Pulse pressure measuring device and pulse pressure measuring method

Abstract

This peripheral blood pressure index calculation unit calculates a peripheral blood pressure index relating to a degree of steepness of a rise in a pulse wave signal measured by a pulse wave sensor attached to a user. A pulse wave feature amount calculation unit calculates an ae-time index including information related to an elapsed time from a peak of an a-wave to a peak of an e-wave of an acceleration pulse wave obtained by second-order differentiation of a waveform of the pulse wave signal. A pulse pressure calculation unit calculates a pulse pressure on the basis of the peripheral blood pressure index and the ae-time index.

Description

[Technical Field]

[0001] The present invention relates to a pulse pressure measuring device and a pulse pressure measuring method. [Background technology]

[0002] A pulse wave measuring device is known that optically acquires pulse wave information from a part of a living body, calculates pulse rate and pulse wave time information from the acquired pulse wave information, and estimates and outputs blood pressure information based on the pulse rate and pulse wave time information (see Patent Document 1). Examples of estimated blood pressure information include blood pressure, blood pressure state, arteriosclerosis, vascular age, and whether or not the subject is prone to stroke. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 205 / 098977 Summary of the Invention [Problem to be solved by the invention]

[0004] Pulse pressure, which is the difference between systolic blood pressure and diastolic blood pressure, is one indicator of health status. Conventional pulse wave measuring devices cannot measure pulse pressure. An object of the present invention is to provide a pulse pressure measuring device and a pulse pressure measuring method that can measure pulse pressure. [Means for solving the problem]

[0005] According to one aspect of the present invention, a peripheral blood pressure index calculation unit that calculates a peripheral blood pressure index related to the steepness of the rising edge of a pulse wave signal measured by a pulse wave sensor worn by a user; a pulse wave feature amount calculation unit that calculates an ae time index including information about the elapsed time from the peak of the a wave to the peak of the e wave of an acceleration pulse wave obtained by second-order differentiation of the waveform of the pulse wave signal; a pulse pressure calculation unit that calculates a pulse pressure based on the peripheral blood pressure index and the ae time index; A pulse pressure measuring device is provided.

[0006] According to another aspect of the present invention, A pulse wave signal is acquired by a pulse wave sensor attached to the user. a pulse pressure measuring device calculating a peripheral blood pressure index related to the steepness of the rising edge of the pulse wave signal; the pulse pressure measuring device calculates an ae time index including information about the elapsed time from the peak of the a wave to the peak of the e wave of an accelerated pulse wave obtained by second-order differentiation of the waveform of the pulse wave signal; There is also provided a pulse pressure measuring method in which the pulse pressure measuring device determines the pulse pressure based on the peripheral blood pressure index and the ae time index. [Effects of the Invention]

[0007] The peripheral blood pressure index, which correlates with blood pressure, also correlates with pulse pressure. The time elapsed from the peak of the a wave to the peak of the e wave of the accelerated pulse wave also correlates with pulse pressure. By using the peripheral blood pressure index and the ae time index, pulse pressure can be calculated with high accuracy. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram and a schematic diagram of a pulse pressure measuring device according to a first embodiment. [Figure 2] FIG. 2 is a block diagram and a schematic diagram of a pulse pressure measuring device according to a modification of the first embodiment. [Figure 3] FIG. 3 is a block diagram and a schematic diagram of a pulse pressure measuring device according to another modification of the first embodiment. [Figure 4] FIG. 4 is a perspective view and a block diagram of a pulse pressure measuring device according to a modification of the first embodiment shown in FIG. [Figure 5] FIG. 5 is a graph showing an example of a pulse wave, a velocity pulse wave, and an acceleration pulse wave. [Figure 6] FIG. 6 is a graph showing an example of a pulse wave and an acceleration pulse wave. [Figure 7]Figures 7A and 7B are graphs showing the relationship between the peripheral blood pressure index "1 / VE0.5" value calculated from the pulse wave measured when the height from the heart to the measurement site (finger) is changed and when the measurement site is adjusted to chest height and the area around the elbow on the side where the measurement site (finger) is located is cooled, and the systolic blood pressure measured at the wrist. [Figure 8] Figures 8A and 8B are graphs showing the relationship between the peripheral blood pressure index "a / S" value calculated from the pulse wave measured when the height from the heart to the measurement site (finger) is changed and when the measurement site is adjusted to chest height and the area around the elbow on the side where the measurement site (finger) is located is cooled, and the systolic blood pressure measured at the wrist. [Figure 9] Figures 9A and 9B are graphs showing the relationship between the peripheral blood pressure index "(ab) / (ad)" value calculated from the pulse wave measured when the height from the heart to the measurement site (finger) is changed and when the measurement site is adjusted to chest height and the area around the elbow on the side where the measurement site (finger) is located is cooled, and the systolic blood pressure measured at the wrist. [Figure 10] 10A and 10B are scatter plots of multiple subjects, with the horizontal axis representing wrist systolic blood pressure and the vertical axis representing the peripheral blood pressure index "1 / VE0.5." [Figure 11] 11A and 11B are scatter plots of multiple subjects, with the horizontal axis representing wrist systolic blood pressure and the vertical axis representing the peripheral blood pressure index "a / S." [Figure 12] 12A and 12B are scatter plots of multiple subjects, with the horizontal axis representing wrist systolic blood pressure and the vertical axis representing the peripheral blood pressure index "(ab) / (ad)." [Figure 13] 13A and 13B are scatter plots of a plurality of subjects, with the vertical axis representing the time elapsed from the peak of the a wave to the peak of the b wave of the accelerated pulse wave and the horizontal axis representing the systolic blood pressure at the wrist. [Figure 14] 14A and 14B are scatter plots of a plurality of subjects, with the vertical axis representing the time elapsed from the peak of the b wave to the peak of the d wave of the accelerated pulse wave and the horizontal axis representing the systolic blood pressure at the wrist. [Figure 15]15A and 15B are scatter plots of a plurality of subjects, with the vertical axis representing the time elapsed from the peak of the d wave to the peak of the e wave of the accelerated pulse wave and the horizontal axis representing the systolic blood pressure at the wrist. [Figure 16] 16A and 16B are scatter plots of multiple subjects, with the vertical axis representing the time elapsed from the peak of the a wave to the peak of the e wave of the accelerated pulse wave and the horizontal axis representing the systolic blood pressure at the wrist. [Figure 17] FIG. 17 is a scatter plot of multiple subjects, with the pulse interval on the vertical axis and the systolic blood pressure at the wrist on the horizontal axis. [Figure 18] 18A and 18B are scatter plots of multiple subjects, with pulse pressure on the horizontal axis and peripheral blood pressure index "1 / VE0.5" on the vertical axis. [Figure 19] 19A and 19B are scatter plots of multiple subjects, with pulse pressure on the horizontal axis and peripheral blood pressure index "(ab) / (ad)" on the vertical axis. [Figure 20] 20A and 20B are scatter plots of multiple subjects, with pulse pressure on the horizontal axis and the feature "de time" on the vertical axis. [Figure 21] 21A and 21B are scatter plots of multiple subjects, with pulse pressure on the horizontal axis and the feature "ae time" on the vertical axis. [Figure 22] FIG. 22 is a scatter plot of multiple subjects, with pulse pressure on the horizontal axis and pulse interval on the vertical axis. [Figure 23] 23A and 23B are scatter plots of multiple subjects, with pulse pressure on the horizontal axis and pulse pressure index value Pa on the vertical axis. [Figure 24] 24A and 24B are scatter plots of multiple subjects, with pulse pressure on the horizontal axis and pulse pressure index value Pad on the vertical axis. [Figure 25] FIG. 25 is a scatter plot showing multiple measurement results obtained by measuring one subject over a long period of time, with pulse pressure on the horizontal axis and pulse pressure index value Pad on the vertical axis. [Figure 26] FIG. 26 is a perspective view and a block diagram of a pulse pressure measuring device according to the third embodiment. [Figure 27] FIG. 27 is a schematic diagram for explaining the procedure for measuring the difference in height between the ring device and the heart. [Figure 28] FIG. 28 is a flowchart showing the steps of a pulse pressure measuring method executed by the pulse pressure measuring device according to the third embodiment. [Figure 29] FIG. 29 is a flowchart showing the steps of a pulse pressure measuring method executed by a pulse pressure measuring device according to a modification of the third embodiment. [Figure 30] FIG. 30 is a perspective view and a block diagram of a pulse pressure measuring device according to the fourth embodiment. [Figure 31] FIG. 31 is a flowchart showing the steps of a pulse pressure measuring method executed by the pulse pressure measuring device according to the fourth embodiment. [Figure 32] FIG. 32 is a perspective view and a block diagram of a pulse pressure measuring device according to the fifth embodiment. [Figure 33] FIG. 33 is a flowchart showing the steps of a pulse pressure measuring method executed by the pulse pressure measuring device according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] [First Example] A pulse pressure measuring device according to a first embodiment will be described with reference to Figures 1, 2, 3, and 4. The pulse pressure measuring device according to the first embodiment calculates pulse pressure based on the waveform of a pulse wave acquired from a subject.

[0010] Pulse waves are used to measure various biological information. For example, they are used to measure pulse rate and oxygen saturation. They are also used to measure autonomic nervous function based on fluctuations in pulse intervals, and to measure respiratory rate based on baseline fluctuations in pulse waves and fluctuations in pulse intervals. Furthermore, technology has been developed to estimate blood pressure from the waveform shape of the pulse wave. Pulse waves are classified into pressure pulse waves (piezoplethysmograms), which are measured using piezoelectric sensors, and volume pulse waves (photoplethysmograms), which are measured using photoplethysmogram sensors.

[0011] Pulse pressure is the difference between systolic and diastolic blood pressure, and its normal value is said to be between 40mmHg and 50mmHg. An example of pulse pressure exceeding the normal range is when the stroke volume increases. Possible causes of increased stroke volume include exercise, hyperthyroidism, and anemia.

[0012] In addition, pulse pressure exceeds the normal range when the elasticity of large blood vessels decreases. When blood vessels become stiff, systolic blood pressure rises. When systolic blood pressure rises, a reaction occurs that dilates peripheral blood vessels, and diastolic blood pressure actually falls. As a result, pulse pressure increases. For example, when arteriosclerosis occurs extensively in the aorta, pulse pressure increases. It has been reported that when pulse pressure exceeds 65 mmHg, the risk of myocardial infarction and cerebrovascular disease increases. Measuring pulse pressure can help identify those who have or are at risk of developing these diseases.

[0013] The pulse pressure measuring device according to the first embodiment can be applied to both piezoelectric pulse waves and photoplethysmograms. More information can be obtained from photoplethysmograms than from piezoelectric pulse waves. The following explanation will be given taking photoplethysmograms as an example.

[0014] 1 is a block diagram and a schematic diagram of a pulse pressure measuring device according to a first embodiment. The pulse pressure measuring device according to the first embodiment includes a processing device 30 and a photoplethysmographic sensor 50. The photoplethysmographic sensor 50 includes a light-emitting element 51 and a light-receiving element 53. The processing device 30 includes a light-emission control unit 31, a pulse wave measurement unit 32, a peripheral blood pressure index calculation unit 33, a pulse wave feature amount calculation unit 34, a pulse pressure calculation unit 35, a control unit 36, and a display unit 37.

[0015] The light-emitting element 51 and the light-receiving element 53 are used by contacting the user's body surface 70. The light-emitting element 51 irradiates measurement light toward the body surface 70. The irradiated light is absorbed, reflected, or scattered (hereinafter, sometimes simply referred to as "reflected") by the epidermal region 71, arterioles 72, and capillaries 73 within the body surface 70. A portion of the reflected light is incident on the light-receiving element 53.

[0016] The arteriole 72 is a thin blood vessel having a diameter of, for example, 20 μm or more and 200 μm or less, and exists between the artery and the capillary 73. A plurality of capillaries 73 branches off from the arteriole 72. The capillary 73 is a thin blood vessel having a diameter of, for example, about 10 μm, and connects the artery and the vein. A plurality of capillaries 73 are distributed in a region shallower than the region where the arteriole 72 is distributed.

[0017] Light-emitting element 51 outputs measurement light under the control of processing device 30. A signal indicating the intensity of the light measured by light-receiving element 53 is input to processing device 30. The signal indicating the intensity of the light detected by light-receiving element 53 is referred to as a "pulse wave signal." Arterial blood contains hemoglobin, which has the property of absorbing measurement light. Blood flow changes with the beating of the heart, and the amount of light absorbed also changes in accordance with the change in blood flow. Therefore, the intensity of the pulse wave signal changes with the beating of the heart.

[0018] The light-emitting element 51 may be, for example, one that outputs light in a wavelength range from blue to yellow-green (a wavelength range of 450 nm to 550 nm), preferably a wavelength range of 500 nm to 550 nm. The light-emitting element 51 may be, for example, a light-emitting diode (LED), a vertical-cavity surface-emitting laser (VCSEL), or the like. The light-receiving element 53 may be, for example, a photodiode (PD), a phototransistor, or the like.

[0019] Light in the blue to yellow-green wavelength range is highly absorbed by biological tissue. Therefore, a pulse wave acquired using light in the blue to yellow-green wavelength range reflects information from a region shallower than the skin surface, particularly a region shallower than the region where arterioles 72 are distributed and where capillaries 73 are primarily distributed. The arrows in FIG. 1 do not indicate the path of light propagation, but rather indicate that light output from light-emitting element 51 passes through epidermal region 71 and the region where capillaries 73 are primarily distributed and is incident on light-receiving element 53. To ensure that information from the region shallower than the region where arterioles 72 are distributed and where capillaries 73 are primarily distributed is primarily reflected in the acquired pulse wave, it is preferable to shorten the distance L1 between light-emitting element 51 and light-receiving element 53. For example, it is preferable to set distance L1 to 1 mm or more and 3 mm or less.

[0020] Light with a wavelength shorter than 450 nm can damage biological tissue. To avoid damaging biological tissue, it is preferable that the wavelength of light used to measure pulse waves be 450 nm or longer.

[0021] FIG. 2 is a block diagram and a schematic diagram of a pulse pressure measuring device according to a modification of the first embodiment. In the modification shown in FIG. 2, a light emitting element 52 having a different emission wavelength is used instead of the light emitting element 51 of the pulse pressure measuring device according to the first embodiment (FIG. 1). The light emitting element 52 used in the modification shown in FIG. 2 outputs light in the wavelength range from red to near-infrared light, for example, in the wavelength range of 750 nm to 950 nm. Light in the wavelength range from red to near-infrared light is less absorbed by biological tissue than light in the wavelength range from blue to yellow-green light. Therefore, a pulse wave acquired using light in the wavelength range from red to near-infrared light reflects information from regions deeper than the skin surface.

[0022] For example, information about the region where capillaries 73 and arterioles 72 are distributed is reflected. The arrows shown in Fig. 2 do not indicate the path of light propagation, but rather indicate that light output from light-emitting element 52 passes through not only capillaries 73 but also the region where arterioles 72 are distributed and is incident on light-receiving element 53. In order to ensure that information about the region where arterioles 72 and capillaries 73 are distributed is significantly reflected in the acquired pulse wave, it is preferable to set distance L2 between light-emitting element 52 and light-receiving element 53 to 5 mm or more and 20 mm or less.

[0023] The absorbance of hemoglobin decreases in the wavelength range longer than 950 nm, so it is preferable to use light in the wavelength range of 950 nm or less to acquire a pulse wave signal.

[0024] 3 is a block diagram and a schematic diagram of a pulse pressure measuring device according to another modification of the first embodiment. The pulse pressure measuring device according to the second modification includes both a light emitting element 51 (FIG. 1) that outputs light in a wavelength range from blue to yellow-green, and a light emitting element 52 that outputs light in a wavelength range from red to near-infrared light. A light receiving element 53 detects light in both wavelength ranges output from the light emitting element 51 and the light output from the light emitting element 52. A preferred range for the distance L1 between the light emitting element 51 and the light receiving element 53 is 1 mm or more and 3 mm or less, and a preferred range for the distance L2 between the light emitting element 52 and the light receiving element 53 is 5 mm or more and 20 mm or less.

[0025] In the modified example shown in Figure 3, one light receiving element 53 is arranged for two light emitting elements 51 and 52, but it is also possible to arrange one light receiving element for one light emitting element 51 and another light receiving element for the other light emitting element 52.

[0026] Next, the function of the processing device 30 (FIGS. 1, 2, and 3) will be described. The control unit 36 ​​of the processing device 30 controls the start and end of measurement, controls display of the measurement results on the display unit 37, controls storage of the measurement results, etc. The light emission control unit 31 controls pulsed emission of the light emitting element 51 or the light emitting element 52. For example, the light emitting element 51 or the light emitting element 52 emits pulsed light at a predetermined frequency of 100 Hz or more and 1000 Hz or less. In the second modified example shown in FIG. 3, the light emitting element 51 and the light emitting element 52 emit light alternately.

[0027] Pulse wave measurement unit 32 generates a pulse wave waveform (hereinafter, sometimes simply referred to as a "pulse wave") from the measurement result (pulse wave signal) input from light-receiving element 53. For example, pulse wave measurement unit 32 generates a pulse wave by reading a measured value of light intensity from light-receiving element 53 at a predetermined sampling rate in synchronization with the pulsed light emitted from light-emitting element 51 or light-emitting element 52. In the second modified example shown in FIG. 3, pulse wave measurement unit 32 reads a measured value of light intensity from light-receiving element 53 at a predetermined sampling rate in synchronization with the pulsed light emitted from light-emitting element 51 or light-emitting element 52, thereby separately generating a pulse wave based on the light output from light-emitting element 51 and a pulse wave based on the light output from light-emitting element 52.

[0028] The peripheral blood pressure index calculation unit 33 calculates a peripheral blood pressure index related to the steepness of the rising edge of the pulse wave from the pulse wave generated by the pulse wave measurement unit 32. The pulse wave feature amount calculation unit 34 calculates an ae time index from the pulse wave generated by the pulse wave measurement unit 32. The peripheral blood pressure index and the ae time index will be explained in detail later. The pulse pressure calculation unit 35 calculates the pulse pressure based on the peripheral blood pressure index and the ae time index, thereby obtaining a measured value of the pulse pressure.

[0029] Fig. 4 is a perspective view and a block diagram of a pulse pressure measuring device according to a modification of the first embodiment shown in Fig. 3. The pulse pressure measuring device according to this modification includes a ring device 61 and a portable mobile terminal 62.

[0030] The ring device 61 will now be described. Two light-emitting elements 51 and 52 and one light-receiving element 53 are attached to the inner surface of an annular wearing member 60. The wearing member 60 is worn on a user's finger when in use. A variety of sizes of wearing members 60 are prepared according to the thickness of the user's finger. When the wearing member 60 is worn on the finger, the light-emitting elements 51 and 52 output light toward the finger. The light-receiving element 53 is attached at a position where light reflected inside the finger is incident.

[0031] The wearing member 60 further incorporates a light emission control unit 31, a pulse wave measurement unit 32, and a communication unit 55. The light emission control unit 31, the pulse wave measurement unit 32, and the communication unit 55 may be configured as a single integrated circuit.

[0032] The functions of the processing device 30 (FIG. 3) are realized by a ring device 61 and a portable mobile terminal 62. The mobile terminal 62 may be, for example, a smartphone, a tablet terminal, or a laptop computer. The mobile terminal 62 includes a communication unit 64, a peripheral blood pressure index calculation unit 33, a pulse wave feature amount calculation unit 34, a pulse pressure calculation unit 35, a control unit 36, and a display unit 37. The functions of the peripheral blood pressure index calculation unit 33, the pulse wave feature amount calculation unit 34, and the pulse pressure calculation unit 35 may be realized by a server. When this configuration is adopted, data communication is performed between the mobile terminal 62 and the server via a communication line.

[0033] Data communication is performed between the communication unit 55 of the ring device 61 and the communication unit 64 of the mobile terminal 62. For communication between the ring device 61 and the mobile terminal 62, various types of short-range wireless communication methods are used, for example.

[0034] The advantageous effects of using the ring device 61 to acquire a pulse wave will now be described. Fingers have a relatively thin epidermis, making them suitable for acquiring pulse waves using the photoplethysmographic sensor 50. Furthermore, the capillary pathways on the finger are less complex than those on the face, making it easier for the values ​​of pulse wave feature quantities to stabilize. This increases the reliability of the pulse pressure obtained from the pulse wave. Furthermore, when using the pulse pressure measuring device continuously or intermittently, the ring device 61 has the excellent effect of causing little discomfort or discomfort even when worn on the finger for long periods of time.

[0035] [Peripheral blood pressure index] Next, with reference to FIGS. 5 to 9B, a peripheral blood pressure index, which is one piece of basic information for determining pulse pressure with the pulse pressure measuring device according to the first embodiment, will be described.

[0036] In this specification, "peripheral blood pressure" is defined as the blood pressure in peripheral arterioles and capillaries. Peripheral blood pressure is sometimes used to mean the blood pressure at the wrist or ankle measured with a cuff-type sphygmomanometer, but the blood pressure at the wrist or ankle is measured in a large artery (such as the radial artery) and is different from the peripheral blood pressure defined in this specification. Blood pressure in blood vessels decreases as one progresses from large arteries to arterioles and capillaries. The degree to which blood pressure decreases varies depending on the measurement site, the individual's vascular condition (presence or absence of arteriosclerosis, etc.), mental state (state of the autonomic nervous system, etc.), environment (temperature, presence or absence of noise, etc.), clothing, etc.

[0037] Among the waveform features of the pulse wave, an index that is effective for determining peripheral blood pressure is adopted as the peripheral blood pressure index. The peripheral blood pressure index is considered to have the following characteristics. First, when blood vessels are healthy and vascular resistance remains unchanged, peripheral blood pressure indices have a positive correlation with blood pressure at the upper arm or wrist. Second, when the area around the measurement site is cooled to constrict blood vessels, peripheral blood pressure indices decrease. When blood vessels constrict, peripheral vascular resistance increases, which can cause blood pressure at the upper arm or wrist to rise.

[0038] Next, various feature quantities of the pulse wave waveform will be described with reference to FIGS.

[0039] FIG. 5 is a graph showing examples of the pulse wave, velocity pulse wave, and acceleration pulse wave. The peripheral blood pressure index calculation unit 33 (FIGS. 1, 2, and 3) performs first-order and second-order differentiation of the pulse wave. The waveforms obtained by first-order and second-order differentiation of the pulse wave are referred to as the velocity pulse wave and acceleration pulse wave, respectively. For example, the velocity pulse wave is obtained by numerically differentiating the intensity of the pulse wave, which is discretely distributed at time intervals corresponding to the sampling rate, at time intervals corresponding to the sampling rate. Furthermore, the magnitude of the velocity pulse wave is numerically differentiated to obtain the acceleration pulse wave.

[0040] The horizontal axis in Figure 5 represents time in units of seconds, the left vertical axis represents the magnitude of the velocity pulse wave and acceleration pulse wave normalized so that the maximum value is 1, and the right vertical axis represents the magnitude of the pulse wave in arbitrary units. The solid line, long-dashed line, and short-dashed line in the graph shown in Figure 2 represent the pulse wave, velocity pulse wave, and acceleration pulse wave, respectively. Generally, five peaks appear in an acceleration pulse wave within one beat. The first, second, third, fourth, and fifth peaks within one beat are called the a-wave, b-wave, c-wave, d-wave, and e-wave, respectively.

[0041] The full width at half maximum of the first upward peak of the velocity pulse wave is labeled "VE0.5." The difference between the peak values ​​of the a wave and the b wave is labeled "ab," and the difference between the peak values ​​of the a wave and the d wave is labeled "ad." A depression called the incisor (IC) appears slightly behind the maximum peak of the pulse wave.

[0042] FIG. 6 is a graph showing an example of a pulse wave and an acceleration pulse wave. The horizontal axis represents time, the left vertical axis represents the amplitude of the pulse wave in arbitrary units, and the right vertical axis represents the amplitude of the acceleration pulse wave in arbitrary units. Five divisions on the horizontal axis correspond to 0.2 s. The peak value of the a-wave of the acceleration pulse wave is labeled "a," and the amplitude of the pulse wave is labeled "S." The amplitude S of the pulse wave corresponds to the difference between the minimum and maximum values ​​after waveform correction is performed so that the minimum values ​​of the pulse wave for two consecutive pulse beats are the same.

[0043] The following three features are examples of pulse wave features that reflect the above two features of peripheral blood pressure indices. The full width at half maximum is the reciprocal of "VE0.5" (hereinafter referred to as "1 / (VE0.5)") The ratio of the amplitude S of the pulse wave to the peak value a of the a wave of the accelerated pulse wave (hereinafter referred to as "a / S") The ratio of the difference "ab" between the peak values ​​of the a wave and the b wave of the accelerated pulse wave to the difference "ad" between the peak values ​​of the a wave and the d wave (hereinafter referred to as "(ab) / (ad)"). In this specification, these characteristic quantities of the pulse wave waveform are referred to as “peripheral blood pressure indices.” These peripheral blood pressure indices are related to the steepness of the rising edge of the pulse wave.

[0044] 7A and 7B are graphs showing the relationship between the peripheral blood pressure index "1 / VE0.5" calculated from pulse waves measured when the height of the measurement site (finger) from the heart is changed and when the measurement site is adjusted to chest height and the area around the elbow on the side where the finger is located is cooled, and the systolic blood pressure measured at the wrist. Figures 7A and 7B show the measurement results when the pulse wave was measured using the pulse pressure measuring device (green light) shown in Figure 1 and the pulse pressure measuring device (near-infrared light) shown in Figure 2, respectively. The pulse wave measured using green light primarily reflects fluctuations in blood flow in the capillaries 73 (Figure 1), while the pulse wave measured using near-infrared light reflects fluctuations in blood flow in the capillaries 73 and arterioles 72 (Figure 2).

[0045] The horizontal axis of the graphs in Figures 7A and 7B represents the systolic blood pressure at the wrist in units of mmHg, and the vertical axis represents the peripheral blood pressure index "1 / (VE0.5)" in units of s -1]. In each graph, the results of measurements taken for three subjects A, B, and C are shown using triangle symbols, square symbols, and circle symbols, respectively. The three hollow symbols shown for each subject indicate the values ​​of pulse wave feature quantities calculated from pulse waves acquired when the height of the measurement site (finger) was set to navel, chest, and forehead, respectively. The peripheral blood pressure index "1 / VE0.5" value decreases in the order of navel, chest, and forehead. The solid black symbols shown for each subject indicate the values ​​of peripheral blood pressure index "1 / VE0.5" calculated from pulse waves acquired when the height of the measurement site was set to chest height and the area around the elbow was cooled.

[0046] Although the degree of correlation varies depending on the subject, it can be seen that when the height of the measurement site is changed, the peripheral blood pressure index "1 / VE0.5" generally has a positive correlation with the systolic blood pressure at the wrist. Furthermore, although there are some exceptions, it can be seen that when the area near the measurement site is cooled to constrict the blood vessels, the peripheral blood pressure index "1 / VE0.5" decreases. This change matches the expected characteristics of the peripheral blood pressure index. Therefore, the peripheral blood pressure index "1 / VE0.5" is considered to be an effective index for estimating peripheral blood pressure.

[0047] The results shown in Figures 7A and 7B indicate that green light is preferable to near-infrared light for measuring the peripheral blood pressure index "1 / VE0.5." Alternatively, the inverse of a parameter representing the width of the maximum peak of the velocity pulse wave may be used as an index instead of the peripheral blood pressure index "1 / VE0.5." Alternatively, a negative exponent of the parameter representing the width of the maximum peak of the velocity pulse wave may be used. More generally, a function may be used as the peripheral blood pressure index, where the parameter representing the width of the maximum peak of the velocity pulse wave is used as a variable, and the value of the function decreases as the peak width increases.

[0048] 8A and 8B are graphs showing the relationship between the peripheral blood pressure index "a / S" value calculated from the pulse wave measured when the height from the heart to the measurement site (finger) is changed and when the measurement site is adjusted to chest height and the vicinity of the elbow on the side where the finger is located is cooled, and the systolic blood pressure measured at the wrist. Figures 8A and 8B show the measurement results when the pulse wave was measured using the pulse pressure measuring device (green light) shown in Figure 1 and the pulse pressure measuring device (near-infrared light) shown in Figure 2, respectively.

[0049] The horizontal axis of the graphs in Figures 8A and 8B represents systolic blood pressure at the wrist in units of mmHg, and the vertical axis represents the peripheral blood pressure index "a / S" in arbitrary units. The meanings of the symbols in Figures 8A and 8B are the same as those of the symbols in the graphs shown in Figures 7A and 7B.

[0050] The measurement results shown in Figures 8A and 8B show similar trends to those shown in Figures 7A and 7B. Therefore, the peripheral blood pressure index "a / S" is considered to be an effective index for estimating peripheral blood pressure. Furthermore, the results shown in Figures 8A and 8B show that green light is preferable to near-infrared light for measuring the peripheral blood pressure index "a / S."

[0051] Instead of the peripheral blood pressure index "a / S," the peripheral blood pressure index may be the product of the peak value a of the a-wave of the accelerated pulse wave raised to a positive power and the amplitude S of the pulse wave raised to a negative power. Alternatively, the peripheral blood pressure index may be calculated based on information regarding the peak value of the a-wave of the accelerated pulse wave and the amplitude of the pulse wave signal. For example, the peripheral blood pressure index may be a function in which the peak value a and the amplitude S are variables, and the value of the function increases as the peak value a increases and decreases as the amplitude S increases.

[0052] 9A and 9B are graphs showing the relationship between the peripheral blood pressure index "(ab) / (ad)" calculated from the pulse wave measured when the height from the heart to the measurement site (finger) is changed and when the measurement site is adjusted to chest height and the vicinity of the elbow on the side where the finger is located is cooled, and the systolic blood pressure measured at the wrist. Figures 9A and 9B show the measurement results when the pulse wave was measured using the pulse pressure measuring device (green light) shown in Figure 1 and the pulse pressure measuring device (near-infrared light) shown in Figure 2, respectively.

[0053] The horizontal axis of the graphs in Figures 9A and 9B represents the systolic blood pressure at the wrist in units of mmHg, and the vertical axis represents the peripheral blood pressure index "(ab) / (ad)." The symbols in Figures 9A and 9B have the same meaning as those in the graphs shown in Figures 7A and 7B.

[0054] The measurement results shown in Figures 9A and 9B show almost the same tendency as the measurement results shown in Figures 7A and 7B. Therefore, the peripheral blood pressure index "(ab) / (ad)" is considered to be an effective index for estimating peripheral blood pressure.

[0055] Instead of the peripheral blood pressure index "(ab) / (ad)", the peripheral blood pressure index may be calculated based on information regarding the difference between the peak values ​​of the a-wave and the b-wave of the accelerated pulse wave and the difference between the peak values ​​of the a-wave and the d-wave. For example, a function may be used as the peripheral blood pressure index, with the difference (ab) between the peak values ​​of the a-wave and the b-wave and the difference (ad) between the peak values ​​of the a-wave and the d-wave as variables, such that the value of the function increases as the value of the difference (ab) increases and decreases as the value of the difference (ad) increases.

[0056] [Relationship between peripheral blood pressure index and systolic blood pressure] An evaluation experiment was conducted to determine the relationship between wrist systolic blood pressure and peripheral blood pressure indexes by increasing the number of subjects. The results of this evaluation experiment will be explained with reference to Figures 10A to 12B. In the evaluation experiment, healthy subjects and diabetic patients were included as subjects to collect data with widely varying extremes. A cuff-type blood pressure monitor was worn on the left or right wrist, and a ring device 61 (Figure 4) equipped with a photoplethysmographic sensor (Figures 1, 2, and 3) was worn on the index finger of the hand on the same side as the cuff-type blood pressure monitor.

[0057] While sitting still, the subject held the hand equipped with the photoplethysmogram sensor at chest height to measure both the photoplethysmogram and blood pressure. Since measuring both simultaneously would obstruct blood flow to the finger due to the cuff, blood pressure was measured using a cuff-type sphygmomanometer after the photoplethysmogram measurement was completed.

[0058] 10A and 10B are scatter plots of multiple subjects, with the horizontal axis representing wrist systolic blood pressure (hereinafter sometimes simply referred to as blood pressure) and the vertical axis representing the peripheral blood pressure index "1 / VE0.5." FIGS. 11A and 11B are scatter plots of multiple subjects, with the horizontal axis representing wrist systolic blood pressure and the vertical axis representing the peripheral blood pressure index "a / S." FIGS. 12A and 12B are scatter plots of multiple subjects, with the horizontal axis representing wrist systolic blood pressure and the vertical axis representing the peripheral blood pressure index "(ab) / (ad)." FIGS. 10A, 11A, and 12A show the results of pulse wave measurements using green light, while FIGS. 10B, 11B, and 12B show the results of pulse wave measurements using near-infrared light. In each graph, filled circles and hollow circles indicate the measurement results of healthy subjects and diabetic patients, respectively.

[0059] Figures 10A and 10B show that the higher the blood pressure, the smaller the peripheral blood pressure index "1 / VE0.5." Furthermore, when measuring pulse waves using green light, the peripheral blood pressure index "1 / VE0.5" of diabetic patients is concentrated in a relatively low range, clearly separated from the range in which the peripheral blood pressure index "1 / VE0.5" of healthy individuals is distributed. The following mechanism is presumed to explain these measurement results.

[0060] If blood sugar levels remain high for a long time, blood vessels become brittle and deteriorate, leading to so-called vascular disease, and arteriosclerosis progresses in large blood vessels. Small blood vessels are also damaged, reducing vascular function (endothelial function) and reducing blood flow.

[0061] Local blood pressure (peripheral blood pressure) decreases as we move from large arteries to arterioles and capillaries. It is believed that the degree of decrease in peripheral blood pressure increases when vascular endothelial function declines. It is said that approximately 40% to 60% of diabetic patients also suffer from hypertension. The evaluation results shown in Figure 10A show that the systolic blood pressure of diabetic patients is higher than that of healthy subjects, but this tendency is not significant. In contrast, there is a clear tendency for the peripheral blood pressure index (1 / VE0.5) of diabetic patients to be lower than that of healthy subjects. This can be explained by the fact that diabetic patients experience peripheral vascular disorders, which impede blood flow to the peripheral blood vessels, resulting in a decrease in the peripheral blood pressure index (1 / VE0.5).

[0062] As shown in Figures 11A and 11B, in healthy individuals, the peripheral blood pressure index "a / S" tends to decrease as blood pressure increases, similar to the peripheral blood pressure index "1 / VE0.5." In diabetic patients, the peripheral blood pressure index "a / S" varies widely, and the correlation between the peripheral blood pressure index "a / S" and blood pressure is unclear. This is presumably because the peak value a of the a-wave of the accelerated pulse wave, and the amplitude S of the pulse wave (Figure 6), are easily affected by various factors.

[0063] As shown in Figures 12A and 12B, the peripheral blood pressure index "(ab) / (ad)" tends to decrease as blood pressure increases, similar to the peripheral blood pressure index "1 / VE0.5." Furthermore, the magnitude of the peripheral blood pressure index "(ab) / (ad)" calculated from the pulse wave acquired using green light clearly separates healthy subjects from diabetic patients. The three measurement results located on the horizontal axis where the peripheral blood pressure index "(ab) / (ad)" is zero represent subjects in whom the b wave of the accelerated pulse wave could not be detected.

[0064] [Pulse wave features thought to be causally related to blood pressure] Next, pulse wave feature quantities that are thought to have a causal relationship with blood pressure will be described with reference to Figures 13A to 17. Figures 13A to 17 are scatter plots of multiple subjects, with wrist systolic blood pressure on the horizontal axis and various pulse wave feature quantities on the vertical axis.

[0065] The vertical axes of Figures 13A and 13B represent the time elapsed from the peak of the a wave to the peak of the b wave of the acceleration pulse wave (hereinafter referred to as "ab time") in units of [s]. The vertical axes of Figures 14A and 14B represent the time elapsed from the peak of the b wave to the peak of the d wave of the acceleration pulse wave (hereinafter referred to as "bd time") in units of [s]. The vertical axes of Figures 15A and 15B represent the time elapsed from the peak of the d wave to the peak of the e wave of the acceleration pulse wave (hereinafter referred to as "de time") in units of [s]. The vertical axes of Figures 16A and 16B represent the time elapsed from the peak of the a wave to the peak of the e wave of the acceleration pulse wave (hereinafter referred to as "ae time") in units of [s]. The vertical axis of Figure 17 represents the pulse interval in units of [s].

[0066] Figures 13A, 14A, 15A, and 16A show the feature quantities of the pulse wave measured using green light, and Figures 13B, 14B, 15B, and 16B show the feature quantities of the pulse wave measured using near-infrared light. The pulse interval shown in Figure 17 is the same whether green light or near-infrared light is used.

[0067] As shown in Figures 13A and 13B, the feature "ab time" and systolic blood pressure have a weak negative correlation. As shown in Figures 14A and 14B, the feature "bd time" and systolic blood pressure have a positive correlation. As shown in Figures 15A and 15B, the feature "de time" and systolic blood pressure have a negative correlation. As shown in Figures 16A, 16B, and 17, the feature "ae time" and pulse interval did not show any correlation with systolic blood pressure.

[0068] Additionally, differences were observed in the feature "de time" between healthy individuals and diabetic patients. Specifically, when the systolic blood pressure was roughly the same, the feature "de time" of diabetic patients tended to be larger than the feature "de time" of healthy individuals. No clear trends were observed between healthy individuals and diabetic patients for other feature values.

[0069] The mechanism by which a negative correlation was observed between the feature "de time" and systolic blood pressure is presumed to be as follows.

[0070] As shown in Figure 5, the time when the peak of the d wave of the accelerated pulse wave appears is close to the time when the pulse wave reaches its maximum value. The area near the b wave of the accelerated pulse wave is considered to be the ejection wave, and the area near the d wave is considered to be the reflected wave, and the pulse wave notch IC appears after that (around 0.4 seconds as shown in Figure 5). Since there is no clear correlation between blood pressure and the "ae time," the tendency for the "de time" to shorten as blood pressure increases means that the position of the peak of the d wave moves later (closer to the position of the peak of the e wave) as blood pressure increases.

[0071] An increase in blood flow means an increase in the ejection wave and reflected wave. Therefore, an increase in blood flow causes the convex part of the pulse wave (ranging from the b wave to the d wave) to spread further back. As a result, it is thought that the position of the peak of the d wave also moves further back. In other words, it is thought that the increase in blood pressure caused an increase in blood flow, and that the increase in blood flow shortened the "de time."

[0072] Figures 15A and 15B show that as blood pressure increases, the "de time" shortens, meaning that the position of the peak of the d wave tends to move closer to the position of the peak of the e wave. Furthermore, in diabetic patients, the position of the peak of the d wave tends to be farther from the position of the peak of the e wave compared to healthy subjects. As speculated above, it is thought that the "de time" shortens as blood flow increases, so the fact that the "de time" in diabetic patients tends to be longer than the "de time" in healthy subjects does not contradict the speculation that peripheral blood pressure decreases in diabetic patients, making it more difficult for blood to flow.

[0073] In the scatter plots in Figures 13A to 14B, the measurement results of some diabetic patients are located on the horizontal axis where the "ab time" or "bd time" is 0 seconds. This indicates that the b wave of the accelerated plethysmogram could not be detected. It can be seen that the number of subjects for whom the b wave could not be detected was greater when measured with green light than when measured with near-infrared light. In subjects with poor peripheral circulation, such as diabetic patients, the b wave of the accelerated plethysmogram is small, making it often difficult to detect.

[0074] From the evaluation results shown in Figures 10A to 17, it can be seen that the pulse wave features that showed significant differences between diabetic patients and healthy subjects include the peripheral blood pressure index "1 / VE0.5" when green light was used (Figure 10A), the peripheral blood pressure index "(ab) / (ad)" when green light was used, and the feature "de time" when green light or near-infrared light was used.

[0075] [Features that are thought to be causally related to pulse pressure] Next, with reference to FIGS. 18A to 22, a description will be given of the feature quantities of the pulse wave that are thought to have a causal relationship with the pulse pressure.

[0076] 18A to 22 are scatter plots of multiple subjects, with the horizontal axis representing pulse pressure and the vertical axis representing various characteristic quantities of the pulse wave.

[0077] The vertical axis of Figures 18A and 18B represents the peripheral blood pressure index "1 / VE0.5" in units [s -1 ]. The vertical axis of Figures 19A and 19B represents the peripheral blood pressure index "(ab) / (ad)". The vertical axis of Figures 20A and 20B represents the feature "de time" in units of [s]. The vertical axis of Figures 21A and 21B represents the feature "ae time" in units of [s]. The vertical axis of Figure 22 represents the pulse interval in units of [s].

[0078] Figures 18A, 19A, 20A, and 21A show the feature quantities of the pulse wave measured using green light, and Figures 18B, 19B, 20B, and 21B show the feature quantities of the pulse wave measured using near-infrared light. The pulse interval shown in Figure 22 is the same whether green light or near-infrared light is used.

[0079] Feature quantities that showed a certain degree of correlation with pulse pressure include the peripheral blood pressure index "1 / VE0.5" (Figs. 18A and 18B), the peripheral blood pressure index "(ab) / (ad)" (Figs. 19A and 19B), and the feature quantity "ae time" (Figs. 21A and 21B). For the peripheral blood pressure index "1 / VE0.5," a stronger correlation was observed when green light was used than when near-infrared light was used. The feature quantity "de time" (Figs. 20A and 20B) and the pulse interval (Fig. 22) did not show a significant correlation with pulse pressure.

[0080] It was confirmed that the peripheral blood pressure index "1 / VE0.5" and the peripheral blood pressure index "(ab) / (ad)" have a negative correlation with pulse pressure. This is similar to the relationship between the peripheral blood pressure index "1 / VE0.5" and the peripheral blood pressure index "(ab) / (ad)" and systolic blood pressure. Subjects with low peripheral blood pressure index "1 / VE0.5" and the peripheral blood pressure index "(ab) / (ad)" are expected to have high vascular resistance. It is generally known that high vascular resistance increases pulse pressure. In other words, the negative correlation between the peripheral blood pressure index "1 / VE0.5" and the peripheral blood pressure index "(ab) / (ad)" and pulse pressure is not inconsistent with this general finding.

[0081] The feature "ae time" was confirmed to have a negative correlation with pulse pressure. There was no significant difference in the feature "ae time" between measurements using green light and near-infrared light. The incisor IC (Figure 5) that appears on the pulse wave is said to be the end of systole, and the position of the peak of the e wave on the accelerated pulse wave corresponds to the position of the incisor IC. Since there was no difference in "ae time" between when green light and when near-infrared light were used, it can be inferred that "ae time" is less susceptible to the influence of factors such as vascular conditions.

[0082] A long "ae time" means that the left ventricle is contracting for a long time. Therefore, "ae time" is thought to have a positive correlation with stroke volume. The fact that pulse pressure has a positive correlation with "ae time" can be explained by the fact that pulse pressure increases as stroke volume increases.

[0083] [Pulse pressure measurement method] Next, a pulse wave measurement method according to a first embodiment will be described. In the first embodiment, pulse pressure is calculated based on a peripheral blood pressure index "1 / VE0.5" that has a correlation with pulse pressure and a feature value "ae time." For example, pulse pressure is calculated using a function that uses the exponential value of the peripheral blood pressure index "1 / VE0.5" and the exponential value of the feature value "ae time" as variables.

[0084] Next, this function will be explained. In the first embodiment, the pulse pressure index value Pa is calculated using the following formula. Pa=(1 / VE0.5) -α ×(ae time) β ···(1) Here, α and β are positive fitting parameters. The actual pulse pressure value can be calculated by multiplying the pulse pressure index value Pa by the coefficient. The fitting parameters α and β and the coefficient can be determined by actually conducting an evaluation experiment.

[0085] Next, the results of an actual evaluation experiment will be described with reference to Figures 23A and 23B. The pulse waves of multiple subjects were measured, and a pulse pressure index value Pa was calculated from the pulse waves. Furthermore, pulse pressure was calculated from the systolic and diastolic blood pressures measured at the wrist. The subjects included multiple healthy subjects and multiple diabetic patients. Pulse wave measurements were performed with ring device 61 (Figure 4) attached to the subject's finger, with the height of the measurement site approximately aligned with the height of the heart.

[0086] Figure 23A is a scatter plot of the measurement results when the fitting parameters α and β in equation (1) are set to α = 1 and β = 1.5, respectively. The horizontal axis represents pulse pressure in units of mmHg, and the vertical axis represents the pulse pressure index value Pa. The peripheral blood pressure index "1 / VE0.5" was obtained from the pulse wave measured using green light, and the feature value "ae time" was obtained from the pulse wave measured using near-infrared light. The black and open circles in Figure 23A represent the measurement results for healthy subjects and diabetic patients, respectively. Overall, it can be seen that there is a positive correlation between the pulse pressure index value Pa and pulse pressure.

[0087] FIG. 23B is a scatter plot showing the measurement results without distinguishing between healthy subjects and diabetic patients. In FIG. 23B, the regression line is shown by a dashed line. In the example shown in FIG. 23B, the coefficient of determination R 2 The correlation coefficient was approximately 0.47. The correlation coefficient was approximately 0.69, which means that there is a sufficient correlation between the pulse pressure index value Pa and the pulse pressure. In this way, the pulse pressure measuring method according to the first embodiment can determine the pulse pressure using a photoplethysmographic sensor.

[0088] From the measured pulse wave, the peripheral blood pressure index "1 / VE0.5" and the feature "ae time" can be obtained, and the pulse pressure can be calculated using equation (1). Note that evaluation experiments can be conducted with a larger number of subjects to improve the accuracy of the fitting parameters α and β.

[0089] In Figures 23A and 23B, the peripheral blood pressure index "1 / VE0.5" is calculated using green light, and the feature "ae time" is calculated using near-infrared light. As another example, the peripheral blood pressure index "1 / VE0.5" may be calculated using near-infrared light, or the feature "ae time" may be calculated using green light. Furthermore, light in the wavelength range from blue to yellow-green may be used instead of green light.

[0090] Instead of the peripheral blood pressure index "1 / VE0.5", other peripheral blood pressure indexes related to the steepness of the rising edge of the pulse wave, such as "a / S" or "(ab) / (ad)" which have a positive correlation with peripheral blood pressure, may be used. Furthermore, instead of the value of the feature "ae time" itself, an index having a positive correlation with "ae time" (referred to as the "ae time index" in this specification) may be used. Furthermore, instead of equation (1), a function may be used in which the value of the function decreases as the peripheral blood pressure index increases and the value of the function increases as the ae time index increases.

[0091] The data for the scatter diagrams shown in FIGS. 23A and 23B was collected by wearing the ring device 61 (FIG. 4) on the subject's finger, but it may also be worn on the subject's fingertip.

[0092] [Modification of the first embodiment] Next, a modification of the first embodiment will be described. In the first embodiment, a ring-shaped ring device 61 (FIG. 5) is worn on a finger, but instead of the ring device 61, a device shaped to be worn on a part of the body other than a finger may be used. For example, a wearable device shaped to be worn on the wrist, neck, face, ear, etc. may be used. For example, the wearable device may be a wristband or watch type worn on the wrist, an earphone type worn on the ear, a patch type attached to the skin, or a neckband type worn around the neck.

[0093] Furthermore, the pulse pressure measuring device does not necessarily have to be wearable, and may be a device that measures pulse waves by pressing a finger against the photoplethysmographic sensor 50 as needed. For example, the pulse pressure measuring device may be a portable device such as a smartphone, or a fixed device.

[0094] In the first embodiment, light reflected by biological tissue such as a finger is detected, but light transmitted through biological tissue may also be detected. When detecting light transmitted through a finger, the light-emitting element and the light-receiving element are arranged opposite each other with the finger sandwiched between them. Depending on the positional relationship between the light-emitting element and the light-receiving element, both light reflected by biological tissue and light transmitted through biological tissue may be detected by the light-receiving element. In other words, the light output from the light-emitting element and transmitted through biological tissue may be detected by the light-receiving element.

[0095] [Second Example] Next, a pulse pressure measuring device and a pulse wave measuring method according to a second embodiment will be described with reference to Figures 24A, 24B, and 25. Below, a description of the configurations common to the pulse pressure measuring device and the pulse wave measuring method according to the first embodiment and its modified example will be omitted.

[0096] In the first embodiment, as shown in Equation (1), pulse pressure is calculated based on the peripheral blood pressure index "1 / VE0.5," which has a correlation with pulse pressure, and the feature "ae time." In contrast, in the second embodiment, pulse pressure is calculated based on the feature "de time" in addition to the peripheral blood pressure index "1 / VE0.5" and the feature "ae time." For example, pulse pressure is calculated using a function with the exponent of the peripheral blood pressure index "1 / VE0.5," the exponent of the feature "ae time," and the exponent of the feature "de time" as variables.

[0097] Next, this function will be explained. In the second embodiment, the pulse pressure index value Pad is calculated using the following formula. Pad=(1 / VE0.5) -α ×(ae time) β ×(de time) -γ ···(2) Here, α, β, and γ are positive fitting parameters. The actual pulse pressure value can be calculated by multiplying the pulse pressure index value Pad by the coefficient. The fitting parameters α, β, γ, and the coefficients can be determined by actually conducting an evaluation experiment.

[0098] Figure 24A is a scatter plot of the measurement results when the fitting parameters α, β, and γ in equation (2) are set to α = 0.8, β = 1.5, and γ = 0.5, respectively. The horizontal axis represents pulse pressure in mmHg, and the vertical axis represents the pulse pressure index value Pad. The peripheral blood pressure index "1 / VE0.5" was calculated from the pulse wave measured using green light, and the feature quantities "ae time" and "de time" were calculated from the pulse wave measured using near-infrared light. The black and open circles in Figure 24A represent the measurement results for healthy subjects and diabetic patients, respectively. Overall, it can be seen that there is a positive correlation between the pulse pressure index value Pad and pulse pressure.

[0099] FIG. 24B is a scatter plot showing the measurement results without distinguishing between healthy subjects and diabetic patients. In FIG. 24B, the regression line is shown by a dashed line. In the example shown in FIG. 24B, the coefficient of determination R 2 The correlation coefficient was approximately 0.52. The correlation coefficient was approximately 0.72, which indicates that there is a strong correlation between the pulse pressure index value Pad and the pulse pressure. In this way, the pulse pressure measurement method according to the second embodiment can determine the pulse pressure using a photoplethysmographic sensor.

[0100] From the measured pulse wave, the peripheral blood pressure index "1 / VE0.5", the feature "ae time", and the feature "de time" can be obtained, and the pulse pressure can be calculated using equation (2). Note that the accuracy of the fitting parameters α, β, and γ can be improved by collecting more subjects and conducting evaluation experiments.

[0101] In Figures 24A and 24B, the peripheral blood pressure index "1 / VE0.5" is calculated using green light, and the feature quantities "ae time" and "de time" are calculated using near-infrared light. As another example, the peripheral blood pressure index "1 / VE0.5" may be calculated using near-infrared light, or the feature quantities "ae time" or "de time" may be calculated using green light. Furthermore, light in the wavelength range from blue to yellow-green may be used instead of green light.

[0102] Instead of the peripheral blood pressure index "1 / VE0.5," other peripheral blood pressure indices related to the steepness of the rising edge of the pulse wave, such as "a / S" or "(ab) / (ad)," which have a positive correlation with peripheral blood pressure, may be used. Furthermore, instead of the value of the feature "ae time" itself, an ae time index having a positive correlation with "ae time" may be used. Instead of the value of "de time" itself, an index having a positive correlation with "de time" (referred to herein as the "de time index") may be used. Furthermore, instead of equation (2), a function may be used in which the value of the function decreases as the peripheral blood pressure index increases, the value of the function increases as the ae time index increases, and the value of the function decreases as the de time index increases.

[0103] Next, with reference to FIG. 25, another advantageous effect of determining pulse pressure using equation (2) will be described.

[0104] Figure 25 is a scatter plot of multiple measurements taken over a long period of time on a single subject. Note that this subject is a healthy individual and is different from the subject used to collect the data shown in Figures 24A and 24B. The horizontal axis of Figure 25 represents pulse pressure in units of mmHg, and the vertical axis represents the pulse pressure index value Pad. The fitting parameters α, β, and γ in equation (2) are the same as those in Figures 24A and 24B. One set of pulse wave measurements was performed by aligning the measurement site height approximately with the navel, chest, and forehead, respectively. 24 sets of measurements were taken over a 20-day period. Measurements were taken in the morning, midday, and evening. Over the 20 days, 9 sets of measurements were taken in the morning, 12 sets of measurements were taken in the midday, and 3 sets of measurements were taken in the evening.

[0105] The measurement procedure is as follows. First, the pulse wave is measured at navel level using a photoplethysmographic sensor, then the wrist blood pressure is measured at navel level. Next, the pulse wave is measured at chest level using a photoplethysmographic sensor, then the wrist blood pressure is measured at chest level. Next, the pulse wave is measured at forehead level using a photoplethysmographic sensor, and finally the wrist blood pressure is measured at forehead level. The pulse wave measurement using the photoplethysmographic sensor and the wrist blood pressure measurement are not performed simultaneously.

[0106] The circles, squares, and triangles in the scatter plot shown in Figure 25 represent measurement results obtained when the measurement site heights were adjusted to forehead height, chest height, and navel height, respectively. The dashed line shown in Figure 25 is the same as the regression line shown in Figure 24B. As can be seen from Figure 25, pulse pressure tends to be relatively high at navel height and relatively low at forehead height.

[0107] The pulse pressure index value Pad varies between the heights of the navel, chest, and forehead, but is distributed in roughly the same range regardless of the height of the measurement site. This distribution nearly overlaps with the distribution of pulse pressure index values ​​Pad for healthy subjects shown in Figure 24A. Therefore, it can be inferred that the pulse pressure index value Pad calculated using equation (2) will not fluctuate significantly even if the height of the measurement site deviates from the height of the heart.

[0108] What is useful to the user is the value of pulse pressure at heart level. Considering user convenience, it is desirable to be able to estimate the value of pulse pressure at heart level even if the measurement site, for example, the height of the finger, is shifted from the heart level. The calculation formula for the pulse pressure index value Pad, Equation (2) used in the second embodiment, is also useful from the viewpoint of user convenience.

[0109] [Third Example] Next, a pulse pressure measuring device and a pulse pressure measuring method according to a third embodiment will be described with reference to Figures 26, 27, and 28. Hereinafter, a description of the configuration common to the pulse pressure measuring device and the pulse pressure measuring method according to the first or second embodiment will be omitted.

[0110] When the measurement site is 10 cm higher than the heart, the blood pressure drops by approximately 7 mmHg to 8 mmHg. In other words, when the height difference between the measurement site and the heart changes within a range of ±10 cm, the measured blood pressure varies by approximately ±8 mmHg. Similarly, the measured pulse pressure is also affected by the height from the heart to the measurement site. In order to utilize the measured pulse pressure as a medically useful value, it is preferable to measure the pulse pressure with the height of the measurement site approximately the same as the height of the subject's heart. The pulse pressure measuring device of the third embodiment has a function to measure the height difference between the measurement site and the heart.

[0111] 26 is a perspective view and a block diagram of a pulse pressure measuring device according to a third embodiment. The pulse pressure measuring device according to the third embodiment includes a ring device 61 and a mobile terminal 62, similar to the pulse pressure measuring device according to the modified example of the first embodiment shown in FIG. 4. The mobile terminal 62 of the pulse pressure measuring device according to the third embodiment includes a camera 63, an acceleration sensor 65, and a height calculation unit 38 in addition to the configuration of the mobile terminal 62 of the pulse pressure measuring device according to the modified example of the first embodiment (FIG. 4). The height calculation unit 38 calculates the difference in height between the ring device 61 and the user's heart.

[0112] Next, the procedure performed by the height calculation unit 38 will be described with reference to FIG. 27. FIG. 27 is a schematic diagram for explaining the procedure for measuring the difference in height between the ring device 61 and the heart. A user who wants to measure pulse pressure wears the ring device 61 on his / her finger, holds the mobile terminal 62 in the hand wearing the ring device 61, and captures an image of his / her face with the camera 63. The height calculation unit 38 (FIG. 26) of the mobile terminal 62 displays the captured image on the display unit 37 in real time. Furthermore, the height calculation unit 38 displays an oval or rectangular shape on the image of the user's face on the display unit 37. While looking at the display unit 37, the user adjusts the relative position of the mobile terminal 62 and his / her face so that the image of his / her face fits within the oval or rectangular shape. Furthermore, the user maintains a posture such that the trunk of the body is aligned vertically.

[0113] Physical information such as the user's height and weight is stored in advance in height calculation unit 38. Furthermore, statistical relationship information between the physical information and the size of the face is stored in height calculation unit 38. Height calculation unit 38 obtains the size of the user's face from the stored physical information using the statistical relationship information between the physical information and the size of the face. From the obtained face size and the size of the image of the user's face, distance L1 from mobile terminal 62 to the user's face (e.g., eyes) is calculated.

[0114] Furthermore, height calculation unit 38 calculates the inclination of mobile terminal 62 with respect to the vertical direction (direction of gravity) from the measurement result of acceleration sensor 65. Based on the inclination of mobile terminal 62 and distance L1 from mobile terminal 62 to the user's eyes, height calculation unit 38 calculates height H1 from mobile terminal 62 to the user's eyes.

[0115] The height calculation unit 38 statistically calculates the height H2 from the heart to the eyes based on the user's physical information. However, errors will occur in the height H2 if the trunk is bent significantly, such as when leaning forward. Here, it is assumed that the trunk is not tilted. For example, the difference between the medial canthus height and the nipple height included in the "AIST Human Body Dimension Database 1991-1992" can be used as the height H2 from the heart to the eyes.

[0116] The height calculation unit 38 (FIG. 26) calculates the difference in height between the mobile terminal 62 and the heart using the height H1 from the mobile terminal 62 to the user's eyes and the height H2 from the heart to the eyes. The height of the ring device 61 (measurement site) can be assumed to be approximately equal to the height of the mobile terminal 62.

[0117] FIG. 28 is a flowchart showing the steps of a pulse pressure measuring method executed by the pulse pressure measuring device according to the third embodiment.

[0118] The height calculation unit 38 (FIG. 26) calculates the difference in height between the ring device 61 and the heart (step SA1). This calculation can be performed by the method described with reference to FIG. 27. The height calculation unit 38 determines whether the calculated difference between the height of the ring device 61 and the heart is within an allowable range (step SA2). If the difference is within the allowable range, the pulse pressure calculation unit 35 (FIG. 26) calculates the pulse pressure based on the measured pulse wave (step SA3). The pulse pressure measurement method according to the first or second embodiment can be used to calculate the pulse pressure.

[0119] Once the pulse pressure value (calculated value) is obtained by calculation, the control unit 36 ​​stores or outputs the calculated pulse pressure value (step SA4). The calculated pulse pressure value is stored, for example, in association with the measurement date and time. The calculated pulse pressure value is output, for example, by displaying it on the display unit 37 (FIG. 26) or transmitting it to a server. The functions of the peripheral blood pressure index calculation unit 33, pulse wave feature amount calculation unit 34, and pulse pressure calculation unit 35 (FIG. 4) may be realized by the server. When this configuration is adopted, the server calculates the pulse pressure, stores the calculated pulse pressure value, and transmits the calculated pulse pressure value to the mobile terminal 62 (FIG. 4).

[0120] If it is determined in step SA2 that the difference is outside the allowable range, the height calculation unit 38 notifies the user that the difference in height between the ring device 61 and the heart is outside the allowable range (step SA5). Upon receiving this notification, the user can adjust the height of the ring device 61 to match the height of the heart and perform measurement again.

[0121] Next, the excellent effects of the third embodiment will be described. In the third embodiment, the height of the measurement site can be adjusted to the height of the heart to measure the pulse pressure. This improves the accuracy of the pulse pressure measurement. It is also possible to measure the pulse pressure even if it is determined in step SA2 that the difference is outside the allowable range, and output the pulse pressure measurement with a note indicating that the measurement is not reliable.

[0122] Next, a modified example of the third embodiment will be described with reference to Fig. 29. Fig. 29 is a flowchart showing the steps of a pulse pressure measurement method executed by a pulse pressure measurement device according to a modified example of the third embodiment. First, as in the third embodiment (Fig. 28), the height calculation unit 38 calculates the difference in height between the ring device 61 and the heart (step SA1). In the first embodiment, if the difference is outside the allowable range, the pulse pressure is not measured. However, in this modified example, the pulse pressure calculation unit 35 calculates the pulse pressure based on the measured pulse wave, regardless of whether the difference is within the allowable range (step SA3).

[0123] Next, pulse pressure calculation unit 35 corrects the calculated value of pulse pressure based on the difference in height between ring device 61 and the heart (step SA5). The relationship between the difference in height between ring device 61 and the heart and pulse pressure may be determined in advance by conducting an evaluation experiment. After correcting the calculated value of pulse pressure, the corrected value of pulse pressure is stored or output (step SA6).

[0124] In the modified example shown in FIG. 29, even if there is a large difference in height between the measurement site and the heart, a highly accurate pulse pressure value can be obtained by correcting the calculated pulse pressure value.

[0125] [Fourth Example] Next, a pulse pressure measuring device and a pulse pressure measuring method according to a fourth embodiment will be described with reference to Figures 30 and 31. Hereinafter, a description of the configuration common to the pulse pressure measuring device and the pulse pressure measuring method according to the first or second embodiment will be omitted.

[0126] During exercise, blood pressure and pulse pressure change depending on the amount of exercise. Furthermore, when the measurement site is moving, inertial forces act on the blood in the blood vessels, causing the waveform of the pulse wave to fluctuate. Medically useful blood pressure and pulse pressure measured in a resting state are those that are medically useful. Furthermore, the contact state between the photoplethysmographic sensor and the skin is likely to change during exercise. If the contact state changes, noise will be superimposed on the measured pulse wave. In the fourth embodiment, the system determines whether the user is at rest and measures the pulse pressure in a resting state that is medically useful.

[0127] 30 is a perspective view and a block diagram of a pulse pressure measuring device according to a fourth embodiment. The pulse pressure measuring device according to the fourth embodiment includes a ring device 61 and a mobile terminal 62, similar to the pulse pressure measuring device according to the modified first embodiment (FIG. 4). In addition to the configuration of the ring device 61 of the pulse pressure measuring device according to the modified first embodiment (FIG. 4), the ring device 61 of the pulse pressure measuring device according to the fourth embodiment is equipped with an acceleration sensor 54. In addition to the configuration of the mobile terminal 62 of the pulse pressure measuring device according to the modified first embodiment, the mobile terminal 62 includes a resting state determination unit 39.

[0128] The resting state determination unit 39 determines whether or not the user is at rest using the measurement results of the acceleration sensor 54. For example, if the acceleration measurement value by the acceleration sensor 54 remains below the determination threshold for a predetermined period of time, for example, five minutes, the resting state determination unit 39 determines that the user is at rest.

[0129] 31 is a flowchart showing the steps of a pulse pressure measurement method executed by a pulse pressure measuring device according to a fourth embodiment. The resting state determination unit 39 determines whether the user wearing the ring device 61 is in a resting state (step SB1). If it is determined that the user is not in a resting state, the determination of the resting state is repeated at regular intervals until the user is in a resting state (step SB2). If it is determined that the user is in a resting state, the pulse pressure calculation unit 35 calculates the pulse pressure based on the pulse wave acquired at that time (step SB3). Thereafter, the calculated pulse pressure value is stored or output (step SB4).

[0130] Next, the excellent effects of the fourth embodiment will be described. In the fourth embodiment, the pulse pressure is calculated based on the pulse wave when the user is in a resting state, and therefore the accuracy of the calculated pulse pressure value can be improved.

[0131] Next, a modified example of the fourth embodiment will be described. In the fourth embodiment, whether or not the person is in a resting state is determined based on acceleration measurements taken by the acceleration sensor 54 mounted on the ring device 61. A gyro sensor may be mounted instead of the acceleration sensor 54, and whether or not the person is in a resting state may be determined based on angular acceleration measurements taken by the gyro sensor. Furthermore, the acceleration sensor 54 and the gyro sensor may be used together to determine whether or not the person is in a resting state.

[0132] [Fifth Example] Next, a pulse pressure measuring device and a pulse pressure measuring method according to a fifth embodiment will be described with reference to Figures 32 and 33. Hereinafter, a description of the configuration common to the pulse pressure measuring device and the pulse pressure measuring method according to the first or second embodiment will be omitted.

[0133] Fig. 32 is a perspective view and a block diagram of a pulse pressure measuring device according to a fifth embodiment. The pulse pressure measuring device according to the fifth embodiment includes a ring device 61 and a mobile terminal 62, similar to the pulse pressure measuring device according to the modified first embodiment (Fig. 4). The ring device 61 of the pulse pressure measuring device according to the fifth embodiment is equipped with an acceleration sensor 54, similar to the ring device 61 of the pulse pressure measuring device according to the fourth embodiment (Fig. 30). The mobile terminal 62 includes a sleep state determination unit 40 in addition to the configuration of the mobile terminal 62 of the pulse pressure measuring device according to the modified first embodiment.

[0134] The sleep state determination unit 40 determines whether the user is in a resting state or not by using the measurement results of the acceleration sensor 54. A method for determining whether the user is in a sleeping state or an awake state will be described below.

[0135] The sleep state determination unit 40 determines that a body movement is occurring when, for example, the acceleration measured by the acceleration sensor 54 exceeds a predetermined threshold. The sleep state determination unit 40 determines that a person is asleep when the number of body movements occurring within a predetermined time period is equal to or less than the predetermined threshold. The predetermined time period may be selected, for example, from a range of 15 minutes to 90 minutes. Although sudden increases in acceleration may occur during sleep due to factors such as turning over in bed, this occurs less frequently than during wakefulness. Therefore, whether or not a person is asleep can be accurately determined based on the number of body movements occurring within a predetermined time period. Fingers move more frequently during wakefulness than the waist, chest, wrist, etc. By utilizing this characteristic, wearing the ring device 61 on a finger can more accurately determine whether or not a person is asleep compared to wearing a photoplethysmographic sensor on another part of the body, such as the wrist.

[0136] 33 is a flowchart showing the steps of a pulse pressure measuring method executed by a pulse pressure measuring device according to Example 5. The sleep state determination unit 40 (FIG. 32) determines whether the user wearing the ring device 61 is asleep or awake (step SC1). If it is determined that the user is not asleep, the determination of whether the user is asleep or awake is repeated at regular intervals (step SC2).

[0137] If the sleep state is determined, pulse wave measurement unit 32 (FIG. 4) measures the pulse wave, and pulse pressure calculation unit 35 (FIG. 4) calculates the pulse pressure (step SC3). After the sleep state is determined, a further determination may be made as to whether the subject is in a resting state, as in step SB1 shown in FIG. 31, and only if the subject is determined to be in a resting state, the pulse wave may be measured and the pulse pressure calculated. Once the calculated pulse pressure value has been obtained, control unit 36 ​​stores or outputs the calculated pulse pressure value (step SC4).

[0138] Next, the excellent effects of the fifth embodiment will be described. In the fifth embodiment, the pulse pressure during sleep can be automatically calculated. If it is determined that the patient is not asleep, the pulse wave is not measured, thereby reducing battery consumption.

[0139] It is known that eating, drinking alcohol, caffeine intake, smoking, and the like affect blood pressure and pulse pressure. Furthermore, exercise, walking, physical activity (e.g., cleaning), bathing, conversation, mental stress, noisy or vibrating environments, and cold environments also affect blood pressure and pulse pressure. These events occur frequently during wakefulness, making it difficult to determine whether the timing of pulse wave measurement coincides with these events. Because the influence of these events is reduced during sleep, measuring pulse pressure while asleep allows for stable measurements.

[0140] Next, a modification of the fifth embodiment will be described. In the fifth embodiment, whether or not a person is asleep is determined based on the frequency of body movements, but other methods may also be used to determine whether or not a person is asleep. It is known that the temperature of the fingers rises during sleep. A temperature sensor may be mounted on the ring device 61 (FIG. 32), and the circadian rhythm may be estimated from the temperature sensor's measurements, and the frequency of body movements may be combined with the temperature measurements to determine whether or not a person is asleep.

[0141] Furthermore, the pulse rate tends to be lower during sleep compared to when awake. Furthermore, the pulse rate is more likely to be affected by respiratory fluctuations. Utilizing this characteristic, the tendency of pulse rate fluctuations may be added to the frequency of body movement to determine whether or not the person is asleep.

[0142] In the fifth embodiment, whether or not the subject is asleep is determined based on the frequency of body movement. As a modification of the fifth embodiment, measurement of the pulse wave may be started when the frequency of body movement falls below a certain frequency, and whether or not the subject is asleep may be determined based on the frequency of body movement and the measured pulse wave. By additionally using the pulse wave to determine whether or not the subject is asleep, the accuracy of determining whether or not the subject is asleep can be improved.

[0143] In the fifth embodiment, pulse wave measurement is not performed when the user is determined to be in an awake state. However, if the battery capacity is large enough, pulse wave measurement and pulse pressure calculation may be performed in both the awake and asleep states. In this case, the calculated pulse pressure value may be stored in association with identification information that distinguishes between the awake and asleep states. This makes it possible to know the difference in the tendency between leg pressure in the awake state and pulse pressure in the asleep state.

[0144] The above-described embodiments are merely examples, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments is possible. Similar effects resulting from similar configurations of multiple embodiments will not be mentioned sequentially for each embodiment. Furthermore, the present invention is not limited to the above-described embodiments. For example, it will be obvious to those skilled in the art that various modifications, improvements, combinations, etc. are possible. [Explanation of symbols]

[0145] 30 Processing equipment 31 Light emission control unit 32 Pulse wave measurement unit 33 Peripheral blood pressure index calculation unit 34 Pulse wave feature calculation unit 35 Pulse pressure calculation unit 36 Control Unit 37 Display section 38 Height Calculation Unit 39 Resting state determination unit 40 Sleep state determination unit 50 Photoplethysmographic sensor 51, 52 Light-emitting element 53 Photodetector 54 Acceleration Sensor 55 Communications Department 56 Gyro sensor 60 Mounting member 61 Ring Device 62 Mobile devices 63 Camera 64 Communications Department 65 Acceleration Sensor 70 User's body surface 71 Epidermal area 72 Arterioles 73 Capillaries

Claims

1. a peripheral blood pressure index calculation unit that calculates a peripheral blood pressure index related to the steepness of the rising edge of a pulse wave signal measured by a pulse wave sensor worn by a user; a pulse wave feature amount calculation unit that calculates an ae time index including information about the elapsed time from the peak of the a-wave to the peak of the e-wave of an acceleration pulse wave obtained by second-order differentiation of the waveform of the pulse wave signal; a pulse pressure calculation unit that calculates a pulse pressure based on the peripheral blood pressure index and the ae time index; A pulse pressure measuring device comprising:

2. the pulse wave feature amount calculation unit further includes a function of calculating a de time index including information on the elapsed time from the peak of the d wave to the peak of the e wave of the acceleration pulse wave; The pulse pressure measuring device according to claim 1 , wherein the pulse pressure calculation unit calculates the pulse pressure based on the peripheral blood pressure index, the ae time index, and the de time index.

3. 3. The pulse pressure measuring device according to claim 1, wherein the pulse wave sensor is configured so that fluctuations in blood pressure in the user's peripheral capillaries are reflected in the pulse wave signal.

4. 4. The pulse pressure measuring device according to claim 3, wherein the pulse wave sensor is a photoplethysmographic sensor that uses light with a wavelength included in the wavelength range from blue to yellow-green.

5. The pulse wave sensor a first light-emitting element that outputs light having a wavelength included in a wavelength range from blue to yellow-green; a first light receiving element that receives light output from the first light emitting element and transmitted through biological tissue; Including, 5. The pulse pressure measuring device according to claim 4, wherein the distance between the first light emitting element and the first light receiving element is 1 mm or more and 3 mm or less.

6. 3. The pulse pressure measuring device according to claim 1, wherein the pulse wave sensor is configured so that fluctuations in blood pressure in the user's peripheral arterioles are reflected in the pulse wave signal.

7. 7. The pulse pressure measuring device according to claim 6, wherein the pulse wave sensor is a photoplethysmographic sensor that uses light having a wavelength within a wavelength range from red to near-infrared.

8. The pulse wave sensor a second light-emitting element that outputs light of a wavelength included in a wavelength range from blue to yellow-green; a second light receiving element that receives light output from the second light emitting element and transmitted through biological tissue; Including, 8. The pulse pressure measuring device according to claim 7, wherein the distance between the second light emitting element and the second light receiving element is 5 mm or more and 20 mm or less.

9. 3. The pulse pressure measuring device according to claim 1, wherein the pulse wave sensor includes a mounting member that is mounted on a user's finger, radiates light toward the user's finger, and generates the pulse wave signal based on the intensity of the light that passes through the biological tissue of the finger.

10. 3. The pulse pressure measuring device according to claim 1, wherein the pulse pressure calculation unit calculates the value of a function having a value of the power of the peripheral blood pressure index and a value of the power of the ae time index as variables to determine the pulse pressure.

11. 11. The pulse pressure measuring device according to claim 10, wherein the peripheral blood pressure index has a positive correlation with peripheral blood pressure, the ae time index has a positive correlation with the elapsed time from the peak of the a wave to the peak of the e wave of the accelerated pulse wave, and the value of the function decreases as the peripheral blood pressure index increases and increases as the ae time index increases.

12. 3. The pulse pressure measuring device according to claim 1, further comprising a height calculation unit that calculates a difference in height between the pulse wave sensor and the user's heart, and notifies the user when the difference in height exceeds an allowable range.

13. The device further includes a height calculation unit that calculates a difference in height between the pulse wave sensor and the user's heart, 3. The pulse pressure measuring device according to claim 1, wherein the pulse pressure calculation unit corrects the calculated pulse pressure value in accordance with the difference in height measured by the height calculation unit.

14. 3. The pulse pressure measuring device according to claim 1, wherein the peripheral blood pressure index calculation unit calculates the peripheral blood pressure index based on information regarding the width of the first peak that appears within one beat of a velocity pulse wave waveform obtained by first-order differentiation of the waveform of the pulse wave signal.

15. 3. The pulse pressure measuring device according to claim 1, wherein the peripheral blood pressure index calculation unit calculates the peripheral blood pressure index based on information relating to the peak value of the a-wave of the accelerated pulse wave and the amplitude of the pulse wave signal.

16. 3. The pulse pressure measuring device according to claim 1, wherein the peripheral blood pressure index calculation unit calculates the peripheral blood pressure index based on information regarding the difference between the peak value of the a-wave and the peak value of the b-wave of the accelerated pulse wave and the difference between the peak value of the a-wave and the peak value of the d-wave.

17. The device further includes a resting state determination unit that determines whether the user is in a resting state, The pulse pressure measuring device according to claim 1 , wherein the pulse pressure calculation unit calculates the pulse pressure from a pulse wave acquired when the resting state determination unit determines that the user is in a resting state.

18. The device further includes a sleep state determination unit that determines whether the user is asleep, 3. The pulse pressure measuring device according to claim 1, wherein the pulse pressure calculation unit calculates the pulse pressure from the pulse wave acquired when the sleep state determination unit determines that the user is asleep, and does not calculate the pulse pressure when the sleep state determination unit determines that the user is not asleep.

19. A pulse wave signal is acquired by a pulse wave sensor attached to the user. a pulse pressure measuring device calculating a peripheral blood pressure index related to the steepness of the rising edge of the pulse wave signal; the pulse pressure measuring device calculates an ae time index including information about the elapsed time from the peak of the a-wave to the peak of the e-wave of an accelerated pulse wave obtained by second-order differentiation of the waveform of the pulse wave signal; A pulse pressure measuring method in which the pulse pressure measuring device determines the pulse pressure based on the peripheral blood pressure index and the ae time index.

20. 20. The pulse pressure measuring method according to claim 19, wherein the pulse wave signal is acquired so as to reflect fluctuations in blood pressure in the user's peripheral capillaries.

21. 21. The pulse pressure measuring method according to claim 19, wherein the pulse wave signal is acquired so as to reflect fluctuations in blood pressure in the user's peripheral arterioles.

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