METHOD FOR ESTIMATING PERIPHERAL BLOOD PRESSURE AND SYSTEM FOR MEASURING BIOLOGICAL DATA

Abstract

A method for estimating peripheral blood pressure and a biological data measurement system are provided, enabling the simple and non-invasive estimation of blood pressure in a peripheral capillary or arteriole. The acquisition of a photoplethysmographic signal 53 from a peripheral capillary or arteriole of a user, who is a subject, using a photoplethysmographic sensor 211; and the calculation of a peripheral blood pressure index based on the steepness of the rising edge of the photoplethysmographic signal 53 are performed on the biological data measurement system 10, where the peripheral blood pressure index serves as a measure of the magnitude of blood pressure in the peripheral capillary or arteriole. The level of blood pressure in the peripheral capillary or arteriole is estimated based on the peripheral blood pressure index.

Description

Technical area

[0001] The present invention relates to a method for estimating peripheral blood pressure and a biological data measuring system for estimating a blood pressure in a capillary or an arteriole at the periphery of a subject (user). Technical background

[0002] A plethysmographic wave propagating in a user's artery is used as an index to estimate the user's health status. A plethysmographic waveform changes in response to a change in the user's blood pressure at a measurement position. Patent Document 1 discloses a plethysmographic waveform measuring device for measuring blood pressure without imposing a heavy burden on the human body. The plethysmographic waveform measuring device according to Patent Document 1 is configured to estimate blood pressure data of a human body based on temporal information regarding the heart rate and the plethysmographic waveform of the human body. REFERENCES Patent documents

[0003] Patent Document 1: International Publication No. 2015 / 098977 DESCRIPTION OF THE INVENTIONTechnical problem

[0004] However, the plethysmographic waveform measuring device according to Patent Document 1 is configured to estimate blood pressure data in an artery and is not configured to estimate blood pressure data in a capillary or an arteriole at the user's periphery.

[0005] The object of the present invention is to provide a method for estimating peripheral blood pressure and a system for measuring biological data with which such peripheral blood pressure data can be estimated in a non-invasive manner. Solution to the problem

[0006] The present invention provides a method for estimating peripheral blood pressure, comprising: detecting a photoplethysmographic signal from a capillary or an arteriole at the periphery of a subject using a photoplethysmographic sensor; and Calculating a peripheral blood pressure index based on the steepness of a rising edge of the photoplethysmographic signal, wherein the peripheral blood pressure index serves as an index of a magnitude of blood pressure in the capillary or arteriole at the periphery; and Estimating the level of blood pressure in the capillary or arteriole at the periphery based on the peripheral blood pressure index, and the acquisition and calculation are performed on a biological data measurement system.

[0007] The present invention further provides a system for measuring biological data, comprising a sensing device having a photoplethysmographic sensor configured to detect a photoplethysmographic signal from a capillary or an arteriole at the periphery of a subject; and a computer including a signal processing device configured to calculate a peripheral blood pressure index based on the steepness of a rising edge of the photoplethysmographic signal, wherein the peripheral blood pressure index serves as an index of a magnitude of blood pressure in the capillary or the arteriole at the periphery.

[0008] According to the invention, a photoplethysmographic signal from a capillary or arteriole at the periphery of a subject is acquired using a photoplethysmographic sensor, and a peripheral blood pressure index, which serves as an index of a blood pressure magnitude in the capillary or arteriole at the periphery of the subject, is calculated based on the steepness of the rising edge of the acquired photoplethysmographic signal. The level of blood pressure in the capillary or arteriole at the periphery of the subject is estimated based on the calculated peripheral blood pressure index. Advantageous effects of the invention

[0009] Accordingly, the present invention can provide a method for estimating peripheral blood pressure and a biological data measurement system that can estimate the level of blood pressure in a capillary or an arteriole at the periphery in a simple and non-invasive manner without causing any burden to the subject. Brief description of the drawings

[0009] Fig. 1 is a diagram showing a configuration of a biological data measurement system according to an embodiment of the present invention. Fig. 2 is a diagram showing the external appearance of a sensing device according to the invention. Fig. 3 is a diagram showing an example of a user's posture to measure biological data. Fig. 4 is a diagram schematically showing the detection of a photoplethysmographic signal using the sensing device according to the invention. Fig. Figure 5 is a diagram describing the maximum excursion of a photoplethysmographic signal. Fig. Figure 6 is a first diagram describing each waveform element required to calculate the plethysmographic waveform feature values ​​for deriving a peripheral blood pressure index. Fig. Figure 7 is a second diagram describing each waveform element required to calculate the plethysmographic waveform feature values ​​for deriving a peripheral blood pressure measure. In Fig. Figure 8 shows graphs graphically depicting correlations between the steepness of the rising edge of a photoplethysmographic signal and the values ​​of the plethysmographic waveform. In Fig. Figure 9 presents the results of the relationships between systolic blood pressure and plethysmographic waveform values ​​derived from photoplethysmographic signals measured with green light. The relationships are determined by changing the height of a measurement site and by cooling an area near the measurement site. In Fig. Figure 10 shows the results of the relationships between systolic blood pressure and plethysmographic waveform values ​​derived from photoplethysmographic signals measured with near-infrared light. The relationships are determined by changing the height of a measurement site and by cooling an area near the measurement site. Fig. 11 is a flowchart illustrating a process of a peripheral blood pressure estimating method according to the embodiment of the present invention. Description of the embodiments

[0010] An embodiment of the present invention will be described below with reference to the drawings. Like reference numerals denote like or similar elements, thus omitting duplicate descriptions.

[0011] Fig. 1 is a diagram showing a configuration of a biological data measurement system 10 according to the embodiment of the present invention. The biological data measurement system 10 includes a sensing device 20 configured to measure biological data of a user who is a subject, and a computer 30 configured to communicate with the sensing device 20.

[0012] Examples of the sensing device 20 include a wearable device having a structure that can be attached to a peripheral part (e.g., a finger) of the user. The sensing device 20 includes a biological sensor 21 configured to obtain biological data from a peripheral part (e.g., a finger) of the user, a control circuit 22 configured to control the operation of the biological sensor 21, a communication module 23 configured to transmit a measurement result obtained through use of the sensing device 20 to the computer 30 via a wireless network or a wired network, and an acceleration sensor 24 configured to measure acceleration during movement of the sensing device 20.

[0013] The biological sensor 21 comprises, for example, a photoplethysmographic sensor 211 configured to measure an index value representing a peripheral blood pressure of the user. Peripheral blood pressure is defined in the context of the present invention as the blood pressure in a capillary or an arteriole in the periphery. A characteristic value representing a blood pressure in an arteriole or a capillary, in particular in a capillary, is referred to in the context of the present invention as a peripheral blood pressure characteristic value. An arteriole is a thin artery with a diameter of, for example, approximately 20 to 200 µm and is a blood vessel located between an artery and a capillary. A capillary is a thin blood vessel with a diameter of, for example, approximately 10 µm that connects an artery and a vein.

[0014] Although the term "peripheral blood pressure" is sometimes used to refer to wrist blood pressure or ankle blood pressure measured with a cuffed sphygmomanometer, peripheral blood pressure in this usage refers to a value measured at a large artery (for example, the radial artery) and, for the purposes of the present invention, is distinct from a blood pressure in an arteriole or a capillary. Blood pressure in a large artery is a blood pressure typically measured with a cuffed sphygmomanometer, and blood pressure in a blood vessel decreases as blood flows from an artery to an arteriole and then to a capillary.The extent of such a drop in blood pressure depends, for example, on the measurement site, the condition of a subject's blood vessels (e.g. arteriosclerosis), the psychological state (e.g. condition of the autonomic nerves), the environment (e.g. air temperature and noise) and clothing.

[0015] The peripheral blood pressure index is expected to have the following two characteristics (1) and (2). (1) For a healthy blood vessel, the peripheral blood pressure index is essentially proportional to the blood pressures (at an upper arm and a wrist) under the condition that blood vessel resistance is invariant. (2) Contraction of a blood vessel by cooling a region near a measurement site lowers the peripheral blood pressure index. Contraction of a blood vessel means an increase in blood vessel resistance in the periphery, which sometimes leads to an increase in blood pressures at the upper arm and wrist.

[0016] The photoplethysmographic sensor 211 is equipped with three LEDs as a light source and is configured to measure a photoplethysmographic signal at three wavelengths (green, red, and near-infrared). Since oxyhemoglobin is present in the blood in an artery and has the property of absorbing incident light, a photoplethysmographic signal can be measured by detecting the amount of blood flow that changes according to cardiac pulsation (the blood vessel volume that changes) as a function of time. A red LED is attached to derive oxygen saturation and is not required for determining the peripheral blood pressure index. The photoplethysmographic sensor 211 is equipped with a photodiode (PD) as a light-sensitive element.The photoplethysmographic sensor 211 is configured to cause the three LEDs to emit light sequentially in a time-sharing mode, and the PD is configured to receive reflected or scattered light coming back from the skin of a finger irradiated with the light from the LEDs.

[0017] The communication module 23 is configured to send a measurement result obtained using the sensing device 20 (for example, a photoplethysmographic signal measured by the photoplethysmographic sensor 211 and the acceleration of the sensing device 20 measured by the acceleration sensor 24) to the computer 30 via the wireless network or the wired network.

[0018] The acceleration sensor 24 is configured to measure acceleration during movement of the sensing device 20 while the user changes posture to measure a photoplethysmographic signal. The acceleration sensor 24 is a triaxial acceleration sensor configured to detect a direction in which gravitational acceleration is applied, and the detected signal is used to estimate the height at which the sensing device 20 is attached to the user, to infer the position at which the sensing device 20 is attached to the user (for example, the position of the user's heart), and to infer the user's posture, for example, standing (standing position), sitting (seated position), or lying flat on their back (reclining position).

[0019] Examples of the computer 30 include a multifunctional mobile phone called a smartphone and a general-purpose computer (e.g., a notebook, a desktop PC, a tablet terminal, and a server computer). The computer 30 includes a communication module 31 and a signal processing device 32. The communication module 31 is configured to receive a measurement result obtained using the biological sensor 21 from the sensing device 20 via the wireless network or the wired network. The signal processing device 32 is configured to perform a process of deriving the user's biological data from the measurement result obtained using the biological sensor 21. The signal processing device 32 includes a processor 321, a memory 322, and an input / output interface 323.

[0020] A green LED and a near-infrared LED are used to measure respective photoplethysmographic waveforms (plethysmographic volume waveforms). The signal processing device 32 is configured to calculate a first derivative (plethysmographic velocity waveform) and a second derivative (plethysmographic acceleration waveform) from each of the two photoplethysmographic waveforms. The signal processing device 32 is configured to derive plethysmographic waveform feature values ​​from each cardiac cycle of the first derivative and the second derivative. Subsequently, the peripheral blood pressure index is calculated based on the plethysmographic waveform feature values.Furthermore, the signal processing device 32 is configured to estimate the height of the location at which the sensing device 20 is attached to the user based on the signal from the acceleration sensor 24 and to derive the user's posture therefrom.

[0021] Fig. 2 is a diagram illustrating the external appearance of the sensing device 20 according to the present invention. Examples of a measurement site for a photoplethysmographic waveform include the wrist, neck, face, and ear, with the finger being a preferred measurement site. This is because a photoplethysmographic waveform is easy to measure because a finger has a relatively thin epidermal area, and the feature values ​​are easy to stabilize because the capillary pathways are not as complicated as those on the face or other sites. A ring-shaped wearable device including an optical sensor and configured to be worn on a finger is preferred as a device for measuring a photoplethysmographic waveform.This is because a ring-shaped wearable device is unlikely to cause significant discomfort or inconvenience when worn for extended periods during continuous or intermittent measurement. However, this example is not intended to be limiting, and a bracelet-type device that attaches to the wrist, a wristwatch-type device, an earbud-type device that attaches to the ear, a patch-type device that attaches to the skin, or a necklace-type device that attaches around the neck can be used as a wearable device. Furthermore, the device does not have to be wearable but can be a portable device, such as a smartphone, or a stationary device configured to perform measurements on a finger in contact with a sensor.

[0022] The sensing device 20 comprises an annular housing 25, which in the present embodiment is configured to be attached to the user's finger. In a Fig. In the example shown in Figure 2, the housing 25 has, for example, a hollow cylindrical shape. The biological sensor 21 is attached to the inner surface of the housing 25 (inner surface of the hollow cylinder) so that it faces the user's fingertip when the sensing device 20 is attached to the user's finger. The shape of the housing 25 is not limited to the hollow cylinder-like shape and may, for example, be a cylinder-like shape that covers the user's finger from above (for example, as a finger splint), with or without the bottom of the cylinder (the part touched by the fingertip).

[0023] Fig. 3 shows an example of a posture of a user 40 for measuring biological data. In this example, the user 40 holds the finger to which the sensing device 20 is attached at the position of a heart 41, and the sensing device 20 obtains biological data from the user 40's finger. The position (measurement position) where the sensing device 20 is located during biological data measurement is not limited to the chest (heart) 41 position of the user 40 and may also be the face (forehead) or the abdomen (navel) position of the user 40. The posture of the user 40 during biological data measurement may be a sitting or lying position.

[0024] Based on Fig. 4 describes the detection of a photoplethysmographic signal using the biological sensor 21. Fig. 4 is a schematic cross-sectional view of the biological sensor 21 closely attached to a body surface S of the user.

[0025] The biological sensor 21 includes light-emitting elements 211a and 211b and a photosensitive element 211c. The biological sensor 21 is configured to emit light toward the body surface S and receive light absorbed or reflected by an epidermal region EP and a plurality of capillaries CA of the user, as well as an arteriole AR from which each of the capillaries CA branches. In the present embodiment, a case will be described where a single photosensitive element 211c is arranged for the light-emitting elements 211a and 211b as a light source. Note that the corresponding photosensitive element may be arranged for each of the light-emitting elements 211a and 211b.

[0026] The light-emitting element 211a is preferably an LED or a laser with a wavelength of, for example, approximately blue to yellow-green (preferably approximately 500 to 550 nm), and is a green LED in the present embodiment. The light-emitting element 211b is preferably an LED or a laser with a wavelength of, for example, approximately red to near-infrared (preferably approximately 750 to 950 nm), and is a near-infrared LED in the present embodiment. The light-emitting element 211a is designed to emit light in a wavelength range that is strongly absorbed by living tissue, and the light-emitting element 211b is designed to emit light in a wavelength range that is relatively weakly absorbed by living tissue. In the following, it is assumed that the light-emitting element 211a is a green LED 211a and the light-emitting element 211b is a near-infrared LED 211b.A photodiode (PD) or a phototransistor is used as the light-sensitive element 211c. A Si photodiode is preferred.

[0027] The green LED 211a is arranged closer to the photosensitive element 211c than the near-infrared LED 211b. For example, the distance between the green LED 211a and the photosensitive element 211c is preferably set to about 1 to 3 mm, and the distance between the near-infrared LED 211b and the photosensitive element 211c is preferably set to about 5 to 20 mm. Because the green LED 211a is arranged closer to the photosensitive element 211c than the near-infrared LED 211b, an optical reception signal generated by the light of the green LED 211a is caused to contain more information regarding a flat area of ​​the skin than an optical reception signal generated by the light of the near-infrared LED 211b.

[0028] The light emitted by the green LED 211a is absorbed by the user's epidermis EP and the capillaries CA on the epidermis EP side, and the transmitted or reflected light is detected by the photosensitive element 211c. The light emitted by the near-infrared LED 211b is absorbed by the epidermis area EP, the capillaries CA, and the arteriole AR, which are located deeper in the body than the user's epidermis area EP, and is detected by the photosensitive element 211c. Fig. 4, the light of the green LED 211a is schematically shown as light along an optical path P1 and the light of the near-infrared LED 211b as light along an optical path P2.

[0029] Plethysmographic waveform feature values ​​that have the features (1) and (2) described for the peripheral blood pressure index are extracted in the following way. Fig. The sensing device 20 shown in FIG. 2, which is equipped with the photoplethysmographic sensor 211 and can be attached to a finger, is prepared. The user 40 puts a cuffed wrist blood pressure monitor on the left wrist (or right wrist) and places the sensing device 20 on the index finger (or another finger) of the left hand. Then, the user 40 sits and holds the left hand, to which the sensing device 20 is attached, at the navel level, at the chest level, and at the face level (forehead level) to measure a photoplethysmographic waveform and blood pressure. Since the cuff obstructs blood flow in the finger during simultaneous measurement of the photoplethysmographic waveform and blood pressure, the blood pressure is measured after the photoplethysmographic waveform measurement is completed. Next, the left elbow is cooled with a coolant while holding the left hand at the chest level.The photoplethysmographic waveform and blood pressure are measured after the elbow has been cooled for several minutes. From the photoplethysmographic waveform thus measured, plethysmographic feature values ​​are derived as follows, which exhibit the features (1) and (2) described for the peripheral blood pressure index.

[0030] The diagram in Fig. Figure 5 shows a plethysmographic acceleration signal 52, which is a second derivative of a photoplethysmographic (volume photoplethysmographic) signal 53. The horizontal axis of the diagram represents time [seconds], and the vertical axis of the diagram represents the signal strength of the plethysmographic acceleration signal 52 and the photoplethysmographic signal 53. As in Fig. 5, the height of the plethysmographic waveform (maximum deflection) S of the photoplethysmographic signal 53 is defined as the height of a local maximum after the baseline has been corrected so that the slope of a straight line connecting local minima becomes zero.

[0031] As shown in the diagram in Fig. 6, VE0.5 refers to the half-width of the highest peak of a plethysmographic velocity signal 51, which is a first derivative of the photoplethysmographic signal 53. The horizontal axis of the diagram in Fig. 6 represents the time [seconds], and the vertical axis of the diagram represents the signal intensities of the plethysmographic velocity signal 51, the plethysmographic acceleration signal 52, and the photoplethysmographic signal 53. The plethysmographic velocity signal 51 and the plethysmographic acceleration signal 52 were subjected to a normalization process so that the maximum of each signal becomes 1. As shown in Fig. As shown in Figure 6, the plethysmographic acceleration signal has 52 peak values ​​(local maxima and local minima), which are referred to as a-wave, b-wave, c-wave, d-wave, and e-wave. The a-wave, c-wave, and e-wave each have a convex upward waveform, and the b-wave and d-wave each have a convex downward waveform. The difference between the peak time of the a-wave and the peak time of the b-wave is called the ab interval. The signal intensities an at the peak of the a-wave, b-wave, c-wave, d-wave, and e-wave are referred to as a, b, c, d, and e, respectively. As shown in the diagram in Fig. 7, for the plethysmographic acceleration signal 52, the difference in peak values ​​between the a-wave and the b-wave is denoted as a - b, and the difference in peak values ​​between the a-wave and the d-wave is denoted as a - d. The horizontal axis and the vertical axis in the diagram of the Fig. 7 are the same as in the diagram in Fig. 6.

[0032] As described above, the peripheral blood pressure index is characterized by the feature (1) to be substantially proportional to the blood pressures at an upper arm and a wrist, and the following three feature values ​​are extracted as plethysmographic waveform feature values ​​characterized by the feature (1). • 1 / VE0.5 • a / S • (a - b) / (a - d)

[0033] As in Fig. As shown in Figure 8, the values ​​of these plethysmographic waveform features correlate with the steepness of the rising edge of a waveform of the photoplethysmographic signal 53. Fig. Figure 8 (a) shows a diagram illustrating two photoplethysmographic signals 53a and 53b with different steepness of the rising edge of a photoplethysmographic waveform. The horizontal axis of the diagram in Fig. 8 (a) represents time [seconds], and the vertical axis of the graph represents the signal intensity of the photoplethysmographic signal 53. It can be seen that, of these two photoplethysmographic signals 53a and 53b, the photoplethysmographic signal 53a represented by a solid line has a steeper rising edge (slope: large) than the photoplethysmographic signal 53b represented by a dashed line.

[0034] The Fig. The diagram shown in Figure 8 (b) shows the dependences of the plethysmographic waveform feature 1 / VE0.5 and the plethysmographic waveform feature a / S on the slope of the photoplethysmographic signals 53a and 53b. The vertical axis of the diagram in Fig. Figure 8 (b) shows the values ​​of the plethysmographic waveform feature 1 / VE0.5 and the plethysmographic waveform feature a / S, and the horizontal axis of the graph is divided into a region for the photoplethysmographic signal 53b with a small slope and a region for the photoplethysmographic signal 53a with a large slope. The graph in Fig. Figure 8(b) shows that the plethysmographic waveform feature value 1 / VE0.5 and the plethysmographic waveform feature value a / S are larger for the photoplethysmographic signal 53a with a large slope than for the photoplethysmographic signal 53b with a small slope.

[0035] The Fig. The diagram shown in Figure 8 (c) shows the dependences of the plethysmographic waveform feature value (a - b) / (a - d) and the plethysmographic waveform feature value 1 / (ab interval) on the slope of the photoplethysmographic signals 53a and 53b. The vertical axis of the diagram in Fig. Figure 8(c) shows the values ​​of the plethysmographic waveform feature (a - b) / (a - d) and the plethysmographic waveform feature 1 / (ab interval), and the horizontal axis of the graph is divided into a region for the photoplethysmographic signal 53b with a small slope and a region for the photoplethysmographic signal 53a with a large slope. The graph in Fig. 8 (c) shows that the plethysmographic waveform feature value (a - b) / (a - d) and the plethysmographic waveform feature value 1 / (ab interval) are larger for the photoplethysmographic signal 53a with a large slope than for the photoplethysmographic signal 53b with a small slope.

[0036] It is thus confirmed that the three plethysmographic waveform feature values ​​1 / VE0.5, a / S, and (a - b) / (a - d) described above correlate with the steepness of the rising edge of a photoplethysmographic waveform. Indeed, the steepness of the rising edge of a photoplethysmographic waveform can be represented using these plethysmographic waveform feature values, and these plethysmographic waveform feature values ​​are expected to exhibit the feature (1) described above. The feature value 1 / (ab interval) for the plethysmographic waveform is added for comparison as another feature value that correlates with the steepness of the rising edge of a photoplethysmographic waveform.

[0037] Fig. 9 and Fig. 10 shows the relationships between the systolic blood pressure and the plethysmographic waveform characteristics measured by the measurement method described above; the relationships between the systolic blood pressure and the plethysmographic waveform characteristics are obtained by changing the height from the heart to a measurement site (finger); the relationships between the systolic blood pressure and the plethysmographic waveform characteristics are also obtained by cooling the area near the elbow of the arm on the same side as the finger held as the measurement site at chest level. Fig. 9 (a), (b), (c) and (d) show the results for the plethysmographic waveform values ​​1 / VE0.5, a / S, (a - b) / (a - d) and 1 / (ab interval), respectively, derived from the photoplethysmographic signal measured with green light emitted from the green LED 211a. Fig. 10 (a), (b), (c) and (d) show the results for the plethysmographic waveform feature values ​​1 / VE0.5, a / S, (a - b) / (a - d) and 1 / (ab interval), respectively, derived from the photoplethysmographic signal measured with near-infrared light emitted from the near-infrared LED 211b.

[0038] The horizontal axis in each graph is the systolic blood pressure [mmHg] measured at a wrist, and the vertical axis is the magnitude of each plethysmographic waveform feature value. The measurement is performed for three users A, B, and C; characteristic curve A connecting the triangles, characteristic curve B connecting the circles, and characteristic curve C connecting the rectangles represent the measurement results for users A, B, and C, respectively, obtained by changing the height from the heart to the measurement site (finger). A dashed line branching off each of the characteristic curves represents a measurement result obtained by cooling the area near the elbow of the arm on the same side as the finger held as the measurement site at chest level.

[0039] The characteristic curves A, B and C show that the Fig. 9 (a), (b), and (c), derived from the photoplethysmographic signal measured with green light, are almost proportional to the systolic blood pressure when the height from the heart to the measurement site (finger) changes. Each of the plethysmographic waveform feature values ​​decreases as the height from the heart to the measurement site (finger) increases from the abdomen to the chest to the face, and the systolic blood pressure decreases almost proportionally to each of the plethysmographic waveform feature values. The dashed lines branching from the characteristic curves confirm that the plethysmographic waveform feature values ​​decrease and the systolic blood pressure increases when the area near the measurement site is cooled. These results are consistent with the features (1) and (2) described above, which would be expected for the peripheral blood pressure characteristic.

[0040] In contrast, the Fig. 9 (d) shows such a tendency not as clearly as that shown in Fig. 9 (a), (b) and (c). In addition, the plethysmographic waveform feature values ​​shown in Fig. 10 (a), (b), (c) and (d) are derived from the photoplethysmographic signals measured with near-infrared light at substantially the same time as with green light, but it can be seen that the calculated results do not show the above-mentioned tendency as clearly as the results derived from the measurement with green light.

[0041] In summary, the plethysmographic waveform values ​​acquired with green light are more consistent with features (1) and (2) of the peripheral blood pressure index. This is because living tissue has a high absorbance for green light, and green light is largely absorbed before reaching an area deep in the skin, so the plethysmographic waveform features acquired with green light only contain information about a shallow area in the skin. Since the measured data only contain information about a shallow area in the skin, the information contained in the photoplethysmographic signal measured with green light mainly concerns the capillaries. Therefore, the Fig. 9 (a), (b), and (c) represent features (1) and (2) of the peripheral blood pressure index, probably because the plethysmographic waveform feature values ​​contain a large amount of information about capillaries. As described above, to acquire information about a flat area in the skin, an LED or a laser with wavelengths in the range of blue to yellow-green (preferably around 500 to 550 nm), which are strongly absorbed by living tissue, is used as the light source in the photoplethysmographic sensor 211. Furthermore, the distance between the light source and the photosensitive detector is preferably short, specifically 1 to 3 mm.

[0042] The following factors must be considered to accurately capture the characteristic values ​​of the plethysmographic waveform intended to represent the peripheral blood pressure index.

[0043] The first factor is the height between the heart and the measuring point. The peripheral blood pressure index depends on the height of the heart, as shown in Fig. 9 and Fig. 10. To observe daily, weekly, or monthly fluctuations, the measurement conditions must be consistent. Measurement at heart level (chest level) is preferred, but the height may deviate from heart level as long as the height above the heart remains constant. For example, a position in which the user sits and holds the biological sensor 21 in his hand at chest height, a position in which the user sits and holds the biological sensor 21 in his hand at face level, a position in which the user sits and holds the biological sensor 21 in his hand at abdominal level, a position in which the user lies on his back on a flat surface and holds the biological sensor 21 in his hand at chest height, and A position in which the user lies supine on a flat surface and holds the biological sensor 21 in their hand at the level of the flat surface are postures that anyone can easily assume and that a person can assume repeatedly with high reproducibility. Further restricting the position from "abdomen" to "navel" or from "face" to "forehead" improves the reproducibility of repetition and reduces fluctuations in the measurement of a photoplethysmographic signal.

[0044] A second factor is the user's resting state. The peripheral blood pressure index stabilizes only when the plethysmographic waveform values ​​intended to constitute the peripheral blood pressure index are measured at rest. There are two main reasons for this. One is that the heart rate and blood pressure, as a physiological response to body movement, do not stabilize for 10 to several tens of seconds or longer, and the other is that the biological sensor 21 is moving relative to the skin. For example, after a slight change in sitting posture, the heart rate increases for 10 to several tens of seconds. After exercise, it sometimes takes several dozen minutes to return to the resting state. The latter is called body movement noise, which is inevitable during vigorous exercise but stops once the movement stops.The sensing device 20 is preferably equipped with an acceleration sensor 24 or a gyroscopic sensor, which can be used to determine that, for example, a rest state has been established when the acceleration remains below a threshold value for a certain period of time, and a photoplethysmographic signal is preferably used which is detected while the rest state is maintained.

[0045] A third factor is excessive pressure exerted by the biological sensor 21 on the skin. When the biological sensor 21 exerts excessive pressure on the skin, the accuracy of the peripheral blood pressure reading sometimes decreases. It has been confirmed that excessive pressure sometimes distorts the photoplethysmographic waveform, and a further increase in pressure impedes blood flow, resulting in the photoplethysmographic waveform becoming undetectable. Therefore, the excessive pressure detection function is preferably incorporated into the sensing device 20. The excessive pressure detection function can be achieved using a piezoelectric sensor or a pressure sensor, or excessive pressure can be detected using a photoplethysmographic waveform.In response to the detection of excessive pressure, the biological data measurement system 10 preferably provides information to the user, such as an instruction not to use the peripheral blood pressure metric observed at that time because the peripheral blood pressure metric is likely to be inaccurate.

[0046] As described above, the peripheral blood pressure index depends on the height at which the sensing device 20 is located relative to the heart. Therefore, the computer 30 in the biological data measurement system 10 may have the function of determining the height between the heart and the sensing device 20 and calculating the peripheral blood pressure index when the sensing device 20 is located at the user's heart level. In this way, the peripheral blood pressure can be estimated with less influence from the change in the peripheral blood pressure index caused by a difference in height from the heart, since the height at which the sensing device 20 is arranged relative to the heart may be limited.

[0047] The computer 30 in the biological data measurement system 10 may be configured to estimate the magnitude of the change in the elevation of the sensing device 20 based on the data from the acceleration sensor 24 in the sensing device 20. The computer 30 may be configured to estimate a peripheral blood pressure based on the peripheral blood pressure index and the magnitude of the elevation change. The change in the elevation of the sensing device 20 affects the peripheral blood pressure index, and the computer 30 is capable of correcting the effect of the change in elevation on the peripheral blood pressure index based on the magnitude of the change in the elevation of the sensing device 20. This correction contributes to improved accuracy of the estimated peripheral blood pressure. In the biological data measurement system 10, the elevation of the sensing device 20 may be input externally via the computer 30.

[0048] Fig.11 is a flowchart illustrating an example of a process of the peripheral blood pressure estimation method according to the embodiment of the present invention. For example, the sensing device 20 and the computer 30 each include an information processing device such as a processor and are configured to execute programs stored in the corresponding non-transitory memory space. Thus, the process by the biological data measurement system 10 is performed by the sensing device 20 and the computer 30.

[0049] In step S1101, the sensing device 20 in the biological data measurement system 10 receives a photoplethysmographic signal from a user's finger to which the sensing device 20 is attached. Specifically, the photoplethysmographic sensor 211 measures the photoplethysmographic signal 53 using green light emitted from the green LED 211a and measures the photoplethysmographic signal 53 using near-infrared light emitted from the near-infrared LED 211b.

[0050] In step S1102, the sensing device 20 sends the measurement result to the computer 30 in the biological data measurement system 10. In step S1103, the computer 30 receives the measurement result obtained from the sensing device 20.

[0051] In step S1104, the computer 30 calculates a peripheral blood pressure index of the user. For example, the computer 30 derives the plethysmographic waveform feature values ​​1 / VE0.5, a / S, and (a - b) / (a - d) from the photoplethysmographic signal 53 measured by the biological sensor 21, and derives a peripheral blood pressure index of the user from the calculated plethysmographic waveform feature values.

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

[0053] An illustrative embodiment of the present invention has already been described above. The method for estimating peripheral blood pressure described in the present embodiment includes acquiring a photoplethysmographic signal 53 from a capillary or an arteriole at the periphery of a user who is a test subject using a photoplethysmographic sensor 211; calculating a peripheral blood pressure index based on the steepness of a rising edge of the photoplethysmographic signal 53, the peripheral blood pressure index serving as an index of a magnitude of blood pressure in the capillary or arteriole at the periphery; and estimating the magnitude of blood pressure in the capillary or arteriole at the periphery based on the peripheral blood pressure index. The acquiring and calculating are performed in the biological data measurement system 10.

[0054] According to the present configuration, the photoplethysmographic signal 53 from the capillary or arteriole at the user's periphery is detected using the photoplethysmographic sensor 211, and the peripheral blood pressure index, which serves as an index of the blood pressure level in the capillary or arteriole at the user's periphery, is calculated based on the steepness of the rising edge of the detected photoplethysmographic signal 53. The blood pressure level in the capillary or arteriole at the user's periphery is estimated based on the calculated peripheral blood pressure index.

[0055] In the method for estimating peripheral blood pressure described above, the steepness of the rising edge of the photoplethysmographic signal 53 is represented by 1 / VE0.5, which is the inverse of the full width at half maximum of a peak value in the waveform of the velocity plethysmographic signal 51, which is a first derivative of the photoplethysmographic signal 53.

[0056] According to the present configuration, the peripheral blood pressure index is calculated based on the plethysmographic waveform feature value 1 / VE0.5 and is less susceptible to the influence of noise and differences in the photoplethysmographic waveform between individuals, and a peripheral blood pressure can be estimated for different users under less influence of noise and differences between individuals.

[0057] In the method for estimating peripheral blood pressure described above, the steepness of the rising edge of the photoplethysmographic signal 53 is represented by a / S, ie the peak value a of the a-wave of the plethysmographic acceleration signal 52 divided by the maximum excursion S of the photoplethysmographic signal 53, where the plethysmographic acceleration signal 52 is a second derivative of the photoplethysmographic signal 53.

[0058] According to the present configuration, the peripheral blood pressure index is calculated based on the plethysmographic waveform feature value a / S. Thus, the peripheral blood pressure index, which serves as an index of the blood pressure level in the capillary or arteriole at the user's periphery, can be calculated using a simple calculation method.

[0059] In the method for estimating peripheral blood pressure described above, the steepness of the rising edge of the photoplethysmographic signal 53 is represented by a value calculated by the expression (a - b) / (a - d), where a, b, c and d denote the peak values ​​of the a-wave, the b-wave, the c-wave and the d-wave, respectively, of the plethysmographic acceleration signal 52, which is a second derivative of the photoplethysmographic signal 53.

[0060] According to the present configuration, the peripheral blood pressure index is calculated based on the plethysmographic waveform feature value (a - b) / (a - d). Thus, in the present configuration, the peripheral blood pressure index, which serves as an index of the blood pressure magnitude in the capillary or arteriole at the user's periphery, can be calculated using a simple calculation method.

[0061] These plethysmographic waveform feature values ​​1 / VE0.5, a / S, and (a - b) / (a - d), from which the peripheral blood pressure index is derived, can be used separately, but the peak values ​​a, b, c, and d of the a-wave, b-wave, c-wave, and d-wave, respectively, are susceptible to the effect of body motion noise and the pressure state of the photoplethysmographic sensor 211 on the skin, and vary greatly due to differences between individuals. Therefore, since 1 / VE0.5 can be relatively stably detected among the plethysmographic waveform features described above, it is preferable to use 1 / VE0.5 alone or to predominantly use 1 / VE0.5 and supplement other features.Furthermore, these plethysmographic waveform feature values ​​may be weighted and averaged to obtain a weighted mean to be used as a feature value, or the magnitudes of these plethysmographic waveform feature values ​​may be normalized and averaged to obtain a value to be used as a feature value.

[0062] In the method for estimating peripheral blood pressure described above, the photoplethysmographic sensor 211 is configured to cause the light source to emit light having a wavelength range from blue to yellow-green.

[0063] According to the present configuration, the light source in the photoplethysmographic sensor 211 is configured to emit light in the wavelength range from blue to yellow-green toward the user's living tissue, which is strongly absorbed by living tissue. Therefore, the photoplethysmographic sensor 211 is configured to detect the photoplethysmographic signal 53, which contains a large amount of information about a flat living tissue area near the skin surface of a body. Accordingly, the blood pressure in a capillary or an arteriole located in a flat living tissue area of ​​the skin at the periphery can be accurately estimated.

[0064] In the method for estimating peripheral blood pressure described above, in the photoplethysmographic sensor 211, the distance between the light source and the photosensitive element configured to receive the light emitted and reflected by the light source is set to 1 to 3 mm.

[0065] According to the present configuration, the distance between the light source and the photosensitive element in the photoplethysmographic sensor 211 is set to a distance that ensures that the light emitted by the light source, which is scattered or reflected by a capillary or arteriole at the periphery and received by the photosensitive element, has sufficient intensity. Accordingly, the blood pressure in the capillary or arteriole located in a flat living tissue area of ​​the skin at the periphery can be more accurately estimated.

[0066] In the method for estimating peripheral blood pressure described above, the photoplethysmographic sensor 211 is included in the sensing device 20 and is attached to the user's finger.

[0067] According to the present configuration, the photoplethysmographic signal 53 can be stably detected continuously or intermittently from the user's finger with the photoplethysmographic sensor 211 included in the sensing device 20. Accordingly, the blood pressure in the capillary or arteriole at the user's periphery can be stably estimated.

[0068] The method for estimating peripheral blood pressure described above may further include detecting a pressure state of the photoplethysmographic sensor 211 against a measurement site of the user. In this case, the sensing device 20 comprises a pressure state detection sensor formed by a device such as a piezoelectric element and configured to detect a pressure state of the photoplethysmographic sensor 211 against a measurement site of the subject. The signal processing device 32 is configured to determine the validity of the estimated peripheral blood pressure index based on the detected pressure state.

[0069] The photoplethysmographic sensor 211 must be in close contact with the skin at the user's measurement site to stably measure the photoplethysmographic signal 53. However, excessive pressure exerted by the photoplethysmographic sensor 211 on the user's measurement site obstructs blood flow, resulting in a reduction in the accuracy of peripheral blood pressure estimation. However, since the present configuration also includes detecting a pressure state of the photoplethysmographic sensor 211 against the user's measurement site using the pressure state detection sensor, a state in which the photoplethysmographic sensor 211 exerts excessive pressure on the user's measurement site is detected, leading to an appropriate operation, such as not using the estimated peripheral blood pressure at that time.

[0070] Accordingly, the present invention can provide a method for estimating peripheral blood pressure, which can estimate the level of blood pressure in a capillary or an arteriole at the periphery in a simple and non-invasive manner without burdening the user. LIST OF REFERENCE SYMBOLS 10 System for measuring biological data 20 Sensing device 21 biological sensor 211 Photoplethysmographic sensor 211a green LED (light-emitting element) 211b Near-infrared LED (light-emitting element) 211c photosensitive element 22 Control circuit 23 Communication module 24 Accelerometer 25 housings 30 computers 31 Communication module 32 Signal processing device [Cross-reference to related applications]

[0071] This application claims priority to Japanese Patent Application No. 2022-061021 (filed on March 31, 2022) and Japanese Patent Application No. 2022-128969 (filed on August 12, 2022), the contents of which are incorporated herein by reference. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2015 / 098977

[0003] JP 2022-061021

[0071] JP 2022-128969

[0071]

Claims

[1] A method for estimating peripheral blood pressure, comprising: Capturing a photoplethysmographic signal from a capillary or arteriole at the periphery of a subject using a photoplethysmographic sensor; Calculating a peripheral blood pressure index based on the steepness of a rising edge of the photoplethysmographic signal, wherein the peripheral blood pressure index serves as an index of a magnitude of blood pressure in the capillary or arteriole at the periphery; and Estimating the level of blood pressure in the capillary or arteriole at the periphery based on the peripheral blood pressure index, where the acquisition and calculation are carried out in a system for measuring biological data. [2] A method for estimating peripheral blood pressure according to claim 1, wherein the slope includes information about the width of a first peak appearing during a single cardiac cycle in a waveform of a photoplethysmographic velocity signal that is a first derivative of the photoplethysmographic signal. [3] A method for estimating peripheral blood pressure according to claim 1, wherein the slope includes information about a peak value of an a-wave of a plethysmographic acceleration signal and a maximum excursion of the photoplethysmographic signal, the plethysmographic acceleration signal being a second derivative of the photoplethysmographic signal. [4] A method for estimating peripheral blood pressure according to claim 1, wherein the slope includes information regarding a difference in peak value (a - b) and a difference in peak value (a - d), where a, b, c and d represent peak values ​​of an a-wave, a b-wave, a c-wave and a d-wave, respectively, of a plethysmographic acceleration signal which is a second derivative of the photoplethysmographic signal. [5] A method for estimating peripheral blood pressure according to any one of claims 1 to 4, wherein the photoplethysmographic sensor includes a light source configured to emit light in a blue to yellow-green wavelength range. [6] The peripheral blood pressure estimating method according to claim 5, wherein a distance between the light source and a photosensitive element in the photoplethysmographic sensor is set to 1 to 3 [mm], the photosensitive element being configured to receive light emitted and reflected from the light source. [7] A method for estimating peripheral blood pressure according to any one of claims 1 to 6, wherein the photoplethysmographic sensor is contained in a device attached to the subject's finger. [8] A method for estimating peripheral blood pressure according to any one of claims 1 to 7, further comprising: Detecting a pressure state of the photoplethysmographic sensor relative to a measuring point of the subject. [9] A system for measuring biological data, comprising: a sensing device comprising a photoplethysmographic sensor configured to detect a photoplethysmographic signal from a capillary or an arteriole at the periphery of a subject; and a computer having a signal processing device configured to calculate a peripheral blood pressure index based on the steepness of a rising edge of the photoplethysmographic signal, wherein the peripheral blood pressure index serves as an index of a magnitude of blood pressure in the capillary or arteriole at the periphery. [10] The biological data measurement system of claim 9, wherein the slope includes information about the width of a first peak appearing during a single cardiac cycle in a waveform of a velocity plethysmography signal that is a first derivative of the photoplethysmography signal. [11] The biological data measurement system of claim 9, wherein the slope includes information about a peak value of an a-wave of a plethysmographic acceleration signal and a maximum excursion of the photoplethysmographic signal, the plethysmographic acceleration signal being a second derivative of the photoplethysmographic signal. [12] A biological data measuring system according to claim 9, wherein the slope includes information regarding a difference in peak value (a - b) and a difference in peak value (a - d), where a, b, c and d represent peak values ​​of an a-wave, a b-wave, a c-wave and a d-wave, respectively, of a plethysmographic acceleration signal which is a second derivative of the photoplethysmographic signal. [13] The biological data measurement system of any one of claims 9 to 12, wherein the photoplethysmographic sensor includes a light source configured to emit light in a blue to yellow-green wavelength range. [14] The biological data measurement system according to claim 13, wherein a distance between the light source and a photosensitive element in the photoplethysmographic sensor is set to 1 to 3 [mm], the photosensitive element being configured to receive light emitted and reflected from the light source. [15] A biological data measurement system according to any one of claims 9 to 14, wherein the photoplethysmographic sensor is included in a device attached to the subject's finger. [16] The biological data measurement system according to any one of claims 9 to 15, wherein the sensing device includes a pressure condition detection sensor configured to detect a pressure condition of the photoplethysmographic sensor against a measurement site of the subject, and the signal processing device is configured to determine the validity of the estimated peripheral blood pressure index based on the pressure condition.

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