the skin becomes excessive, the accuracy of the peripheral blood pressure index may decrease. Examples where the photoelectric pulse wave waveform is distorted during excessive pressure have been confirmed. Furthermore, when the pressure becomes stronger, blood flow is inhibited and the photoelectric pulse wave cannot be detected. Therefore, it is desirable for the sensing device 20 to be equipped with a function to detect excessive pressure. The function to detect excessive pressure may be realized by a piezoelectric sensor, a pressure sensor, etc., or may be detected from the waveform shape of the photoelectric pulse wave. When the biological information measurement system 10 detects excessive pressure, since the accuracy of the peripheral blood pressure index at that time is presumed to be poor, it is preferable to notify the user of information such as not using that peripheral blood pressure index.

[0046] As described above, the peripheral blood pressure index changes according to the relative height of the sensing device 20 with respect to the heart. Therefore, in the biological information measurement system 10, the computer 30 may be provided with a function of determining the height of the sensing device 20 from the heart, and when the sensing device 20 is at the height of the user's heart, the peripheral blood pressure index may be calculated. Thereby, since the relative height of the sensing device 20 with respect to the heart can be limited, it is possible to suppress the influence of the change in the peripheral blood pressure index due to the difference in the relative height and estimate the peripheral blood pressure.

[0047] Further, in the biological information measurement system 10, the computer 30 may be provided with a function of estimating the amount of change in the height of the sensing device 20 based on the information from the acceleration sensor 24 of the sensing device 20. The computer 30 may estimate the peripheral blood pressure based on the peripheral blood pressure index and the amount of change in height. The computer 30 can correct the influence on the peripheral blood pressure index due to the change in the height of the sensing device 20 that affects the peripheral blood pressure index, based on the amount of change. Thereby, the estimation accuracy of the peripheral blood pressure is improved. Note that in the biological information measurement system 10, the height of the sensing device 20 may be input from the outside through the computer 30.

[0048] FIG. 11 is a flowchart showing an example of the processing in the peripheral blood pressure estimation method according to the embodiment of the present invention. The processing by the biological information measurement system 10 is performed, for example, when programs stored in non-temporary storage areas of the sensing device 20 and the computer 30, respectively, are executed by the sensing device 20 and the computer 30 each including an information processing device such as a processor.

[0049] In step S1101, the sensing device 20 of the biological information measurement system 10 measures a photoplethysmogram signal from the finger of the user wearing the sensing device 20. Specifically, the photoplethysmogram sensor 211 measures the photoplethysmogram signal 53 by the green light emitted by the green LED 211a and also measures the photoplethysmogram signal 53 by the near-infrared light emitted by the near-infrared LED 211b.

[0050] In step S1102, the sensing device 20 transmits the measurement result to the computer 30 of the biological information measurement system 10. In step S1103, the computer 30 receives the measurement result of the sensing device 20.

[0051] In step S1104, the computer 30 calculates the peripheral blood pressure index of the user. For example, the computer 30 calculates the pulse wave characteristic quantities 1 / VE0.5, a / S, and (a - b) / (a - d) from the photoplethysmogram signal 53 measured by the biological sensor 21, and calculates the peripheral blood pressure index of the user from the calculated pulse wave characteristic quantities.

[0052] In step S1105, the computer 30 estimates the peripheral blood pressure of the user based on the peripheral blood pressure index stored in the storage unit such as the memory 322.

[0053] As described above, the exemplary embodiments of the present invention have been described. The peripheral blood pressure estimation method described in this embodiment includes a step of acquiring, by the photoplethysmogram sensor 211, the photoplethysmogram signal 53 of the capillaries or arterioles in the periphery of the user who is the subject, and a step of calculating, by the biological information measurement system 10, a peripheral blood pressure index that is an index of the magnitude of the blood pressure of the capillaries or arterioles in the periphery based on the steepness of the rise of the photoplethysmogram signal 53, and estimating the magnitude of the blood pressure of the capillaries or arterioles in the periphery based on the peripheral blood pressure index.

[0054] According to this configuration, the photoplethysmogram signal 53 of the capillaries or arterioles in the user's periphery is acquired by the photoplethysmogram sensor 211, and based on the steepness of the rising edge of the acquired photoplethysmogram signal 53, a peripheral blood pressure index serving as an index of the magnitude of the blood pressure of the capillaries or arterioles in the user's periphery is calculated. The magnitude of the blood pressure of the capillaries or arterioles in the user's periphery is estimated based on the calculated peripheral blood pressure index.

[0055] Also, in the above-described peripheral blood pressure estimation method, the steepness of the rising edge of the photoplethysmogram signal 53 is represented by the reciprocal 1 / VE0.5 of the width at the half-value of the peak value of the waveform of the velocity plethysmogram signal 51 obtained by differentiating the photoplethysmogram signal 53 once.

[0056] According to this configuration, the peripheral blood pressure index is calculated based on the pulse feature quantity 1 / VE0.5, and it becomes an index that is less affected by noise and individual differences in the photoplethysmogram waveform. Thus, the peripheral blood pressure can be estimated with less influence from noise and individual differences for a wide range of users.

[0057] Also, in the above-described peripheral blood pressure estimation method, the steepness of the rising edge of the photoplethysmogram signal 53 is represented by the value a / S obtained by dividing the peak value a of the a-wave of the acceleration plethysmogram signal 52 obtained by differentiating the photoplethysmogram signal 53 twice by the maximum amplitude value S of the photoplethysmogram signal 53.

[0058] According to this configuration, the peripheral blood pressure index is calculated based on the pulse feature quantity a / S. Therefore, with a simple calculation method, a peripheral blood pressure index serving as an index of the magnitude of the blood pressure of the capillaries or arterioles in the user's periphery can be calculated.

[0059] Also, in the above-described peripheral blood pressure estimation method, the steepness of the rising edge of the photoplethysmogram signal 53 is represented by the value calculated by the arithmetic expression (a - b) / (a - d) when the peak values of the a-wave, b-wave, c-wave, and d-wave of the acceleration plethysmogram signal 52 obtained by differentiating the photoplethysmogram signal 53 twice are a, b, c, and d, respectively.

[0060] According to this configuration, the peripheral blood pressure index is calculated based on the pulse wave characteristic quantity (a - b) / (a - d). Therefore, also according to this configuration, it is possible to calculate a peripheral blood pressure index, which is an index of the magnitude of the blood pressure of the capillaries or arterioles in the periphery of the user, by a simple calculation method.

[0061] These pulse wave characteristic quantities 1 / VE0.5, a / S, and (a - b) / (a - d) that form the basis of the peripheral blood pressure index may be used alone. However, the values of the peak values a, b, c, and d of the a wave, b wave, c wave, and d wave are easily affected by the pressing state of the pulse wave sensor 211 on the skin and body movement noise, and there is also a large variation due to individual differences. Therefore, among the above pulse wave characteristic quantities, 1 / VE0.5 is a relatively stable feature quantity that can be obtained. Therefore, it is desirable to use 1 / VE0.5 alone or use other feature quantities supplementarily based on 1 / VE0.5. Also, a value obtained by weighting these pulse wave characteristic quantities and performing an averaging process, or a value obtained by normalizing the magnitudes of these pulse wave characteristic quantities and performing an averaging process may be used.

[0062] Also, in the above peripheral blood pressure estimation method, the photoelectric pulse wave sensor 211 emits light in a wavelength band from blue to yellow - green from a light source.

[0063] According to this configuration, light in a wavelength band from blue to yellow - green, which is strongly absorbed by the living body, is emitted from the light source of the photoelectric pulse wave sensor 211 to the living body of the user. Therefore, a photoelectric pulse wave signal 53 containing a lot of information on a shallow living body region is obtained by the photoelectric pulse wave sensor 211 from the skin surface of the living body. For this reason, it is possible to accurately estimate the blood pressure of the capillaries or arterioles in the periphery in the shallow living body region of the skin.

[0064] Also, in the above peripheral blood pressure estimation method, the distance between the photoelectric pulse wave sensor 211 and a light - receiving element that receives the reflected light of the light emitted from the light source is set to 1 - 3 [mm].

[0065] According to this configuration, the distance between the light source and the light receiving element of the photoelectric plethysmogram sensor 211 is set to a distance at which the light emitted from the light source and scattered / reflected by the peripheral capillaries or arterioles is sufficiently received by the light receiving element. Therefore, the blood pressure of the peripheral capillaries or arterioles in the shallow biological region of the skin can be estimated with higher accuracy.

[0066] Further, in the above-described peripheral blood pressure estimation method, the photoelectric plethysmogram sensor 211 is mounted on the sensing device 20 worn on the user's finger.

[0067] According to this configuration, the photoelectric plethysmogram sensor 211 mounted on the sensing device 20 can continuously or intermittently and stably acquire the photoelectric plethysmogram signal 53 from the user's finger. Therefore, the blood pressure of the peripheral capillaries or arterioles of the user can be stably estimated.

[0068] Further, in the above-described peripheral blood pressure estimation method, a step of detecting the pressing state of the photoelectric plethysmogram sensor 211 on the user's measurement site may be further provided. In this case, the sensing device 20 includes a pressing state detection sensor composed of, for example, a piezoelectric element that detects the pressing state of the photoelectric plethysmogram sensor 211 on the subject's measurement site. The signal processing device 32 determines based on the pressing state in which the validity of the estimated peripheral blood pressure index is detected.

[0069] In order to stably measure the photoelectric plethysmogram signal 53, the photoelectric plethysmogram sensor 211 needs to be in close contact with the skin of the user's measurement site. However, if the pressure from the photoelectric plethysmogram sensor 211 to the user's measurement site is excessive, blood flow will be inhibited and the peripheral blood pressure estimation accuracy will decrease. However, according to this configuration, since a step of detecting the pressing state of the photoelectric plethysmogram sensor 211 on the user's measurement site with the pressing state detection sensor is further provided, it is possible to detect a state where the pressure from the photoelectric plethysmogram sensor 211 to the user's measurement site is excessive and, for example, not use the peripheral blood pressure estimation value at that time to cope with it.

[0070] Therefore, according to the present invention, it is possible to provide a peripheral blood pressure estimation method that can non-invasively and simply estimate the magnitude of the blood pressure in peripheral capillaries or arterioles without imposing a burden on the user.

Explanation of Signs

[0071] 10…Biological information measurement system, 20…Sensing device, 21…Biological sensor, 211…Photoelectric plethysmogram sensor, 211a…Green LED (light emitting element), 211b…Near-infrared LED (light emitting element), 211c…Light receiving element, 22…Control circuit, 23…Communication module, 24…Acceleration sensor, 25…Housing, 30…Computer, 31…Communication module, 32…Cross-reference to related applications

[0072] This application claims priority based on Japanese Patent Application No. 2022-061021 filed with the Japan Patent Office on March 31, 2022, and Japanese Patent Application No. 2022-128969 filed with the Japan Patent Office on August 12, 2022, and all of their disclosures are incorporated herein by reference in their entirety.

Claims

1. A step of acquiring a photoplethysmogram signal of a capillary or arteriole in the subject's periphery using a photoplethysmogram sensor; A step of calculating a peripheral blood pressure index, which is an index of the magnitude of the blood pressure of the capillary or arteriole in the periphery, based on the steepness of the rise of the photoplethysmogram signal, including information regarding the width of the peak that first appears within one heartbeat of the waveform of the velocity plethysmogram signal obtained by first differentiating the photoplethysmogram signal; A peripheral blood pressure estimation method for estimating the magnitude of the blood pressure of the capillary or arteriole in the periphery based on the peripheral blood pressure index by executing the method with a biological information measurement system.

2. A step of acquiring a photoplethysmogram signal of a capillary or arteriole in the subject's periphery using a photoplethysmogram sensor; A step of calculating a peripheral blood pressure index, which is an index of the magnitude of the blood pressure of the capillary or arteriole in the periphery, based on the steepness of the rise of the photoplethysmogram signal, including information regarding the peak differences (a - b) and (a - d) when the peak values of the a-wave, b-wave, c-wave, and d-wave of the acceleration plethysmogram signal obtained by second differentiating the photoplethysmogram signal are respectively a, b, c, and d; A peripheral blood pressure estimation method for estimating the magnitude of the blood pressure of the capillary or arteriole in the periphery based on the peripheral blood pressure index by executing the method with a biological information measurement system.

3. A sensing device having a photoplethysmogram sensor for acquiring a photoplethysmogram signal of a capillary or arteriole in the subject's periphery; A computer including a signal processing device for calculating a peripheral blood pressure index, which is an index of the magnitude of the blood pressure of the capillary or arteriole in the periphery, based on the steepness of the rise of the photoplethysmogram signal, including information regarding the width of the peak that first appears within one heartbeat of the waveform of the velocity plethysmogram signal obtained by first differentiating the photoplethysmogram signal; A biological information measurement system comprising the above.

4. A sensing device having a photoplethysmogram sensor for acquiring a photoplethysmogram signal of a capillary or arteriole in the subject's periphery; A computer including a signal processing device for calculating a peripheral blood pressure index, which is an index of the magnitude of the blood pressure of the capillary or arteriole in the periphery, based on the steepness of the rise of the photoplethysmogram signal, including information regarding the peak differences (a - b) and (a - d) when the peak values of the a-wave, b-wave, c-wave, and d-wave of the acceleration plethysmogram signal obtained by second differentiating the photoplethysmogram signal are respectively a, b, c, and d; A biological information measurement system comprising the above.

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