Blood pressure measurement device, blood pressure measurement method, and blood pressure measurement program

Abstract

To stably measure blood pressure with cuff pressure lower than systolic blood pressure. This blood pressure measurement device includes: a cuff wound around a measurement site; a pressure detection unit for detecting the cuff pressure in the cuff; a pressure control unit for controlling the cuff pressure; a pulse wave acquisition unit for acquiring pulse waves of a subject from the cuff pressure; a blood pressure calculation unit for calculating the blood pressure of the subject on the basis of the pulse waves acquired before the cuff pressure reaches a stop cuff pressure at which pressurization of the cuff is stopped; and a stop cuff pressure determination unit for determining the value of the stop cuff pressure on the basis of characteristics of the pulse waves acquired at a cuff pressure lower than the stop cuff pressure.

Description

Blood pressure measurement device, blood pressure measurement method, and blood pressure measurement program

[0001] The present invention relates to a blood pressure measurement device, a blood pressure measurement method, and a blood pressure measurement program.

[0002] In recent years, health management has become commonplace by measuring information about an individual's physical and health, such as blood pressure values, using a measuring device and recording and analyzing the measurement results. One example of such a measuring device is a sphygmomanometer that measures blood pressure, including systolic blood pressure, based on a pressure pulse wave acquired during the process of inflating a cuff attached to a measurement site, such as the upper arm or wrist, of the person being measured (see, for example, Patent Documents 1 and 2).

[0003] The blood pressure monitor disclosed in Patent Document 1 estimates blood pressure values ​​at cuff pressures lower than systolic blood pressure by machine learning the relationship between pressure pulse waves acquired based on cuff pressure and blood pressure values. Specifically, by setting the cuff pressure to, for example, less than 130 mmHg, blood pressure can be measured at a cuff pressure lower than systolic blood pressure even for subjects with high blood pressure.

[0004] In addition, the blood pressure monitor disclosed in Patent Document 2 determines a pulse score from an envelope curve for multiple heartbeats obtained based on the cuff pressure, and when the pulse score exceeds a threshold, stops pressurization without occluding the blood vessel and determines a blood pressure value from the envelope curve. As an example of the pulse score, Patent Document 2 discloses a scale that indicates the possibility that the envelope curve has reached its peak.

[0005] However, if the range of cuff pressure to be inflated is set to a fixed pressure value, as in the technology described in Patent Document 1, the cuff will be inflated to a high pressure even for subjects whose blood pressure can be measured at a lower cuff pressure range, and it is not possible to measure all subjects at a cuff pressure lower than the systolic blood pressure. Furthermore, as in the technology described in Patent Document 2, threshold determination based on a single index, the pulse score, makes it difficult to set optimal conditions for stopping inflation for various conditions of various subjects. It is also difficult to stop inflation at a predetermined timing.

[0006] US Patent Application Publication No. 2020 / 0383579 US Patent No. 9750419 JP 03-280932

[0007] In view of the above-described conventional techniques, an object of the present invention is to provide a technique that enables stable blood pressure measurement at a lower cuff pressure.

[0008] In order to solve the above problems, the present invention provides a blood pressure measurement device comprising: a cuff to be wrapped around a part to be measured; a pressure detection unit to detect cuff pressure in the cuff; a pressure control unit to control the cuff pressure; a pulse wave acquisition unit to acquire a pulse wave of the person to be measured from the cuff pressure; a blood pressure calculation unit to calculate the blood pressure of the person to be measured based on the pulse waves acquired until the cuff pressure reaches a stop cuff pressure at which inflation of the cuff is stopped; and a stop cuff pressure determination unit to determine the value of the stop cuff pressure based on characteristics of the pulse waves acquired at a cuff pressure lower than the stop cuff pressure.

[0009] This allows the stop cuff pressure, which is the cuff pressure value at which a pulse wave sufficient to calculate the subject's blood pressure can be obtained in the blood pressure calculation unit, to be determined based on the characteristics of the pulse wave obtained at a cuff pressure lower than the stop cuff pressure, so that inflation can be stopped at a lower cuff pressure and blood pressure can be measured stably.

[0010] In the present invention, the stop cuff pressure may be lower than the cuff pressure corresponding to the systolic blood pressure of the subject.

[0011] This allows the stop cuff pressure to be determined based on the characteristics of the pulse wave obtained at a cuff pressure lower than the cuff pressure corresponding to the subject's systolic blood pressure, thereby enabling stable blood pressure measurement at a cuff pressure lower than the systolic blood pressure.

[0012] In the present invention, the stop cuff pressure determination unit may determine the value of the stop cuff pressure based on the cuff pressure corresponding to the diastolic blood pressure of the subject.

[0013] This allows the value of the stop cuff pressure to be determined based on the diastolic blood pressure corresponding to the lower cuff pressure, so that inflation can be stopped at a lower cuff pressure, allowing stable blood pressure measurement.

[0014] The stop cuff pressure determination unit may determine the value of the stop cuff pressure based on the cuff pressure at which a first derivative of an envelope of the pulse wave is maximized or locally maximized.

[0015] This allows the value of the stop cuff pressure to be determined based on the cuff pressure at which the first derivative of the pulse wave envelope is maximum or locally maximum, corresponding to a lower cuff pressure, so that inflation can be stopped at a lower cuff pressure, allowing blood pressure to be measured stably.

[0016] The stop cuff pressure determination unit may determine the value of the stop cuff pressure based on an index related to the pulse wave for one beat.

[0017] In the present invention, the stop cuff pressure determination unit may determine the value of the stop cuff pressure based on the cuff pressure at which a second derivative of an envelope of the pulse wave is maximized or locally maximized.

[0018] This allows the value of the stop cuff pressure to be determined based on the cuff pressure at which the second derivative of the pulse wave envelope is maximum or locally maximum, which corresponds to a lower cuff pressure, so that inflation can be stopped at a lower cuff pressure, allowing blood pressure to be measured stably.

[0019] The present invention also provides a blood pressure measurement method comprising the steps of: detecting a cuff pressure in a cuff wrapped around a part to be measured; controlling the cuff pressure; acquiring a pulse wave of the person to be measured from the cuff pressure; calculating a blood pressure of the person to be measured based on the pulse wave acquired before the cuff pressure reaches a stop cuff pressure at which inflation of the cuff is stopped; and determining a value of the stop cuff pressure based on characteristics of the pulse wave acquired at a cuff pressure lower than the stop cuff pressure.

[0020] This allows the stop cuff pressure, which is the cuff pressure value at which a pulse wave sufficient to calculate the subject's blood pressure can be obtained, to be determined based on the characteristics of the pulse wave obtained at a cuff pressure lower than the stop cuff pressure, so that inflation can be stopped at a lower cuff pressure and blood pressure can be measured stably.

[0021] In the present invention, the stop cuff pressure may be lower than the cuff pressure corresponding to the systolic blood pressure of the subject.

[0022] This allows the stop cuff pressure to be determined based on the characteristics of the pulse wave obtained at a cuff pressure lower than the cuff pressure corresponding to the subject's systolic blood pressure, thereby enabling stable blood pressure measurement at a cuff pressure lower than the systolic blood pressure.

[0023] In the present invention, the stop cuff pressure value may be determined based on the cuff pressure corresponding to the diastolic blood pressure of the subject.

[0024] This allows the value of the stop cuff pressure to be determined based on the diastolic blood pressure corresponding to the lower cuff pressure, so that inflation can be stopped at a lower cuff pressure, allowing stable blood pressure measurement.

[0025] In the present invention, the value of the stop cuff pressure may be determined based on the cuff pressure at which the first derivative of the envelope of the pulse wave is maximized or locally maximized.

[0026] This allows the value of the stop cuff pressure to be determined based on the cuff pressure at which the first derivative of the pulse wave envelope is maximum or locally maximum, corresponding to a lower cuff pressure, so that inflation can be stopped at a lower cuff pressure, allowing blood pressure to be measured stably.

[0027] In the present invention, the value of the rest cuff pressure may be determined based on an index related to the pulse wave for one beat.

[0028] In the present invention, the stop cuff pressure value may be determined based on the cuff pressure at which the second derivative of the envelope of the pulse wave is maximized or locally maximized.

[0029] This allows the value of the stop cuff pressure to be determined based on the cuff pressure at which the second derivative of the pulse wave envelope is maximum or locally maximum, which corresponds to a lower cuff pressure, so that inflation can be stopped at a lower cuff pressure, allowing blood pressure to be measured stably.

[0030] The present invention also provides a blood pressure measurement program that causes a computer to execute the following steps: detecting the cuff pressure in a cuff wrapped around a part to be measured; controlling the cuff pressure; acquiring a pulse wave of the person to be measured from the cuff pressure; calculating the blood pressure of the person to be measured based on the pulse wave acquired before the cuff pressure reaches a stop cuff pressure at which inflation of the cuff is stopped; and determining the value of the stop cuff pressure based on characteristics of the pulse wave acquired at a cuff pressure lower than the stop cuff pressure.

[0031] This allows the stop cuff pressure, which is the cuff pressure value at which a pulse wave sufficient to calculate the subject's blood pressure can be obtained, to be determined based on the characteristics of the pulse wave obtained at a cuff pressure lower than the stop cuff pressure, so that inflation can be stopped at a lower cuff pressure and blood pressure can be measured stably.

[0032] According to the present invention, blood pressure can be measured stably at a lower cuff pressure.

[0033] FIG. 1 is a diagram illustrating an outline of the hardware configuration of a blood pressure measurement device according to a first embodiment. FIG. 2 is a functional block diagram of the blood pressure measurement device according to the first embodiment. FIG. 3 is a schematic diagram illustrating the relationship between the cuff pressure and the pressure pulse wave in the blood pressure measurement device according to the first embodiment. FIG. 4 is a flowchart illustrating the overall processing procedure of the blood pressure measurement device according to the first embodiment. FIGS. 5A, 5B, and 5C are diagrams illustrating indices associated with one pulse wave in the blood pressure measurement device according to the first embodiment. FIG. 6 is a flowchart illustrating the overall processing procedure of the blood pressure measurement device according to a modified example of the first embodiment. FIG. 7 is a graph illustrating the envelope of the pressure pulse wave and its first derivative in the blood pressure measurement device according to the modified example of the first embodiment. FIG. 8 is a functional block diagram of a blood pressure measurement device according to a second embodiment. FIG. 9 is a flowchart illustrating the overall processing procedure of the blood pressure measurement device according to the second embodiment. FIG. 10 is a graph illustrating the pressure pulse wave and its first derivative and second derivative in the blood pressure measurement device according to the second embodiment. FIG. 11 is a schematic diagram illustrating the relationship between the cuff pressure and the pressure pulse wave in the blood pressure measurement device according to the second embodiment.

[0034] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

[0035] Example 1 An example of an embodiment of the present invention will be described below. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this example are not intended to limit the scope of the present invention to those only.

[0036] (Device Configuration) FIG. 1 is a schematic diagram of the hardware configuration of a blood pressure measurement device 1 according to this embodiment.

[0037] The blood pressure measurement device 1 includes a cuff 11, a pressure sensor 12, a pressure pump 13, an exhaust valve 14, an air tube 15, an oscillator circuit 21, a pump drive circuit 22, a valve drive circuit 23, a display unit 25, a memory 24, an operation switch 26, a power supply 27, and a CPU 100. The blood pressure measurement device 1 corresponds to the blood pressure measurement device of the present invention. The cuff 11 corresponds to the cuff of the present invention. The blood pressure measurement device 1 including the CPU 100 and the memory corresponds to the computer of the present invention.

[0038] The cuff 11 includes an air bag 11a containing air. The cuff 11 is provided with a pressure sensor 12 for detecting the pressure in the air bag 11a of the cuff 11 (hereinafter referred to as "cuff pressure") via an air tube 15, a pressure pump 13 for supplying air to the air bag 11a, and an exhaust valve 14 that opens and closes to maintain the pressure in the air bag 11a or to exhaust the air from the air bag 11a.

[0039] Furthermore, the blood pressure measuring device 1 includes a CPU (Central Processing Unit) 100 for controlling each part of the device, a memory 24 for storing a program executed for determining an inflation stop position (to be described later), a program executed for blood pressure measurement processing, and data such as cuff pressure, pressure pulse wave, and blood pressure measurement results, a display unit 25 for displaying various information such as blood pressure measurement results, an operation switch 26 for inputting various instructions for measurement, and a power supply 27 for supplying power to each part of the device, such as the CPU.

[0040] Furthermore, the oscillator circuit 21 outputs a signal having an oscillation frequency corresponding to the output value of the pressure sensor 12 to the CPU 100. The pump drive circuit 22 controls the drive of the pressure pump 13 based on a control signal output from the CPU 100. The valve drive circuit 23 controls the opening and closing of the exhaust valve 14 based on the control signal output from the CPU 100.

[0041] 2 is a functional block diagram of the CPU 100 of the blood pressure measurement device 1. The CPU 100 includes a pressure detection unit 110, a pressure control unit 120, an SBP calculation unit 130, a DBP calculation unit 140, and a stop cuff pressure calculation unit 150. The pressure detection unit 110, the pressure control unit 120, the SBP calculation unit 130, and the DBP calculation unit 140 correspond to the pressure detection unit, the pressure control unit, and the blood pressure calculation unit, respectively, of the present invention. The DBP calculation unit 140 and the stop cuff pressure calculation unit 150 correspond to the stop cuff pressure determination unit of the present invention.

[0042] The output signal of the oscillator circuit 21 is input to the pressure detection unit 110. The pressure detection unit 110 detects the oscillation frequency of the input signal and converts the detected oscillation frequency into a pressure value signal. The pressure detection unit 110 includes an HPF (High Pass Filter) unit 111 that applies HPF (High Pass Filter) processing to the pressure value signal to extract and output a pressure pulse wave signal, and an LPF (Low Pass Filter) unit 112 that applies LPF (Low Pass Filter) processing to the pressure value signal to extract and output a cuff pressure signal. The pressure pulse wave signal detected in time series by the HPF unit 111 of the pressure detection unit 110 and the cuff pressure signal indicating the cuff pressure detected in time series by the LPF unit 112 are stored in a predetermined area of ​​the memory 24. Here, the HPF unit 111 corresponds to a pulse wave acquisition unit of the present invention.

[0043] Fig. 3 is a graph schematically showing the relationship between the cuff pressure and the pressure pulse wave detected by the pressure detection unit 110. Generally, as shown in Fig. 3, a diastolic blood pressure (DBP) and a systolic blood pressure (SBP) are calculated as cuff pressures corresponding to specific fluctuation patterns of the pressure pulse wave, and when the cuff is inflated, the diastolic blood pressure is calculated, and after a peak occurs in the envelope of the pressure pulse wave, the systolic blood pressure is calculated at a higher cuff pressure.

[0044] The pressure control unit 120 controls the operation of the pump drive circuit 22 and the valve drive circuit 23 to control the cuff pressure of the cuff 11 .

[0045] The DBP calculation unit 140 and the SBP calculation unit 130 receive the pressure pulse wave signal extracted by the HPF unit 111 of the pressure detection unit 110 and process the received pressure pulse wave signal to calculate the diastolic blood pressure (minimum blood pressure, DBP) and the systolic blood pressure (maximum blood pressure, SBP). The DBP and SBP calculation process will be described later.

[0046] The stop cuff pressure calculation unit 150 calculates the value of the stop cuff pressure, which is the cuff pressure at which inflation of the cuff 11 is stopped, from the cuff pressure corresponding to the DBP calculated by the DBP calculation unit 140. The stop cuff pressure calculation process will be described later.

[0047] (Blood pressure measurement method) Fig. 4 is a flowchart showing the overall processing procedure of the blood pressure measurement method by the blood pressure measurement device 1. The overall processing of blood pressure measurement shown in Fig. 4 is stored in advance in a predetermined area of ​​the memory 24 as a blood pressure measurement program, and is realized by the CPU 100 reading and executing the program from the memory 24. The program may be stored in a computer-readable storage medium and read into the blood pressure measurement device 1 from the storage medium.

[0048] When measuring blood pressure, the subject wraps the cuff 11 around the part to be measured in advance. In the following description, an example is given in which the part to be measured is the upper arm, but the part to be measured is not limited to this and may be the wrist, etc. The description also assumes that the subject performs predetermined settings using the operation switch 26 and issues a command to start blood pressure measurement. Upon receiving the command to start blood pressure measurement, the blood pressure measurement device 1 performs predetermined initialization, such as opening the exhaust valve 14 and setting the cuff pressure to atmospheric pressure (initial pressure).

[0049] When blood pressure measurement is started, the pressure control unit 120 starts pressure control to pressurize the cuff 11 (step S1).

[0050] During the process of pressure control, the HPF unit 111 of the pressure detection unit 110 acquires a pressure pulse wave (step S2).

[0051] The DBP calculation unit 140 calculates the DBP from the detected pressure pulse wave information (step S3). Specifically, the DBP calculation unit 140 determines whether the cuff pressure being inflated has reached the cuff pressure corresponding to the DBP using an index obtained based on the pressure pulse wave information. The unit 140 continues inflation and acquires further pressure pulse waves until the cuff pressure reaches the cuff pressure corresponding to the DBP (step S2), and repeats the process of step S3. The DBP calculation unit 140 then calculates the cuff pressure value corresponding to the DBP as the DBP and stores it in a predetermined area of ​​the memory 24.

[0052] Known indices based on pressure pulse wave information include RAV, WID, and DFN, as disclosed in Patent Document 3. These indices are calculated for each beat of the pressure pulse wave, and RAV, WID, and DFN represent the area, width, and slope of the pulse wave for one beat, respectively. FIG. 5(A) illustrates RAV, FIG. 5(B) illustrates WID, and FIG. 5(C) illustrates DFN. The waveform in FIG. 5(A) shows a pulse wave for one beat. RAV is the pulse wave area for each beat indicated by the diagonal lines in FIG. 5(A) normalized by amplitude, and is expressed as (pulse wave area / pulse wave amplitude within one beat)×100. WID is the waveform width, which is the time width from the maximum amplitude (Maximum) to a threshold (Threshold), normalized by the pulse wave period, and is expressed as (waveform width / pulse wave period)×100, as shown in FIG. 5(B). As shown in FIG. 5C, DFN is the minimum value of the first derivative of the pressure pulse wave normalized by the pulse wave amplitude, and is expressed as (minimum value from 0 of the first derivative of the pulse wave / pulse wave amplitude of the first derivative of the pulse wave).

[0053] When the cuff pressure that results in DBP is Pd, it is expressed as a function of RAV, WID, and DFN, such as Pd = f(RAV, WID, DFN). Here, Pd is expressed as a function of the three indices RAV, WID, and DFN, but it may be expressed as any one or two of these indices. The form of the function f is not particularly limited, but the DBP calculation unit 140 determines whether the cuff pressure has reached DBP by calculating these indices for each beat of the acquired pressure pulse wave. For example, it can be determined that the cuff pressure has reached DBP when RAV or WID reaches a minimum value or DFN reaches a maximum value.

[0054] Once DBP is calculated in step S3, the stop cuff pressure calculation unit 150 calculates the stop cuff pressure value based on DBP (step S4). When the stop cuff pressure is P1, the relationship between the stop cuff pressure value and DBP is expressed by a predetermined relational expression, such as P1 = g(Pd). The form of the function g is not particularly limited, but may be, for example, P1 = αPd, where α is a constant.

[0055] The stop cuff pressure P1 can be set to any appropriate value. However, as described below, when the cuff pressure reaches the stop cuff pressure P1, the cuff 11 stops compressing the measurement site. From the perspective of reducing the burden on the subject, it is desirable to terminate blood pressure measurement earlier after inflation begins, i.e., by inflating to a lower cuff pressure. On the other hand, from the perspective of ensuring blood pressure measurement accuracy, it is desirable to terminate blood pressure measurement later after inflation begins, i.e., after inflation to a higher cuff pressure, since this allows for more cuff pressure (pressure pulse wave) data to be acquired. As shown in FIG. 3 , DBP can be detected before the peak in the envelope of the pressure pulse wave, i.e., at a cuff pressure lower than the cuff pressure corresponding to the peak. Furthermore, the peak in the envelope of the pressure pulse wave occurs before the SBP, i.e., the cuff pressure corresponding to the peak is lower than the cuff pressure corresponding to the SBP. Therefore, an appropriate stop cuff pressure P1 is set taking these factors into consideration. For example, the peak of the envelope of the pressure pulse wave shown in FIG. 3 can be used as the stop cuff pressure P1. The inventors' extensive research has revealed that the peak of the pressure pulse wave envelope has a specific relationship with a region or point prior to the peak that is related to some characteristic of the pressure pulse wave envelope, such as the DBP described above. When the rest cuff pressure P1 is the peak of the pressure pulse wave envelope, the function g or constant α described above, which expresses the relationship between P1 and Pd, expresses this relationship.

[0056] After the stop cuff pressure value is calculated in step S4, the pressure control unit 120 determines whether the cuff pressure detected by the pressure detection unit 110 is greater than the stop cuff pressure (step S5). The determination in step S5 is repeated while continuing the inflation control.

[0057] When the pressure control unit 120 determines that the cuff pressure has become greater than the stop cuff pressure, it controls the pump drive circuit 22 to stop pressurizing the cuff 11 (step S6), and controls the valve drive circuit 23 to open the exhaust valve 14 and discharge the air from the air bag 11a.

[0058] The SBP calculation unit 130 calculates the SBP based on the pressure pulse wave acquired before the cuff pressure reaches the stop cuff pressure P1 (step S7). Here, the SBP is estimated based on the pressure pulse wave acquired before the cuff pressure reaches the stop cuff pressure P1 using an estimation model included in the blood pressure measurement program. This estimation model uses, for example, pressure pulse waves detected from the subject while the cuff 11 is inflated until the amplitude of the pressure pulse wave reaches its maximum as training samples, and is machine-learned so that the estimated values ​​obtained by the estimation model match the true values ​​of the blood pressure values ​​(here, SBP) when these training samples are detected. The pressure pulses detected from the subject while the cuff 11 is inflated until the amplitude of the pressure pulse wave reaches its maximum may also be used as training samples. The training samples may include at least one of envelope data and amplitude data of the pressure pulse wave, or may include cuff pressure data and beat-by-beat features of the pressure pulse wave. The beat-by-beat feature of the pressure pulse wave may be, for example, a statistical quantity such as a maximum value, a minimum value, a variance, a standard deviation, an n% tile value, a skewness, or a kurtosis, or may be the RAV, WID, or DFN described above. The machine learning model constituting such an estimation model may be, for example, a neural network, a regression model, a decision tree model, a support vector machine, or other functional formulas (computational models). The machine learning method may be appropriately selected depending on the employed machine learning model (e.g., backpropagation). The estimation model may be configured to directly derive an estimated value of SBP. Alternatively, the estimation model may be configured to indirectly derive an estimated value of SBP by predicting the time point of SBP on the assumption that the increase in cuff pressure follows a predetermined condition (e.g., is constant). In this case, the estimated value of SBP can be derived by calculating the value of cuff pressure at the time point predicted by the estimation model.

[0059] The CPU 100 displays the measurement results, such as the DBP calculated in step S3 and the SBP calculated in step S7, on the display unit 25 of the blood pressure measurement device 1 (step S8). The CPU 100 records the measurement results, such as the calculated blood pressure value, in a predetermined area of ​​the memory 24 of the blood pressure measurement device 1, and ends the blood pressure measurement process.

[0060] In this way, the timing to stop inflation can be determined from the characteristics of the pressure pulse wave waveform at an earlier stage after inflation has started, making it possible to stably measure blood pressure at a lower cuff pressure for any subject, regardless of their blood pressure level or other attributes.

[0061] <Modification> A modification of Example 1 will be described below. In Example 1, DBP is calculated based on an index such as RAV, but the DBP calculation method is not limited to this. Here, as a modification, an example using a different DBP calculation method will be described. FIG. 6 is a flowchart showing the overall processing procedure of a blood pressure measurement method in the blood pressure measurement device 1 according to the modification. Except for the envelope acquisition process, the differential value acquisition process, the DBP calculation process, and the stop cuff pressure calculation process, the hardware configuration and blood pressure measurement process of the blood pressure measurement device 1 according to Example 1 are the same as those of the blood pressure measurement device 1 according to Example 1, and therefore the same reference numerals will be used and detailed description will be omitted.

[0062] 7 shows the envelope of the pressure pulse wave output from the HPF unit 111 of the pressure detection unit 110 and the waveform of the first derivative of the pressure pulse wave envelope. The horizontal axis of the graph shown in FIG. 7 represents the cuff pressure (mmHg), the left vertical axis represents the magnitude of the envelope of the pressure pulse wave, and the right vertical axis represents the magnitude of the first derivative of the envelope of the pressure pulse wave. Here, the DBP calculation unit 140 obtains the envelope of the pressure pulse wave obtained by the HPF unit 111 of the pressure detection unit 110 (step S11). Furthermore, the DBP calculation unit 140 obtains the derivative of the envelope of the pressure pulse wave (step S12).

[0063] Here, the DBP calculation unit 140 calculates the cuff pressure corresponding to the DBP by detecting the maximum value (or local maximum value) of the first derivative of the envelope of the pressure pulse wave. That is, the DBP calculation unit 140 calculates the DBP by detecting the maximum value (or local maximum value) of the first derivative of the envelope of the pressure pulse wave from the differential value of the envelope of the acquired pressure pulse wave (step S3). The acquisition of the pressure pulse wave (step S2), its envelope (step S11), and the differential value of the envelope (step S12) are repeated until the maximum value (or local maximum value) of the first derivative of the envelope of the pressure pulse wave is detected.

[0064] When the DBP calculation unit 140 detects the maximum value (or local maximum value) of the first derivative of the envelope of the pressure pulse wave, the stop cuff pressure calculation unit 150 calculates the stop cuff pressure based on the maximum value (or local maximum value) of the first derivative of the envelope of the pressure pulse wave (step S4). At this time, for example, the stop cuff pressure calculation unit 150 calculates the stop cuff pressure as the cuff pressure value at which the first derivative of the envelope of the pressure pulse wave is N% of the maximum value (or local maximum value). The value of N can be set as appropriate and is stored in a predetermined area of ​​the memory 24. Here, the stop cuff pressure is given as the differential value of the envelope of the pressure pulse wave. Therefore, the pressure control unit 120 determines whether the cuff pressure is greater than the stop cuff pressure (step S5) based on whether the differential value of the envelope of the pressure pulse wave is greater than N% of the maximum value (or local maximum value).

[0065] When the pressure control unit 120 determines that the differential value of the envelope of the pressure pulse wave has reached N% of the maximum value (or local maximum value), it controls the pump drive circuit 22 to stop inflating the cuff 11 (step S6) and controls the valve drive circuit 23 to open the exhaust valve 14 and discharge the air from the air bladder 11a. In the above example, the stop cuff pressure was set to the cuff pressure at which the first differential of the envelope of the pressure pulse wave is N% of the maximum value (or local maximum value). However, the method for determining the stop cuff pressure is not limited to this. For example, the cuff pressure at which the first differential of the envelope of the pressure pulse wave is zero (zero cross) can also be set to the stop cuff pressure. In this case, the pressure control unit 120 determines whether the cuff pressure is greater than the stop cuff pressure (step S5) based on whether the differential value of the envelope of the pressure pulse wave is greater than zero. The cuff pressure at which the first differential of the envelope of the pressure pulse wave is zero (zero cross) is a value that approximates the peak of the envelope of the pressure pulse wave.

[0066] Even with this modification, the position where inflation should be stopped can be determined from the characteristics of the pressure pulse wave envelope at an earlier stage after inflation has begun, making it possible to stably measure blood pressure at a lower cuff pressure for any subject, regardless of their blood pressure level or other attributes.

[0067] Example 2 The overall configuration of a blood pressure measurement device 2 according to Example 2 is similar to that of the blood pressure measurement device 1 according to Example 1 shown in FIG. 8. FIG. 8 is a functional block diagram of a CPU 100A of the blood pressure measurement device 2. FIG. 9 is a flowchart showing the overall processing procedure of a blood pressure measurement method by the blood pressure measurement device 2. The same components and processes as those of the blood pressure measurement device 1 according to Example 1 are designated by the same reference numerals, and their description will be omitted. In Example 2, the CPU 100A has a blood pressure calculation unit 130A instead of the SBP calculation unit 130 and DBP calculation unit 140 shown in FIG. 2. The blood pressure measurement device 2 having the CPU 100A and the memory 24 corresponds to the computer of the present invention. The blood pressure calculation unit 130A corresponds to the blood pressure calculation unit of the present invention.

[0068] In the blood pressure measurement device 2 according to the second embodiment, the inflation stop position is determined based on the cuff pressure at the point where the envelope of the pressure pulse wave begins to stabilize (also referred to as the stable point). The CPU 100A of the blood pressure measurement device 2 includes a stable point calculation unit 160 that calculates the stable point instead of the DBP calculation unit 140. Such a stable point corresponds to a region of cuff pressure near 40 mmHg, for example. Here, the stable point calculation unit 160 and the stop cuff pressure calculation unit 150 correspond to the stop cuff pressure determination unit of the present invention.

[0069] The stable point of the pressure pulse wave envelope corresponds to the maximum value (or local maximum value) of the second derivative of the pressure pulse wave envelope. The upper part of FIG. 10 shows the pressure pulse wave envelope, the middle part shows the first derivative of the pressure pulse wave envelope, and the lower part shows the second derivative of the pressure pulse wave envelope. The maximum value (or local maximum value) of the second derivative of the pressure pulse wave envelope is indicated by a circle in the lower graph. The point of the pressure pulse wave envelope that corresponds to the maximum value (or local maximum value) of the second derivative of the pressure pulse wave envelope is indicated by a circle in the upper graph. It can also be seen from FIG. 9 that the maximum value (or local maximum value) of the second derivative of the pressure pulse wave envelope indicates the stable point of the pressure pulse wave envelope.

[0070] 9, the stable point calculation unit 160 obtains an envelope of the pressure pulse wave obtained by the HPF unit 111 of the pressure detection unit 110 (step S11). Furthermore, the stable point calculation unit 160 obtains a second derivative of the envelope of the pressure pulse wave (step S13).

[0071] Here, the stable point calculation unit 160 calculates the cuff pressure corresponding to the stable point by detecting the maximum value (or local maximum value) of the second derivative of the envelope of the pressure pulse wave. That is, the stable point calculation unit 160 calculates the stable point by detecting the maximum value (or local maximum value) of the second derivative of the envelope of the pressure pulse wave from the second derivative value of the envelope of the acquired pressure pulse wave (step S14). Acquisition of the pressure pulse wave (step S2), acquisition of its envelope (step S11), and acquisition of the second derivative value of the envelope (step S13) are repeated until the maximum value (or local maximum value) of the second derivative of the envelope of the pressure pulse wave is detected, i.e., until the envelope becomes stable.

[0072] A stable point is calculated by detecting the maximum value (or local maximum value) of the second derivative of the envelope of the pressure pulse wave (step S14).

[0073] Once the stable point is calculated in step S14, the stop cuff pressure calculation unit 150 calculates the value of the stop cuff pressure based on the cuff pressure at the stable point (step S4). When the cuff pressure corresponding to the stable point is Ps and the stop cuff pressure is P2, the relationship between the stop cuff pressure and the cuff pressure corresponding to the stable point is expressed by a predetermined relational expression, such as P2 = h(Ps). The form of the function h is not particularly limited, but may be, for example, P2 = βPs, where β is a constant.

[0074] The stop cuff pressure P2 can be set to any appropriate value. However, as described in Example 1, the stop cuff pressure P2 is set appropriately taking into consideration reducing the burden on the subject and ensuring the accuracy of blood pressure measurement. For example, as shown in FIG. 11, the peak of the pressure pulse wave envelope can be used as the stop cuff pressure P2. Similar to FIG. 3, FIG. 11 is a graph schematically illustrating the relationship between the cuff pressure detected by the pressure detection unit 110 and the pressure pulse wave. The inventors' extensive research has revealed that the peak of the pressure pulse wave envelope has a specific relationship with a region or point prior to the peak that is related to some characteristic of the pressure pulse wave envelope, such as the stable point described above. When the stop cuff pressure P2 is the peak of the pressure pulse wave envelope, the function h or constant β described above, which represents the relationship between P2 and Ps, expresses this relationship.

[0075] Once the stop cuff pressure is calculated in step S4, the pressure control unit 120 determines whether the cuff pressure detected by the pressure detection unit 110 is greater than the stop cuff pressure (step S5). The determination in step S5 is repeated while continuing inflation control.

[0076] When the pressure control unit 120 determines that the cuff pressure has become greater than the stop cuff pressure, it controls the pump drive circuit 22 to stop pressurizing the cuff 11 (step S6), and controls the valve drive circuit 23 to open the exhaust valve 14 and discharge the air from the air bag 11a.

[0077] The blood pressure calculation unit 130A calculates blood pressure values ​​(DBP and SBP) based on the pressure pulse wave acquired before the cuff pressure reaches the stop cuff pressure P2 (step S7). The blood pressure calculation unit 130A acquires the DBP and SBP based on the pressure pulse wave acquired before the cuff pressure reaches the stop cuff pressure P2 using the estimation model described for the SBP calculation unit 130 in Example 1.

[0078] The CPU 100A displays the measurement results, such as DBP and SBP, calculated in step S7 on the display unit 25 of the blood pressure measurement device 2 (step S8). The CPU 100A records the measurement results, such as the calculated blood pressure value, in a predetermined area of ​​the memory 24 of the blood pressure measurement device 2, and ends the blood pressure measurement process.

[0079] In this way, the timing to stop inflation can be determined from the characteristics of the envelope of the pressure pulse wave at an earlier stage after inflation has started, making it possible to stably measure blood pressure at a lower cuff pressure for any subject, regardless of their blood pressure level or other attributes.

[0080] REFERENCE SIGNS LIST 1, 2... Blood pressure measurement device 11... Cuff 110... Pressure detection unit 120... Pressure control unit 130... SBP calculation unit 130A... Blood pressure calculation unit 140... DBP calculation unit 150... Stop cuff pressure calculation unit 160... Stable point calculation unit

Claims

1. A blood pressure measuring device comprising: a cuff to be wrapped around a part to be measured; a pressure detection unit to detect the cuff pressure in the cuff; a pressure control unit to control the cuff pressure; a pulse wave acquisition unit to acquire the pulse wave of the person to be measured from the cuff pressure; a blood pressure calculation unit to calculate the blood pressure of the person to be measured based on the pulse waves acquired until the cuff pressure reaches a stop cuff pressure at which inflation of the cuff is stopped; and a stop cuff pressure determination unit to determine the value of the stop cuff pressure based on characteristics of the pulse waves acquired at a cuff pressure lower than the stop cuff pressure.

2. The blood pressure measuring device according to claim 1, wherein the stop cuff pressure is lower than the cuff pressure corresponding to the systolic blood pressure of the subject.

3. A blood pressure measuring device according to claim 1 or 2, characterized in that the stop cuff pressure determining unit determines the value of the stop cuff pressure based on the cuff pressure corresponding to the diastolic blood pressure of the subject.

4. A blood pressure measuring device as described in claim 1 or 2, characterized in that the stop cuff pressure determination unit determines the value of the stop cuff pressure based on the cuff pressure at which the first derivative of the envelope of the pulse wave is maximum or local maximum.

5. A blood pressure measuring device according to claim 1 or 2, characterized in that the stop cuff pressure determining unit determines the value of the stop cuff pressure based on an index related to the pulse wave for one beat.

6. A blood pressure measuring device as described in claim 1 or 2, characterized in that the stop cuff pressure determination unit determines the value of the stop cuff pressure based on the cuff pressure at which the second derivative of the envelope of the pulse wave is maximum or local maximum.

7. A blood pressure measurement method comprising the steps of: detecting the cuff pressure in a cuff wrapped around a part to be measured; controlling the cuff pressure; acquiring the pulse wave of the person to be measured from the cuff pressure; calculating the blood pressure of the person to be measured based on the pulse wave acquired until the cuff pressure reaches a stop cuff pressure at which inflation of the cuff is stopped; and determining the value of the stop cuff pressure based on characteristics of the pulse wave acquired at a cuff pressure lower than the stop cuff pressure.

8. A blood pressure measurement method according to claim 7, wherein the stop cuff pressure is lower than the cuff pressure corresponding to the systolic blood pressure of the subject.

9. A blood pressure measurement method according to claim 7 or 8, characterized in that the value of the stop cuff pressure is determined based on the cuff pressure corresponding to the diastolic blood pressure of the subject.

10. A blood pressure measurement method according to claim 7 or 8, characterized in that the value of the stop cuff pressure is determined based on the cuff pressure at which the first derivative of the envelope of the pulse wave is maximum or local maximum.

11. A blood pressure measurement method according to claim 7 or 8, characterized in that the value of the rest cuff pressure is determined based on an index related to the pulse wave for one beat.

12. A blood pressure measurement method according to claim 7 or 8, characterized in that the value of the stop cuff pressure is determined based on the cuff pressure at which the second derivative of the envelope of the pulse wave is maximum or local maximum.

13. A blood pressure measurement program that causes a computer to execute the following steps: detecting the cuff pressure in a cuff wrapped around a part to be measured; controlling the cuff pressure; acquiring the pulse wave of the person to be measured from the cuff pressure; calculating the blood pressure of the person to be measured based on the pulse wave acquired until the cuff pressure reaches a stop cuff pressure at which inflation of the cuff is stopped; and determining the value of the stop cuff pressure based on characteristics of the pulse wave acquired at a cuff pressure lower than the stop cuff pressure.

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