Electronic blood pressure monitor and blood pressure measuring method

Abstract

To accurately measure a blood pressure of a site to be measured noninvasively manner in principle in a fundamentally correct manner.SOLUTION: There is provided a bag-shaped pressing cuff that applies pressure to a site to be measured upon being fed a fluid for pressurization. There is provided, separately from the pressing cuff, a bag-shaped sensing cuff for accommodating a fluid for pressure transmission, on the inner circumferential side of the pressing cuff. A direct current component of data representing the pressure Pc of the pressing cuff is subtracted from data representing the pressure Ps of the sensing cuff during a decompression process, and the pressure of a rising start point PWa and the pressure of a peak point PWp exhibited every beat by pressure pulse waves PW are obtained. A first time point t1 at which the pressure of the peak point PWp for each beat shifts between zero level and a positive value during the decompression process is obtained, and the pressure Pc of the pressing cuff at the first time point t1 is obtained as a systolic blood pressure value; and a second time point t2 at which the pressure of the rising start point Pwa for each beat shifts between zero level and a positive value is obtained, and the pressure Pc of the pressing cuff at the second time point t2 is obtained as a diastolic blood pressure value.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an electronic blood pressure monitor, and more particularly to an electronic blood pressure monitor and a blood pressure measuring method for non-invasively measuring blood pressure at a measurement site. [Background technology]

[0002] Conventionally, as disclosed in Patent Document 1 (JP Patent Publication 9-299339A), for example, an electronic blood pressure monitor of this type is known that compresses a measurement site with a blood pressure measurement cuff and calculates the blood pressure at the measurement site by an oscillometric method. Specifically, when the blood pressure measurement cuff is in the inflation or deflation process, an envelope is set for the series of pulse wave amplitudes obtained from the cuff pressure, and threshold levels (including a systolic threshold level and a diastolic threshold level) of a predetermined ratio (proportion) are set for the maximum value of the envelope, and the cuff pressures at the time when the envelope crosses these threshold levels are calculated as the maximum blood pressure (systolic blood pressure) and the minimum blood pressure (diastolic blood pressure), respectively. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-299339 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, the threshold level for the systolic blood pressure is set to 0.5 to 0.6, and the threshold level for the diastolic blood pressure is set to 0.7 to 0.8 in order to statistically match the systolic and diastolic blood pressures calculated by the oscillometric method with those measured by a standard measurement method (e.g., traditional auscultation).

[0005] For this reason, although the systolic and diastolic blood pressures calculated by the above-mentioned oscillometric method are statistically guaranteed to be accurate, there is a problem that for some people there may be a difference between the systolic and diastolic blood pressures calculated by the oscillometric method and those measured by a standard measurement method.

[0006] Therefore, an object of the present invention is to provide an electronic blood pressure monitor and a blood pressure measurement method that can measure blood pressure at a measurement site non-invasively and correctly in principle. Here, "correctly in principle" means that the method is based on the same mechanism as the principle of the standard measurement method. [Means for solving the problem]

[0007] In order to solve the above problems, the electronic blood pressure monitor disclosed herein comprises: An electronic blood pressure monitor that non-invasively measures blood pressure at a measurement site, a bag-shaped pressure cuff that is attached around the measurement site in a circumferential direction so as to receive a supply of pressurizing fluid and pressurize the measurement site; a bag-shaped sensing cuff for accommodating a fluid for transmitting pressure, which is disposed on the inner circumferential side of the pressure cuff and faces the artery of the measurement site, and which is separate from the pressure cuff; the sensing cuff compresses the artery of the measurement site via the fluid for transmitting pressure by the pressure of the pressure cuff, and receives a pressure pulse wave from the artery; a first pressure sensor that detects the pressure of the sensing cuff; A second pressure sensor for detecting the pressure of the pressure cuff; a pressure control unit that controls the pressure of the pressure cuff by supplying the pressurizing fluid to the pressurizing cuff or discharging the pressurizing fluid from the pressurizing cuff; 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 a process of a change in the pressure of the pressing cuff by the pressure control unit, The blood pressure calculation unit is a DC component of the data representing the pressure of the compression cuff or a value approximating the DC component is subtracted from the data representing the pressure of the sensing cuff during the pressure change process to obtain a pressure at a rising start point and a pressure at a peak point shown for each beat of the pressure pulse wave; A first time point at which the pressure at the peak point for each beat transitions between a zero level and a positive value during the pressure change process is obtained, and the pressure of the pressure cuff at this first time point is obtained as a systolic blood pressure value, and a second time point at which the pressure at the rising start point for each beat transitions between a zero level and a positive value is obtained, and the pressure of the pressure cuff at this second time point is obtained as a diastolic blood pressure value. It is characterized by:

[0008] In this specification, the "fluid for transmitting pressure" may be sealed in the sensing cuff during the manufacturing stage of the electronic blood pressure monitor, or may be contained in the sensing cuff and discharged from the sensing cuff each time blood pressure is measured.

[0009] Furthermore, the "fluid" for pressurization and pressure transmission is typically air, but may be other gases or liquids.

[0010] The "DC component" of the data representing the pressure of the pressure cuff means a component obtained by removing a fluctuating component (e.g., a fluctuating component for each beat resulting from the pressure pulse wave from the artery) from the data representing the pressure of the pressure cuff. Also, the "value approximating the DC component" refers to a value approximating a straight line determined by the data of the pressure of the pressure cuff at one point and the decompression speed during the decompression process at a constant decompression speed, for example.

[0011] "Determining the pressure at the rising start point and the peak point shown by the pressure pulse wave for each beat" means determining the pressure when the pressure pulse wave detected by the first pressure sensor indicates the rising start point and the peak point for each beat. Note that, for example, in the pressure section where the pressure of the compression cuff is higher than the systolic blood pressure value during the decompression process, the blood flow in the artery is stopped, so the "rising start point" and the "peak point" are not observed, and therefore these pressures cannot be determined.

[0012] The terms "first time point" and "second time point" are used for the convenience of distinguishing those time points from each other, and do not necessarily refer to a time point before or after those time points.

[0013] In the electronic blood pressure monitor disclosed in this disclosure, a bag-shaped pressure cuff is attached to surround the measurement site in the circumferential direction. In this attached state, a bag-shaped sensing cuff is disposed on the inner circumferential side of the pressure cuff and facing the artery of the measurement site. For example, it is assumed that a fluid for transmitting pressure is sealed in the sensing cuff in advance during the manufacturing process of the electronic blood pressure monitor.

[0014] During blood pressure measurement, a pressure control unit 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 sensing cuff compresses the artery of the measurement site via the pressure transmission fluid by the pressure of the pressure cuff, while receiving a pressure pulse wave from the artery. A first pressure sensor detects the pressure of the sensing cuff, and a second pressure sensor detects the pressure of the pressure cuff. A blood pressure calculation unit 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 process of the pressure of the pressure cuff being changed by the pressure control unit. Specifically, the blood pressure calculation unit subtracts a DC component or a value approximating the DC component of the data representing the pressure of the pressure cuff from data representing the pressure of the sensing cuff during the pressure change process to obtain the pressure at the start of the rise and the pressure at the peak point shown for each beat of the pressure pulse wave. The blood pressure calculation unit also obtains a first time point at which the pressure at the peak point for each beat transitions between a zero level and a positive value during the pressure change process, and obtains the pressure of the pressure cuff at this first time point as a systolic blood pressure value, and obtains a second time point at which the pressure at the start of the rise for each beat transitions between a zero level and a positive value, and obtains the pressure of the pressure cuff at this second time point as a diastolic blood pressure value.

[0015] As a result, this electronic blood pressure monitor can, in principle, accurately measure blood pressure at a measurement site in a non-invasive manner. The reason for this will be described in detail in the embodiment section with reference to the drawings.

[0016] In one embodiment, the electronic blood pressure monitor comprises: The pressure change process is a decompression process after the blood flow through the artery is temporarily stopped by pressurization of the compression cuff, the first time point is a time point at which the pressure at the peak point for each beat begins to indicate a positive value from a zero level, The second time point is a time point after the first time point when the pressure at the rising start point of each beat starts to indicate a positive value from the zero level. It is characterized by:

[0017] In the electronic blood pressure monitor of this embodiment, the first time point corresponds to a time point when blood flow through the artery is resumed after being temporarily stopped by pressurization of the pressure cuff, i.e., a time point when the pressure of the pressure cuff falls below the systolic blood pressure. Therefore, the pressure of the pressure cuff at the first time point is determined as a systolic blood pressure value. The second time point corresponds to a time point when the pressure of the pressure cuff falls below the diastolic blood pressure. Therefore, the pressure of the pressure cuff at the second time point is determined as a diastolic blood pressure value.

[0018] In one embodiment, the electronic blood pressure monitor comprises: The pressure change process is a pressurization process of the pressure cuff, the second time point is a time point at which the pressure at the rising start point of each beat falls from a positive value to a zero level, The first time point is a time point after the second time point at which the pressure at the peak point for each beat falls from a positive value to a zero level. It is characterized by:

[0019] In the electronic blood pressure monitor of this embodiment, the second time point corresponds to a time point when the pressure of the pressure cuff exceeds the diastolic blood pressure. Therefore, the pressure of the pressure cuff at the second time point is determined as a diastolic blood pressure value. The first time point corresponds to a time point when the pressure of the pressure cuff exceeds the systolic blood pressure. Therefore, the pressure of the pressure cuff at the first time point is determined as a systolic blood pressure value.

[0020] In one embodiment, the electronic blood pressure monitor comprises: the sensing cuff is fluidly connected to the first pressure sensor via a first fluid line; the pressure cuff is fluidly connected to the second pressure sensor via a second fluid line; The first fluid pipe and the second fluid pipe are spaced apart from each other.

[0021] In the electronic blood pressure monitor of this embodiment, the first fluid pipe and the second fluid pipe are separated from each other. Therefore, for example, a fluctuation component (e.g., due to a pressure pulse wave from the artery) included in the pressure of the first fluid pipe connected to the sensing cuff can be prevented from mixing as noise into the pressure of the second fluid pipe connected to the pressure cuff. Conversely, a fluctuation component included in the pressure of the second fluid pipe connected to the pressure cuff can be prevented from mixing as noise into the pressure of the first fluid pipe connected to the sensing cuff.

[0022] In one embodiment of the electronic blood pressure monitor, with respect to the width direction of the pressure cuff along the direction in which the artery of the measurement site passes, the range occupied by the sensing cuff is within the remaining range of the width direction dimension of the pressure cuff excluding a predetermined range from the upstream side of the artery.

[0023] Suppose that the range of the sensing cuff in the width direction of the pressure cuff along the direction of the artery of the measurement site is within, for example, 1 / 3 of the width direction dimension of the pressure cuff from the upstream side of the artery. Then, even if the pressure of the pressure cuff is in a pressure section higher than the systolic blood pressure value during the decompression process and blood flow in the artery is stopped, a pulse wave moving from the upstream side of the artery to just below the pressure cuff may be mixed as noise (fluctuation component) into the pressure of the sensing cuff detected by the first pressure sensor. Therefore, in the electronic blood pressure monitor of this embodiment, the range of the sensing cuff in the width direction of the pressure cuff along the direction of the artery of the measurement site is within the remaining range excluding a predetermined range from the upstream side of the artery in the width direction dimension of the pressure cuff. Therefore, when the pressure of the compression cuff during the decompression process is within a pressure range higher than the systolic blood pressure value and blood flow in the artery is stopped, it is possible to prevent a pulse wave traveling from the upstream side of the artery to just below the compression cuff from being mixed as noise (fluctuation component) in the pressure of the sensing cuff detected by the first pressure sensor.

[0024] In one embodiment, the electronic blood pressure monitor is provided with a back plate interposed between the pressure cuff and the sensing cuff, and this back plate transmits the pressure of the pressure cuff to the sensing cuff and blocks the transmission of pressure fluctuation components between the pressure cuff and the sensing cuff.

[0025] In the electronic blood pressure monitor of this embodiment, the back plate can reliably transmit the pressure of the pressure cuff to the sensing cuff. Therefore, the sensing cuff can reliably compress the artery of the measurement site by the pressure of the pressure cuff via the pressure transmission fluid. At the same time, the back plate blocks the transmission of pressure fluctuation components between the pressure cuff and the sensing cuff. Therefore, for example, it is possible to suppress the fluctuation components included in the pressure of the sensing cuff (e.g., due to the pressure pulse wave from the artery) from being mixed into the pressure of the pressure cuff as noise. Conversely, it is possible to suppress the fluctuation components included in the pressure of the pressure cuff from being mixed into the pressure of the sensing cuff as noise.

[0026] In one embodiment of the electronic blood pressure monitor, the first fluid piping is characterized in that the pressure cuff is pulled out to the outside of the area surrounding the measured area in a manner that is removed from the artery when viewed in a planar view from a thickness direction perpendicular to the outer peripheral surface of the measured area.

[0027] By "off-artery" it is meant that it does not overlap with the artery and is spaced apart from the artery.

[0028] In the electronic blood pressure monitor of this embodiment, the first fluid piping is drawn out of the area surrounding the measurement site in such a manner that the pressure cuff is removed from the artery in a plan view seen from a thickness direction perpendicular to the outer circumferential surface of the measurement site. Therefore, the first fluid piping does not prevent the pressure of the pressure cuff from compressing the artery of the measurement site via the sensing cuff. Furthermore, the first fluid piping does not prevent the sensing cuff from receiving a pressure pulse wave from the artery.

[0029] In one embodiment, the electronic blood pressure monitor comprises: the pressure cuff has a through hole penetrating in a thickness direction in a part of a region facing the sensing cuff, The first fluid pipe is drawn from the sensing cuff through the through hole of the pressure cuff to the outer circumferential side of the pressure cuff. It is characterized by:

[0030] The "thickness direction" of the pressure cuff (and the sensing cuff) refers to a direction perpendicular to the outer circumferential surface of the measurement site when the cuff is attached to the measurement site.

[0031] In the electronic blood pressure monitor of this embodiment, the first fluid piping is drawn from the sensing cuff through the through hole of the pressure cuff to the outside of the pressure cuff. Therefore, the first fluid piping does not prevent the pressure of the pressure cuff from compressing the artery of the measurement site via the sensing cuff. Furthermore, the first fluid piping does not prevent the sensing cuff from receiving a pressure pulse wave from the artery.

[0032] In one embodiment of the electronic blood pressure monitor, a predetermined amount of the pressure transmitting fluid is sealed in the sensing cuff.

[0033] The "predetermined amount" refers to an amount that can prevent, for example, the bag constituting the sensing cuff from being crushed in the thickness direction by the pressure of the pressure cuff, causing the sheets constituting the bag to come into close contact with each other. By preventing such a situation, the sensing cuff can reliably compress the artery at the measurement site by the pressure of the pressure cuff via the pressure transmission fluid, while reliably receiving a pressure pulse wave from the artery.

[0034] In the electronic blood pressure monitor of this embodiment, the sensing cuff is filled with a predetermined amount of the fluid for pressure transmission, which eliminates the need to fill the sensing cuff with the fluid for pressure transmission every time blood pressure is measured, for example.

[0035] In one embodiment, the electronic blood pressure monitor is characterized in that it is provided with a fluid containment control unit that supplies and seals a predetermined amount of the pressure transmission fluid to the sensing cuff via the first fluid piping before the pressure control unit starts to pressurize the compression cuff each time a blood pressure measurement is performed, and that controls the discharge of the pressure transmission fluid from the sensing cuff via the first fluid piping after the blood pressure calculation unit has completed calculation of the blood pressure value.

[0036] In the electronic blood pressure monitor of this embodiment, the pressure transmission fluid can be automatically filled into the sensing cuff before the start of pressurization of the pressure cuff each time blood pressure measurement is performed, and the pressure transmission fluid can be automatically discharged from the sensing cuff after the calculation of the blood pressure value is completed.

[0037] In one embodiment, the electronic blood pressure monitor comprises: the pressure control unit includes a pump for supplying air as the pressurizing fluid to the pressure cuff through the second fluid piping, and a discharge valve for discharging the air from the pressure cuff through the second fluid piping; the fluid accommodation control section includes a switching valve connected between the first fluid piping and the second fluid piping, and the switching valve is capable of taking a first position in which the first fluid piping and the second fluid piping are separated from each other, and a second position in which the first fluid piping and the second fluid piping are allowed to communicate with each other and the pressure cuff is sealed; The fluid containment control section includes: when supplying and sealing the pressure transmission fluid to the sensing cuff prior to the start of pressurization of the pressure cuff by the pressure control unit, switching the switching valve to the second position and using the pump to supply air as the pressure transmission fluid to the sensing cuff; maintaining the switching valve in the first position while the pressure control unit is pressurizing or depressurizing the pressure cuff; When discharging the pressure transmitting fluid from the sensing cuff after the blood pressure calculation unit has completed calculation of the blood pressure value, the switching valve is switched to the second position and the air is discharged from the sensing cuff using the discharge valve. A blood pressure monitor characterized by the above.

[0038] In the electronic blood pressure monitor of this embodiment, with a relatively small number of parts, air can be automatically sealed in the sensing cuff as the pressure transmitting fluid, and the air can be automatically discharged from the sensing cuff.

[0039] In one embodiment, the electronic blood pressure monitor comprises: A storage unit capable of storing data, The blood pressure calculation unit is a difference obtained by subtracting the pressure at the start point of the rising edge from the pressure at the peak point for each beat is calculated as a pulse wave amplitude, and data on each pulse wave amplitude is stored in the storage unit in a chronological order in association with data representing the pressure of the compression cuff at the time when the pulse wave amplitude was shown; The stored contents of the storage unit are referenced, and the time point at which the pulse wave amplitude reaches a maximum value during the process of change in the pressure is determined as the second time point. It is characterized by:

[0040] Since the pressure pulse wave received by the sensing cuff usually includes noise, it may be difficult to determine the time (second time point) at which the pressure at the rising start point transitions between the zero level (buried in noise) and a positive value. Therefore, in the electronic blood pressure monitor of this embodiment, the blood pressure calculation unit calculates the difference obtained by subtracting the pressure at the rising start point from the pressure at the peak point for each beat as the pulse wave amplitude, and stores data of each pulse wave amplitude during the pressure change process in the memory unit in chronological order in association with data of the pressure of the pressure cuff at the time when the pulse wave amplitude was shown. Then, the blood pressure calculation unit refers to the contents stored in the memory unit and determines the time point at which the pulse wave amplitude was maximum during the pressure change process as the second time point. As a result, the pressure of the pressure cuff corresponding to the determined second time point is obtained as the diastolic blood pressure value. Here, whether or not the pulse wave amplitude has reached the maximum value is determined by comparing the pulse wave amplitudes with each other, so that it can be determined more accurately than when it is determined by comparing with the zero level (buried in noise). Therefore, in the electronic blood pressure monitor of this embodiment, the second time point can be determined with high accuracy, and the diastolic blood pressure value can be obtained with high accuracy.

[0041] In one embodiment, the electronic blood pressure monitor comprises: The blood pressure calculation unit is multiplying the maximum value of the pulse wave amplitude by a predetermined ratio to set a threshold level for determining the first time point; With reference to the contents stored in the storage unit, the time point at which the pulse wave amplitude crosses the threshold level during the change in the pressure is determined as the first time point. It is characterized by:

[0042] The "predetermined ratio" is set to be greater than the actual noise level while being as small as possible in order to accurately determine the first time point. With respect to the maximum value of the pulse wave amplitude, the "predetermined ratio" is set to, for example, about 0.1.

[0043] Since the pressure pulse wave received by the sensing cuff usually includes noise, it may be difficult to determine the time (first time point) at which the pressure at the peak point transitions between the zero level (buried in noise) and a positive value. In this embodiment of the electronic blood pressure monitor, the blood pressure calculation unit multiplies the maximum value of the pulse wave amplitude by a predetermined ratio to set a threshold level for determining the first time point. Then, the blood pressure calculation unit refers to the contents stored in the storage unit and determines the time point at which the pulse wave amplitude crosses the threshold level during the pressure change process as the first time point. As a result, the pressure of the pressure cuff corresponding to the determined first time point is obtained as the systolic blood pressure value. Here, whether or not the pulse wave amplitude crosses the threshold level is determined by comparing the pulse wave amplitude with the set threshold level, and therefore, it can be determined more accurately than when it is determined by comparing with the zero level (buried in noise). Therefore, in the electronic blood pressure monitor of this embodiment, the first time point can be determined with high accuracy, and the systolic blood pressure value can be obtained with high accuracy.

[0044] In one embodiment of the electronic blood pressure monitor, the blood pressure calculation unit calculates the pulse wave amplitude for each beat, then smoothes the pulse wave amplitude by taking a moving average over a predetermined number of beats, and stores the smoothed pulse wave amplitude in the memory unit in chronological order.

[0045] The "predetermined number of beats" is, for example, five beats.

[0046] Normally, blood pressure fluctuates for each beat, and the pulse wave amplitude also fluctuates due to the influence of the blood pressure. Therefore, in the electronic blood pressure monitor of this embodiment, the blood pressure calculation unit calculates the pulse wave amplitude for each beat, then takes a moving average over multiple beats to smooth the pulse wave amplitude for each beat, and stores the smoothed pulse wave amplitude in time series in the storage unit. As a result, the smoothed pulse wave amplitude is stored in time series in the storage unit. This makes it possible to accurately determine the systolic blood pressure value and the diastolic blood pressure value.

[0047] In another aspect, the blood pressure measuring method of the present disclosure includes: By using the electronic blood pressure monitor A blood pressure measurement method for non-invasively measuring blood pressure at a measurement site, comprising: The blood pressure calculation unit acquiring 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 a process of a change in the pressure of the pressure cuff by the pressure control unit; a DC component of the data representing the pressure of the compression cuff or a value approximating the DC component is subtracted from the data representing the pressure of the sensing cuff during the pressure change process to obtain a pressure at a rising start point and a pressure at a peak point shown for each beat of the pressure pulse wave; A first time point at which the pressure at the peak point for each beat transitions between a zero level and a positive value during the pressure change process is obtained, and the pressure of the pressure cuff at this first time point is obtained as a systolic blood pressure value, and a second time point at which the pressure at the rising start point for each beat transitions between a zero level and a positive value is obtained, and the pressure of the pressure cuff at this second time point is obtained as a diastolic blood pressure value. It is characterized by:

[0048] According to the disclosed blood pressure measurement method, blood pressure at a measurement site can be measured non-invasively and, in principle, correctly.

[0049] In yet another aspect, the electronic blood pressure monitor of the present disclosure comprises: An electronic blood pressure monitor that non-invasively measures blood pressure at a measurement site, a bag-shaped pressure cuff that is attached around the measurement site in a circumferential direction so as to receive a supply of pressurizing fluid and pressurize the measurement site; a bag-shaped sensing cuff for accommodating a fluid for transmitting pressure, which is disposed on the inner circumferential side of the pressure cuff and faces the artery of the measurement site, and which is separate from the pressure cuff; the sensing cuff compresses the artery of the measurement site via the fluid for transmitting pressure by the pressure of the pressure cuff, and receives a pressure pulse wave from the artery; a first pressure sensor that detects the pressure of the sensing cuff; A second pressure sensor for detecting the pressure of the pressure cuff; a pressure control unit that controls the pressure of the pressure cuff by supplying the pressurizing fluid to the pressurizing cuff or discharging the pressurizing fluid from the pressurizing cuff; 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 a process of a change in the pressure of the pressing cuff by the pressure control unit, The blood pressure calculation unit is a DC component of the data representing the pressure of the compression cuff or a value approximating the DC component is subtracted from the data representing the pressure of the sensing cuff during the pressure change process to obtain a pressure at a rising start point and a pressure at a peak point shown for each beat of the pressure pulse wave; A first time point is obtained on a coordinate plane defined by a horizontal axis representing time and a vertical axis representing pressure, corresponding to a point at which a first curve connecting the peak points for each beat during the process of pressure change transitions between a zero level and a positive value, and the pressure of the pressure cuff at this first time point is obtained as a systolic blood pressure value, and a second time point is obtained on the coordinate plane corresponding to a point at which a second curve connecting the rising start points for each beat during the process of pressure change transitions between a zero level and a positive value, and the pressure of the pressure cuff at this second time point is obtained as a diastolic blood pressure value. It is characterized by:

[0050] Here, "obtaining a first time point on a coordinate plane, (omitted) corresponding to a point where the first curve transitions between the zero level and a positive value" means that it is sufficient to obtain a first time point, and does not necessarily require a process of drawing the first curve on the coordinate plane. Similarly, "obtaining a second time point on a coordinate plane, (omitted) corresponding to a point where the second curve transitions between the zero level and a positive value" means that it is sufficient to obtain a second time point, and does not necessarily require a process of drawing the second curve on the coordinate plane.

[0051] The terms "first time point" and "second time point" are used for the convenience of distinguishing those time points from each other, and do not necessarily refer to a time point before or after those time points.

[0052] According to the disclosed electronic blood pressure monitor, blood pressure at a measurement site can be measured non-invasively and in principle correctly. Effect of the Invention

[0053] As is apparent from the above, according to the electronic blood pressure monitor and blood pressure measuring method disclosed herein, blood pressure at a measurement site can be measured non-invasively and, in principle, correctly. [Brief description of the drawings]

[0054] [Figure 1] 1 is a diagram showing a block configuration of an electronic blood pressure monitor (hereinafter, abbreviated as "blood pressure monitor") according to an embodiment of the present invention. [Diagram 2] 2 is a cross-sectional view showing a state in which a cuff (including a pressure cuff and a sensing cuff) constituting the blood pressure monitor of FIG. 1 is attached to a measurement site, together with an air piping system. FIG. [Diagram 3] FIG. 2 is a diagram showing a schematic flow of blood pressure measurement by the sphygmomanometer of FIG. 1. [Figure 4] FIG. 4 is a diagram showing a detailed flow of a method for calculating blood pressure included in the flow of FIG. 3. [Diagram 5] Fig. 5(A) is a diagram showing both data representing the pressure Pc of the pressure cuff and data representing the pressure Ps of the sensing cuff during the decompression process. Fig. 5(B) is a diagram showing data representing the waveform (pressure) of the pressure pulse wave PW obtained by subtracting the DC component of the data representing the pressure Pc of the pressure cuff from the data representing the pressure Ps of the sensing cuff, with the cuff pressure Pc on the horizontal axis. [Figure 6] FIG. 5(B) is an enlarged view of the vicinity of a portion in FIG. 5(B) where the cuff pressure Pc on the horizontal axis corresponds to the diastolic blood pressure value DIA. [Figure 7] 4A to 4C are diagrams for explaining the principle of how the blood pressure is calculated by the above-mentioned sphygmomanometer. [Figure 8] FIG. 1 is a diagram showing the correspondence relationship (tube law) between the difference in pressure between the inside and outside of an artery and the volume of the artery. [Figure 9] 9(A) to 9(E) are diagrams showing various possible arrangements of the first air pipe connected to the sensing cuff. [Figure 10] Figures 10(A) and 10(B) are a cross-sectional view and a plan view showing another possible arrangement of the first air pipe, and Figure 10(C) is a cross-sectional view of the cuff when an inner cloth is provided. [Figure 11] 2 is a diagram showing a block configuration of a blood pressure monitor which is a modification of the blood pressure monitor of FIG. 1. FIG. [Figure 12] Fig. 12(A) is a cross-sectional view showing a state in which a cuff constituting the blood pressure monitor of Fig. 11 is attached to a measurement site together with an air piping system. Fig. 12(B) is a view showing a state in which a switching valve included in the air piping system is switched to a second position (operating position). [Figure 13] FIG. 12 is a diagram showing a schematic flow of blood pressure measurement using the sphygmomanometer of FIG. [Figure 14] 1. FIG. 4 is a diagram showing another schematic flow of blood pressure measurement by the sphygmomanometer of FIG. [Figure 15] FIG. 15 is a diagram showing a detailed flow of a method for calculating blood pressure included in the flow of FIG. 14. [Figure 16] Fig. 16(A) is a diagram showing both data representing the pressure Pc of the pressure cuff and data representing the pressure Ps of the sensing cuff during the pressurization process, and Fig. 16(B) is a diagram showing data representing the waveform (pressure) of the pressure pulse wave PW obtained by subtracting the DC component of the data representing the pressure Pc of the pressure cuff from the data representing the pressure Ps of the sensing cuff, with the cuff pressure Pc on the horizontal axis. [Figure 17] Fig. 17(A) is a diagram showing a state in which a general cuff presses against a measurement site. Fig. 17(B) is a diagram showing data representing the pressure Pc' of the general cuff during the decompression process, together with data on the waveform (pressure) of the pressure pulse wave PW' contained in the pressure Pc'. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0056] (Blood pressure monitor configuration) 1 shows a schematic block diagram of a blood pressure monitor 1 according to an embodiment of the present invention. This blood pressure monitor 1 mainly comprises a cuff 20 to be attached to a measurement site such as the wrist or upper arm (in this example, the upper arm), and a main body 10.

[0057] The cuff 20 includes a bag-shaped pressure cuff 23 that receives a supply of air as a pressurizing fluid to compress the measurement area 90, and a bag-shaped sensing cuff 21 that is separate from the pressure cuff 23 and contains air as a pressure transmission fluid.

[0058] The main body 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. The main body 10 is further equipped with A / D conversion circuits 300, 310 that convert analog signals into digital signals, a pump drive circuit 320 that drives the pump 32, and a valve drive circuit 330 that drives the discharge valve 33. An air pipe 37a connected to the first pressure sensor 30 is connected to the sensing cuff 21 as a flexible first air pipe 37 so as to be capable of fluidly communicating therewith (in this example, the air pipe 37a and the air pipe 37a are collectively referred to as the first air pipe 37). The air pipes 38a, 38b, and 38c respectively connected to the second pressure sensor 31, the pump 32, and the discharge valve 33 are joined together to form a flexible second air pipe 38, which is connected to the pressing cuff 23 in a fluid-distributable 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 respectively constitute the first fluid pipe and the second fluid pipe. In this example, the first air pipe 37 and the second air pipe 38 are completely separated from each other. Therefore, for example, a fluctuation component (due to, for example, a pressure pulse wave from an artery) contained in the pressure of the first air pipe 37 connected to the sensing cuff 21 can be suppressed from being mixed as noise into the pressure of the second air pipe 38 connected to the pressing cuff 23. Conversely, it is possible to suppress a fluctuation component (mainly due to vibration of pump 32) contained in the pressure of second air piping 38 connected to pressure cuff 23 from being mixed as noise into the pressure of first air piping 37 connected to sensing cuff 21. Hereinafter, first air piping 37 and second air piping 38 will be collectively referred to as air piping systems 37, 38 as appropriate.

[0059] The display device 50 includes a display, an indicator, and the like, and displays predetermined information (eg, blood pressure measurement results) according to a control signal from the CPU 110.

[0060] In this example, the operation unit 52 has a measurement switch 52A for receiving an instruction to start / stop blood pressure measurement, and a memory switch 52B for calling up past measurement results. These switches 52A and 52B input operation signals to the CPU 110 according to instructions from the user.

[0061] Memory 51 stores data of a program for controlling the sphygmomanometer 1, data used for controlling the sphygmomanometer 1, setting data for setting various functions of the sphygmomanometer 1, data of blood pressure measurement results, etc. Memory 51 is also used as a work memory when a program is executed.

[0062] The power supply unit 53 supplies power to each part of the sphygmomanometer 1, including the CPU 110, the first pressure sensor 30, the second pressure sensor 31, the pump 32, the exhaust valve 33, the display 50, the memory 51, the A / D conversion circuits 300, 310, the pump drive circuit 320, and the valve drive circuit 330.

[0063] Pump 32 supplies air as a fluid to pressure cuff 23 via second air piping 38 in order to pressurize pressure cuff 23 contained in cuff 20 (represented by the symbol "Pc"). Exhaust valve 33 opens and closes to control pressure Pc of pressure cuff 23 by discharging or sealing air in pressure cuff 23 via second air piping 38. Pump drive circuit 320 drives pump 32 based on a control signal provided by CPU 110. Valve drive circuit 330 opens and closes exhaust valve 33 based on a control signal provided by CPU 110.

[0064] In this example, the first pressure sensor 30 is a piezoresistive pressure sensor, and detects the pressure (represented by the symbol "Ps") of the sensing cuff 21 via a 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 an A / D conversion circuit 300 and input to the CPU 110. Similarly, the second pressure sensor 31 is a piezoresistive pressure sensor, and detects the pressure Pc of the pressure cuff 23 via a second air pipe 38. The pressure Pc of the pressure cuff 23 output by the second pressure sensor 31 is converted from an analog signal to a digital signal by an A / D conversion circuit 310 and input to the CPU 110.

[0065] The CPU 110, as a control unit, controls the operation of the entire blood pressure monitor 1. Specifically, the CPU 110 works as a pressure control unit in accordance with a program for controlling the blood pressure monitor 1 stored in the memory 51, and controls the driving of the pump 32 and the discharge valve 33 in response to an operation signal from the operation unit 52. The CPU 110 also works as a blood pressure calculation unit, and calculates a blood pressure value 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 controls the display 50 and the memory 51. A specific method of measuring blood pressure will be described later.

[0066] 2 shows a cross section of cuff 20 (including sensing cuff 21 and pressure cuff 23) constituting sphygmomanometer 1 when attached to measurement site 90, together with air piping systems 37, 38. As can be seen from Fig. 2, cuff 20 generally includes band-shaped outer cloth 29 located at the outermost periphery, previously described pressure cuff 23 provided along surface 29i of outer cloth 29 on the side facing measurement site 90 (inner circumferential side), back plate 22 provided along surface 23i of pressure cuff 23 on the side facing measurement site 90 (inner circumferential side), and previously described sensing cuff 21 provided along surface 22i of back plate 22 on the side facing measurement site 90 (inner circumferential side).

[0067] For ease of understanding, FIG. 2 also shows an XYZ orthogonal coordinate system indicating the "longitudinal direction Y," "width direction X," and "thickness direction Z" of the cuff 20. With respect to the cuff 20, the "longitudinal direction Y" refers to the direction in which the outer cloth 29 extends in a strip-like shape, and corresponds to the circumferential direction surrounding the measurement site 90 in the worn state. The "width direction X" refers to the direction perpendicular to the longitudinal direction Y in a plane along the outer cloth 29, and corresponds to the direction in which the artery 91 passes through the measurement site 90 in the worn state. The "upstream side" and "downstream side" refer to the upstream side and downstream side, respectively, with respect to the blood flow flowing through the artery 91. The "thickness direction Z" refers to the direction perpendicular to both the longitudinal direction Y and the width direction X (i.e., the outer cloth 29), and corresponds to the direction perpendicular to the outer peripheral surface 90a of the measurement site 90 in the worn state. This XYZ orthogonal coordinate system is also shown in Figures 9(A), 10(A), 10(B), 10(C), and 12(A), which will be described later.

[0068] FIG. 9(A) is a schematic diagram showing a planar layout of the cuff 20 in an unfolded state. As shown in this planar layout, the outer cloth 29 has a belt-like shape (a rectangle with rounded corners in this example) extending in the longitudinal direction Y (the horizontal direction in FIG. 9(A)) in this example. The outer cloth 29 can be curved or bent, but is configured to be substantially non-stretchable in order to restrict the sensing cuff 21 and the pressure cuff 23 from expanding in a direction away from the measurement site 90 during blood pressure measurement. Here, the "cloth" is not limited to a knitted one, and may be made of one or more layers of resin. In this example, the longitudinal dimension of the outer cloth 29 is set to be longer than the circumference of the upper arm as the measurement site 90.

[0069] The pressure cuff 23 has a rectangular shape with rounded corners in a plane along the outer cloth 29. The planar dimensions of the pressure cuff 23 are required to have a certain degree of length and width in order to press the artery 91 and temporarily stop the bleeding. In this example (an example of a cuff for the upper arm), the planar dimensions of the pressure cuff 23 are set to, for example, a dimension of 24 cm in the longitudinal direction Y and a dimension of 13 cm in the width direction X (indicated by X23 in FIG. 2). In this example, the pressure cuff 23 is configured in a bag shape by opposing a pair of sheets (in this example, stretchable polyurethane sheets) in the thickness direction Z and welding the peripheral portions of the pair of sheets to each other with the vicinity of the end of the second air pipe 38 in between.

[0070] In this example, the back plate 22 is made of a plate-shaped resin (polypropylene in this example) having 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 those of the sensing cuff 21 described below. Since the back plate 22 is interposed between the pressure cuff 23 and the sensing cuff 21, the pressure Pc of the pressure cuff 23 can be reliably transmitted to the sensing cuff 21. Therefore, the sensing cuff 21 can reliably press the artery 91 of the measurement site 90 by the pressure Pc of the pressure cuff 23 through the air (fluid for transmitting pressure) contained in the sensing cuff 21. 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 fluctuation components (e.g., due to the pressure pulse wave from the artery 91) contained in the pressure Ps of the sensing cuff 21 from being mixed as noise into the pressure Pc of the pressure cuff 23. Conversely, it is possible to prevent the fluctuation components contained in the pressure Pc of the pressure cuff 23 from being mixed into the pressure Ps of the sensing cuff 21 as noise.

[0071] As shown in FIG. 9A, the sensing cuff 21 has a rectangular shape with rounded corners in a plane along the outer cloth 29 (and the pressure cuff 23) in this example. In this example, the sensing cuff 21 is formed into a bag shape by opposing a pair of sheets (in this example, stretchable polyurethane sheets) in the thickness direction Z and fusing the peripheral edges of the pair of sheets to each other with the vicinity of the end of the first air pipe 37 in between. Here, the dimension of the width direction X of the sensing cuff 21 is preferably shorter than the occlusion distance Dp (shown in FIG. 17A for a general cuff 20′) by which the artery 91 is occluded when the pressure Pc of the pressure cuff 23 becomes the systolic blood pressure value SYS. In the example of FIG. 9A (an example of a cuff for the upper arm), the planar dimensions of the sensing cuff 21 are set to, for example, 7 cm in the longitudinal direction Y and 4 cm in the width direction X (indicated by X21 in FIG. 2). With this structure, only the volume change of the artery 91 at a location where the pressure Pc of the pressure cuff 23 is sufficiently applied is reflected as the pressure pulse wave (its amplitude) acquired by the sensing cuff 21. Therefore, the blood pressure measurement accuracy is improved.

[0072] In principle, blood pressure measurement is possible if the planar dimensions of sensing cuff 21 are equal to or larger than the diameter of artery 91. However, taking into consideration that positional deviation may occur when cuff 20 is attached to measurement site 90, the planar dimensions of sensing cuff 21 are set to, for example, 1 cm x 1 cm or more.

[0073] 2, in the width direction X along the direction in which the artery 91 of the measurement site 90 passes, the range X21 occupied by the sensing cuff 21 is within the remaining 2 / 3 range Xa obtained by subtracting a predetermined 1 / 3 range Xb from the upstream side of the artery 91 of the width direction dimension X23 of the pressure cuff 23. It is assumed that in the width direction X of the pressure cuff 23, the range X21 occupied by the sensing cuff 21 is within the 1 / 3 range Xb of the width direction dimension X23 of the pressure cuff 23 from the upstream side of the artery 91. In this case, even if the pressure Pc of the pressure cuff 23 is in a pressure section higher than the systolic blood pressure value SYS during the decompression process and the blood flow of the artery 91 is stopped, the pulse wave moving from the upstream side of the artery 91 to directly below the pressure cuff 23 may be mixed as noise into the pressure Ps of the sensing cuff 21 detected by the first pressure sensor 30. In this example, the range X21 occupied by the sensing cuff 21 in the width direction X of the pressure cuff 23 is set within the remaining 2 / 3 range Xa, excluding the 1 / 3 range Xb from the upstream side of the artery 91, of the width direction dimension of the pressure cuff 23. Therefore, for example, when the pressure Pc of the pressure cuff 23 during the decompression process is value When the blood flow in the artery 91 is stopped within a pressure range higher than SYS, the pulse wave traveling from the upstream side of the artery 91 to just below the pressure cuff 23 can be prevented from being mixed as noise into the pressure Ps of the sensing cuff 21 detected by the first pressure sensor 30.

[0074] In the examples of Figures 2 and 9(A), in order to interfere with the measurement as little as possible, the first air pipe 37 and the second air pipe 38 are pulled out to the outside along the width direction X of the cuff 20 from the sides corresponding to the downstream sides of the sensing cuff 21 and the pressure cuff 23, respectively.

[0075] 10(C), an outer cloth 29 and a stretchable inner cloth 28 may be arranged opposite each other to form a bag, and the pressure cuff 23, the back panel 22, and the sensing cuff 21 may be housed integrally in the bag. The peripheral edge of the outer cloth 29 and the peripheral edge of the inner cloth 28 (i.e., the peripheral edge 20e of the cuff 20) are attached to each other by sewing or welding, sandwiching the first air piping 37 and the second air piping 38. This allows the cuff 20 to be handled as a whole, and also protects the sensing cuff 21 and the like housed in the bag.

[0076] (Blood pressure measurement method) 3 shows a schematic operational flow of blood pressure measurement by the sphygmomanometer 1. This operational flow is a flow for calculating blood pressure during the decompression process.

[0077] When the user (subject) turns on measurement switch 52A provided on main body 10 to instruct the start of measurement while cuff 20 is attached to the measurement site (upper arm in this example) 90 (see FIG. 2), CPU 110 initializes the pressure sensor as shown in step S1 of FIG. 3. Specifically, CPU 110 initializes the processing memory area, stops pump 32, and adjusts first pressure sensor 30 and second pressure sensor 31 to 0 mmHg (sets atmospheric pressure to 0 mmHg) with exhaust valve 33 open.

[0078] In this example, a predetermined amount of air as a fluid for transmitting pressure is filled in sensing cuff 21 (and first air pipe 37) at the manufacturing stage of blood pressure monitor 1. Therefore, for example, the effort of filling sensing cuff 21 with air every time blood pressure is measured can be omitted. Here, the "predetermined amount" refers to an amount that can prevent, for example, a situation in which the bag constituting sensing cuff 21 is crushed in thickness direction Z by pressure Pc of pressure cuff 23 and the sheets constituting the bag are tightly attached to each other. By preventing such a situation, sensing cuff 21 can reliably compress artery 91 of measurement site 90 by pressure Pc of pressure cuff 23 via air as a fluid for transmitting pressure, while reliably receiving a pressure pulse wave from artery 91.

[0079] Next, in step S2 of FIG. 3, the CPU 110 closes the exhaust valve 33 via the valve drive circuit 330. Then, in step S3, the CPU 110 works 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 pressurizing cuff 23) (pressurizing process). The CPU 110 controls the pressurizing speed to be substantially constant (for example, within a range of 20 mmHg / sec to 40 mmHg / sec) based on the output of the second pressure sensor 31 while supplying air from the pump 32 to the pressurizing cuff 23 through the second air piping 38. As a result, the pressure Pc of the pressurizing cuff 23 rises substantially linearly, as shown in the pressurizing period tP in FIG. 5(A). Since the pressurizing cuff 23 presses the sensing cuff 21 toward the measurement site 90 via the back plate 22, the pressure Ps of the sensing cuff 21 also rises with the pressure Pc of the pressurizing cuff 23.

[0080] Next, in step S4 in FIG. 3, the CPU 110 judges whether the pressure Pc of the pressure cuff 23 has reached a predetermined pressure (predetermined pressure) (indicated as Pu in FIG. 5(A)). Here, the predetermined pressure Pu is the assumed systolic blood pressure of the subject. value It is assumed that the pressure Pc is set sufficiently higher than the pressure SYS. In this example, the predetermined pressure Pu is set to 150 mmHg. If the pressure Pc of the pressure cuff 23 has not reached the predetermined pressure Pu (NO in step S4 of FIG. 3), the CPU 110 returns to step S3 and continues pressurization. If the pressure Pc of the pressure cuff 23 has reached the predetermined pressure Pu (YES in step S4 of FIG. 3), the CPU 110 stops the pump 32 in step S5.

[0081] Next, in step S6 of Fig. 3, the CPU 110 operates as a pressure control unit and gradually opens the exhaust valve 33 via the valve drive circuit 330. As a result, the CPU 110 gradually reduces the pressure Pc of the pressure cuff 23 at a constant speed (5 mmHg / sec in this example) based on the output of the second pressure sensor 31, as shown in the decompression period tD in Fig. 5(A) (decompression process). During this decompression process, as shown in step S7 of Fig. 3, the CPU 110 operates 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 pressure cuff 23 from the second pressure sensor 31, which are acquired at this time point. That is, the CPU 110 subtracts the DC component (which can be extracted from the raw data via a low-pass filter) of the data representing the pressure Pc of the compression cuff 23 from the data representing the pressure Ps of the sensing cuff 21 during the decompression process, after correlating the times at which these pieces of data were generated, to obtain the pressure at the start of the rise PWa and the pressure at the peak point PWp shown for each beat by the pressure pulse wave PW, as shown in Figures 5(B) and 6. Then, as shown in Fig. 5(B) and Fig. 6, the CPU 110 obtains the pressure Pc of the pressure cuff 23 at the first time point t1 when the pressure at the peak point PWp of each beat starts to indicate a positive value from the zero level during this decompression process as the systolic blood pressure value SYS, and obtains the pressure Pc of the pressure cuff 23 at the second time point t2 when the pressure at the rising start point PWa of each beat starts to indicate a positive value from the zero level as the diastolic blood pressure value DIA (Note that Fig. 6 shows an enlarged view of the vicinity of the portion corresponding to the second time point t2 in Fig. 5(B), in other words, the vicinity of the portion where the cuff pressure Pc on the horizontal axis corresponds to the diastolic blood pressure value DIA). Note that the principle of blood pressure calculation and a more specific method of calculating blood pressure will be described in detail later.

[0082] At this point, if the blood pressure value still cannot be calculated due to insufficient data (NO in step S8 in FIG. 3), the processes in steps S6 to S8 are repeated.

[0083] When the blood pressure value has been calculated in this manner (YES in step S8), in step S9, CPU 110 performs control to open exhaust valve 33 via valve drive circuit 330 to rapidly exhaust air from inside pressure cuff 23. Furthermore, in step S10, CPU 110 performs control to display the blood pressure measurement result on display 50 and store the blood pressure measurement result in memory 51.

[0084] (Principle of blood pressure calculation) The principle of how the blood pressure is calculated by the sphygmomanometer 1 is explained as follows. For example, FIG. 7 shows a schematic diagram of how the blood pressure is calculated during the above-mentioned decompression process, assuming that the systolic blood pressure value SYS of the measurement site 90 of the subject is 120 mmHg and the diastolic blood pressure value DIA is 60 mmHg. In FIG. 7, the vertical axis on the left side represents the DC component of the pressure Pc of the pressure cuff 23 (for simplicity, this DC component is called "cuff pressure Pc" using the same symbol) and the intra- and extra-arterial pressure difference Ptr of the measurement site 90. The vertical axis on the right side represents the arterial volume V. The horizontal axis represents the cuff pressure Pc. In this example, the speed of decompression by the pressure control unit is constant (5 mmHg / sec in this example). Therefore, the horizontal axis also corresponds to time t.

[0085] Here, the arterial pressure difference Ptr is defined as the difference between the arterial pressure (represented as "Pa") at the measurement site 90 and the cuff pressure Pc. That is, Ptr=Pa-Pc. Here, it is generally known that there is a correspondence relationship (called the "tube law") between the arterial pressure difference Ptr and the arterial (blood vessel) volume (represented as "arterial volume V") as illustrated by the curve C0 in FIG. 8. As the arterial pressure difference Ptr becomes positive and large, the arterial volume V increases monotonically and gradually becomes saturated. Even when pulse waves PW1, PW1' showing the same wave height ΔP are applied to the artery, if the arterial pressure difference Ptr differs due to the difference in the cuff pressure Pc, the generated volume pulse waves VW1, VW1' 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 the cuff pressure Pc are in equilibrium, the arterial volume is defined as V0 (this is called the "equilibrium level").

[0086] 7, in the pressure section PcH where the cuff pressure Pc is higher than the systolic blood pressure value SYS (120 mmHg in this example), the arterial pressure difference Ptr is always less than 0, regardless of the pulse wave (pulsation). This completely stops the blood flow through the artery 91. Therefore, the arterial volume V does not change and does not rise from the equilibrium level V0.

[0087] It is assumed that the pressure reduction by the pressure control unit progresses and the cuff pressure Pc enters the pressure section PcM between the systolic blood pressure value SYS (120 mmHg in this example) and the diastolic blood pressure value DIA (60 mmHg in this example). At the point where the cuff pressure Pc falls below the systolic blood pressure value SYS (this point is called the "blood flow restart point As"), blood starts to flow from the upstream side to the downstream side. In this pressure section PcM, during the period in which the arterial pressure Pa exceeds the cuff pressure Pc during the cycle T of one beat (a partial period of the cycle T of one beat), the arterial pressure difference Ptr>0. In FIG. 7, this positive arterial pressure difference Ptr is shown by a broken line. When the arterial pressure difference Ptr>0, the volume pulse wave VW appears with a peak, as shown by a solid line in FIG. 7, in accordance with the above-mentioned tube law (curve C0 in FIG. 8). This volume pulse wave VW is detected as a fluctuation component of the pressure Ps of the sensing cuff 21 (pressure pulse wave PW shown in FIG. 5(B) and FIG. 6). During the remaining period of one beat period T, the intra-arterial pressure difference Ptr≦0. Therefore, the volume pulse wave VW includes a flat portion VW0 (a portion indicating the equilibrium level V0). Accordingly, as shown in FIG. 6, the pressure of the pressure pulse wave PW detected by the sensing cuff 21 also includes a flat portion PW0.

[0088] Here, the curve C1 connecting the upper peaks (peak points) VWp of the volume pulse wave VW shown in FIG. 7 represents the relationship between the pressure (SYS-Pc) obtained by subtracting the cuff pressure Pc from the systolic blood pressure value SYS (=120 mmHg) and the arterial volume V according to the above-mentioned tube law (curve C0 in FIG. 8). That is, in this pressure section PcM (and the pressure section PcL described next), as the cuff pressure Pc decreases, the upper peak VWp of the volume pulse wave VW rises along the curve C1 for each beat. In response to this, the upper peak (peak point) PWp indicated by the pressure of the pressure pulse wave PW shown in FIG. 5(B) and FIG. 6 also rises along the first curve C1' (corresponding to the curve C1 in FIG. 7) for each beat (in principle, it increases monotonically and gradually saturates). Here, the first curve C1' is defined as a curve connecting the peak points PWp (or a curve approximating it).

[0089] As can be seen from the above description, in the above decompression process, the first time point t1 at which the pressure at the peak point PWp of each beat of the pressure pulse wave PW starts to indicate a positive value from the zero level (i.e., the time point at which the first curve C1' transitions from the zero level to a positive value) shown in Fig. 5(B) corresponds to the time point at which blood flow resumes, i.e., the point at which the cuff pressure Pc falls below the systolic blood pressure value SYS (the blood flow resumes point As in Fig. 7). Therefore, the cuff pressure Pc at the first time point t1 corresponds in principle to the systolic blood pressure value SYS.

[0090] In FIG. 7, it is assumed that the pressure reduction by the pressure control unit has progressed further and the cuff pressure Pc has entered a pressure range PcL lower than the diastolic blood pressure value DIA (60 mmHg in this example). The artery is completely opened from the point where the cuff pressure Pc falls below the diastolic blood pressure value DIA (this is called the "DIA restart point Ad"). In this range PcL, the flat part VW0 included in the volume pulse wave VW in the previous range PcM disappears, and the waveform of the volume pulse wave VW becomes a sharpened complete waveform. Here, the curve C2 shown in FIG. 7, which connects the lower peaks (rising start points) VWa of the volume pulse wave VW, represents the relationship between the pressure amount (DIA-Pc) obtained by subtracting the cuff pressure Pc from the diastolic blood pressure value DIA (=60 mmHg) and the arterial volume V according to the above-mentioned tube law (curve C0 in FIG. 8). That is, in this range PcL, as the cuff pressure Pc decreases, the lower peak (starting point of rising) VWa of the volume pulse wave VW rises along the curve C2 for each beat. In response to this, the lower peak (starting point of rising) PWa of the pressure of the pressure pulse wave PW shown in Figures 5(B) and 6 also rises along the second curve C2' (corresponding to the curve C2 in Figure 7) for each beat (in principle, it increases monotonically and gradually saturates). Here, the second curve C2' is defined as a curve connecting the starting points of rising PWa (or a curve approximating it).

[0091] As can be seen from the above explanation, the second time point t2 when the pressure at the rising start point PWa of the pressure pulse wave PW for each beat starts to indicate a positive value from the zero level (i.e., the time point when the second curve C2' transitions from the zero level to a positive value) shown in Figures 5(B) and 6 corresponds to the point when the cuff pressure Pc falls below the diastolic blood pressure value DIA (the DIA restart point Ad in Figure 7). Therefore, the cuff pressure Pc at the second time point t2 corresponds in principle to the diastolic blood pressure value DIA.

[0092] Here, in FIG. 7, the curve C2 corresponds to the curve C1 shifted to the right by the difference (SYS-DIA) between the systolic blood pressure value SYS and the diastolic blood pressure value DIA. According to the tube law shown in FIG. 8, the curves C1 and C2 rise from the blood flow restart point As and the DIA restart point Ad, respectively, and both increase monotonically and gradually saturate. Therefore, at the DIA restart point Ad, the amplitude of the volume pulse wave VW shows a maximum value VWmax. Accordingly, the amplitude of the pressure pulse wave PW shown in FIG. 5(B) and FIG. 6 (called the "pulse wave amplitude AM") also shows a maximum value AMmax. Therefore, the cuff pressure Pc at the time when the pulse wave amplitude AM shows the maximum value AMmax (the second time point t2) can be obtained correctly as the diastolic blood pressure value DIA in principle. As shown in FIG. 6, the pulse wave amplitude AM is defined as the difference between the pressure at the peak point PWp of the pressure pulse wave PW and the pressure at the rising start point PWa.

[0093] As shown in Fig. 17(A), a general cuff 20' does not include the sensing cuff 21 in this embodiment, but includes a single fluid bag equivalent to the pressure cuff 23. In a general oscillometric method, the pressure Pc' of the cuff 20' is passed through a high-pass filter to obtain the fluctuation component (pulse wave amplitude AM') of the pressure pulse wave PW' as shown in Fig. 17(B). An envelope is set for the series of this pulse wave amplitude AM', and threshold levels (including a systolic threshold level and a diastolic threshold level) of a predetermined ratio (proportion) are set for the maximum value (corresponding to AMmax') of the envelope, and the cuff pressures at the time when the envelope crosses these threshold levels are calculated as the systolic blood pressure value SYS and the diastolic blood pressure value DIA, respectively. In the method using the general cuff 20', the second point t2 shown in Figures 5(B) and 6 (i.e., the point at which the second curve C2' shown in Figures 5(B) and 6 transitions from the zero level to a positive value) does not appear. Therefore, in the method using the general cuff 20', the diastolic blood pressure value DIA cannot be obtained according to the principle described above.

[0094] (Specific method for calculating blood pressure) FIG. 4 shows a detailed flow of the method of calculating blood pressure in step S7 of FIG. 3 according to the principle of blood pressure calculation of the present invention described above.

[0095] In step S11 of FIG. 4, the CPU 110 subtracts the DC component (cuff pressure Pc) of the pressure Pc of the compression cuff 23 from the second pressure sensor 31 from the data representing the pressure Ps of the sensing cuff 21 from the first pressure sensor 30, after correlating the times at which these pieces of data were generated, to obtain the pressure at the start point PWa of the rise and the pressure at the peak point PWp shown for each beat by the pressure pulse wave PW, as shown in FIG. 5(B) and FIG. 6.

[0096] Next, in step S12 in FIG. 4, CPU 110 calculates the difference obtained by subtracting the pressure at the rising start point PWa from the pressure at peak point PWp for each beat as pulse wave amplitude AM shown in FIGS. 5(B) and 6.

[0097] 4, CPU 110 smoothes the pulse wave amplitude AM for each beat by taking a moving average over a predetermined number of beats (five 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 S14, CPU 110 stores the smoothed data of each pulse wave amplitude AM in chronological order in memory 51 in association with data representing the cuff pressure Pc at the time when the pulse wave amplitude AM was shown. In this example, the cuff pressure Pc is extracted as a DC component from the raw data representing the pressure Pc of compression cuff 23 via a low-pass filter.

[0098] Next, in step S15 of FIG. 4, the CPU 110 refers to the contents stored in the memory 51 and determines whether the pulse wave amplitude AM has reached the maximum value AMmax shown in FIG. 5(B) and FIG. 6. If the pulse wave amplitude AM does not reach the maximum value AMmax at this point (NO in step S15 of FIG. 4), the process repeats steps S11 to S15. On the other hand, if the pulse wave amplitude AM has reached the maximum value AMmax (YES in step S15 of FIG. 4), the process proceeds to step S16, where the CPU 110 determines the time when the pulse wave amplitude AM reached the maximum value AMmax as the second time point t2 (i.e., the time when the second curve C2′ shown in FIG. 5(B) and FIG. 6 transitions from the zero level to a positive value), and obtains the cuff pressure Pc corresponding to the determined second time point t2 as the diastolic blood pressure value DIA. Here, whether the pulse wave amplitude AM has reached the maximum value AMmax is determined by comparing the pulse wave amplitudes AM with each other, and therefore can be determined more accurately than when it is determined by comparing with the zero level (buried in noise). Therefore, in this blood pressure monitor 1, the second point in time t2 can be determined with high accuracy, and the diastolic blood pressure value DIA can be obtained with high accuracy.

[0099] Next, in step S17 of Fig. 4, CPU 110 multiplies the maximum value AMmax of pulse wave amplitude AM by a predetermined ratio to set a threshold level AMth for determining a first point in time t1 (i.e., the point in time when the first curve C1' shown in Fig. 5(B) transitions from the zero level to a positive value) as shown in Fig. 5(B). Here, the "predetermined ratio" is set to be greater than the actual noise level while being as small as possible in order to accurately determine the first point in time t1. For the maximum value AMmax of pulse wave amplitude AM, the "predetermined ratio" is set to, for example, about 0.1.

[0100] Next, in step S18 of FIG. 4, the CPU 110 refers to the contents stored in the memory 51 and determines the time point (indicating the blood flow restart point) when the pulse wave amplitude AM crosses the threshold level AMth during this decompression process as the first time point t1. More specifically, among the data in which the pulse wave amplitude AM exceeds the threshold level AMth before the second time point t2, data with the maximum corresponding cuff pressure Pc is searched for, and the time point indicated by the data is determined as the first time point t1. Then, in step S19 of FIG. 4, the CPU 110 obtains the cuff pressure Pc corresponding to the determined first time point t1 as the systolic blood pressure value SYS. Here, whether or not the pulse wave amplitude AM exceeds the threshold level AMth is determined by comparing the pulse wave amplitude AM with the set threshold level AMth, so that it can be determined more accurately than when it is determined by comparing with the zero level (buried in noise). Therefore, in this blood pressure monitor 1, the first time point t1 can be determined with high accuracy, and the systolic blood pressure value SYS can be obtained with high accuracy.

[0101] In this manner, according to this blood pressure monitor 1, the blood pressure at the measurement site 90 can be measured non-invasively and in principle correctly.

[0102] (Variation 1) In the example of Fig. 9(A), the first air piping 37 is drawn out from approximately the center of the side 21a on the downstream side (+X side) of the sensing cuff 21 along the width direction X of the cuff 20 to the outside. However, this is not limited to this. As shown in Figs. 9(B) to 9(E), various variations in the arrangement of the first air piping 37 are possible, such as a mode in which the first air piping 37 is off the artery 91 in a plan view seen from the thickness direction Z perpendicular to the measurement site 90 (the outer peripheral surface 90a of the measurement site 90) (for simplicity, the outer cloth 29 and the back panel 22 are omitted from Figs. 9(B) to 9(E).).

[0103] Specifically, in the example of FIG. 9(B), the first air piping 37 is drawn out from the end of the downstream side 21a of the sensing cuff 21 in parallel with and spaced apart from the artery 91. In the examples of FIG. 9(C) and FIG. 9(D), the first air piping 37 is drawn out from approximately the center and end of the -Y side of the sensing cuff 21 along the longitudinal direction Y of the cuff 20 to the outside. In the example of FIG. 9(E), the first air piping 37 is drawn out from approximately the center of the -Y side of the sensing cuff 21, extends slightly in the longitudinal direction Y, bends in the width direction X, and is drawn out in parallel with and spaced apart from the artery 91. In these examples, the first air piping 37 is drawn out to the outside of the cuff 20 (in other words, the area where the pressure cuff 23 surrounds the measured site 90) in a state where it is removed from the artery 91. Therefore, the first air piping 37 does not prevent the pressure of the pressure cuff 23 from compressing the artery 91 of the measured site 90 via the sensing cuff 21. Furthermore, the first air pipe 37 does not prevent the sensing cuff 21 from receiving the pressure pulse wave PW from the artery 91 .

[0104] (Variation 2) 9(A) to 9(E), the first air piping 37 is drawn out to the outside of the cuff 20 within a plane (XY plane) along the outer cloth 29 (and the pressure cuff 23), but is not limited to this. As shown in the cross-sectional view of Fig. 10(A) and the plan view of Fig. 10(B), the first air piping 37 may pass through the pressure cuff 23 and be drawn out to the outside of the cuff 20 in the thickness direction Z (for simplicity, the outer cloth 29 is omitted in Figs. 10(A) and 10(B)).

[0105] More specifically, in this modification 2, as shown in Fig. 10(A), a through hole 23h penetrating in the thickness direction Z is provided in the pressing cuff 23. As shown in Fig. 10(B), this through hole 23h is provided in the center of the pressing cuff 23 in the XY plane (corresponding to a part of the area facing the sensing cuff 21). Accordingly, as shown in Fig. 10(A), a cylindrical through hole 22h penetrating in the thickness direction Z is also provided in the center of the XY plane of the back plate 22. The inner diameters of the through holes 22h and 23h are set to be slightly larger than the outer diameter of the first air pipe 37 so that the first air pipe 37 can pass through. The first air pipe 37 extends upward (in the +Z direction) from the upper surface of the sensing cuff 21 in Fig. 10(A) and is drawn out to the outside of the cuff 20 through the through holes 22h and 23h. In this modification 2, similarly to modification 1, the first air piping 37 does not prevent the pressure of the pressure cuff 23 from compressing the artery 91 of the measurement site 90 via the sensing cuff 21. Moreover, the first air piping 37 does not prevent the sensing cuff 21 from receiving the pressure pulse wave PW from the artery 91.

[0106] In this modification 2, an inner peripheral surface 23hs of the through hole 23h of the pressure cuff 23 is formed in a bellows shape. Therefore, the pressure cuff 23 can be easily expanded and contracted in the thickness direction Z.

[0107] (Variation 3) In the above example, a predetermined amount of air as a fluid for transmitting pressure is sealed in sensing cuff 21 (and first air piping 37) during the manufacturing stage of sphygmomanometer 1. However, this is not limited to this. Air as a fluid for transmitting pressure may be sealed in sensing cuff 21 each time blood pressure is measured, and the air may be discharged from sensing cuff 21 after calculation of the blood pressure value is completed.

[0108] FIG. 11 shows a block diagram of such a modified blood pressure monitor 1 (hereinafter referred to as "blood pressure monitor 1A"). In addition to the components of blood pressure monitor 1, this blood pressure monitor 1A is equipped with a switching valve 34, which is a three-port two-position solenoid valve, and a valve drive circuit 340 that drives the switching valve 34, in main body 10. In FIG. 11, components that are the same as those in FIG. 1 are given the same reference numerals, and duplicated explanations will be omitted. In particular, cuff 20 is the same as cuff 20 shown in FIG. 1.

[0109] An air pipe 38b connected to the pump 32 and an air pipe 38c connected to the discharge valve 33 are joined together to form an air pipe 38d, which is fluidically connected to one port 34a of the switching valve 34. Air pipes 37e and 38f are fluidically connected to the remaining ports 34b and 34c of the switching valve 34, respectively. These air pipes 37e and 38f are fluidically connected to the first air pipe 37 and the second air pipe 38, respectively. The valve drive circuit 340 switches the switching valve 34 between a rest position (when not energized) as a first position shown in FIG. 12(A) and an operating position (when energized) as a second position shown in FIG. 12(B) based on a control signal provided by the CPU 110, in this example. Here, FIG. 12(A) corresponds to FIG. 2, and shows a cross section of the cuff 20 constituting the sphygmomanometer 1A attached to the measurement site 90 together with the air pipe systems 37 and 38.

[0110] 12(A), the switching valve 34 fluidly connects the air pipe 38d to the air pipe 38f. As a result, the pump 32 and the discharge valve 33 are fluidly connected to the pressing cuff 23 and the second pressure sensor 31 via the air pipes 38b, 38c, 38d, 38f, and 38. At this time, the sensing cuff 21 is separated from the pump 32 and the discharge valve 33 and sealed together with the first pressure sensor 30. On the other hand, the switching valve 34 fluidly connects the air pipe 38d to the air pipe 37e at the operating position shown in FIG. 12(B). As a result, the pump 32 and the discharge valve 33 are fluidly connected to the sensing cuff 21 and the first pressure sensor 30 via the air pipes 38b, 38c, 38d, 37e, and 37. At this time, the pressure cuff 23 together with the second pressure sensor 31 is isolated from the pump 32 and the exhaust valve 33 and sealed.

[0111] FIG. 13 shows a schematic flow of blood pressure measurement by the sphygmomanometer 1A.

[0112] When the user (subject) turns on the measurement switch 52A provided on the main body 10 to instruct the start of measurement while the cuff 20 is attached to the measurement site (upper arm in this example) 90 (see FIG. 12(A)), the CPU 110 initializes the pressure sensor as shown in step S101 of FIG 13. This initialization process is similar to that in step S1 of FIG 3.

[0113] 13, the CPU 110 closes the discharge valve 33. Then, in step S103, the CPU 110 switches the switching valve 34 to the operating position shown in FIG 12(B). This connects the pump 32 and the discharge valve 33 to the sensing cuff 21 and the first pressure sensor 30 via the air pipes 38b, 38c, 38d, 37e, and 37 so as to be capable of fluid communication.

[0114] Next, in step S104 of FIG. 13, CPU 110 operates as a fluid storage control unit, drives pump 32, and supplies air as a fluid for pressure transmission to sensing cuff 21 through air pipes 38b, 38d, 37e, and 37 in this order. Next, in step S105, CPU 110 determines whether a predetermined time (predetermined time, for example, within a range of 3 to 10 seconds) has elapsed. Here, if the predetermined time has not elapsed (NO in step S105), the process returns to step S104, and the supply of air continues until the predetermined time has elapsed. Then, when the predetermined time has elapsed (YES in step S105), the process proceeds to step S106, and pump 32 is stopped. In this way, a predetermined amount of air as a fluid for pressure transmission can be automatically sealed in sensing cuff 21 prior to the start of pressurization of pressure cuff 23. Here, the "predetermined amount" refers to an amount that can prevent a situation in which the bag constituting sensing cuff 21 is crushed in thickness direction Z by pressure Pc of pressure cuff 23 and the sheets constituting the bag are brought into close contact with each other, as in the previous example. By preventing such a situation, sensing cuff 21 can reliably compress artery 91 of measurement site 90 by pressure Pc of pressure cuff 23 via air as the pressure transmission fluid, while reliably receiving a pressure pulse wave from artery 91.

[0115] Next, in step S107 of FIG. 13, the CPU 110 functions as a fluid storage control unit and switches the switching valve 34 to the rest position shown in FIG. 12(A). This connects the pump 32 and the discharge valve 33 to the pressing cuff 23 and the second pressure sensor 31 via the air pipes 38b, 38c, 38d, 38f, and 38 so that the fluid can flow through them. At this time, the sensing cuff 21, together with the first pressure sensor 30, is separated from the pump 32 and the discharge valve 33 and sealed. Therefore, the flow path formed by the air pipe systems 37 and 38 is substantially in the same state as the flow path shown in FIG. 1. This state is maintained until steps S108 to S114 of FIG. 13, which will be described next.

[0116] Next, from step S108 to step S114 in Fig. 13, the CPU 110 functions as a pressure control unit and a blood pressure calculation unit, and proceeds with the same processes as in steps S3 to S9 in Fig. 3. As a result, the blood pressure values ​​(systolic blood pressure value SYS and diastolic blood pressure value DIA) of the measurement site 90 are calculated correctly in principle.

[0117] Next, in step S115 of Fig. 13, the CPU 110 functions as a fluid storage control unit and switches the switching valve 34 to the operating position shown in Fig. 12(B). This connects the pump 32 and the discharge valve 33 to the sensing cuff 21 and the first pressure sensor 30 via the air pipes 38b, 38c, 38d, 37e, and 37 so as to be capable of fluid communication.

[0118] 13, CPU 110 functions as a fluid storage control unit and opens exhaust valve 33. This causes air, which serves as a fluid for transmitting pressure, to be exhausted from sensing cuff 21 through air pipes 37, 37e, 38d, and 38c, and exhaust valve 33, in that order. Thereafter, in step S117, CPU 110 displays the blood pressure measurement results on display 50, and also performs control to store the blood pressure measurement results in memory 51.

[0119] In this way, with a relatively small number of parts, this blood pressure monitor 1A can automatically fill sensing cuff 21 with a predetermined amount of air as a fluid for transmitting pressure each time blood pressure is measured, prior to the start of pressurization of pressure cuff 23. In addition, air as a fluid for transmitting pressure can be automatically discharged from sensing cuff 21 after calculation of the blood pressure value is completed.

[0120] In addition, in this blood pressure monitor 1A, the pump 32 and the discharge valve 33 are connected to the sensing cuff 21 and the first pressure sensor 30 in a fluid communication manner (the switching valve 34 is in the operating position shown in FIG. 12(B)) only during the temporary periods of steps S103 to S106 and steps S115 to S116. Therefore, the power consumption related to the switching valve 34 can be saved.

[0121] (Variation 4) In the above example, the DC component (cuff pressure Pc) of the pressure Pc of the pressure cuff 23, which is the basis for calculating the blood pressure, is extracted from the raw data through a low-pass filter, but this is not limited to this. For example, in the depressurization process at the constant speed (5 mmHg / sec in the above example), a value approximated by a straight line determined by data of the pressure Pc of the pressure cuff 23 at one point and the depressurization speed may be used as the cuff pressure Pc. Alternatively, in the depressurization process, a value approximated by a straight line determined by data of the pressure Pc of the pressure cuff 23 at two or more points (i.e., data of the pressure Pc at different times) may be used as the cuff pressure Pc. Alternatively, a tentative systolic blood pressure value SYS and a tentative diastolic blood pressure value DIA may be obtained once by a general oscillometric method, and a value approximated by a straight line determined by them may be used as the cuff pressure Pc.

[0122] (Variation 5) In the above example, the blood pressure calculation is performed during the depressurization process, but the present invention is not limited to this, and the blood pressure calculation may be performed during the pressurization process.

[0123] For example, FIG. 14 shows a schematic operational flow of blood pressure measurement using the sphygmomanometer 1 of FIG. 1, in which blood pressure calculation is performed during the pressurization process.

[0124] When the user (subject) turns on the measurement switch 52A provided on the main body 10 to instruct the start of measurement while the cuff 20 is attached to the measurement site (upper arm in this example) 90 (see FIG. 2), the CPU 110 initializes the pressure sensor as shown in step S201 of FIG 14. The specific process of this initialization is the same as that described with respect to step S1 of FIG 3.

[0125] In this example, as described with respect to the operational flow of Figure 3, it is assumed that a predetermined amount of air as a fluid for transmitting pressure is sealed in sensing cuff 21 (and first air piping 37) during the manufacturing stage of blood pressure monitor 1.

[0126] Next, in step S202 of FIG. 14, the CPU 110 closes the exhaust valve 33 via the valve drive circuit 330. Then, in step S203, the CPU 110 works 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 pressurizing cuff 23) (pressurizing process). While supplying air from the pump 32 to the pressurizing cuff 23 through the second air piping 38, the CPU 110 controls the pressurizing speed to be substantially constant (in this example, 3 mmHg / sec) from a value sufficiently lower than the expected diastolic blood pressure value DIA of the subject based on the output of the second pressure sensor 31 (in this example, about 10 mmHg). As a result, the pressure Pc of the pressurizing cuff 23 rises substantially linearly as shown in the pressurizing period tP′ in FIG. 16(A). Since pressure cuff 23 presses sensing cuff 21 toward measurement site 90 via back plate 22 , pressure Ps of sensing cuff 21 also increases along with pressure Pc of pressure cuff 23 .

[0127] 14, the CPU 110 operates 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 data representing the pressure Ps of the sensing cuff 21 from the first pressure sensor 30 and data representing the pressure Pc of the pressure cuff 23 from the second pressure sensor 31, both of which are acquired at this time. That is, the CPU 110 subtracts the DC component (which can be extracted from the raw data via a low-pass filter) 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, after associating the times of generation of these data with each other, to obtain the pressure at the rising start point PWa and the pressure at the peak point PWp shown for each beat by the pressure pulse wave PW, as shown in FIG. 16(B). Then, as shown in Fig. 16B, the CPU 110 obtains the pressure Pc of the pressure cuff 23 at the second time t2' when the pressure at the rising start point PWa of each beat falls from a positive value to the zero level as the diastolic blood pressure value DIA during this pressurization process, and obtains the pressure Pc of the pressure cuff 23 at the first time t1' when the pressure at the peak point PWp of each beat falls from a positive value to the zero level as the systolic blood pressure value SYS. The principle of blood pressure calculation during this pressurization process is the same as that during the depressurization process described above, except that the change in the pressure Pc of the pressure cuff 23 over time is in the opposite direction to that during the depressurization process. A more specific method of blood pressure calculation will be described in detail later.

[0128] At this point, if the blood pressure value still cannot be calculated due to insufficient data (NO in step S205 in FIG. 14), the processes in steps S203 to S205 are repeated.

[0129] When the blood pressure value has been calculated in this manner (YES in step S205), CPU 110 functions as a pressure control unit, stops pump 32 via pump drive circuit 320 in step S206, and opens exhaust valve 33 via valve drive circuit 330 in step S207 to rapidly exhaust air from pressure cuff 23. Note that FIG. 16A shows time t5 when pump 32 is stopped and the subsequent rapid exhaust period tD'. Furthermore, in step S208, CPU 110 displays the measurement result of the blood pressure value on display 50, and also performs control to store the measurement result of the blood pressure value in memory 51.

[0130] FIG. 15 shows a detailed flow of the method of calculating blood pressure in step S204 of FIG.

[0131] In step S211 in Fig. 15, the CPU 110 subtracts the DC component (cuff pressure Pc) of the pressure Pc of the pressure cuff 23 from the second pressure sensor 31 from the data indicating the pressure Ps of the sensing cuff 21 from the first pressure sensor 30, after correlating the times at which these data were generated, to obtain the pressure at the rising start point PWa and the pressure at the peak point PWp shown for each beat of the pressure pulse wave PW, as shown in Fig. 16(B). In this example, a first curve C1'' connecting the peak points PWp and a second curve C2'' connecting the rising start points PWa are shown in Fig. 16(B).

[0132] Next, in step S212 in FIG. 15, CPU 110 calculates the difference obtained by subtracting the pressure at the rising start point PWa from the pressure at peak point PWp for each beat as pulse wave amplitude AM shown in FIG. 16(B).

[0133] 15, CPU 110 smoothes the pulse wave amplitude AM for each beat by taking a moving average over a predetermined number of beats (five 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 S214, CPU 110 stores the smoothed data of each pulse wave amplitude AM in chronological order in memory 51 in association with data representing the cuff pressure Pc at the time when the pulse wave amplitude AM was shown. In this example, the cuff pressure Pc is extracted as a DC component from the raw data representing the pressure Pc of compression cuff 23 via a low-pass filter.

[0134] Next, in step S215 of FIG. 15, CPU 110 determines whether or not diastolic blood pressure value DIA has been determined. In the first turn of this process, it is assumed that diastolic blood pressure value DIA has not yet been determined (NO in step S215 of FIG. 15). In this case, the process proceeds to step S216, and CPU 110 refers to the contents stored in memory 51 and determines whether or not pulse wave amplitude AM has reached maximum value AMmax shown in FIG. 16(B). If pulse wave amplitude AM does not reach maximum value AMmax at this point (NO in step S216 of FIG. 15), the processes of steps S211 to S216 are repeated. On the other hand, if the pulse wave amplitude AM has reached its maximum value AMmax (YES in step S216 in FIG. 15), the process proceeds to step S217, where the CPU 110 determines the point in time when the pulse wave amplitude AM has reached its maximum value AMmax as the second point in time t2' (i.e., the point in time when the second curve C2" shown in FIG. 16(B) falls from a positive value to the zero level), and obtains the cuff pressure Pc corresponding to this determined second point in time t2' as the diastolic blood pressure value DIA. Here, whether or not the pulse wave amplitude AM has reached its maximum value AMmax is determined by comparing the pulse wave amplitudes AM with each other, so that this can be determined more accurately than when it is determined by comparing with the zero level (which is buried in noise). Therefore, with this sphygmomanometer 1, the second point in time t2' can be determined with high accuracy, and the diastolic blood pressure value DIA can be obtained with high accuracy.

[0135] Next, in step S218 of FIG. 15, CPU 110 multiplies the maximum value AMmax of the pulse wave amplitude AM by a predetermined ratio to set a threshold level AMth for determining a first point in time t1' (i.e., the point in time when the first curve C1'' shown in FIG. 16(B) falls from a positive value to the zero level), as shown in FIG. 16(B). Here, the "predetermined ratio" is set to be greater than the actual noise level, but as small as possible in order to accurately determine the first point in time t1'. With respect to the maximum value AMmax of the pulse wave amplitude AM, the "predetermined ratio" is set to, for example, about 0.1.

[0136] Next, in step S219 of FIG. 15, the CPU 110 refers to the contents stored in the memory 51 and determines the point in time when the pulse wave amplitude AM crosses the threshold level AMth during this pressurization process (indicating the point where blood flow resumes) as the first point in time t1'. More specifically, after the second point in time t2', among data in which the pulse wave amplitude AM falls below the threshold level AMth, data with the smallest corresponding cuff pressure Pc is searched for, and the point indicated by that data is determined as the first point in time t1'. Then, in step S220 of FIG. 15, the CPU 110 obtains the cuff pressure Pc corresponding to the determined first point in time t1' as the systolic blood pressure value SYS. Here, whether the pulse wave amplitude AM exceeds the threshold level AMth is determined by comparing the pulse wave amplitude AM with the set threshold level AMth, so that the determination can be made more accurately than when it is based on a comparison with the zero level (buried in noise). Therefore, in this blood pressure monitor 1, the first point in time t1' can be determined with high accuracy, and the systolic blood pressure value SYS can be obtained with high accuracy.

[0137] In this manner, the blood pressure at the measurement site 90 can, in principle, be non-invasively and correctly measured not only during the depressurization process but also during the pressurization process by the blood pressure monitor 1. Similarly, the blood pressure at the measurement site 90 can, in principle, be non-invasively and correctly measured not only during the depressurization process but also during the pressurization process by the blood pressure monitor 1A of FIG.

[0138] (Other variations) In the above example, the planar shape of the sensing cuff 21 is a rectangle with rounded corners, but is not limited to this. The planar shape of the sensing cuff 21 may be, for example, a circle. This allows the pressure Ps of the sensing cuff 21 to better reflect only the volume change of the artery 91 at a location where the pressure Pc of the pressure cuff 23 is sufficiently applied. This improves the accuracy of blood pressure measurement.

[0139] In the above example, the measurement site 90 is the upper arm, and accordingly the cuff 20 is an upper arm cuff, but this is not limited thereto. The measurement site 90 may be the wrist or the lower leg. Accordingly, the cuff 20 may be a wrist cuff or a lower leg cuff. In the example of a wrist cuff, the planar dimensions of the pressure cuff 23 are set smaller than in the above example (the example of the upper arm cuff), and therefore the planar dimensions of the sensing cuff 21 are set to, for example, 2 cm x 2 cm or less.

[0140] In the above example, the "fluid" for pressurization and pressure transmission is air, but is not limited to this. The "fluid" for pressurization and pressure transmission may be other gases or liquids. In particular, when the "fluid" for pressure transmission is sealed in the sensing cuff 21 during the manufacturing stage, the "fluid" for pressure transmission may be a liquid.

[0141] The above-mentioned embodiments are merely examples, and various modifications are possible without departing from the scope of the present invention. The above-mentioned embodiments can be realized independently, but the embodiments can also be combined with each other. In addition, the various features of the different embodiments can be realized independently, but the features of the different embodiments can also be combined with each other. [Explanation of symbols]

[0142] 1,1A Sphygmomanometer 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 Exhaust valve 34 Switching valve

Claims

1. An electronic blood pressure monitor that non-invasively measures blood pressure at a measurement site, a bag-shaped pressure cuff that is attached around the measurement site in a circumferential direction so as to receive a supply of pressurizing fluid and pressurize the measurement site; a bag-shaped sensing cuff for accommodating a fluid for transmitting pressure, which is disposed on the inner circumferential side of the pressure cuff and faces the artery of the measurement site, and which is separate from the pressure cuff; the sensing cuff compresses the artery of the measurement site via the fluid for transmitting pressure by the pressure of the pressure cuff, and receives a pressure pulse wave from the artery; a first pressure sensor that detects the pressure of the sensing cuff; A second pressure sensor for detecting the pressure of the pressure cuff; a pressure control unit that controls the pressure of the pressure cuff by supplying the pressurizing fluid to the pressurizing cuff or discharging the pressurizing fluid from the pressurizing cuff; 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 a process of a change in the pressure of the pressing cuff by the pressure control unit, The blood pressure calculation unit is a DC component of the data representing the pressure of the compression cuff or a value approximating the DC component is subtracted from the data representing the pressure of the sensing cuff during the pressure change process to obtain a pressure at a rising start point and a pressure at a peak point shown for each beat of the pressure pulse wave; A first time point is determined when the pressure at the peak point for each beat transitions between a zero level and a positive value during the pressure change process, and the pressure of the pressure cuff at this first time point is determined as a systolic blood pressure value, and a second time point is determined when the pressure at the rising start point for each beat transitions between a zero level and a positive value, and the pressure of the pressure cuff at this second time point is determined as a diastolic blood pressure value. An electronic blood pressure monitor characterized by:

2. 2. The electronic blood pressure monitor according to claim 1, The pressure change process is a decompression process after the blood flow through the artery is temporarily stopped by pressurization of the compression cuff, the first time point is a time point at which the pressure at the peak point for each beat begins to indicate a positive value from a zero level, The second time point is a time point after the first time point when the pressure at the rising start point of each beat starts to indicate a positive value from the zero level. An electronic blood pressure monitor characterized by:

3. 2. The electronic blood pressure monitor according to claim 1, The pressure change process is a pressurization process of the pressure cuff, the second time point is a time point at which the pressure at the rising start point of each beat falls from a positive value to a zero level, The first time point is a time point after the second time point at which the pressure at the peak point for each beat falls from a positive value to a zero level. An electronic blood pressure monitor characterized by:

4. The electronic blood pressure monitor according to any one of claims 1 to 3, the sensing cuff is fluidly connected to the first pressure sensor via a first fluid line; the pressure cuff is fluidly connected to the second pressure sensor via a second fluid line; The first fluid pipe and the second fluid pipe are spaced apart from each other. An electronic blood pressure monitor characterized by:

5. The electronic blood pressure monitor according to any one of claims 1 to 4, With respect to the width direction of the pressure cuff along the direction in which the artery of the measurement site passes, the range occupied by the sensing cuff is within a remaining range of the width direction dimension of the pressure cuff excluding a predetermined range from the upstream side of the artery. An electronic blood pressure monitor characterized by:

6. 6. The electronic blood pressure monitor according to claim 1, A back plate is provided between the pressure cuff and the sensing cuff, and the back plate transmits the pressure of the pressure cuff to the sensing cuff and blocks the transmission of pressure fluctuation components between the pressure cuff and the sensing cuff. An electronic blood pressure monitor characterized by:

7. 5. The electronic blood pressure monitor according to claim 4, The first fluid pipe is configured so that the pressure cuff is pulled out to the outside of the area surrounding the measurement site in a state where the pressure cuff is out of the artery when viewed in a plan view from a thickness direction perpendicular to the outer circumferential surface of the measurement site. An electronic blood pressure monitor characterized by:

8. 5. The electronic blood pressure monitor according to claim 4, the pressure cuff has a through hole penetrating in a thickness direction in a part of a region facing the sensing cuff, The first fluid pipe is drawn from the sensing cuff to the outer periphery of the pressure cuff through the through hole of the pressure cuff. An electronic blood pressure monitor characterized by:

9. 9. The electronic blood pressure monitor according to claim 1, A predetermined amount of the pressure transmitting fluid is enclosed in the sensing cuff. An electronic blood pressure monitor characterized by:

10. 9. The electronic blood pressure monitor according to claim 4, 7 or 8, a fluid containment control unit that controls the supply of the pressure transmission fluid to the sensing cuff via the first fluid piping before the pressure control unit starts pressurizing the pressing cuff each time blood pressure measurement is performed, and controls the discharge of the pressure transmission fluid from the sensing cuff via the first fluid piping after the blood pressure calculation unit completes calculation of the blood pressure value. An electronic blood pressure monitor comprising:

11. The electronic blood pressure monitor according to claim 10, the pressure control unit includes a pump for supplying air as the pressurizing fluid to the pressure cuff via the second fluid piping, and a discharge valve for discharging the air from the pressure cuff via the second fluid piping, the fluid accommodation control section includes a switching valve connected between the first fluid piping and the second fluid piping, and the switching valve is capable of taking a first position in which the first fluid piping and the second fluid piping are separated from each other, and a second position in which the first fluid piping and the second fluid piping are allowed to communicate with each other and the pressure cuff is sealed; The fluid containment control section includes: when supplying and sealing the pressure transmission fluid to the sensing cuff prior to the start of pressurization of the pressure cuff by the pressure control unit, switching the switching valve to the second position and using the pump to supply air as the pressure transmission fluid to the sensing cuff; maintaining the switching valve in the first position while the pressure control unit is inflating or deflating the pressure cuff; When discharging the pressure transmitting fluid from the sensing cuff after the blood pressure calculation unit has completed calculation of the blood pressure value, the switching valve is switched to the second position and the air is discharged from the sensing cuff using the discharge valve. An electronic blood pressure monitor characterized by:

12. A blood pressure measurement method for non-invasively measuring blood pressure at a measurement site using the electronic blood pressure meter according to claim 1, comprising: The blood pressure calculation unit acquiring 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 a process of a change in the pressure of the pressing cuff by the pressure control unit; a DC component of the data representing the pressure of the compression cuff or a value approximating the DC component is subtracted from the data representing the pressure of the sensing cuff during the pressure change process to obtain a pressure at a rising start point and a pressure at a peak point shown for each beat of the pressure pulse wave; A first time point is determined when the pressure at the peak point for each beat transitions between a zero level and a positive value during the pressure change process, and the pressure of the pressure cuff at this first time point is determined as a systolic blood pressure value, and a second time point is determined when the pressure at the rising start point for each beat transitions between a zero level and a positive value, and the pressure of the pressure cuff at this second time point is determined as a diastolic blood pressure value. A blood pressure measuring method comprising:

Images