blood pressure measuring device

Abstract

To provide a blood pressure measuring apparatus capable of estimating diastolic pressure with high accuracy.SOLUTION: An intercept β and an inclination α included in a linear regression line expression (2) leading a diastolic pressure estimation equation (5) are mutually in a constant linear relation as shown in equation (4) and are not influenced by a person to be measured, and thus are unlikely to be influenced by individual biological features of a person to be measured, so diastolic pressure value DAPe can be measured with high accuracy. There is a merit that there is no need to perform calibration as a conventional one which performs blood pressure estimation using pulse wave velocity PWV.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a blood pressure measuring device and method that includes a compression cuff that is wrapped around a compressed part of a living body, and that estimates the diastolic (minimum) blood pressure of the living body based on the compression pressure applied by the compression cuff and the pulse wave velocity of the arterial blood vessel that passes through the compressed part. [Background technology]

[0002] In blood pressure measurement using the Korotkoff sound auscultation method, which is commonly used in clinical practice, a compression cuff is placed on the upper arm, and the systolic blood pressure (SAP) and diastolic blood pressure (DAP) are determined based on the compression pressure (Pc) at the onset and disappearance of vascular sounds (Korotkoff sounds) that occur in synchronization with the heartbeat as the compression pressure of the cuff is changed. The systolic blood pressure (SAP) and diastolic blood pressure (DAP) determined by this auscultation method are the most trusted among medical professionals. Because blood pressure measurement using this auscultation method requires a high level of expertise, automated blood pressure measuring devices that determine blood pressure using the easy-to-operate oscillometric method are commonly used for everyday blood pressure monitoring at home or in non-medical facilities.

[0003] The oscillometric method uses a cuff similar to that used in the auscultatory method. During the process of inflating the cuff to a pressure higher than the systolic (maximum) blood pressure and then lowering it, a cuff pulse wave (volume pulse wave), which is a minute fluctuation component superimposed on the cuff pressure, is extracted. A threshold determined experimentally or empirically is applied, and the cuff pressure at which the amplitude of the cuff pulse wave suddenly changes is determined as the systolic blood pressure and diastolic blood pressure. Because the physical relationship between the auscultatory method and the oscillometric method is unclear, the threshold used to determine the sudden change in the amplitude of the cuff pulse wave when determining the systolic and diastolic blood pressures is preset using a constant based on the maximum value observed at the compression pressure corresponding to the mean blood pressure (MAP), ensuring consistency with measurements obtained using the auscultatory method. Examples of such blood pressure measuring devices include those described in Patent Document 1 and Non-Patent Document 1.

[0004] Another known method for estimating blood pressure is to calculate the pulse wave velocity from the time difference (pulse wave propagation time) between the occurrence of an R wave in an electrocardiogram and the occurrence of a pulse wave obtained from the compression pressure of a cuff, based on a preset relationship between the blood pressure of a living body and the pulse wave velocity of the living body, and then estimate the blood pressure of the living body based on the actual pulse wave velocity from the preset relationship. For example, a blood pressure monitoring device described in Patent Document 2 is such a method. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-071059 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-116608 [Non-patent literature]

[0006] [Non-Patent Document 1] LAGeddes, M.Voelz, C.Combs, D.Reiner, CFBabbs, “Characterization of the oscillometric method for measuring indirect blood pressure,” Ann. Biomed Eng., vol. 10, pp. 271-280, 1982 [Non-patent document 2] FK Forster and D. Turney, “Oscillometric determination of diastolic, mean, and systric blood pressure-A numerical model,” J. Biomech. Eng., vol. 108, pp. 359-364, Nov. 1986. [Non-patent document 3] Forouzanfar M, Dajani HR, Groza VZ, Bolic M, Ratkin I. “Oscillometlic blood pressure estimation: past, present, and future.”IEEE Rev Biomed Eng 2015;8:44-63. Summary of the Invention [Problem to be solved by the invention]

[0007] When measuring blood pressure using the oscillometric method, a preset threshold value is uniformly applied to each individual blood pressure measurement using a constant based on the mean blood pressure value MAP so as to match the measurement value using the auscultation method, but the relationship between the threshold value and the actual blood pressure value can be affected and changed by the individual biological characteristics of the person being measured, such as arterial vascular compliance, pulse rate, pulse pressure value, and arterial pulse pressure, which can result in a decrease in the accuracy of blood pressure measurement. This problem is pointed out in Non-Patent Document 2.

[0008] Furthermore, in blood pressure estimation using pulse wave velocity calculated based on the time difference between the R wave of an electrocardiogram and the detection of a pulse wave, the time difference includes the time from the occurrence of the R wave of an electrocardiogram to the start of the heart's ejection of blood (pre-ejection period (PEP)), and is measured as pulse arrival time (PAT) rather than the strict pulse wave propagation time (PTT). This causes errors in the calculation of pulse wave velocity, resulting in large blood pressure measurement errors. Furthermore, although the pulse wave from the heart propagates through the aorta (elastic artery) to the brachial artery (muscular artery), this is not a strict propagation time due to the different vascular compositions. This problem is pointed out in Non-Patent Document 3.

[0009] Blood pressure measurement devices with large measurement errors in blood pressure values ​​increase the likelihood of sustained hypertension due to insufficient antihypertensive treatment or of hypotension due to excessive antihypertensive treatment, contributing to problems such as an increased risk of vascular complications and dementia.In contrast, blood pressure measurement devices that can measure blood pressure values ​​with high accuracy can reduce the likelihood of insufficient antihypertensive treatment causing sustained hypertension and lower the likelihood of hypotension due to excessive antihypertensive treatment, thereby reducing the risk of vascular complications and dementia.

[0010] The present invention has been made in light of the above circumstances, and its purpose is to provide a blood pressure measurement method and blood pressure measurement device that can measure diastolic (minimum) blood pressure with high accuracy, without being affected by the individual biological characteristics of the subject. [Means for solving the problem]

[0011] The inventors conducted various studies and found that the relationship between the cross-sectional area A of the arterial blood vessel, which is the cross-sectional area Ao of the arterial blood vessel when the transmural pressure Pt (= diastolic blood pressure DAP - compression pressure Pc) at the time of diastolic blood pressure is zero, and the transmural pressure Pt of the arterial blood vessel is expressed mathematically by applying the Bramwell-Hill equation to the vascular model equation. 2 The theoretical nonlinear exponential curve (Equation (1)) showing the relationship between transmural pressure Pt and squared pulse wave velocity PWV obtained in a goat experiment was 2 We found that the relationship between the exponential curve and the cross-sectional area ratio Ao / Am can be accurately approximated by the logarithmic equation (2) by switching the horizontal and vertical axes of the exponential curve. This logarithmic equation (2) is the squared value of the pulse wave velocity PWV 2 If the logarithm of is regarded as an independent variable, it can be regarded as a linear regression line with a slope α and an intercept β. There is a point in the linear relationship (4) between the slope α and the intercept β, which is constant regardless of the subject. Furthermore, the linear regression line (2) can be transformed into equation (3). Therefore, the slope α is a function of the pulse wave velocity PWV. 2The intercept β of the linear regression equation can be calculated based on the slope α from the linear relationship equation (4). The squared value of the actual pulse wave velocity PWV is calculated from the diastolic blood pressure estimation equation (5) to which the slope α and intercept β are applied. 2 It was found that the diastolic blood pressure value DAPe can be estimated based on the compression pressure Pc.

[0012] PWV 2 =(1 / ρ·b)(1 / (1-Ao / Am))·e^(b·Pt) -(1 / ρ b) (1) Pt = α·ln(PWV 2 )+β (2) -Pc=α·ln(PWV 2 )+(β-DAP) (3) β=γ α+δ (4) DAPe = α·ln(PWV 2 )+(β+Pc) (5)

[0013] In other words, in the vascular model equation, the transmural pressure Pt of the arterial blood vessel is the estimated diastolic blood pressure DAPe - compression pressure Pc, so the transmural pressure Pt of the arterial blood vessel and the squared value of the pulse wave velocity PWV 2 The linear regression line (2) that expresses the relationship with the logarithm of the transmural pressure Pt can be transformed into equation (3). The slope α of equation (3) is the same as equation (2), and the slope α of the measured multiple sets of compression pressure Pc and pulse wave velocity PWV 2 The slope α can be calculated by performing a regression analysis on the logarithm of . In this way, the slope α specific to each subject can be calculated even if the diastolic blood pressure DAP is unknown, i.e., the transmural pressure Pt is unknown. The intercept β specific to each subject can be calculated by substituting the calculated slope α into the empirically established linear relationship (4) between the previously calculated slope α and intercept β. Once the slope α and intercept β specific to each subject are determined in this way, the diastolic blood pressure DAPe can be expressed by the diastolic blood pressure estimation equation (5), which is a modification of equation (3) for the transmural pressure Pt. This allows the compression pressure Pc and the squared value of the pulse wave velocity PWV to be calculated. 2A diastolic blood pressure estimation equation (5) is set, which has a variable Pc and includes a slope α and an intercept β. From this diastolic blood pressure estimation equation (5), the diastolic blood pressure of the subject can be estimated based on the actual compression pressure Pc applied to the compression site of the subject and the pulse wave velocity in the arterial blood vessel that passes through the compression site of the subject. The present invention was made based on this finding.

[0014] The gist of a first invention is a blood pressure measurement device that estimates the diastolic blood pressure of a subject using a compression pressure applied by a compression cuff that compresses an arterial blood vessel at a compressed site of the subject and a squared value of the pulse wave velocity of the arterial blood vessel passing through the compressed site, the blood pressure measurement device comprising: (b) a pulse wave velocity measurement unit that measures the pulse wave velocity PWV of the compressed site under compression by the compression cuff; (c) a slope calculation unit that calculates a slope α of the linear regression line equation based on the compression pressure and the pulse wave velocity of the compressed site measured at the compression pressure, using a conversion equation from a linear regression line equation between the logarithm of the squared value of the pulse wave velocity and the transmural pressure of the arterial blood vessel; and (d) a slope calculation unit that calculates a slope α of the linear regression line equation based on the compression pressure and the pulse wave velocity of the compressed site measured at the compression pressure. (e) a diastolic blood pressure estimation equation setting unit that sets a diastolic blood pressure estimation equation by substituting the compression pressure to be subtracted from the diastolic blood pressure representing the transmural pressure, the pulse wave velocity of the compressed area, the slope of the linear regression equation calculated by the slope calculation unit, and the intercept of the linear regression equation calculated by the intercept calculation unit into the linear regression equation; and (f) a diastolic blood pressure estimation unit that estimates the diastolic blood pressure DAP of the subject from the diastolic blood pressure estimation equation based on the actual compression pressure Pc and pulse wave velocity PWV of the compressed area.

[0015] The gist of the second invention is that in the first invention, the linear regression line formula is expressed by the formula (2).

[0016] The gist of the third invention is that in the first or second invention, the conversion formula from the linear regression line formula is expressed by the formula (3).

[0017] The gist of the fourth invention is that in any one of the first to third inventions, the linear relationship is expressed by the formula (4).

[0018] The gist of the fifth invention is that in any one of the first to fourth inventions, the diastolic blood pressure estimation formula is expressed by the formula (5).

[0019] The gist of the sixth invention is that in any one of the first to fifth inventions, the diastolic blood pressure estimation unit estimates the diastolic blood pressure of the subject from the diastolic blood pressure estimation formula based on the actual compression pressure Pc and the pulse wave velocity of the compressed area for each of multiple types of compression pressure applied by the compression cuff, and determines the average value of the diastolic blood pressures estimated for each of the multiple types of compression pressure as the diastolic blood pressure.

[0020] The gist of the seventh invention is that in any one of the first to sixth inventions, the diastolic blood pressure estimation unit estimates the diastolic blood pressure DAP of the subject based on the actual compression pressure and the pulse wave velocity PWV of the compressed area, when the compression pressure applied by the compression cuff is set lower than the diastolic blood pressure DAP of the subject.

[0021] The gist of the eighth invention is that in any one of the first to seventh inventions, a pair of pulse wave sensors are arranged at two positions along the arterial blood vessel, spaced a predetermined distance from each other, to detect pulse waves, and the pulse wave velocity is calculated based on the time difference between the pulse waves detected by the pair of pulse wave sensors and the predetermined distance.

[0022] The gist of the ninth invention is that, in any one of the first to eighth inventions, it comprises a compression pressure control unit that maintains the compression pressure applied by the compression cuff at a monitor pressure that is lower than the diastolic blood pressure of the living body, and a blood pressure fluctuation determination unit that determines the occurrence of blood pressure fluctuations based on whether the pulse wave velocity measured during the period in which the monitor pressure is maintained falls outside a predetermined fluctuation determination range, and when the blood pressure fluctuation determination unit determines the occurrence of blood pressure fluctuations, the diastolic blood pressure estimation unit estimates the diastolic blood pressure of the person being measured using the diastolic blood pressure estimation formula based on the actual compression pressure and the pulse wave velocity of the compressed area. [Effects of the Invention]

[0023] According to the blood pressure measurement device of the first invention, the intercept and slope included in the linear regression equation from which the diastolic blood pressure estimation equation is derived have a constant linear relationship with each other and are not affected by the subject. Therefore, the measurement is less affected by the subject's individual biological characteristics, allowing for highly accurate measurement of the diastolic blood pressure value. Another advantage is that calibration is not required for each subject, as is the case with conventional blood pressure measurement devices that use pulse wave velocity to estimate blood pressure.

[0024] According to the blood pressure measuring device of the second aspect of the invention, the predetermined linear regression line formula representing the physical model formula of the arterial blood vessel is expressed by the above-mentioned formula (2). This linear regression line formula is based on the Bramwell-Hill formula (a3) ​​and the physical model formula (a1) of the arterial blood vessel, which represents the behavior of actual blood vessels, in which the blood vessel cross-sectional area is greater than zero when the transmural pressure is zero and the blood vessel cross-sectional area increases and saturates as the transmural pressure increases. Therefore, the diastolic (minimum) blood pressure value can be measured with high accuracy.

[0025] In the blood pressure measurement device of the third aspect of the invention, the conversion formula from the linear regression line formula is expressed by the above formula (3). Based on this conversion formula (3), the slope can be calculated by linear regression analysis of the logarithm of the square of the pulse wave velocity obtained by actual measurement and the compression pressure, even if the diastolic blood pressure and the intercept are unknown.

[0026] According to the blood pressure measurement device of the fourth aspect of the invention, the linear relationship is expressed by the above-mentioned formula (4). This linear relationship indicates that the intercept and slope included in the linear regression line equation are mutually constant and independent of each other, and this relationship is not affected by the subject. Therefore, the diastolic blood pressure value can be measured with high accuracy without being affected by the subject's individual biological characteristics.

[0027] According to the blood pressure measurement device of the fifth aspect of the invention, the diastolic blood pressure estimation formula is expressed by the formula (5). This diastolic blood pressure estimation formula uses the measurable compression pressure and pulse wave velocity, and the intercept and slope included in the linear regression line calculated from these two measurable variables, as variables, so that the diastolic blood pressure of the subject can be estimated by substituting and calculating the two measured variables.

[0028] According to the blood pressure measurement device of the sixth aspect of the invention, the diastolic blood pressure estimation unit estimates the diastolic blood pressure DAP of the subject for each of a plurality of types of compression pressure applied by the compression cuff based on the actual compression pressure Pc and the pulse wave velocity of the compressed area from the diastolic blood pressure estimation formula, and determines the average value of the diastolic blood pressures estimated for each of the plurality of types of compression pressure as the diastolic blood pressure, thereby enabling diastolic blood pressure values ​​to be measured with even greater accuracy.

[0029] According to the blood pressure measurement device of the seventh invention, the diastolic blood pressure estimation unit estimates the diastolic blood pressure DAP of the subject based on the actual compression pressure Pc and the pulse wave velocity of the compressed area, at a compression pressure applied by the compression cuff that is set lower than the diastolic blood pressure of the subject. This reduces the burden (stress) of compression by the compression cuff on the subject, provides a stable blood pressure value, and improves the accuracy of blood pressure measurement.

[0030] According to the blood pressure measurement device of the eighth aspect of the invention, the pulse wave velocity is calculated based on the time difference between pulse waves detected by a pair of pulse wave sensors arranged at two positions along an arterial blood vessel, a predetermined distance apart, and the predetermined distance. This allows for highly accurate estimation of diastolic blood pressure, since there is no error in the delay time (pre-ejection time) from the occurrence of the R wave in an electrocardiogram compared with the pulse wave velocity used for blood pressure estimation. In other words, according to the eighth aspect of the invention, the pulse wave propagation time measured purely reflects the characteristics of the arterial blood vessel, and therefore the measurement is not affected by fluctuations in the delay time (pre-ejection time), which is also dependent on the state of the heart, resulting in high reproducibility of blood pressure measurements.

[0031] A blood pressure measurement device according to a ninth aspect of the present invention includes a compression pressure control unit that maintains the compression pressure applied by the compression cuff at a monitor pressure lower than the diastolic blood pressure of the subject, and a blood pressure fluctuation determination unit that determines the occurrence of blood pressure fluctuations based on whether the pulse wave velocity measured while the monitor pressure is maintained deviates from a preset fluctuation determination value. When the blood pressure fluctuation determination unit determines the occurrence of blood pressure fluctuations, the diastolic blood pressure estimation unit estimates the diastolic blood pressure of the subject using the diastolic blood pressure estimation formula based on the actual compression pressure and the pulse wave velocity of the compressed area. This allows for long-term blood pressure monitoring with less strain on the subject. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a block diagram illustrating the configuration of a blood pressure measurement device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a view showing the compression garment of FIG. 1 with a portion of the outer circumferential surface cut away. [Figure 3] 3 is a plan view showing an upstream inflation bag, an intermediate inflation bag, and a downstream inflation bag provided in the compression band of FIG. 2. FIG. [Figure 4] 4 is a cross-sectional view taken along line IV-IV in FIG. 3, showing the upstream inflatable bag, the intermediate inflatable bag, and the downstream inflatable bag cut in the width direction. [Figure 5]2 is a functional block diagram for explaining the main control functions provided in the electronic control device of FIG. 1. FIG. [Figure 6] 6 is a time chart illustrating the main part of the compression pressure control operation by the compression pressure control unit of FIG. 5. [Figure 7] FIG. 1 is a diagram showing a theoretical vascular model showing the relationship between transmural pressure and cross-sectional area of ​​an arterial blood vessel in a living body. [Figure 8] FIG. 8 is a graph showing the result of a numerical simulation of the relationship between transmural pressure and the square of pulse wave velocity, which is a combination of the equation showing the relationship between the transmural pressure of the vascular model shown in FIG. 7 and the cross-sectional area of ​​the arterial blood vessel and the Bramwell-Hill equation. [Figure 9] FIG. 9 is a diagram showing a state where the theoretical relationship in FIG. 8 is approximated by a logarithmic function indicated by a dashed line in a relationship where the vertical and horizontal axes are interchanged. [Figure 10] FIG. 1 is a graph showing the relationship between the square of pulse wave velocity and transmural pressure measured using the upper arm of a goat. [Figure 11] FIG. 10 is a diagram showing a plot of the relationship between the slope and intercept of the six logarithmic relationship approximations in FIG. 9. [Figure 12] This figure shows plots of the relationship between the slope and intercept of 15 logarithmic relationship approximations obtained in additional experiments using the same goat, in addition to the relationship between the slope and intercept of the eight logarithmic relationship approximations in Figure 10. [Figure 13] FIG. 10 shows the relationship between the slope and intercept when the relationship between the squared value of pulse wave velocity and transmural pressure for 111 data sets obtained from seven goats is approximated by a logarithmic function. [Figure 14] FIG. 10 shows the relationship between the slope and intercept when the relationship between the squared value of pulse wave velocity and transmural pressure for 90 data sets obtained from 30 people is approximated by a logarithmic function. [Figure 15] FIG. 1 shows the correlation between the diastolic blood pressure DAP estimated by equation (5) from the pulse wave velocity PWV and compression pressure Pc actually measured for 30 subjects, and the diastolic blood pressure DAP measured by the Korotkoff sound auscultation method. [Figure 16]6 is a flowchart illustrating the main control operations of the electronic control device 70 of FIG. 5, showing the control for setting a formula for estimating diastolic blood pressure and calculating and estimating the diastolic blood pressure. [Figure 17] 17 is a flowchart illustrating the main control operations of the electronic control device 70 of FIG. 5, showing the diastolic blood pressure estimation formula setting routine of FIG. 16. [Figure 18] 17 is a flowchart illustrating the main control operations of the electronic control device 70 of FIG. 5, showing the diastolic blood pressure estimation routine of FIG. 16. [Figure 19] 6 is a flowchart illustrating a main part of the control operation of the electronic control device 70 of FIG. 5, showing blood pressure monitoring control. [Figure 20] 7 is a time chart illustrating another control operation of the electronic control device 70 of FIG. 5, and corresponds to FIG. 6. FIG. [Figure 21] 6 is a diagram illustrating changes in the shape of the pulse wave during the process of reducing the compression pressure by the compression pressure control unit of FIG. 5. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0033] An embodiment of the present invention will be described in detail below with reference to the drawings. Note that in the following embodiment, the drawings are appropriately simplified or modified, and the dimensional ratios and shapes of the various parts are not necessarily drawn accurately. [Example]

[0034] 1 shows a blood pressure measurement device (diastolic blood pressure estimation device) 10 according to an example of the present invention, which includes an upper arm compression cuff 12 wrapped around a compressed part of a limb, such as an arm or ankle, of a living subject 14, e.g., the upper arm 16. This blood pressure measurement device 10 sequentially extracts pulse waves (volume pulse waves), which are pressure oscillations of the compression pressure Pc in the compression cuff 12 that occur in response to changes in the volume of the arterial blood vessel 18, during the process of lowering the compression pressure Pc of the compression cuff 12 that has been increased to a value sufficient to occlude the arterial blood vessel 18 in the upper arm 16, and measures the systolic blood pressure value SAP and diastolic blood pressure value DAP of the living subject 14 based on information obtained from the pulse waves.

[0035] Figure 2 is a cutaway view of the compression belt 12 showing a portion of the outer peripheral side nonwoven fabric 20a. As shown in Figure 2, the compression belt 12 comprises a strip-shaped outer bag 20 consisting of an outer peripheral side nonwoven fabric 20a and an inner peripheral side nonwoven fabric 20b made of synthetic resin fiber, the back surfaces of which are laminated together with a synthetic resin such as PVC (polyvinyl chloride), and an upstream inflatable bag 22, an intermediate inflatable bag 24, and a downstream inflatable bag 26, which are sequentially contained in the width direction within the strip-shaped outer bag 20 and are made of a flexible sheet such as a soft polyvinyl chloride sheet, and are capable of independently compressing the upper arm 16. The compression belt 12 is removably attached to the upper arm 16 by removably adhering a hook-and-loop fastener 28a attached to the end of the outer peripheral side nonwoven fabric 20a to a raised pile 28b attached to the end of the inner peripheral side nonwoven fabric 20b.

[0036] The upstream inflation bag 22, the intermediate inflation bag 24, and the downstream inflation bag 26 are connected in the width direction of the longitudinal compression belt 12, and each have an independent air chamber that compresses the upper arm 16. The tube connection connectors 32, 34, and 36 are provided on their outer circumferential surfaces. The tube connection connectors 32, 34, and 36 are exposed to the outer circumferential surface of the compression belt 12 through the outer circumferential side nonwoven fabric 20a.

[0037] Fig. 3 is a plan view showing the upstream inflation bag 22, intermediate inflation bag 24, and downstream inflation bag 26 provided in the compression belt 12, and Fig. 4 is a cross-sectional view taken along the line IV-IV of Fig. 3. The upstream inflation bag 22, intermediate inflation bag 24, and downstream inflation bag 26 are used to detect pulse waves, which are pressure vibrations generated in response to changes in the volume of the arterial blood vessel 18 compressed by them, and each is longitudinally shaped. The upstream inflation bag 22 and downstream inflation bag 26 are disposed adjacent to both sides of the intermediate inflation bag 24, and the intermediate inflation bag 24 is disposed in the widthwise center of the compression belt 12, sandwiched between the upstream inflation bag 22 and the downstream inflation bag 26. The centers of the upstream inflation bag 22 and the intermediate inflation bag 24 are separated by a distance L12, and the centers of the upstream inflation bag 22 and the downstream inflation bag 26 are separated by a distance L13. When the compression belt 12 is wrapped around the upper arm 16, the upstream inflation bag 22 and the downstream inflation bag 26 are positioned at a predetermined distance in the longitudinal direction of the upper arm 16, and the intermediate inflation bag 24 is positioned between the upstream inflation bag 22 and the downstream inflation bag 26 so as to be connected in the longitudinal direction of the upper arm 16.

[0038] The intermediate inflation bag 24 has side edges with a so-called gusset structure on both sides. That is, a pair of fold grooves 24f, 24g made of a flexible sheet are formed at both ends of the intermediate inflation bag 24 in the longitudinal direction of the upper arm 16 (i.e., in the width direction of the compression belt 12). The fold grooves 24f, 24g are made of a flexible sheet that is folded toward each other so that the fold grooves become deeper as they approach each other. The ends 22a, 26a of the upstream inflation bag 22 and the downstream inflation bag 26 that are adjacent to the intermediate inflation bag 24 are inserted into the fold grooves 24f, 24g, respectively. This results in an overlapping structure in which the end 24a of the intermediate inflation bag 24 overlaps the end 22a of the upstream inflation bag 22, and the end 24b of the intermediate inflation bag 24 overlaps the end 26a of the downstream inflation bag 26. Therefore, when the upstream inflation bag 22, the intermediate inflation bag 24, and the downstream inflation bag 26 compress the upper arm 16 with equal pressures, uniform pressure distribution is achieved near their boundaries.

[0039] The upstream and downstream inflation bags 22 and 26 also have gusseted side edges at their ends 22b and 26b opposite the intermediate inflation bag 24. Specifically, the end 22b of the upstream inflation bag 22 opposite the intermediate inflation bag 24 has a fold groove 22f made of a flexible sheet folded toward each other so that the grooves become deeper as they approach each other. Similarly, the end 26b of the downstream inflation bag 26 opposite the intermediate inflation bag 24 has a fold groove 26g made of a flexible sheet folded toward each other so that the grooves become deeper as they approach each other. To prevent the sheet from protruding in the width direction of the compression belt 12, the sheet constituting the fold groove 22f is connected to the opposite side, i.e., the side facing the intermediate inflation bag 24, via a connecting sheet 38 with a through hole disposed in the upstream inflation bag 22. Similarly, the sheet constituting the fold groove 26g is connected to the opposite side, i.e., the side facing the intermediate inflation bag 24, via a connecting sheet 40 with a through hole disposed in the downstream inflation bag 26.

[0040] As a result, the compression pressure Pc on the arterial blood vessel 18 of the upper arm 16 is applied to the ends 22b, 26b of the upstream inflatable bag 22 and the downstream inflatable bag 26 in the same manner as in other parts, so that the effective compression width in the width direction of the compression belt 12 is equal to the width of the compression belt 12. The compression belt 12 is approximately 12 cm wide, and because the three inflatable bags (upstream inflatable bag 22, intermediate inflatable bag 24, and downstream inflatable bag 26) are arranged in that width direction, each of them must essentially have a width of approximately 4 cm. To fully generate compression function even with such a narrow width, both ends 24a, 24b of the intermediate inflatable bag 24 overlap with the end 22a of the upstream inflatable bag 22 and the end 26a of the downstream inflatable bag 26, forming an overlap structure, and the ends 22b, 26b of the upstream inflatable bag 22 and the downstream inflatable bag 26 opposite the intermediate inflatable bag 24 form side edges with a so-called gusset structure.

[0041] Between the ends 22a, 26a of the upstream and downstream inflation bags 22, 26, which are on the intermediate inflation bag 24 side, and the inner wall surfaces, i.e., the opposing groove side surfaces, of the pair of folding grooves 24f, 24g into which they are inserted, are interposed longitudinal shielding members 42n, 42m, each of which has anisotropic rigidity such that the bending rigidity in the width direction of the compression belt 12 is higher than the bending rigidity in the longitudinal direction of the compression belt 12. The shielding member 42n has a length dimension similar to the overlapping dimension between the upstream inflation bag 22 and the intermediate inflation bag 24. Similarly, the shielding member 42m has a length dimension similar to the overlapping dimension between the downstream inflation bag 26 and the intermediate inflation bag 24.

[0042] 3 and 4, longitudinal shielding members 42n, 42m are interposed in the outer peripheral gap between the end 22a of the upstream inflatable bag 22 and the folding groove 24f into which it is inserted, and in the outer peripheral gap between the end 26a of the downstream inflatable bag 26 and the folding groove 24g into which it is inserted. In this embodiment, the outer peripheral gap has a greater shielding effect than the inner peripheral gap, so the longitudinal shielding members 42n, 42m are provided in the outer peripheral gap, but they may also be provided in both the outer peripheral gap and the inner peripheral gap.

[0043] Shielding members 42n, 42m are formed by arranging multiple flexible hollow resin tubes 44 parallel to one another in the longitudinal direction of the upper arm 16 (i.e., the width direction of the compression belt 12) in a row in the circumferential direction of the upper arm 16 (i.e., the longitudinal direction of the compression belt 12), and connecting the flexible hollow tubes 44 directly by molding or bonding, or indirectly via other members such as flexible sheets such as adhesive tape. Shielding member 42n is hooked onto multiple hanging sheets 46 provided at multiple locations on the outer periphery of end 22a of upstream inflation bag 22, which faces the intermediate inflation bag 24. Similarly, shielding member 42m is hooked onto multiple hanging sheets 46 provided at multiple locations on the outer periphery of end 26a of downstream inflation bag 26, which faces the intermediate inflation bag 24.

[0044] Returning to FIG. 1 , in blood pressure measurement device 10, air pump 50, quick exhaust valve 52, and exhaust control valve 54 are each connected to main pipe 56. A first branch pipe 58 connected to upstream inflation bag 22, a second branch pipe 62 connected to intermediate inflation bag 24, and a third branch pipe 64 connected to downstream inflation bag 26 branch off from main pipe 56. First branch pipe 58 is equipped with a first on-off valve E1 for directly opening and closing communication between air pump 50 and upstream inflation bag 22. Second branch pipe 62 is equipped with a second on-off valve E2 for directly opening and closing communication between air pump 50 and intermediate inflation bag 24. Third branch pipe 64 is equipped with a third on-off valve E3 for directly opening and closing communication between air pump 50 and downstream inflation bag 26.

[0045] A first pressure sensor T1 is connected to the first branch pipe 58 to detect the pressure value in the upstream inflation bag 22, a second pressure sensor T2 is connected to the second branch pipe 62 to detect the pressure value in the intermediate inflation bag 24, a third pressure sensor T3 is connected to the third branch pipe 64 to detect the pressure value in the downstream inflation bag 26, and a fourth pressure sensor T4 is connected to the main pipe 56 to detect the compression pressure Pc of the compression cuff 12.

[0046] The electronic control device 70 is supplied with an output signal from the first pressure sensor T1 indicating the pressure value in the upstream inflation bag 22, i.e., the compression pressure Pc1 of the upstream inflation bag 22, an output signal from the second pressure sensor T2 indicating the pressure value in the intermediate inflation bag 24, i.e., the compression pressure Pc2 of the intermediate inflation bag 24, an output signal from the third pressure sensor T3 indicating the pressure value in the downstream inflation bag 26, i.e., the compression pressure Pc3 of the downstream inflation bag 26, and an output signal from the fourth pressure sensor T4 indicating the compression pressure Pc of the compression belt 12.

[0047] The electronic control device 70 is a so-called microcomputer including a CPU 72, RAM 74, ROM 76, display device 78, and an I / O port (not shown). The CPU 72 processes input signals in accordance with a program pre-stored in the ROM 76 while utilizing the storage function of the RAM 74. In response to operation of a blood pressure estimation start button 80, the electronic control device 70 controls the electric air pump 50, the rapid exhaust valve 52, the exhaust control valve 54, the first on-off valve E1, the second on-off valve E2, and the third on-off valve E3, thereby executing automatic blood pressure measurement control and displaying the measurement results on the display device 78. Figure 6 shows the change in the compression pressure Pc of the compression cuff 12 controlled by the compression pressure control unit 86 of the electronic control device 70.

[0048] (Explanation of diastolic blood pressure estimation algorithm) The diastolic blood pressure estimation algorithm executed by the electronic control unit 70 function shown in FIG. 5 will now be described.

[0049] FIG. 7 shows a model of an arterial blood vessel 18 showing the relationship between transmural pressure Pt and the cross-sectional area A of the arterial blood vessel 18. As the transmural pressure Pt increases, the cross-sectional area A increases exponentially toward a saturation value Am, and when the transmural pressure Pt is zero, it indicates the Ao value. The characteristic showing the relationship between the transmural pressure Pt of the arterial blood vessel 18 in FIG. 7 and the cross-sectional area A of the arterial blood vessel 18 is expressed by the following vascular model formula. The transmural pressure Pt is the value (AP-Pc) obtained by subtracting the external arterial pressure, i.e., the compression pressure (cuff pressure) Pc, from the intra-arterial pressure AP. The transmural pressure Pt at the time of diastolic blood pressure in a living body is the value (DAP-Pc) obtained by subtracting the compression pressure Pc from the diastolic blood pressure DAP. Formula (a1) is described in Non-Patent Document 3. In formula (a1), b is an index related to vascular hardness (compliance or elasticity). A=Am+(Ao-Am)e^(-b·Pt) ··· (a1)

[0050] The theoretical nonlinear exponential curve equation (1) obtained by applying the Bramwell-Hill equation to this vascular model equation (a1) is the transmural pressure Pt and the squared value of pulse wave velocity PWV obtained in the goat experiment. 2The relationship between the exponential curve and the cross-sectional area ratio Ao / Am is very similar to the exponential curve. The relationship shown by switching the horizontal and vertical axes of the exponential curve becomes a logarithmic function, and the logarithmic function approximation curve, which can be accurately approximated to the logarithmic function, can be converted into a linear regression line (2) that is independent of the constant b or the cross-sectional area ratio Ao / Am. The transmural pressure Pt of the arterial blood vessel 18 at the time of diastolic pressure is (estimated diastolic pressure DAPe - compression pressure Pc), so the arterial transmural pressure Pt and the squared value of the pulse wave velocity PWV 2 The linear regression line (2) that expresses the relationship between the transmural pressure Pt and the pressure Pc can be transformed into the equation (3). Since the slope α of the equation (3) is the same as that of the equation (2), the squared value of the compression pressure Pc and the pulse wave velocity PWV 2 The slope α can be determined by performing a regression analysis between the slope α and the intercept β. The intercept β can be determined by substituting the slope α into the previously determined linear relationship (4) between the slope α and the intercept β. Once the slope α and the intercept β are determined in this way, the diastolic blood pressure DAPe can be expressed by the diastolic blood pressure estimation equation (5), which is a modification of equation (3) for the transmural pressure Pt. From this diastolic blood pressure estimation equation (5), the squared value PWV of the actual pulse wave velocity can be calculated. 2 The diastolic blood pressure value DAPe is estimated based on the compression pressure Pc.

[0051] PWV 2 =(1 / ρ·b)(1 / (1-Ao / Am))·e^(b·Pt) -(1 / ρ b) (1)

[0052] This nonlinear exponential function formula (1) is based on formula (a1) which shows the relationship between the transmural pressure Pt (=DAP-Pc) at the time of diastolic pressure of the arterial blood vessel 18 and the cross-sectional area A of the arterial blood vessel 18, as shown in Figure 7. In formula (1), ρ represents blood density.

[0053] The following new vascular model equation (a2), which is obtained by differentiating both sides of equation (a1) with respect to Pt, together with the well-known Bramwell-Hill equation (a3) ​​and equation (a4), which differentiates the volume V of the arterial blood vessel 18 with respect to the cross-sectional area A, can be used to summarize the three equations to obtain equation (a5) shown below. L in equation (a4) represents the effective length of the arterial blood vessel 18 in the upper arm. dA / dPt=-b(Ao-Am)e^(-b·Pt) ··· (a2) PWV 2 =(dPt / ρ) (V / dV) (a3) dV=dA·L (a4) PWV 2 =(1 / ρb)(1 / (1-Ao / Am))·e^(b·Pt) -(1 / ρb) (a5)

[0054] In this equation (a5), the variable related to the cross-sectional area A is the ratio Ao / Am of the saturated value Am of the cross-sectional area A to the cross-sectional area Ao when the transmural pressure Pt is zero. Therefore, the PWV in equation (a5) is 2 The relationship between Pt and Pt is not affected by the absolute value of the cross-sectional area A of the arterial blood vessel 18. In other words, it is thought to be unaffected by the physique of each individual living organism. The relationship in equation (a5) depends on the cross-sectional area ratio Ao / Am of the arterial blood vessel 18 and a constant b related to the hardness of the arterial blood vessel 18.

[0055] Previous research has reported that b = 0.03 and Ao / Am = 0.25, so when we performed a numerical simulation of the relationship in equation (a5) assuming b = 0.03, 0.06, 0.09, Ao / Am = 0.25, 0.5, the result was as shown in Figure 8.

[0056] To consider the relationship between the constant b and the cross-sectional area ratio Ao / Am, we reciprocally convert both sides of equation (a2) to equation (a6), which shows that as the constant b increases, dPt / dA, i.e., the elastic modulus, increases within a given range for a given transmural pressure Pt. dPt / dA=e^(b·Pt) / b(Am-Ao) ··· (a6)

[0057] The inventors conducted an experiment in which the above-mentioned compression cuff 12 was attached to the front leg (upper arm) of a goat whose blood pressure was changed with medication for each measurement, and the compression cuff 12 was used to measure the compression pressure Pc and the pulse wave velocity PWV based on the time difference between the pulse wave obtained from the upstream inflation bag 22 and the pulse wave obtained from the downstream inflation bag 26 for each pressure step. The squared value PWV of the obtained pulse wave velocity PWV 2 The relationship between the transmural pressure Pt and the stenosis pressure Pt was very similar to that shown in FIG.

[0058] The theoretical relationship in Figure 8 above becomes the relationship shown in Figure 9 when the vertical and horizontal axes are interchanged, and can be approximated by the logarithmic function shown by the dashed line, regardless of the constant b or the cross-sectional area ratio Ao / Am of the arterial blood vessel 18. The coefficient of determination R of this logarithmic function approximation curve 2 The squared value of the pulse wave velocity PWV obtained using the goat is 0.97-0.99, which can be approximated with high accuracy. 2 The relationship between the transmural pressure Pt and the coefficient of determination R 2 The average coefficient of determination for all 23 logarithmic function approximation curves was 0.91±0.11, indicating that a very good logarithmic function approximation curve was obtained. Such a logarithmic function approximation curve uses the squared value of pulse wave velocity (PWV) as the independent variable. 2 Logarithm of (ln(PWV 2 )), it can be expressed by the linear regression line (2) converted into a linear form. The same is true for humans. Pt = α·ln(PWV 2 )+β (2)

[0059] Here, the slope α of the logarithmic function approximation curve shown in Figure 10 is expressed as ln(PWV 2) and -Pc. By substituting transmural pressure Pt = DAP - Pc into the left side of equation (2), it can be converted to the following equation (3) for the linear regression line -Pc. In this way, equation (3) for the linear regression line -Pc converted from equation (2) for the linear regression line Pt, i.e., conversion equation (3), can be obtained as a linear regression line of multiple data points representing the measurable pulse wave velocity PWV and the compression pressure Pc when that pulse wave velocity PWV was actually measured, and by determining the slope of the obtained linear regression line, the above-mentioned slope α for each subject can be calculated. -Pc=α·ln(PWV 2 )+(β-DAP) (3)

[0060] When the relationship between the slope α and intercept β of the six logarithmic functions in Figure 9 is plotted using six data points representing each slope α and intercept β, it is expressed as a regression line shown by the dashed line in Figure 11. This result can be said to have theoretically confirmed that the slope α and intercept β of the logarithmic function are linearly correlated even when the index b related to vascular stiffness and the cross-sectional area ratio Ao / Am of the arterial blood vessel 18, which are constants specific to the biological state, are varied over a wide range. Similarly, when the relationship between the slope α and intercept β of the 23 logarithmic functions obtained from the experiment using the goat's upper arm shown in Figure 10 is plotted, it is also clear that there is a linear correlation, as shown in Figure 12. This reveals that PWV 2 When the relationship between Pt and Pt is approximated by a logarithmic function, if a stable linear correlation between the slope α and intercept β can be obtained regardless of the state of the living body, it can be used to estimate the intercept β of the logarithmic function.

[0061] Therefore, we used experimental data from seven goats' upper arms to calculate the PWV of 111 data sets. 2 Figure 13 shows the linear relationship between the slope α and intercept β when the relationship between Pt and β is approximated by a logarithmic function. The numbers shown on the right side of Figure 13 are the individual identification numbers of the seven goats. In Figure 13, when y of the linear relationship is β and x is α, the linear regression line is y = -1.921x + 11.4, as shown by the dashed line in Figure 13, and the coefficient of determination of this linear regression line is R 2The PWV of 90 data points obtained from 30 subjects was 0.86. 2 The linear relationship between the slope α and the intercept β when the relationship between Pt and Pt is approximated by a logarithmic function is shown in Figure 14. The linear regression line shown by the dashed straight line in Figure 14 is y = -3.6137x + 14.833, and the coefficient of determination of this linear regression line R 2 was 0.7071. As is clear from Figures 13 and 14, the same linear relationship can be approximated regardless of the individual living body, and the following linear relationship (4) was experimentally obtained. The linear relationship (4) showing the constant relationship between this slope α and intercept β is previously calculated and stored in the linear relationship storage unit 84 described below. The slope γ of the linear relationship (4) is, for example, -3.6137, and the intercept δ is, for example, 14.833. β=γ α+δ (4)

[0062] In this way, regardless of the state of the individual body, the squared value of the pulse wave velocity PWV 2 If the relationship between the transmural pressure Pt and the pressure Pc can be roughly approximated by equation (2), then the intercept β can be calculated by substituting the slope α calculated from equation (2) or its modified equation (3) based on the measured compression pressure Pc and pulse wave velocity PWV into the linear relationship equation (4). By modifying equation (3), the following diastolic blood pressure estimation equation (5) is obtained. Therefore, by substituting the obtained slope α and intercept β, the measured PWV and the compression pressure Pc at the time of measurement into equation (5), the estimated diastolic blood pressure value DAPe can be obtained. DAPe = α·ln(PWV 2 )+(β+Pc) (5)

[0063] Figure 15 shows the correlation between the diastolic blood pressure (DAPe) estimated by equation (5) from the pulse wave velocity (PWV) and compression pressure (Pc) actually measured for 30 people, and the diastolic blood pressure (DAP) measured by blood pressure measurement using Korotkoff sound auscultation. The linear regression line passing through the 90 data points is y = 1.0094x - 1.2482, as shown by the solid line in Figure 15, and the coefficient of determination of this linear regression line is R 2 was 0.6416.

[0064] Returning to Fig. 5, Fig. 5 is a functional block diagram illustrating the main control functions of the electronic control device 70. In Fig. 5, the electronic control device 70 functionally comprises a linear regression line storage unit 82, a linear relationship storage unit 84, a compression pressure control unit 86, a pulse wave extraction unit 88, a pulse wave velocity calculation unit 90, a specific relationship generation unit 94, a blood pressure estimation unit 102, and a blood pressure fluctuation determination unit 108.

[0065] The linear regression line storage unit 82 stores in advance the equation (3) of the linear regression line -Pc converted from the equation (2) of the linear regression line Pt, i.e., the conversion equation (3). The linear relationship storage unit 84 stores in advance the linear relationship equation (4) between the slope α and the intercept β, in which the constant slope γ and intercept δ are set empirically and experimentally.

[0066] In response to operation of the blood pressure estimation start operation button 80, the compression pressure control unit 86 first closes the rapid exhaust valve 52 and the exhaust control valve 54, opens the first on-off valve E1, the second on-off valve E2, and the third on-off valve E3, and operates the air pump 50 to rapidly increase the compression pressure Pc of the compression cuff 12 on the living body 14 to a pressure sufficiently higher than the systolic blood pressure value SAP of the living body 14, for example, to a preset upper pressure limit PCM of 180 mmHg, in order to obtain the actual pulse wave velocity PWV for each of the multiple compression pressures Pc near the diastolic blood pressure DAP during the compression pressure Pc decrease period.

[0067] Next, the compression pressure controller 86 repeatedly opens the exhaust control valve 54 for a predetermined period at a predetermined cycle to gradually decrease the compression pressure Pc of the compression cuff 12 in a stepwise manner at a predetermined rate until the compression pressure Pc of the compression cuff 12 becomes smaller than the predetermined reduced pressure limit PCE, such that a plurality of constant step pressures P1, P2, P3, ... Px are sequentially maintained at predetermined increments of approximately 2 to 5 mmHg until the compression pressure Pc of the compression cuff 12 reaches a pressure sufficiently lower than the diastolic blood pressure DAP of the living body 14, for example, a predetermined reduced pressure limit PCE of approximately 40 to 60 mmHg. The compression pressure Pc of the compression cuff 12 thus controlled is applied to the living body 14 by the upstream inflation bag 22, the intermediate inflation bag 24, and the downstream inflation bag 26, but FIG. 6 shows the compression pressure Pc of the compression cuff 12 detected by the fourth pressure sensor.

[0068] After the specific relationship generating unit 94 described below has generated, for example, the aforementioned diastolic blood pressure estimation equation (5), the compression pressure control unit 86 controls the compression pressure Pc in response to a blood pressure monitoring start operation so as to maintain the compression pressure Pc at a monitoring maintenance pressure PcHm that is preferably set to a pressure sufficiently lower than the diastolic blood pressure value DAP of the living body 14, for example, in the range of 20 to 60 mmHg, in order to monitor the diastolic blood pressure value of the living body 14. The monitoring maintenance pressure PcHm is set to a value as low as possible within a range in which the pulse wave included in the compression pressure Pc of the compression cuff 12 can be reliably obtained.

[0069] When the monitor pressure maintenance period ends, the compression pressure control unit 86 uses the quick exhaust valve 52 to exhaust the pressure in the upstream inflation bag 22, the intermediate inflation bag 24, and the downstream inflation bag 26 to atmospheric pressure.

[0070] During the interval in which the compression pressure Pc is maintained, the pulse wave extraction unit 88 extracts and stores a pair of pulse waves MW1 and MW3 from the output signal from the first pressure sensor T1 indicating the compression pressure Pc1 in the upstream inflation bag 22 and the output signal from the third pressure sensor T3 indicating the compression pressure Pc3 in the downstream inflation bag 26, passing them through a pulse wave discrimination bandpass filter of, for example, 0.5 Hz to 20 Hz. The pair of pulse waves MW1 and MW3 are pressure oscillation waves that occur in synchronization with the pulse and are superimposed on the compression pressure Pc. The pulse wave extraction unit 88 associates the pulse waves MW1 and MW3 with the compression pressure Pc at the time they occurred and stores them.

[0071] The pulse wave velocity calculation unit 90 sequentially calculates the pulse wave velocity PWV (= L13 / Δt) for each of a plurality of preset step pressures for each pulse wave, based on the time difference Δt between the rising or peak points of a pair of pulse waves MW1 and MW3 obtained while the compression pressure Pc is maintained and the known distance L13 between the upstream inflation bag 22 and the downstream inflation bag 26. The plurality of preset step pressures are a predetermined number (e.g., six) of consecutive step pressures starting from a pressure value (equivalent to diastolic blood pressure) calculated from a step pressure having an amplitude that is a predetermined percentage of the maximum amplitude of the step pressure (equivalent to mean blood pressure) at which the amplitude of the pulse wave extracted by the pulse wave extraction unit 88 is maximum as the compression pressure Pc of the compression cuff 12 decreases. Alternatively, the above-mentioned plurality of preset step pressures may be a predetermined number (e.g., six) of consecutive step pressures that are a predetermined number (e.g., two) of step pressures after the step pressure at which the amplitude of the pulse wave extracted by the pulse wave extraction unit 88 reaches its maximum value as the compression pressure Pc of the compression cuff 12 decreases.

[0072] The pulse wave velocity calculation unit 90 stores, for each of the predetermined number of step pressures, a set of data: the pulse wave velocity PWV (=L13 / Δt) calculated for each occurrence of a pulse wave from the time difference Δt between the rising points or peak points of a pair of pulse waves MW1 and MW3 obtained while the compression pressure Pc is maintained and the known distance L13 between the upstream inflation bag 22 and the downstream inflation bag 26; and the step pressure, i.e., the compression pressure Pc, at which the pulse wave occurred.

[0073] The compression pressure Pc for each step pressure may be the average of the cuff pressures Pc corresponding to the rising points of multiple pulse waves within a step. Alternatively, the pulse wave velocity PWV may be calculated from the slope of a regression line obtained by linearly regressing a known distance L12 between the upstream inflation bag 22 and the intermediate inflation bag 24 and the time difference Δt1 between the rising points of the pulse wave, and a known distance L13 between the upstream inflation bag 22 and the downstream inflation bag 26 and the time difference Δt3 between the rising points of the pulse wave, using the upstream inflation bag 22 as the reference point, in a two-dimensional coordinate system with the time difference between the rising points of a pair of pulse waves as the horizontal axis and the distance between the inflation bags as the vertical axis.

[0074] The characteristic relationship generating unit 94 includes a slope α calculating unit 96, an intercept β calculating unit 98, and a diastolic blood pressure estimation equation setting unit 100.

[0075] The slope α calculation unit 96 calculates the slope α by 2 In a two-dimensional coordinate system with an axis representing -Pc and an axis representing -Pc, the logarithm ln(PWV) of the square of the pulse wave velocity PWV (= L / Δt) stored for each of the predetermined number of step pressures (for example, six) is calculated. 2 By performing a linear regression analysis of six measured data points representing six sets of measured data between the pressure Pc and the step pressure, i.e., compression pressure Pc, at which the pulse wave occurred, the coefficient value of the first term on the right-hand side of equation (3) for the linear regression line -Pc is determined as the slope α.

[0076] The intercept β calculation unit 98 calculates the intercept β based on the slope α calculated from the linear relational expression (4) by the slope α calculation unit 96. That is, the intercept β is calculated by substituting the slope α calculated by the slope α calculation unit 96 into the linear relational expression (4).

[0077] The diastolic blood pressure estimation equation setting unit 100 substitutes the slope α calculated by the slope α calculation unit 96 and the intercept β calculated by the intercept β calculation unit 98 into equation (5) converted from the linear regression line equation (2), and sets and stores the diastolic blood pressure estimation equation (5) that reflects the inherent relationship of the living body.

[0078] The blood pressure estimation unit 102 includes a diastolic blood pressure estimation unit 104 that performs blood pressure estimation, for example, during the period from time t2 to time t11 in FIG. 6 where the compression pressure is increased or decreased, or during the monitoring period from time tm1 onward where the monitor pressure PcHm is maintained. The diastolic blood pressure estimation unit 104 repeatedly calculates the estimated diastolic blood pressure value DAPe by substituting the pulse wave velocity PWV and compression pressure Pc, which are actually measured at a predetermined interval, for example, from one pulse cycle to several dozen pulse cycles, into the diastolic blood pressure estimation equation (5). Alternatively, a moving average of the calculated diastolic blood pressure values ​​DAPe may be calculated. The diastolic blood pressure estimation unit 104 displays the calculated estimated diastolic blood pressure values ​​DAPe chronologically on the display device 78.

[0079] The blood pressure fluctuation determination unit 108 determines the occurrence of blood pressure fluctuation in the living body based on the fact that the change in pulse wave velocity PWV falls outside the predetermined fluctuation determination range PWV1 to PWVh during the monitoring period in which the monitor pressure PcHm is maintained from time tm1 onwards in Figure 6, or based on the fact that the change in the estimated diastolic blood pressure DAPe falls outside the predetermined fluctuation determination range DAPe1 to DAPeh, and displays the occurrence of blood pressure fluctuation in the living body on the display device 78.

[0080] Figures 16, 17, 18, and 19 are flowcharts explaining the main control operations of the electronic control device 70. Figure 16 shows the control for setting a diastolic blood pressure estimation formula and collecting actual measurement data for calculating and estimating diastolic blood pressure, Figure 17 shows the diastolic blood pressure estimation formula setting routine of Figure 16, Figure 18 shows the diastolic blood pressure estimation routine of Figure 16, and Figure 19 shows blood pressure monitoring control.

[0081] When operation button 80, which starts setting the diastolic blood pressure estimation formula, is turned on, in step S1 (hereinafter, "step" will be omitted) corresponding to compression pressure control unit 86, compression pressure Pc of compression cuff 12 is increased. Specifically, as shown in FIG. 6 , rapid exhaust valve 52 and exhaust control valve 54 are closed, and air pump 50 is activated, which sends compressed air to main pipe 56, which rapidly increases the pressure in upstream inflation bag 22, intermediate inflation bag 24, and downstream inflation bag 26 connected thereto, and compression of upper arm 16 by compression cuff 12 begins.

[0082] Next, in S2 corresponding to the compression pressure control unit 86, it is determined whether the compression pressure Pc of the compression cuff 12 is equal to or greater than a preset target pressure PCM (e.g., 180 mmHg) that is equal to or greater than the systolic blood pressure of the living body, based on the output signal of the fourth pressure sensor T4 indicating the compression pressure Pc. Before time t2 in Figure 6, the determination in S2 above is negative, and S1 and subsequent steps in Figure 16 are repeatedly executed.

[0083] If the compression pressure Pc reaches the target pressure PCM and the determination in S2 is affirmative, S3, corresponding to the compression pressure control unit 86, stops the air pump 50 and activates the exhaust control valve 54 and the first, second, and third on-off valves E1, E2, and E3 to slowly exhaust the compression pressure Pc of the compression cuff 12 in a stepwise manner, with predetermined step pressures P1, P2, P3, . . . Px, each set at a fixed interval, e.g., 2-5 mmHg / sec. To maintain the step pressures P1, P2, P3, . . . Px, the first, second, and third on-off valves E1, E2, and E3 are closed. Time t2 in Figure 6 marks the start of the slow exhaust, and the period between t3 and t4 indicates the time during which the compression pressure Pc of the compression cuff 12 is maintained at the step pressure P1 for a predetermined period, e.g., two heartbeats.

[0084] Next, in S4 corresponding to pulse wave extraction unit 88, pulse waves are extracted during the intervals during which compression pressures P1, P2, P3, ..., Px are maintained for a predetermined period of time. Specifically, the output signals from first pressure sensor T1, second pressure sensor T2, and third pressure sensor T3 are subjected to pulse wave collection bandpass filtering, which discriminates signals in a wavelength band of, for example, 0.5 Hz to less than 20 Hz, to extract pulse wave signals MW1, MW2, and MW3 representing pulse waves from upstream inflation bag 22, intermediate inflation bag 24, and downstream inflation bag 26. The output signal from fourth pressure sensor T4 is also subjected to lowpass filtering, for example, in a wavelength band of less than several Hz, to extract compression pressure Pc of compression cuff 12 from which AC components have been removed. This compression pressure Pc represents the step pressure at that time, and the pulse wave signals MW1, MW2, and MW3 are stored sequentially for each step along with the compression pressure Pc at that time. At each step, a plurality of pulse wave signals MW1, MW2, and MW3 are stored.

[0085] In S5, which corresponds to the compression pressure control unit 86, it is determined whether the compression pressure Pc is equal to or less than a preset measurement end pressure value PCE (e.g., 60 mmHg). If the determination in S5 is negative, i.e., before time t11 in FIG. 6, the determination in S5 is negative and S3 and subsequent steps are repeatedly executed. If the determination in S5 is positive, rapid exhaust is initiated in S6 at time t11.

[0086] Next, in S7 corresponding to the pulse wave velocity measurement step or the pulse wave velocity calculation unit 90, the pulse wave velocity PWV (= L13 / Δt) is calculated sequentially for each pulse wave occurrence from the time difference Δt between the rising or peak points of a pair of pulse waves MW1 and MW3 obtained at multiple (e.g., six) consecutive step pressures from pressure values ​​(values ​​corresponding to mean blood pressure) calculated from step pressures having an amplitude that is a predetermined percentage of the maximum amplitude based on the step pressure value (value corresponding to mean blood pressure) at which the amplitude of the pulse wave extracted by the pulse wave extraction unit 88 is maximized as the compression pressure Pc of the compression cuff 12 is reduced, or from multiple (e.g., six) consecutive step pressures after a predetermined number (e.g., two) steps from the step pressure at which the amplitude of the pulse wave extracted by the pulse wave extraction unit 88 is maximized as the compression pressure Pc of the compression cuff 12 is reduced. The pulse wave velocity PWV is the logarithm of the squared value ln(PWV 2 ) and the logarithm of the squared value ln(PWV 2 ) and the compression pressure Pc at the time of pulse wave generation used to calculate the pulse wave velocity PWV at that time are used to create a set of actual measurement data [ln(PWV 2 ), Pc], and one set of actual measurement data [ln(PWV1 2 ), Pc1)····〔ln(PWVn 2 ), Pcn] are stored.

[0087] Next, in S8 corresponding to the inherent relationship generating unit 94 or the inherent relationship generating step, the diastolic blood pressure estimation equation setting routine shown in Fig. 17 is started. In Fig. 17, in S81 corresponding to the slope α calculating unit 96 or the slope calculating step, a plurality of sets (six sets in this embodiment) of actual measurement data [ln(PWV 2 ), Pc1)····〔ln(PWVn 2 ), Pcn], the coefficient value of the first term on the right side of equation (3) of the linear regression line -Pc, which is obtained approximately by regression analysis, can be calculated as the slope α.

[0088] Next, in S82 corresponding to the intercept β calculation unit 98 or the intercept calculation step, the slope α calculated in S81 is substituted for x in the linear relation equation (4) stored in advance in the linear relation storage unit 84, thereby calculating y, i.e., the intercept β.

[0089] In S83, which corresponds to the diastolic blood pressure estimation equation setting unit 100 or the diastolic blood pressure estimation equation setting step, the slope α calculated in S81 and the intercept β calculated in S82 are substituted into the diastolic blood pressure estimation equation (5), thereby setting and storing the diastolic blood pressure estimation equation (5) that reflects the inherent relationship of the living body from which the actual measurement data was obtained between the diastolic blood pressure DAPe, the pulse wave velocity PWV, and the compression pressure Pc when the diastolic blood pressure DAPe was obtained.

[0090] Then, in S9 corresponding to the diastolic blood pressure estimation unit 104 or the diastolic blood pressure estimation step, the diastolic blood pressure estimation routine shown in FIG. 18 is started. In FIG. 18, in S91, n sets of actual measurement data [ln(PWV1 2 ), Pc1)····〔ln(PWVn 2 ), Pcn)] is substituted into the diastolic blood pressure estimation formula (5), thereby calculating at least one diastolic blood pressure DAPe, which is displayed on the display device 78. In S92, when multiple sets of actual measurement data for multiple steps are substituted into the diastolic blood pressure estimation formula (5), thereby calculating multiple diastolic blood pressures DAPe, the average value of these values ​​is stored as the diastolic blood pressure DAPe and displayed on the display device 78.

[0091] 19 shows a blood pressure monitoring routine that is executed in response to the operation of the blood pressure monitoring mode start operation button 81 after the diastolic blood pressure estimation formula (5) has been set. In FIG. 20, in S31 corresponding to the compression pressure control section 86, the compression pressure Pc of the compression cuff 12 is set to a pressure equal to or lower than the diastolic blood pressure, for example, in the range of 20 to 60 mmHg. The pressure is controlled to a preset constant monitor maintenance pressure PcHm. Next, in S32, which corresponds to the pulse wave extraction unit 88, a pair of pulse waves MW1 and MW3 are extracted for each beat from the signals of the compression pressure Pc1 obtained from the upstream inflation bag 22 and the compression pressure Pc3 obtained from the downstream inflation bag 26, through a bandpass filter for pulse wave discrimination, and the extracted signals are sequentially stored. In S33, which corresponds to the pulse wave velocity calculation unit 90, the pulse wave velocity PWV (= L13 / Δt) is sequentially calculated for each pulse wave generated, based on the time difference Δt between the rising points or peak points of the pair of pulse waves MW1 and MW3 obtained at the monitor maintenance pressure PcH and the known distance L13 between the upstream inflation bag 22 and the downstream inflation bag 26.

[0092] Next, in S34 corresponding to the diastolic blood pressure estimation unit 104 and the diastolic blood pressure estimation step, the logarithm ln(PWV 2 ) is calculated, and a set of actual measurement data [ln(PWV 2 ), PcHm] is constructed. Then, the set of measured data [ln(PWV 2 ), PcHm) into the diastolic blood pressure estimation equation (5), the estimated diastolic blood pressure DAPe is calculated for each pulse wave extraction cycle or at cycles that are an integral multiple of the pulse wave extraction cycle. Then, in S35, the estimated diastolic blood pressure DAPe calculated in S34 is stored and output to the display device 78.

[0093] Next, in S36, the occurrence of blood pressure fluctuations in the subject is determined based on whether the fluctuation range of the pulse wave velocity PWV calculated in S33 falls outside the preset fluctuation determination range PWVl to PWVh, or based on whether the fluctuation range of the estimated diastolic blood pressure DAPe calculated in S34 falls outside the preset fluctuation determination range DAPel to DAPeh. If the determination in S36 is negative, S37 is skipped and S38 and subsequent steps are executed. However, if the determination in S36 is positive, the occurrence of fluctuations in the estimated diastolic blood pressure DAPe is output to the display device 78 in S37.

[0094] Next, in S38, it is determined whether the blood pressure monitoring mode operation button 81 has been operated again. If the determination in S38 is negative, S31 and subsequent steps are repeatedly executed. If the determination is positive, in S39, the compression cuff 12 is rapidly vented and the blood pressure monitoring mode is terminated.

[0095] As described above, in the blood pressure measurement device 10 of this embodiment, the intercept β and slope α included in the linear regression line equation (2) from which the diastolic blood pressure estimation equation (5) is derived have a constant linear relationship with each other as shown in equation (4), and are not affected by the subject. Therefore, the diastolic blood pressure value DAPe can be measured with high accuracy because it is less affected by the subject's individual biological characteristics. Another advantage is that calibration for each subject is not required, as is the case with conventional blood pressure estimation using pulse wave velocity PWV.

[0096] Furthermore, in the blood pressure measurement device 10 of this embodiment, the preset linear regression line equation representing the physical model equation of the arterial blood vessel 18 is expressed by the above-mentioned equation (2). The linear regression line equation (2) is based on the Bramwell-Hill equation (a3) ​​and the physical model equation (a1) of the arterial blood vessel 18, which represents the behavior of actual blood vessels, in which the blood vessel cross-sectional area A is greater than zero when the transmural pressure is zero and increases and saturates as the transmural pressure increases. Therefore, the diastolic blood pressure value DAPe can be measured with high accuracy.

[0097] Furthermore, in the blood pressure measurement device 10 of this embodiment, the conversion equation from the linear regression line equation (2) is expressed by equation (3). Based on this conversion equation (3), the slope α can be calculated by linear regression analysis of the logarithm of the square of the pulse wave velocity PWV obtained by actual measurement and the compression pressure Pc, even if the diastolic blood pressure DAP and the intercept β are unknown.

[0098] Furthermore, in the blood pressure measurement device 10 of this embodiment, the linear relationship is expressed by equation (4). The linear relationship (4) indicates that the intercept β and the slope α included in the linear regression line equation (2) have a constant linear relationship with each other, regardless of the individual, and this relationship is not affected by the subject, so the diastolic blood pressure value DAPe can be measured with high accuracy without being affected by the subject's individual biological characteristics.

[0099] Furthermore, in the blood pressure measurement device 10 of this embodiment, the diastolic blood pressure estimation formula is expressed by formula (5). Formula (5) for estimating diastolic blood pressure has two variables, the measurable compression pressure Pc and the pulse wave velocity PWV, so that the diastolic blood pressure DAPe of the subject can be estimated by substituting the two measured variables.

[0100] Furthermore, according to the blood pressure measurement device 10 of this embodiment, the diastolic blood pressure estimation unit 104 estimates the diastolic blood pressure DAPe of the subject for each of the multiple types of compression pressures (step pressures) applied by the compression cuff 12 based on the actual compression pressure Pc and the pulse wave velocity PWV of the compressed area using the diastolic blood pressure estimation formula (5), and determines the average value of the diastolic blood pressures DAPe obtained for each step pressure as the diastolic blood pressure DAPe, thereby enabling the diastolic blood pressure value to be measured with even greater accuracy.

[0101] Furthermore, according to the blood pressure measuring device 10 of this embodiment, the diastolic blood pressure estimation unit 104 estimates the diastolic blood pressure DAPe of the subject based on the actual compression pressure Pc and the pulse wave velocity PWV of the compressed area, which are obtained at multiple compression pressures applied by the compression cuff 12 and are set lower than the subject's diastolic blood pressure DAP. This reduces the burden (stress) on the subject caused by compression by the compression cuff 12, thereby obtaining stable blood pressure values ​​and improving the accuracy of blood pressure measurement.

[0102] Furthermore, with the blood pressure measurement device 10 of this embodiment, the pulse wave velocity PWV (= L13 / Δt) is calculated for each pulse wave from the time difference Δt between the rising or peak points of a pair of pulse waves MW1 and MW3 detected by a pair of pulse wave sensors (first pressure sensor T1, third pressure sensor T3) positioned at two positions separated by a predetermined distance along the arterial blood vessel 18, and the known distance L13 between the upstream inflation bag 22 and the downstream inflation bag 26. This allows for highly accurate estimation of the diastolic blood pressure DAPe, since there is no error in the delay time (pre-ejection period) from the occurrence of the R wave to the ejection of the heart, compared with the pulse wave velocity calculated based on the occurrence of the electrocardiogram R wave. In other words, because the measured pulse wave velocity PWV purely reflects the characteristics of the arterial blood vessels, it is not affected by fluctuations in the delay time (pre-ejection period), which is also dependent on the state of the heart, resulting in high measurement reproducibility.

[0103] Furthermore, the blood pressure measurement device 10 of this embodiment includes a compression pressure control unit 86 that maintains the compression pressure Pc applied by the compression cuff 12 at a monitor pressure PcHm that is lower than the diastolic blood pressure of the subject, and a blood pressure fluctuation determination unit 108 that determines the occurrence of blood pressure fluctuations based on whether the pulse wave velocity PWV measured while the monitor pressure PcHm is maintained falls within the preset fluctuation determination values ​​PWV1 to PWVh. When the blood pressure fluctuation determination unit 108 determines the occurrence of blood pressure fluctuations, the diastolic blood pressure estimation unit 104 estimates the diastolic blood pressure DAPe of the subject based on the actual compression pressure Pc and the pulse wave velocity PWV of the compressed area using the diastolic blood pressure estimation formula (5). This allows long-term blood pressure monitoring with less strain on the subject. [Example]

[0104] Figure 20 is a time chart illustrating another control operation of the electronic control device 70, and corresponds to Figure 6. In this embodiment, parts common to the previous embodiment are given the same reference numerals and will not be described again. In this embodiment, the method for setting the diastolic blood pressure estimation formula (5) is different, but the rest is the same.

[0105] In Figure 20, in order to set equation (5) for estimating the diastolic blood pressure DAPe of the living body 14 being measured, the compression pressure control unit 86 gradually reduces the compression pressure Pc so that a first maintenance interval (from time tk1 to time tk2) in which a constant first maintenance pressure PcH1 is temporarily maintained, a second maintenance interval (from time tk3 to time tk4) in which a second maintenance pressure PcH2 lower than the first maintenance pressure PcH1 is maintained, and a third maintenance interval (from time tk5 to time tk6) in which a third maintenance pressure PcH3 lower than the second maintenance pressure PcH2 is maintained, are sequentially formed, and then the pressure in the upstream inflation bag 22, the intermediate inflation bag 24, and the downstream inflation bag 26 is each exhausted to atmospheric pressure using the rapid exhaust valve 52. The first maintenance pressure PcH1, the second maintenance pressure PcH2 and the third maintenance pressure PcH3 are low pressures below the diastolic blood pressure value DAP of the subject living body 14, for example, values ​​in multiple stages (three stages in this embodiment) that are preset within the range of 20 to 60 mmHg.

[0106] During the first, second, and third maintenance intervals in which the compression pressure Pc is maintained, the pulse wave extraction unit 88 extracts and stores a pair of pulse waves MW1 and MW3 from the output signal indicating the compression pressure Pc1 in the upstream inflation bag 22 from the first pressure sensor T1 and the output signal indicating the compression pressure Pc3 in the downstream inflation bag 26 from the third pressure sensor T3, passing them through a pulse wave discrimination bandpass filter of, for example, 0.5 Hz to 20 Hz.

[0107] For each of the three first, second, and third maintenance intervals during which compression pressure Pc is maintained, pulse wave velocity calculation unit 90 calculates, as described above, pulse wave velocity PWV (=L13 / Δt) for each pulse wave generated from the time difference Δt between the rising or peak points of a pair of pulse waves MW1 and MW3 obtained while compression pressure Pc is maintained and the known distance L13 between upstream inflation bag 22 and downstream inflation bag 26. The calculation also calculates the step pressure, i.e., compression pressure Pc, at which the pulse wave was generated. Three sets of measured data are then stored. A linear regression analysis can be performed based on the three measured data points.

[0108] The slope α calculation unit 96 calculates the logarithm ln(PWV 2 In the two-dimensional coordinate system with the axis representing -Pc and the axis representing -Pc, the logarithm ln(PWV) of the squared value of the pulse wave velocity PWV (= L / Δt) stored for each of the three step pressures is 2 ) and the step pressure, or compression pressure, Pc, at which the pulse wave occurred. By performing a linear regression analysis of three sets of measured data points, the logarithm of the squared value of the pulse wave velocity, ln(PWV 2 The coefficient value of the first term on the right side of equation (3) of the linear regression line -Pc converted from equation (2) of the linear regression line previously obtained between Pc and the transmural pressure Pt of the arterial blood vessel is calculated as the slope α.

[0109] The intercept β calculation unit 98 calculates the intercept β based on the slope α calculated from the linear relational expression (4) by the slope α calculation unit 96. That is, the intercept β is calculated by substituting the slope α calculated by the slope α calculation unit 96 into the linear relational expression (4).

[0110] The diastolic blood pressure estimation equation setting unit 100 substitutes the slope α calculated by the slope α calculation unit 96 and the intercept β calculated by the intercept β calculation unit 98 into the diastolic blood pressure estimation equation (5), sets and stores the diastolic blood pressure estimation equation (5) that reflects the inherent relationship of the living body.

[0111] The blood pressure estimation unit 102 repeatedly calculates an estimated diastolic blood pressure value DAPe by substituting the pulse wave velocity PWV and compression pressure Pc, measured at a predetermined period, for example, one pulse cycle to several dozen pulse cycles, into the diastolic blood pressure estimation equation (5) during a monitoring period in which the monitor pressure PcHm is maintained, for example, from time tm1 in FIG. 20 onward. A moving average of the calculated diastolic blood pressure values ​​DAPe may also be calculated. The diastolic blood pressure estimation unit 104 causes the display device 78 to display the calculated estimated diastolic blood pressure values ​​DAPe in chronological order. The monitor maintenance pressure PcHm is preferably set lower than the diastolic blood pressure of the living body and may be the same as or a different maintenance pressure from any of the first to third maintenance pressures PcH1 to PcH3.

[0112] In this embodiment, as in the first embodiment, the intercept β and slope α included in the linear regression line equation (2) from which the diastolic blood pressure estimation equation (5) is derived are in a constant linear relationship with each other as shown in equation (4) and are not affected by the subject. Therefore, the diastolic blood pressure value DAPe can be measured with high accuracy because it is less affected by the subject's individual biological characteristics. Another advantage is that calibration is not required, as is the case with conventional blood pressure estimation methods that use pulse wave velocity PWV. [Example]

[0113] In the first embodiment described above, in order to set equation (5) for estimating the diastolic blood pressure DAPe of the living body 14 being measured, the pulse wave velocity calculation unit 90 calculates the pulse wave velocity PWV (= L13 / Δt) from the pulse waves obtained at a predetermined number (e.g., six) of consecutive step pressures from a pressure value (equivalent to a mean blood pressure) calculated from a step pressure having an amplitude that is a predetermined percentage of the maximum amplitude of the pulse wave extracted by the pulse wave extraction unit 88 based on the pressure value (equivalent to a mean blood pressure) of the step pressure at which the amplitude of the pulse wave is maximum. Alternatively, the above-mentioned predetermined plurality of step pressures refers to a predetermined number (e.g., six) of consecutive step pressures after passing through a predetermined number (e.g., two) of step pressures from the step pressure at which the amplitude of the pulse wave extracted by the pulse wave extraction unit 88 is maximum as the compression pressure Pc of the compression cuff 12 decreases. However, in the third embodiment, the compression pressure control unit 86 focuses on the fact that the pulse wave shape obtained by the pulse wave extraction unit 88 changes sequentially in the process of decreasing from the systolic blood pressure SAP, and determines whether to start collecting actual measurement data based on the change in the pulse wave shape. Then, from the pulse waves collected at the subsequent multiple step pressures, calculation of the pulse wave velocity PWV (= L13 / Δt) for setting equation (5) for estimating the diastolic blood pressure DAPe of the living body 14 is started.

[0114] During the process of decreasing the compression pressure Pc of the compression cuff 12, the shape of the pulse wave (cuff pulse wave), which is the pressure oscillation of the compression pressure Pc inside the compression cuff 12 generated in response to volume changes in the arterial blood vessel 18, exhibits a downward section LP, which shows a substantially constant value, as shown in Figure 21. This downward section LP becomes shorter as the compression pressure Pc decreases and eventually disappears, as indicated by the dashed circle. This downward section LP is thought to be a section of one pulse wave cycle near the diastolic pressure point where changes in vascular volume are suppressed due to complete occlusion of the arterial blood vessel 18.

[0115] In this embodiment, the pulse wave velocity calculation unit 90 sequentially calculates the pulse wave velocity PWV (= L / Δt) for several steps, for example, six steps, from the step pressure at which the downward section LP disappeared or the next step pressure after the step pressure at which the downward section LP disappeared, and multiple sets of measured data of the compression pressure Pc and the pulse wave velocity PWV [ln(PWV 2 ), Pc1)····〔ln(PWVn 2 ), Pcn] are collected and stored.

[0116] Next, as in the previous embodiment, the slope α calculation unit 96 calculates the logarithm ln(PWV 2By performing linear regression analysis of multiple measured data points representing multiple sets of measured data in two-dimensional coordinates with an axis representing -Pc and an axis representing -Pc, the coefficient value of the first term on the right-hand side of equation (3) of the linear regression line -Pc converted from equation (2) of the linear regression line is obtained as the slope α. Similarly to the above-described embodiment, the intercept β calculation unit 98 calculates the intercept β based on the slope α calculated by the slope α calculation unit 96 from the linear relational equation (4). That is, the intercept β is calculated by substituting the slope α calculated by the slope α calculation unit 96 into equation (4). Similarly to the above-described embodiment, the diastolic blood pressure estimation equation setting unit 100 substitutes the slope α calculated by the slope α calculation unit 96 and the intercept β calculated by the intercept β calculation unit 98 into equation (5), thereby setting and storing the diastolic blood pressure estimation equation (5) that reflects the inherent relationship of the living body. As in the previous embodiment, the blood pressure estimation unit 102 repeatedly calculates the estimated diastolic blood pressure DAPe by substituting the pulse wave velocity PWV and compression pressure Pc actually measured at a predetermined period, for example, one pulse cycle to a dozen pulse cycles, into the diastolic blood pressure estimation formula (5) during the monitoring period in which the monitor pressure PcHm is maintained, for example, from time tm1 onwards in FIG. 20 .

[0117] In this embodiment, as in the first and second embodiments, the intercept β and slope α included in the linear regression line (2) from which the diastolic blood pressure estimation formula (5) is derived are linearly related to each other as shown in formula (4) and are not affected by the subject. Therefore, the diastolic blood pressure value DAPe can be measured with high accuracy because it is less affected by the subject's individual biological characteristics. Another advantage is that calibration is not required, as in conventional blood pressure estimation methods using pulse wave velocity (PWV). Furthermore, in this embodiment, the start of measurement data collection is determined after the end of the descending section (LP) within one pulse wave cycle, which indicates a vascular occlusion state. Therefore, the step pressure for analyzing pulse wave velocity (PWV) can be more accurately limited to a range below the diastolic blood pressure without being affected by variations in the difference between mean blood pressure and diastolic blood pressure. This allows for more accurate estimation of diastolic blood pressure, compared to the previous embodiments.

[0118] Although one embodiment of the present invention has been described in detail above with reference to the drawings, the present invention is not limited to this embodiment and can be implemented in other modes.

[0119] For example, in the embodiment, the compression cuff 12 has three inflation bags, namely the upstream inflation bag 22, the intermediate inflation bag 24, and the downstream inflation bag 26. However, if there is a pulse wave velocity detection means using a pair of pressure pulse wave sensors instead of the time difference between the pulse wave from the upstream inflation bag 22 and the pulse wave from the downstream inflation bag 26, then at least one inflation bag may be provided. A single-chamber compression cuff may also be used.

[0120] Pulse wave velocity PWV may be detected at any location apart from the compression cuff, as long as it is an artery passing through the compression cuff, or may be detected using a pressure pulse wave sensor, an impedance pulse wave, or ultrasonic Doppler.

[0121] In the above-mentioned Example 1, the estimated diastolic blood pressure value DAPe was calculated using the average value of the diastolic blood pressures DAPe1, DAPe2, and DAPe3 obtained for each of the first maintenance pressure PcH1, the second maintenance pressure PcH2, and the third maintenance pressure PcH3, but the diastolic blood pressure DAPe may also be estimated using a single maintenance pressure.

[0122] In the above-described embodiment, the diastolic blood pressure DAPe was estimated when a change in pulse wave velocity PWV occurred in the monitoring period in which the monitoring maintenance pressure PcHm was maintained, resulting in a positive judgment in S34. However, the diastolic blood pressure DAPe may also be estimated continuously for each beat.

[0123] Furthermore, although the compression cuff 12 in the above-described embodiment employs a stepwise pressure reduction method for measuring blood pressure, it may employ a continuous pressure reduction method in which the compression pressure Pc is continuously changed.

[0124] Furthermore, the compression cuff 12 in the above-described embodiment employs a stepwise pressure reduction method for measuring blood pressure, but it may also employ a stepwise pressure increase method in which the compression pressure Pc is increased in steps, or a continuous pressure increase method in which the compression pressure Pc is increased continuously.

[0125] The above is merely one embodiment, and although other examples will not be given, the present invention can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art within the scope of the present invention. [Explanation of symbols]

[0126] 10: Blood pressure measuring device 12: Compression band 14: Living body (subject) 16: Upper arm (compressed area) 18: Arterial blood vessels 22: Upstream expansion bag (expansion bag) 24: Intermediate expansion bag (expansion bag) 26: Downstream expansion bag (expansion bag) 82: Linear regression line formula memory section 84: Linear relation memory section 86: Compression pressure control unit 88: Pulse wave extraction unit 90: Pulse wave velocity calculation unit 94: Unique relation generation unit 102: Blood pressure estimation unit 104: Diastolic blood pressure estimation unit 108: Blood pressure fluctuation determination unit

Claims

1. A blood pressure measurement device that estimates the diastolic blood pressure of a subject using a compression cuff that compresses an arterial blood vessel at a compressed part of the subject and a square value of the pulse wave velocity of the arterial blood vessel passing through the compressed part, a pulse wave velocity measuring unit for measuring a pulse wave velocity PWV of the compressed area under compression by the compression cuff; a gradient calculation unit that calculates a gradient α of the linear regression equation based on the compression pressure and the pulse wave velocity of the compressed area measured at the compression pressure, from a transformation equation from a previously determined linear regression equation between the logarithm of the squared value of the pulse wave velocity and the transmural pressure of the arterial blood vessel; an intercept calculation unit that calculates an intercept β of the linear regression line equation based on the slope α of the linear regression line equation from a pre-stored linear relationship between the intercept β and the slope α included in the linear regression line equation; a diastolic blood pressure estimation equation setting unit that sets a diastolic blood pressure estimation equation by substituting the compression pressure to be subtracted from the diastolic blood pressure representing the transmural pressure, the pulse wave velocity of the compressed area, the slope of the linear regression line equation calculated by the slope calculation unit, and the intercept calculated by the intercept calculation unit into a conversion equation from the linear regression line equation; and a diastolic blood pressure estimation unit that estimates the diastolic blood pressure DAP of the subject based on the actual compression pressure Pc and the pulse wave velocity PWV of the compressed area from the diastolic blood pressure estimation formula. A blood pressure measuring device characterized by:

2. The linear regression line equation is expressed by the following equation (2):

2. The blood pressure measuring device according to claim 1. Pt=α・ln(PWV ２ )+b・・・(2) Here, Pt is the transmural pressure (= diastolic blood pressure DAP - compression pressure Pc), and PWV is the pulse wave velocity.

3. The conversion formula from the linear regression line formula is expressed by the following formula (3):

2. The blood pressure measuring device according to claim 1. -Pc=α・ln(PWV ２ )+(β-DAP) ・・・ (3)

4. The pre-stored linear relationship is expressed by the following equation (4):

2. The blood pressure measuring device according to claim 1. β=γ・α+δ... (4) where γ is a constant indicating the slope of the linear relationship, and δ is a constant indicating the intercept of the linear relationship.

5. The diastolic blood pressure estimation formula is expressed by the following formula (5):

2. The blood pressure measuring device according to claim 1. DAP=α・ln(PWV) ２ )+(β+Pc) ・・・ (5) Here, DAPe is an estimated blood pressure value.

6. The diastolic blood pressure estimation unit estimates the diastolic blood pressure of the subject for each of a plurality of types of compression pressures applied by the compression cuff based on the actual compression pressure and the pulse wave velocity of the compressed area, and estimates the average value of the diastolic blood pressures obtained for each of the plurality of types of compression pressures as the diastolic blood pressure.

2. The blood pressure measuring device according to claim 1.

7. The diastolic blood pressure estimation unit estimates the diastolic blood pressure of the subject based on the actual compression pressure and the pulse wave velocity of the compressed part when the compression pressure applied by the compression cuff is lower than the diastolic blood pressure of the subject.

2. The blood pressure measuring device according to claim 1.

8. A pair of pulse wave sensors is provided, which are arranged at two positions along the arterial blood vessel at a predetermined distance from each other to detect pulse waves, and the pulse wave velocity is calculated based on the time difference between the pulse waves detected by the pair of pulse wave sensors and the predetermined distance.

2. The blood pressure measuring device according to claim 1.

9. a compression pressure control unit that maintains the compression pressure applied by the compression cuff at a monitor pressure that is lower than the diastolic blood pressure of the living body; and a blood pressure fluctuation determination unit that determines the occurrence of blood pressure fluctuations based on whether the pulse wave velocity measured during the period in which the monitor pressure is maintained falls outside a predetermined fluctuation determination range, The diastolic blood pressure estimation unit estimates the diastolic blood pressure of the subject based on the actual compression pressure and the pulse wave velocity of the compressed area from the diastolic blood pressure estimation formula when the blood pressure fluctuation determination unit determines that a blood pressure fluctuation has occurred.

2. The blood pressure measuring device according to claim 1.

Images