Electronic blood pressure monitor and blood pressure measurement method
The electronic blood pressure monitor uses a dual-cuff system to accurately and rapidly measure blood pressure by subtracting DC components from pressure data, addressing discomfort and prolonged measurement times in conventional methods.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- OMRON HEALTHCARE CO LTD
- Filing Date
- 2025-09-26
- Publication Date
- 2026-05-21
AI Technical Summary
Conventional blood pressure measurement methods using oscillometric techniques require pressurizing the cuff to a level higher than the systolic pressure, causing discomfort and prolonged measurement times, especially for individuals with hypertension, and do not accurately measure blood pressure without invasive methods.
An electronic blood pressure monitor with a pressure cuff and a separate sensing cuff that uses pressure sensors to detect and calculate blood pressure values based on the pressure of the sensing cuff and the cuff, subtracting DC components to determine systolic and diastolic pressures from pressure data, allowing for non-invasive and rapid measurement.
The system enables accurate blood pressure measurement at lower pressures and in shorter times compared to conventional methods, reducing discomfort and measurement duration.
Smart Images
Figure JP2025034106_21052026_PF_FP_ABST
Abstract
Description
Electronic Sphygmomanometer and Blood Pressure Measurement Method
[0001] This invention relates to an electronic sphygmomanometer, and more particularly to an electronic sphygmomanometer that non-invasively measures the blood pressure of a measurement site. It also relates to a blood pressure measurement method for measuring blood pressure with such an electronic sphygmomanometer.
[0002] Generally, an electronic sphygmomanometer compresses the measurement site with a blood pressure measurement cuff and calculates the blood pressure of the measurement site by the oscillometric method. Specifically, an envelope line is set for a series of pulse wave amplitudes obtained from the cuff pressure when the blood pressure measurement cuff is in the pressurization process or the decompression process, and a threshold level (including a threshold level for systolic blood pressure and a threshold level for diastolic blood pressure) at a predetermined ratio (rate) with respect to the maximum value of the envelope line is set. The cuff pressure at the time when the envelope line crosses those threshold levels is calculated as the maximum blood pressure (systolic blood pressure) and the minimum blood pressure (diastolic blood pressure), respectively. For example, the threshold level for systolic blood pressure is set to 0.5 to 0.6, and the threshold level for diastolic blood pressure is set to 0.7 to 0.8. The reason for this is to statistically match the systolic blood pressure value and diastolic blood pressure value calculated by the oscillometric method with the systolic blood pressure value and diastolic blood pressure value measured by a reference measurement method (for example, the traditional auscultation method). Therefore, there is no theoretical basis that the systolic blood pressure value and diastolic blood pressure value calculated by the oscillometric method are correct in principle.
[0003] Therefore, as disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2023-019652), the applicant has proposed a blood pressure measurement method that can non-invasively and theoretically correctly measure the blood pressure of the measurement site. Here, "can be measured correctly in principle" means that it is based on the same mechanism as the principle of the reference measurement method (traditional auscultation method).
[0004] Japanese Patent Application Laid-Open No. 2023-019652
[0005] However, even with the general oscillometric method, and also with the blood pressure measurement method described in Patent Document 1, when performing measurements during the decompression process, it is necessary to pressurize the cuff pressure to be approximately 30 mmHg to 40 mmHg higher than the systolic blood pressure value in order to reliably stop blood flow at the measurement site. For this reason, problems such as pain from cuff compression and prolonged measurement time remain for subjects with hypertension, for example.
[0006] When measuring blood pressure during the pressurization process, the cuff pressure can be rapidly released the moment the systolic blood pressure value is determined, allowing for blood pressure measurement to be completed at a slightly lower cuff pressure than during the decompression process. However, even during pressurization, the cuff is still pressurized to the systolic blood pressure value, so it is not a definitive solution to reducing pain caused by cuff compression. Furthermore, because the pressurization must be gradual, the measurement time cannot be drastically shortened.
[0007] Therefore, the object of this invention is to provide an electronic blood pressure monitor and blood pressure measurement method that can measure blood pressure at the measurement site non-invasively and accurately in principle, and can complete blood pressure measurement at a lower pressure and in a shorter time.
[0008] To solve the above problems, the electronic blood pressure monitor of this disclosure is an electronic blood pressure monitor that non-invasively measures blood pressure at a site to be measured, comprising: a bag-shaped pressure cuff that is attached around the circumferential direction of the site to be measured in order to compress the site to be measured by receiving a supply of pressurizing fluid; a bag-shaped sensing cuff that is positioned on the inner circumference of the pressure cuff and in a part that should face the artery of the site to be measured, and which contains a pressure transmission fluid separately from the pressure cuff, wherein the sensing cuff compresses the artery of the site to be measured via the pressure transmission fluid due to the pressure of the pressure cuff, and receives changes in the volume of the artery as changes in pressure; a first pressure sensor that detects the pressure of the sensing cuff; a second pressure sensor that detects the pressure of the pressure cuff; and a pressure control unit that supplies the pressurizing fluid to the pressure cuff or discharges the pressurizing fluid from the pressure cuff to control the pressure of the pressure cuff. The system includes a blood pressure calculation unit that calculates a blood pressure value based on data representing the pressure of the sensing cuff from the first pressure sensor and data representing the pressure of the pressing cuff from the second pressure sensor during the pressurization process of the pressing cuff by the pressure control unit, and a storage unit that can store the data, wherein the blood pressure calculation unit, during the pressurization process, subtracts the DC component of the data representing the pressure of the pressing cuff or a value approximating the DC component from the data representing the pressure of the sensing cuff to determine the pressure at the start of the rise and the pressure at the peak point of the pressure pulse wave shown for each beat, The data representing the pressure at the peak point shown by the pulse wave for each beat is associated with the data representing the pressure of the compression cuff at the time the peak pressure occurred to form a first data set, and the data representing the pressure at the start of the rise is associated with the data representing the pressure of the compression cuff at the time the rise start pressure occurred to form a second data set. The first and second data sets are stored in the memory unit in chronological order, and as a result, the first and second data sets define a first and second curve, respectively, according to the pipe law, on a coordinate plane defined by the horizontal axis representing the pressure of the compression cuff and the vertical axis representing the pressure of the pulse wave.The method is characterized by determining the diastolic blood pressure value by calculating the pressure on the compression cuff at the point of transition when the pressure at the onset point of each beat drops from a positive value to zero, subtracting the data representing the pressure at the onset point from the data representing the pressure at the peak point of the beat that occurred at the transition point, and determining the maximum pulse wave amplitude by calculating the difference. Based on the second dataset stored in the memory unit, the method searches for and finds a past point in time on the coordinate plane when the second curve shows a positive value equal to the maximum pulse wave amplitude, and determines the pressure on the compression cuff at that past point. The method is characterized by determining the pulse pressure equivalent by subtracting the data representing the pressure on the compression cuff at the past point from the data representing the pressure on the compression cuff at the transition point, and adding the pulse pressure equivalent to the diastolic blood pressure value to determine the systolic blood pressure value.
[0009] In this specification, the "pressure transmission fluid" may be sealed in the sensing cuff during the manufacturing stage of the electronic blood pressure monitor, or it may be contained in the sensing cuff and discharged from the sensing cuff each time blood pressure is measured.
[0010] Furthermore, the "fluid" used for pressurization and pressure transmission is typically air, but it may be another gas or liquid.
[0011] The "DC component" of the data representing the pressure of the above-mentioned compression cuff refers to the component obtained by removing the fluctuating component (for example, the beat-by-beat fluctuating component originating from the pressure pulse wave from the artery) from the data representing the pressure of the above-mentioned compression cuff. Furthermore, the "value approximated by the above-mentioned DC component" refers to a value approximated by a straight line determined by the pressure data at a single point in the compression cuff during a pressurization process at a constant pressurization rate, for example.
[0012] "A beat occurring at the above transition point" does not mean a beat that occurred precisely at the above transition point, but rather a beat that occurred closest to the above transition point.
[0013] "Pulse pressure equivalent" refers to the amount obtained by conversion as equivalent to pulse pressure (the difference between systolic and diastolic blood pressure).
[0014] In the electronic blood pressure monitor of this disclosure, a pouch-shaped pressure cuff is attached around the circumference of the area to be measured. In this attached state, a pouch-shaped sensing cuff is positioned separately from the pressure cuff, on the inner circumference of the pressure cuff, in a location that faces the artery of the area to be measured. For example, it is assumed that a pressure-transmitting fluid is pre-filled into the sensing cuff during the manufacturing stage of this electronic blood pressure monitor.
[0015] During blood pressure measurement, the pressure control unit controls the pressure of the pressure cuff by supplying the pressurizing fluid to the pressure cuff or by discharging the pressurizing fluid from the pressure cuff. The sensing cuff compresses the artery at the measurement site via the pressure transmission fluid due to the pressure of the pressure cuff, while also receiving the pressure pulse wave from the artery. The first pressure sensor detects the pressure of the sensing cuff, and the second pressure sensor detects the pressure of the pressure cuff. The blood pressure calculation unit generally calculates blood pressure values (systolic blood pressure and diastolic blood pressure) based on data representing the pressure of the sensing cuff from the first pressure sensor and data representing the pressure of the pressure cuff from the second pressure sensor during the pressurizing process of the pressure cuff by the pressure control unit.
[0016] Specifically, the blood pressure calculation unit calculates the systolic blood pressure and diastolic blood pressure during the pressurization process as follows:
[0017] First, the DC component of the data representing the pressure of the pressure cuff, or a value approximating the DC component, is subtracted from the data representing the pressure of the sensing cuff to determine the pressure at the onset point and the peak point of the pressure pulse wave shown for each beat.
[0018] Next, the data representing the pressure at the peak point shown by the pulse wave for each beat is associated with the data representing the pressure of the compression cuff at the time the pressure at the peak point occurred to form a first data set. Similarly, the data representing the pressure at the start of the rise is associated with the data representing the pressure of the compression cuff at the time the pressure at the start of the rise occurred to form a second data set. The first and second data sets are then stored in the memory unit in chronological order. As a result, on a coordinate plane defined by the horizontal axis representing the pressure of the compression cuff and the vertical axis representing the pressure of the pulse wave, the first and second data sets define a first and second curve, respectively, that follow the pipe law.
[0019] Next, the pressure on the compression cuff at the point when the pressure at the onset of the rise for each beat drops from a positive value to zero is determined as the diastolic blood pressure value. At the same time, the difference between the data representing the pressure at the peak point of the beat that occurred at the transition point and the data representing the pressure at the onset of the rise is determined as the maximum pulse wave amplitude. Here, the point at which the pressure at the onset of the rise for each beat drops from a positive value to zero (the transition point) corresponds to the point at which the pressure on the compression cuff exceeds the diastolic blood pressure value. Therefore, the pressure on the compression cuff at the transition point can, in principle, be correctly determined as the diastolic blood pressure value.
[0020] Next, based on the second dataset stored in the memory unit, the system searches for and finds a past time point on the coordinate plane where the second curve showed a positive value equal to the maximum pulse wave amplitude, and determines the pressure of the compression cuff at that past time point.
[0021] Next, the difference obtained by subtracting the data representing the pressure of the cuff at a past time from the data representing the pressure of the cuff at the transition point is calculated as the pulse pressure equivalent. The reason why the difference obtained by subtracting the data representing the pressure of the cuff at a past time from the data representing the pressure of the cuff at the transition point is calculated as the pulse pressure equivalent is that, with respect to the horizontal axis, the portion of the first curve defined between the cuff pressure at the transition point (= diastolic blood pressure value) and the systolic blood pressure value to be determined, and the portion of the second curve defined between the cuff pressure at a past time and the cuff pressure at the transition point, have the same shape according to the same pipe law.
[0022] Next, the pulse pressure equivalent is added to the diastolic blood pressure value to obtain the systolic blood pressure value. Based on the above, the blood pressure calculation unit calculates the diastolic blood pressure value and the systolic blood pressure value.
[0023] As a result, this electronic blood pressure monitor can, in principle, accurately measure blood pressure at the measurement site non-invasively, similar to the blood pressure measurement method described in Patent Document 1. Moreover, this electronic blood pressure monitor can complete blood pressure measurement at a lower pressure and in a shorter time compared to conventional methods that use a pressurizing process (pressurizing up to the systolic blood pressure value).
[0024] In one embodiment of the electronic blood pressure monitor, the blood pressure calculation unit calculates the difference between the data representing the pressure at the peak point and the data representing the pressure at the start of the rise point for each beat during the pressurization process, and associates the data of each pulse wave amplitude with the data representing the pressure of the pressure cuff at the time the pulse wave amplitude was shown to form a third data set. The third data set is stored in the memory unit in time series, and the maximum value shown by the pulse wave amplitude is determined as the maximum pulse wave amplitude by referring to the third data set, and the time when the pulse wave amplitude shows the maximum pulse wave amplitude is determined as the transition time.
[0025] Normally, the pressure pulse wave received by the sensing cuff is superimposed with noise, making it difficult to determine the point in time (second point in time) when the pressure at the rise point transitions between zero level (buried in noise) and a positive value. Therefore, in this embodiment of the electronic blood pressure monitor, the blood pressure calculation unit determines the transition point during the pressurization process as follows.
[0026] First, for each beat, the difference between the data representing the pressure at the peak point and the data representing the pressure at the start of the rise is calculated as the pulse wave amplitude. This data for each pulse wave amplitude is then associated with the data representing the pressure of the compression cuff at the time the pulse wave amplitude was observed to form a third data set, and this third data set is stored in the memory unit in chronological order.
[0027] Next, the maximum value of the pulse wave amplitude is determined by referring to the third dataset described above, and the point in time when the pulse wave amplitude reaches the maximum value is determined as the transition point.
[0028] Here, whether or not the pulse wave amplitude reached its maximum value is determined by comparing the pulse wave amplitudes with each other, which allows for more accurate determination compared to comparing with a zero level (buried in noise). Therefore, in this embodiment of the electronic blood pressure monitor, the transition time can be determined with high accuracy, and thereby the diastolic blood pressure value can be determined with high accuracy.
[0029] In one embodiment of the electronic blood pressure monitor, the pressure control unit terminates the pressurization process and discharges the pressurizing fluid from the pressure cuff, triggered by the blood pressure calculation unit calculating the systolic blood pressure value.
[0030] According to this embodiment of the electronic blood pressure monitor, blood pressure measurement can be completed at a lower pressure and in a shorter time before the systolic blood pressure value is reached during the pressurization process.
[0031] In another aspect, the blood pressure measurement method of this invention is a blood pressure measurement method for non-invasively measuring blood pressure at a site to be measured using the above-mentioned electronic blood pressure monitor, wherein the blood pressure calculation unit subtracts the DC component of the data representing the pressure of the pressing cuff or a value approximating the DC component from the data representing the pressure of the sensing cuff during the pressurization process to determine the pressure at the onset point and the peak point of the pressure pulse wave shown for each beat, The data representing the pressure at the peak point shown by the above-mentioned pressure pulse wave for each beat is associated with the data representing the pressure of the compression cuff at the time the pressure at the peak point occurred to form a first data set, and the data representing the pressure at the start of the rise is associated with the data representing the pressure of the compression cuff at the time the pressure at the start of the rise occurred to form a second data set, and the first and second data sets are stored in the memory unit in a time series, so that the first and second data sets define a first curve and a second curve, respectively, according to the pipe law on a coordinate plane defined by the horizontal axis representing the pressure of the compression cuff and the vertical axis representing the pressure of the pressure pulse wave, and the pressure of the compression cuff at the time when the pressure at the start of the rise for each beat drops from a positive value to zero is determined as the diastolic blood pressure value, and the difference obtained by subtracting the data representing the pressure at the start of the rise from the data representing the pressure at the peak point of the beat that occurred at the time of the transition is determined as the maximum pulse wave amplitude. Based on the second dataset stored in the memory unit, the system searches for and finds a past time point on the coordinate plane where the second curve showed a positive value equal to the maximum pulse wave amplitude, determines the pressure of the compression cuff at that past time point, calculates the difference between the data representing the pressure of the compression cuff at the transition point and the data representing the pressure of the compression cuff at the past time point, and calculates the pulse pressure equivalent as the difference, and adds the pulse pressure equivalent to the diastolic blood pressure value to obtain the systolic blood pressure value.
[0032] This blood pressure measurement method allows for blood pressure measurement to be completed at a lower pressure and in a shorter time compared to conventional methods that involve pressurizing the blood pressure (to the systolic blood pressure value).
[0033] As is clear from the above, the electronic blood pressure monitor and blood pressure measurement method disclosed herein allow for blood pressure measurement to be completed at a lower pressure and in a shorter time compared to conventional methods that use a pressurizing process.
[0034] This figure shows the block structure of an electronic blood pressure monitor (hereinafter abbreviated as "blood pressure monitor") according to one embodiment of the present invention. This figure shows a cross-section of the cuffs (including the pressure cuff and sensing cuff) constituting the blood pressure monitor of Figure 1 when they are attached to the measurement site, along with the air piping system. This figure shows a planar layout of the cuffs (including the pressure cuff and sensing cuff) constituting the blood pressure monitor of Figure 1 when they are attached to the measurement site, along with the air piping system. This figure shows a schematic flow of blood pressure measurement using the blood pressure monitor of Figure 1. This figure shows a detailed flow of the blood pressure calculation method included in the flow of Figure 4. Figure 6(A) is a figure showing data representing the pressure Pc of the pressure cuff and data representing the pressure Ps of the sensing cuff together during the pressurization process. Figure 6(B) is a figure illustrating the specific method of blood pressure calculation using the blood pressure monitor of Figure 1. This figure illustrates the principle of blood pressure calculation using the blood pressure monitor of Figure 1. Figure 8(A) is a figure showing the correspondence between the pressure difference inside and outside the artery and the volume of the artery (arterial law). Figure 8(B) is a diagram showing the corresponding relationship in Figure 8(A) but reversed horizontally.
[0035] The embodiments of this invention will now be described in detail with reference to the drawings.
[0036] (Structure of the blood pressure monitor) Figure 1 shows a schematic block structure of a blood pressure monitor 1 according to one embodiment of the present invention. This blood pressure monitor 1 comprises a cuff 20 that is attached to the measurement site, such as the wrist or upper arm (in this example, the upper arm), and a main body 10.
[0037] The cuff 20 includes a bag-shaped pressure cuff 23 for receiving air as a pressurizing fluid to compress the area to be measured 90, and a separate bag-shaped sensing cuff 21 for containing air as a pressure transmission fluid.
[0038] The main unit 10 is equipped with a CPU (Central Processing Unit) 110 as a control unit, a display 50, a memory 51 as a storage unit, an operation unit 52, a power supply unit 53, a first pressure sensor 30, a second pressure sensor 31, a pump 32, and a discharge valve 33. Furthermore, the main unit 10 is equipped with A / D conversion circuits 300 and 310 that convert analog signals to digital signals, a pump drive circuit 320 that drives the pump 32, and a valve drive circuit 330 that drives the discharge valve 33. The air pipe 37a connected to the first pressure sensor 30 is connected to the sensing cuff 21 in a fluid-flowable manner as a flexible first air pipe 37 (in this example, the air pipe 37a is collectively referred to as the first air pipe 37). The air pipes 38a, 38b, and 38c connected to the second pressure sensor 31, pump 32, and discharge valve 33, respectively, merge into a single flexible second air pipe 38, which is connected to the pressure cuff 23 in a fluid-flowable manner (in this example, the air pipes 38a, 38b, and 38c are collectively referred to as the second air pipe 38). In this example, the first air pipe 37 and the second air pipe 38 are completely separated from each other. Therefore, for example, it is possible to suppress the mixing of fluctuating components (for example, due to pressure pulse waves from arteries) contained in the pressure of the first air pipe 37 connected to the sensing cuff 21 as noise into the pressure of the second air pipe 38 connected to the pressure cuff 23. Conversely, it is possible to suppress the mixing of fluctuating components (mainly due to vibrations of the pump 32) contained in the pressure of the second air pipe 38 connected to the pressure cuff 23 as noise into the pressure of the first air pipe 37 connected to the sensing cuff 21. Hereafter, the first air pipe 37 and the second air pipe 38 will be collectively referred to as the air piping systems 37 and 38, as appropriate.
[0039] The display unit 50 includes a display and indicators, and displays predetermined information (for example, blood pressure measurement results) according to control signals from the CPU 110.
[0040] In this example, the operation unit 52 includes a measurement switch 52A for receiving instructions to start / stop blood pressure measurement, and a memory switch 52B for recalling past measurement results. These switches 52A and 52B input operation signals to the CPU 110 in response to user instructions.
[0041] The memory 51 stores data of programs for controlling the sphygmomanometer 1, data used for controlling the sphygmomanometer 1, setting data for setting various functions of the sphygmomanometer 1, and data of measurement results of blood pressure values. Also, the memory 51 is used as a work memory when the program is executed.
[0042] The power supply unit 53 supplies power to each part of this sphygmomanometer 1 including the CPU 110, the first pressure sensor 30, the second pressure sensor 31, the pump 32, the discharge valve 33, the display 50, the memory 51, the A / D conversion circuits 300 and 310, the pump drive circuit 320, and the valve drive circuit 330.
[0043] The pump 32 supplies air as a fluid to the pressing cuff 23 via the second air pipe 38 in order to pressurize the pressure of the pressing cuff 23 (represented by the symbol "Pc") enclosed in the cuff 20. The discharge valve 33 is opened and closed via the second air pipe 38 to discharge or enclose the air in the pressing cuff 23 and control the pressure Pc of the pressing cuff 23. The pump drive circuit 320 drives the pump 32 based on a control signal given from the CPU 110. The valve drive circuit 330 opens and closes the discharge valve 33 based on a control signal given from the CPU 110.
[0044] The first pressure sensor 30 is a piezoresistive pressure sensor in this example, and detects the pressure of the sensing cuff 21 (represented by the symbol "Ps") via the first air pipe 37. The pressure Ps of the sensing cuff 21 output by the first pressure sensor 30 is converted from an analog signal to a digital signal by the A / D conversion circuit 300 and input to the CPU 110. Also, the second pressure sensor 31 is a piezoresistive pressure sensor similar to the first pressure sensor 30, and detects the pressure Pc of the pressing cuff 23 via the second air pipe 38. The pressure Pc of the pressing cuff 23 output by the second pressure sensor 31 is converted from an analog signal to a digital signal by the A / D conversion circuit 310 and input to the CPU 110.
[0045] The CPU 110 acts as a control unit, controlling the operation of the entire blood pressure monitor 1. Specifically, the CPU 110 acts as a pressure control unit according to a program for controlling the blood pressure monitor 1 stored in the memory 51, and controls the pump 32 and discharge valve 33 in response to operation signals from the operation unit 52. The CPU 110 also acts as a blood pressure calculation unit, calculating blood pressure values based on data representing the pressure Ps of the sensing cuff 21 from the first pressure sensor 30 and data representing the pressure Pc of the pressing cuff 23 from the second pressure sensor 31, and controlling the display unit 50 and the memory 51. The specific method of measuring blood pressure will be described later.
[0046] Figure 2 shows a cross-section of the cuff 20 (including the sensing cuff 21 and the pressure cuff 23) that constitutes the blood pressure monitor 1 when it is attached to the area to be measured 90, along with the air piping systems 37 and 38. As can be seen in Figure 2, the cuff 20 generally comprises a strip-shaped outer cloth 29 located on the outermost periphery, the aforementioned pressure cuff 23 provided along the surface 29i of the outer cloth 29 facing the area to be measured 90 (inner circumferential side), a back plate 22 provided along the surface 23i of the pressure cuff 23 facing the area to be measured 90 (inner circumferential side), and the aforementioned sensing cuff 21 provided along the surface 22i of the back plate 22 facing the area to be measured 90 (inner circumferential side).
[0047] Here, Figure 2 also shows the XYZ Cartesian coordinate system indicating the "longitudinal direction Y," "width direction X," and "thickness direction Z" of the cuff 20 for ease of understanding. For the cuff 20, the "longitudinal direction Y" means the direction in which the outer fabric 29 extends in a band shape, and in the worn state, it corresponds to the circumferential direction surrounding the area to be measured 90. The "width direction X" means the direction perpendicular to the longitudinal direction Y within the plane along the outer fabric 29, and in the worn state, it corresponds to the direction in which the artery 91 passes through the area to be measured 90. "Upstream side" and "downstream side" refer to the upstream and downstream sides, respectively, with respect to the blood flow through the artery 91. The "thickness direction Z" is the direction perpendicular to both the longitudinal direction Y and the width direction X (i.e., the outer fabric 29), and in the worn state, it corresponds to the direction perpendicular to the outer circumferential surface 90a of the area to be measured 90. This XYZ Cartesian coordinate system is also shown in Figure 3, which will be described next.
[0048] Figure 3 schematically shows the planar layout of the cuff 20 in the deployed state. As shown in this planar layout, the outer fabric 29 has a strip-like (in this example, a rectangle with rounded corners) shape that extends in the longitudinal direction Y (the horizontal direction in FIG. 3). The outer fabric 29 can be curved or bent, but is configured to not substantially stretch or contract in order to generally regulate the expansion of the sensing cuff 21 and the pressing cuff 23 away from the measurement site 90 during blood pressure measurement. Here, the "fabric" is not limited to being woven and may be composed of one or more layers of resin. The longitudinal dimension of the outer fabric 29 is set to be longer than the peripheral length of the upper arm as the measurement site 90 in this example.
[0049] The pressing cuff 23 has a rectangle with rounded corners in the plane along the outer fabric 29. The planar dimensions of the pressing cuff 23 require a certain length and width in order to press the artery 91 to temporarily stop bleeding. In this example (an example of a cuff for the upper arm), the planar dimensions of the pressing cuff 23 are set such that, for example, the dimension in the longitudinal direction Y is 24 cm and the dimension in the width direction X (represented by X23 in FIG. 2) is 13 cm. In this example, the pressing cuff 23 has a pair of sheets (in this example, stretchable polyurethane sheets) opposed in the thickness direction Z, and the peripheral edges of those pair of sheets are welded to each other with the vicinity of the end of the second air pipe 38 sandwiched therebetween, thereby being configured in a bag shape.
[0050] In this example, the back plate 22 is made of a plate-shaped resin (polypropylene in this example) with a thickness of about 1 mm. In this example, the shape and planar dimensions of the back plate 22 are set to be approximately the same as the shape and planar dimensions of the sensing cuff 21, which will be described below. Since the back plate 22 is interposed between the pressure cuff 23 and the sensing cuff 21, it can reliably transmit the pressure Pc of the pressure cuff 23 to the sensing cuff 21. Therefore, the sensing cuff 21 can reliably compress the artery 91 of the measurement site 90 via the air (pressure transmission fluid) contained within the sensing cuff 21 by the pressure Pc of the pressure cuff 23. At the same time, the back plate 22 blocks the transmission of pressure fluctuation components between the pressure cuff 23 and the sensing cuff 21. Therefore, for example, it is possible to suppress the mixing of fluctuation components (for example, due to the pressure pulse wave from the artery 91) contained in the pressure Ps of the sensing cuff 21 as noise into the pressure Pc of the pressure cuff 23. Conversely, it is possible to suppress the inclusion of fluctuating components contained in the pressure Pc of the pressing cuff 23 as noise in the pressure Ps of the sensing cuff 21.
[0051] As shown in Figure 3, the sensing cuff 21 has a rectangular shape with rounded corners in the plane along the outer fabric 29 (and pressure cuff 23). In this example, the sensing cuff 21 is constructed in a bag-like shape by placing a pair of sheets (stretchable polyurethane sheets in this example) opposite each other in the thickness direction Z, and welding the periphery of the pair of sheets together near the end of the first air pipe 37. Here, it is desirable that the width X dimension of the sensing cuff 21 is shorter than the occlusion distance at which the artery 91 is closed when the pressure Pc of the pressure cuff 23 becomes the systolic blood pressure value SYS. In the example in Figure 3 (example of a cuff for the upper arm), the planar dimensions of the sensing cuff 21 are set, for example, to a length Y dimension of 7 cm and a width X dimension (represented as X21 in Figure 2) of 4 cm. This structure ensures that the pressure pulse wave (amplitude) acquired by the sensing cuff 21 reflects only the volume change of the artery 91 at the point where sufficient pressure Pc from the pressure cuff 23 is applied. Therefore, the accuracy of blood pressure measurement is improved.
[0052] In principle, blood pressure measurement is possible if the planar dimensions of the sensing cuff 21 are greater than or equal to the diameter of the artery 91. However, considering that misalignment may occur when attaching the cuff 20 to the measurement site 90, the planar dimensions of the sensing cuff 21 are set to, for example, 1 cm x 1 cm or larger.
[0053] In the examples shown in Figures 2 and 3, the first air pipe 37 and the second air pipe 38 are routed outwards from the sides corresponding to the downstream side of the sensing cuff 21 and the pressing cuff 23, respectively, along the width direction X of the cuff 20, so as not to interfere with the measurement.
[0054] (Blood pressure measurement method) Figure 4 shows a schematic operation flow of blood pressure measurement using the blood pressure monitor 1 in Figure 1, where the measurement is performed during the pressurization process.
[0055] With the cuff 20 attached to the area to be measured (in this example, the upper arm) 90 (see Figure 2), when the user (subject) turns on the measurement switch 52A provided on the main unit 10 to instruct the start of measurement, the CPU 110 initializes the pressure sensors as shown in step S201 of Figure 4. Specifically, the CPU 110 initializes the processing memory area, stops the pump 32, and opens the discharge valve 33, setting the atmospheric pressure to 0 mmHg for the first pressure sensor 30, and setting the pressure with the cuff 20 attached to the area to be measured 90 to 0 mmHg for the second pressure sensor 31.
[0056] In this example, it is assumed that, during the manufacturing process of the blood pressure monitor 1, a predetermined amount of air is sealed in the sensing cuff 21 (and the first air piping 37) as a fluid for pressure transmission.
[0057] Next, in step S202 of Figure 4, the CPU 110 closes the discharge valve 33 via the valve drive circuit 330. Subsequently, in step S203, the CPU 110 acts as a pressure control unit and drives the pump 32 via the pump drive circuit 320 to start pressurizing the cuff 20 (more precisely, the pressure cuff 23) (pressurization process). While supplying air from the pump 32 to the pressure cuff 23 through the second air pipe 38, the CPU 110 controls the pressurization rate to be approximately constant (5 mmHg / sec in this example) from a value well below the subject's assumed diastolic blood pressure value DIA (approximately 10 mmHg in this example) based on the output of the second pressure sensor 31. As a result, the pressure Pc of the pressure cuff 23 rises approximately linearly, as shown in the pressurization period tP in Figure 6(A). As the sensing cuff 21 is pressed toward the measurement area 90 via the back plate 22 by the pressing cuff 23, the pressure Ps of the sensing cuff 21 also increases in accordance with the pressure Pc of the pressing cuff 23.
[0058] During this pressurization process, as shown in step S204 of Figure 4, the CPU 110 acts as a blood pressure calculation unit and attempts to calculate blood pressure values (systolic blood pressure value SYS and diastolic blood pressure value DIA) based on the data representing the pressure Ps of the sensing cuff 21 from the first pressure sensor 30 and the data representing the pressure Pc of the pressing cuff 23 from the second pressure sensor 31, which have been acquired at this point. The principle of blood pressure calculation and a more specific method of blood pressure calculation will be described in detail later.
[0059] If, at this point, the blood pressure value cannot be calculated due to insufficient data (NO in step S205 of Figure 4), the process from steps S203 to S205 is repeated.
[0060] Once the blood pressure value has been calculated in this manner (YES in step S205), the CPU 110 acts as a pressure control unit and, in step S206, stops the pump 32 via the pump drive circuit 320, and in step S207, opens the discharge valve 33 via the valve drive circuit 330 to rapidly exhaust the air from the pressure cuff 23. In this example, the pump 32 is stopped at the stop time tC shown in Figure 6(A), and rapid exhaust is performed during the rapid exhaust period tD shown in Figure 6(A). Furthermore, in step S208 in Figure 4, the CPU 110 displays the blood pressure measurement result on the display 50 and also controls the storage of the blood pressure measurement result in the memory 51.
[0061] (Principle of blood pressure calculation) The method of calculating blood pressure using blood pressure monitor 1 can be explained in principle as follows.
[0062] Generally, it is known that there is a correspondence between the intra-arterial pressure difference Ptr and the volume of the artery (blood vessel) (represented as "arterial volume V"), as illustrated by curve C0 in Figure 8(A) (this is called the "tube law"). Here, the intra-arterial pressure difference Ptr is defined as the difference between the internal pressure of the artery at the measurement site 90 (represented as "Pa") and the cuff pressure Pc. That is, Ptr = Pa - Pc. As the intra-arterial pressure difference Ptr becomes positive and larger, the arterial volume V increases monotonically and gradually saturates. Even when pulse waves PW1 and PW1' with the same wave height ΔP are applied to the artery, if the intra-arterial pressure difference Ptr differs due to different cuff pressures Pc, the resulting volume pulse waves VW1 and VW1' will differ according to the above-mentioned tube law (curve C0). Here, when the intra-arterial pressure difference Ptr = 0, that is, when the intra-arterial pressure Pa and cuff pressure Pc are in equilibrium, the arterial volume is defined as V0 (this is called the "equilibrium level"). The curve C0r shown in Figure 8(B) is, for ease of understanding, a horizontal inversion of the curve C0 in Figure 8(A).
[0063] Here, Figure 7 shows the pressure at the onset point PWa and the peak point PWp of the pressure pulse wave PW, which are shown for each beat, when the CPU 110 acts as a blood pressure calculation unit and subtracts the DC component (which can be extracted from the raw data via a low-pass filter; hereafter referred to as cuff pressure Pcdc) of the data representing the pressure Pc of the pressure cuff 23 from the data representing the pressure Ps of the sensing cuff 21 during the pressurization process, while correlating the timing of their generation with each other. The horizontal axis of Figure 7 is represented by the conversion from elapsed time t to cuff pressure Pcdc during the pressurization process via a constant pressurization rate (5 mmHg / sec in this example). The vertical axis of Figure 7 represents the pressure (mmHg) of the pressure pulse wave PW.
[0064] In the pressure range PcL (in this example, less than approximately 88 mmHg) where the cuff pressure Pcdc is lower than the diastolic blood pressure value DIA, the intra-arterial pressure difference Ptr > 0 is always true, regardless of the pulse wave (pulsation), and the artery is completely open. In this range PcL, as the cuff pressure Pcdc increases, the starting point PWa of the pressure pulse wave PW decreases with each beat according to the above-mentioned tube law (curve C0r in Figure 8(B)). The peak point PWp of the pressure pulse wave PW also decreases with each beat according to the above-mentioned tube law (curve C0r in Figure 8(B)). Here, the second curve C2 is defined as a curve connecting the starting points PWa (or a curve that approximates it). The first curve C1 is defined as a curve connecting the peak points PWp (or a curve that approximates it).
[0065] Assume that the cuff pressure Pcdc falls within the pressure interval PcM, which is between the diastolic blood pressure DIA (approximately 88 mmHg in this example) and the systolic blood pressure SYS (approximately 135 mmHg in this example). Within this pressure interval PcM, during the period of one beat cycle when the arterial pressure Pa exceeds the cuff pressure Pcdc (a partial period of one beat cycle), the intra-arterial pressure difference Ptr > 0. When the intra-arterial pressure difference Ptr > 0, according to the above-mentioned tube law (curve C0r in Figure 8(B)), the pressure pulse wave PW appears with each beat, showing a peak point PWp, as shown in Figure 7. The peak point PWp, indicated by the pressure of the pressure pulse wave PW, decreases with each beat according to the above-mentioned tube law (curve C0r in Figure 8(B)). During the period of one beat cycle when the arterial pressure Pa is below the cuff pressure Pcdc, the intra-arterial pressure difference Ptr < 0. Therefore, the starting point PWa, which indicates the rise of the pressure pulse wave PW for each beat, is cut off (trimmed), and the second curve C2 remains at zero.
[0066] In the pressure interval PcH, where the cuff pressure Pcdc is higher than the systolic blood pressure SYS (approximately 135 mmHg in this example), the intra-arterial pressure difference Ptr < 0 is always present, regardless of the pulse wave (pulse). As a result, blood flow through artery 91 is completely stopped. Consequently, even the peak point PWp shown by the pressure pulse wave PW does not appear with each beat, and the first curve C1 remains at zero.
[0067] (1) How to determine the diastolic blood pressure value DIA As can be seen from the above explanation, first, the diastolic blood pressure value DIA can be correctly determined in principle by first determining the point tA at which the rise point PWa (i.e., the second curve C2) indicated by the pressure of the pressure pulse wave PW for each beat drops from a positive value to zero (this is called the "transition point"). For ease of understanding, the point on the second curve C2 at the transition point tA is shown as point A in Figure 7.
[0068] Furthermore, since the pressure pulse wave PW received by the sensing cuff 21 is usually superimposed with noise, it can be difficult to determine the transition time tA at which the pressure at the rising point PWa transitions between a positive value and zero level (buried in noise). Here, as shown in Figure 7, at the transition time tA, the pulse wave amplitude AM shows the maximum pulse wave amplitude AMmax. Therefore, in order to accurately determine the above transition time tA, the pulse wave amplitude AM can be calculated as the difference obtained by subtracting the data representing the pressure at the rising point PWa from the data representing the pressure at the peak point PWp for each beat, and the transition time tA can be determined at the point when the pulse wave amplitude AM shows the maximum pulse wave amplitude AMmax. In this case, whether or not the pulse wave amplitude AM has shown the maximum value AMmax can be determined by comparing the pulse wave amplitudes AM with each other, so it can be determined with more accuracy than when comparing with zero level (buried in noise).
[0069] (2) How to determine the systolic blood pressure value SYS With respect to the horizontal axis in Figure 7, the portion C1e of the first curve C1 defined between the cuff pressure PcA (=DIA) at transition time tA and the systolic blood pressure value SYS to be determined, and the portion C2e of the second curve C2 defined between the cuff pressure PcB at past time tB and the cuff pressure PcA at transition time tA, have the same shape according to the same pipe law (i.e., they are in a parallel translation relationship). Therefore, i) The difference obtained by subtracting the data representing the pressure at the rise start point PWa from the data representing the pressure at the peak point PWp of the beat that occurred at transition time tA is determined as the maximum pulse wave amplitude AMmax shown in Figure 7. ii) On the coordinate plane Q, search for and find the past time tB in which the second curve C2 showed a positive value equal to the maximum pulse wave amplitude AMmax, and determine the cuff pressure PcB at that past time tB. For ease of understanding, the point on the second curve C2 at past time point tB is shown as point B in Figure 7. iii) With respect to the horizontal axis in Figure 7, the difference obtained by subtracting the cuff pressure PcB at past time point tB from the cuff pressure PcA (=DIA) at transition time point tA is calculated as the pulse pressure equivalent PP. vi) The pulse pressure equivalent PP is added to the diastolic blood pressure value DIA to obtain the systolic blood pressure value SYS. Thus, the diastolic blood pressure value DIA and the systolic blood pressure value SYS can be correctly determined in principle.
[0070] (Specific method for calculating blood pressure)
[0071] Figure 5 shows a detailed flowchart of how blood pressure is calculated in step S204 of Figure 4.
[0072] In step S211 of Figure 5, the CPU 110 subtracts the cuff pressure Pcdc from the second pressure sensor 31 from the data representing the pressure Ps of the sensing cuff 21 from the first pressure sensor 30, while associating the timing of their generation with each other, to obtain the pressure at the rising point PWa and the peak point PWp of the pressure pulse wave PW shown for each beat, as shown in Figure 6(B).
[0073] Next, in step S212 of Figure 5, the CPU 110 associates data representing the pressure at the peak point PWp shown by the pressure pulse wave PW for each beat with data representing the cuff pressure Pcdc at the time the pressure at the peak point PWp occurred to form a first data set, and associates data representing the pressure at the rise start point PWa with data representing the cuff pressure Pcdc at the time the pressure at the rise start point PWa occurred to form a second data set. Then, as illustrated in Tables 1 and 2 below, the CPU 110 stores the first data set and the second data set in memory 51 in chronological order. (Table 1) First Data Set Here, t1, t2, t3, ... indicate the time for each peak point PWp of the beat. Pc1, Pc2, Pc3, ... indicate the cuff pressure Pcdc at the respective times t1, t2, t3, ... PWp1, PWp2, PWp3, ... indicate the pressure at the peak point PWp at the respective times t1, t2, t3, ... In reality, specific numerical values will be inserted into t1, t2, t3, ..., Pc1, Pc2, Pc3, ..., PWp1, PWp2, PWp3, ... (Table 2) Second Dataset Here, t1', t2', t3', ... indicate the time for each beat onset point PWa, which in this example corresponds to a time slightly earlier than time t1, t2, t3, ... (the time from the onset point PWa to the peak point PWp). Pc1', Pc2', Pc3', ... indicate the cuff pressure Pcdc at time t1', t2', t3', ... respectively. PWa1, PWa2, PWa3, ... indicate the pressure at the onset point PWa at time t1', t2', t3', ... respectively. In reality, specific numerical values will be inserted into t1', t2', t3', ..., Pc1', Pc2', Pc3', ..., PWa1, PWa2, PWa3, ...
[0074] In this example, the CPU 110 plots the first data set (Table 1) and the second data set (Table 2) stored in memory 51 on a coordinate plane Q defined by the horizontal axis representing the cuff pressure Pcdc and the vertical axis representing the pressure of the pulse wave PW, as shown in Figure 6(B). As a result, the first plotted point group corresponding to the first data set and the second plotted point group corresponding to the second data set define the first curve C1 and the second curve C2, respectively, which follow the pipe law. In this example, Figure 6(B) shows the first curve C1, which connects adjacent peak points PWp, and the second curve C2, which connects adjacent rising point PWa.
[0075] Next, in step S213 of Figure 5, the CPU 110 calculates the difference between the pressure at the peak point PWp and the pressure at the rise start point PWa for each beat, and uses this difference as the pulse wave amplitude AM shown in Figure 6(B).
[0076] Next, in step S214 of Figure 5, the CPU 110 smooths the pulse wave amplitude AM for each beat by taking a predetermined moving average over multiple beats (5 beats in this example) in order to accurately determine the systolic blood pressure value SYS and the diastolic blood pressure value DIA. Then, in step S215, as illustrated in Table 3 below, the CPU 110 associates the data of each smoothed pulse wave amplitude AM with data representing the cuff pressure Pcdc at the time the pulse wave amplitude AM was observed, and stores it in memory 51 as a third dataset in time series. Note that this third dataset in Table 3 may be stored together with the first dataset in Table 1 and the second dataset in Table 2. (Table 3) Third Dataset Here, t1, t2, t3, ... indicate the time for each peak point PWp of the beat. Pc1, Pc2, Pc3, ... indicate the cuff pressure Pcdc at the respective times t1, t2, t3, .... These t1, t2, t3, ... and Pc1, Pc2, Pc3, ... are the same values as those in Table 1. AM1, AM2, AM3, ... indicate the smoothed pulse wave amplitude (hereinafter simply referred to as "pulse wave amplitude") obtained at the respective times t1, t2, t3, .... In practice, specific numerical values will be inserted into AM1, AM2, AM3, ...
[0077] Next, in step S216, the CPU 110 refers to the third data set (Table 3) stored in memory 51 and determines whether the pulse wave amplitude AM has reached the maximum value AMmax shown in Figure 6(B). If, at this point, the pulse wave amplitude AM has not reached the maximum value AMmax (NO in step S216 in Figure 5), the processing in steps S211 to S216 is repeated. On the other hand, if the pulse wave amplitude AM has reached the maximum value AMmax (YES in step S216 in Figure 5), the process proceeds to step S217, where the CPU 110 determines the time when the pulse wave amplitude AM reached the maximum value AMmax as the time (transition time) tA when the pressure at the rise start point PWa for each beat drops from a positive value to zero level, and calculates the cuff pressure PcA at this determined transition time tA as the diastolic blood pressure value DIA. In the example in Figure 6(B), DIA was calculated as 88 (mmHg). This transition time tA corresponds to the point in time when the second curve C2, shown in Figure 6(B), drops from a positive value to the zero level. As with Figure 7 described above, the point on the second curve C2 at transition time tA is shown as point A in Figure 6(B).
[0078] The reason why the cuff pressure PcA at transition time tA can be determined as the diastolic blood pressure value DIA is that the transition time (i.e., the time when the pressure at the start of each beat PWa falls from a positive value to zero) tA corresponds to the time when the cuff pressure Pc exceeds the diastolic blood pressure value DIA. Therefore, the cuff pressure PcA at transition time tA can, in principle, be correctly determined as the diastolic blood pressure value DIA.
[0079] In this example, whether or not the pulse wave amplitude AM reached its maximum value AMmax is determined by comparing pulse wave amplitudes AM with each other. Therefore, this method can be used to determine the pulse wave amplitude more accurately than by comparing the pressure at the onset point PWa with the zero level (buried in noise). Consequently, this blood pressure monitor 1 can accurately determine the transition time tA, and thereby accurately determine the diastolic blood pressure value DIA.
[0080] Next, in step S218 of Figure 5, the CPU 110 searches for and finds a past time point tB on the coordinate plane Q shown in Figure 6(B) where the second curve C2 showed a positive value equal to the maximum pulse wave amplitude AMmax, based on the second data set (Table 2) stored in memory 51, and determines the cuff pressure PcB at that past time point tB. As with Figure 7 described above, the point on the second curve C2 at past time point tB is shown as point B in Figure 6(B).
[0081] Next, in step S219 of Figure 5, the CPU 110 calculates the difference between the data representing the cuff pressure PcA (=DIA) at transition time tA and the data representing the cuff pressure PcB at past time tB, as the pulse pressure equivalent PP shown in Figure 6(B). That is, PP = PcA - PcB. In the example in Figure 6(B), PcA = 88 (mmHg) and PcB = 41 (mmHg), and therefore PP = 47 (mmHg).
[0082] The reason why the difference obtained by subtracting the data representing the cuff pressure PcB at past time tB from the data representing the cuff pressure PcA at transition time tA is obtained as the pulse pressure equivalent PP is because, with respect to the horizontal axis, the portion C1e of the first curve C1, which is defined from the cuff pressure PcA (=DIA) at transition time tA to the systolic blood pressure value SYS to be determined, and the portion C2e of the second curve C2, which is defined from the cuff pressure PcB at past time tB to the cuff pressure PcA at transition time tA, have the same shape according to the same pipe law.
[0083] Next, in step S220 of Figure 5, the systolic blood pressure value SYS is obtained by adding the pulse pressure equivalent amount PP to the diastolic blood pressure value DIA. On the coordinate plane Q of Figure 7, this process corresponds to adding a pressure of the same magnitude as the pulse pressure equivalent amount PP to the diastolic blood pressure value DIA, as indicated by arrow E. As a result, the CPU 110 can correctly calculate the diastolic blood pressure value DIA and the systolic blood pressure value SYS in principle. In the example of Figure 6(B), DIA = 88 (mmHg) and PP = 47 (mmHg), and therefore SYS = 135 (mmHg).
[0084] After this, the CPU 110, triggered by the calculation of the systolic blood pressure value SYS, proceeds to step S206 in Figure 4. The CPU 110 acts as a pressure control unit and, in step S206, stops the pump 32 via the pump drive circuit 320, and in step S207, opens the discharge valve 33 via the valve drive circuit 330 to rapidly exhaust the air from the pressure cuff 23. As previously described, in this example, the pump 32 is stopped at the stop time tC shown in Figure 6(A), and rapid exhaust is performed during the rapid exhaust period tD shown in Figure 6(A). Accordingly, the process of storing the first, second, and third data sets in the memory 51 in time series is also completed, and the process of defining the first curve C1 and the second curve C2 on the coordinate plane Q, as shown in Figure 6(B), is also completed.
[0085] For example, with the processing power of a typical CPU 110, if the pressurization speed is 5 mmHg / second and the pulse rate is 60 beats / minute, blood pressure measurement can be completed by pressurizing the cuff to a level 1 to 2 beats higher (approximately 5 mmHg to 10 mmHg) than the diastolic blood pressure value DIA from the start of measurement. In the example in Figure 6(A), pressurization was stopped at tC = 35 (seconds) from the start of blood pressure measurement (t = 0), and rapid deflation was completed in a rapid deflation period of approximately 3 seconds (tD). In other words, blood pressure measurement could be completed in approximately 38 seconds from the start of measurement.
[0086] Thus, with this blood pressure monitor 1, blood pressure at the measurement site (diastolic blood pressure value DIA and systolic blood pressure value SYS) can be measured non-invasively and in principle correctly, similar to the blood pressure measurement method described in Patent Document 1. Moreover, with this blood pressure monitor 1, blood pressure measurement can be completed at a lower pressure and in a shorter time compared to, for example, pressurizing to the systolic blood pressure value SYS at a constant pressurization rate.
[0087] The embodiments described above are illustrative, and various modifications are possible without departing from the scope of this invention. Each of the above embodiments can stand on its own, but they can also be combined. Furthermore, various features within different embodiments can stand on their own, but they can also be combined.
[0088] 1. Blood pressure monitor 10. Main unit 20. Cuff 21. Sensing cuff 22. Back plate 23. Pressure cuff 30. First pressure sensor 31. Second pressure sensor 32. Pump 33. Discharge valve
Claims
1. An electronic blood pressure monitor for non-invasively measuring blood pressure at a site to be measured, comprising: a bag-shaped pressure cuff that is attached around the circumferential direction of the site to be measured in order to compress the site to be measured by receiving a supply of pressurizing fluid; a bag-shaped sensing cuff that is positioned on the inner circumference of the pressure cuff and in a part that should face the artery of the site to be measured, and which contains a pressure transmission fluid separately from the pressure cuff, wherein the sensing cuff compresses the artery of the site to be measured via the pressure transmission fluid due to the pressure of the pressure cuff, and at the same time receives changes in the volume of the artery as changes in pressure; a first pressure sensor for detecting the pressure of the sensing cuff; a second pressure sensor for detecting the pressure of the pressure cuff; and a pressure control unit for supplying the pressurizing fluid to the pressure cuff or discharging the pressurizing fluid from the pressure cuff to control the pressure of the pressure cuff. The system includes a blood pressure calculation unit that calculates a blood pressure value based on data representing the pressure of the sensing cuff from the first pressure sensor and data representing the pressure of the pressing cuff from the second pressure sensor during the pressurization process of the pressing cuff by the pressure control unit, and a storage unit that can store the data, wherein the blood pressure calculation unit, during the pressurization process, subtracts the DC component of the data representing the pressure of the pressing cuff or a value approximating the DC component from the data representing the pressure of the sensing cuff to determine the pressure at the start of the rise and the pressure at the peak point of the pressure pulse wave shown for each beat, The data representing the pressure at the peak point shown by the pulse wave for each beat is associated with the data representing the pressure of the compression cuff at the time the peak pressure occurred to form a first data set, and the data representing the pressure at the start of the rise is associated with the data representing the pressure of the compression cuff at the time the rise start pressure occurred to form a second data set. The first and second data sets are stored in the memory unit in chronological order, and as a result, the first and second data sets define a first and second curve, respectively, according to the pipe law, on a coordinate plane defined by the horizontal axis representing the pressure of the compression cuff and the vertical axis representing the pressure of the pulse wave.An electronic blood pressure monitor characterized by determining the pressure of the pressure cuff at the point of transition when the pressure at the onset point of the rise for each beat drops from a positive value to zero, determining the diastolic blood pressure value, subtracting the data representing the pressure at the onset point from the data representing the pressure at the peak point of the beat that occurred at the transition point, and determining the maximum pulse wave amplitude by the difference between these two points. Based on the second data set stored in the memory unit, the device searches for and finds a past point in time on the coordinate plane when the second curve shows a positive value equal to the maximum pulse wave amplitude, and determines the pressure of the pressure cuff at that past point. The device is characterized by determining the pulse pressure equivalent by subtracting the data representing the pressure of the pressure cuff at the past point from the data representing the pressure of the pressure cuff at the transition point, and adding the pulse pressure equivalent to the diastolic blood pressure value to determine the systolic blood pressure value.
2. An electronic blood pressure monitor according to claim 1, wherein the blood pressure calculation unit, during the pressurization process, calculates the difference between the data representing the pressure at the peak point and the data representing the pressure at the start of the rise for each beat as the pulse wave amplitude, associates the data of each pulse wave amplitude with the data representing the pressure of the pressure cuff at the time the pulse wave amplitude was shown to form a third data set, stores the third data set in the memory unit in time series, determines the maximum value shown by the pulse wave amplitude by referring to the third data set as the maximum pulse wave amplitude, and determines the time when the pulse wave amplitude showed the maximum pulse wave amplitude as the transition time.
3. An electronic blood pressure monitor according to claim 1 or 2, characterized in that, triggered by the blood pressure calculation unit calculating the systolic blood pressure value, the pressure control unit terminates the pressurization process and discharges the pressurizing fluid from the pressure cuff.
4. A blood pressure measurement method for non-invasively measuring blood pressure at a site to be measured using the electronic blood pressure monitor described in claim 1, wherein the blood pressure calculation unit subtracts the DC component of the data representing the pressure of the pressure cuff or a value approximating the DC component from the data representing the pressure of the sensing cuff during the pressurization process to determine the pressure at the onset point and the peak point of the pressure pulse wave shown for each beat. The data representing the pressure at the peak point shown by the above-mentioned pressure pulse wave for each beat is associated with the data representing the pressure of the compression cuff at the time the pressure at the peak point occurred to form a first data set, and the data representing the pressure at the start of the rise is associated with the data representing the pressure of the compression cuff at the time the pressure at the start of the rise occurred to form a second data set, and the first and second data sets are stored in the memory unit in a time series, so that the first and second data sets define a first curve and a second curve, respectively, according to the pipe law on a coordinate plane defined by the horizontal axis representing the pressure of the compression cuff and the vertical axis representing the pressure of the pressure pulse wave, and the pressure of the compression cuff at the time when the pressure at the start of the rise for each beat drops from a positive value to zero is determined as the diastolic blood pressure value, and the difference obtained by subtracting the data representing the pressure at the start of the rise from the data representing the pressure at the peak point of the beat that occurred at the time of the transition is determined as the maximum pulse wave amplitude. A blood pressure measurement method characterized by searching for and finding a past time point on the coordinate plane where the second curve showed a positive value equal to the maximum pulse wave amplitude, based on the second dataset stored in the memory unit, determining the pressure of the pressure cuff at that past time point, calculating the difference obtained by subtracting the data representing the pressure of the pressure cuff at the past time point from the data representing the pressure of the pressure cuff at the transition point, and adding the pulse pressure equivalent to the diastolic blood pressure value to determine the systolic blood pressure value.