JP2668996B2 - Electronic sphygmomanometer - Google Patents

Description

The present invention relates to a non-invasive electronic sphygmomanometer using a cuff, and more particularly to an electronic sphygmomanometer using an oscillometric method.

(B) Conventional technology In general, when a cuff is wound around an arbitrary measurement site, and is gradually pressurized after being pressurized by a pressurizing pump or the like, pressure oscillation occurs in the cuff internal pressure in synchronization with a pulse. . This pressure oscillation is called a pulse wave, and the oscillometric method is a general term for a method of calculating (determining) blood pressure by analyzing the waveform of this pulse wave.
In the conventional oscillometric method, the blood pressure is calculated by recognizing the change in the amplitude of the pulse wave. In other words, when the cuff pressure is increased above the systolic pressure (systolic blood pressure) and then gradually reduced, the amplitude of the pulse wave is initially small and gradually increases, around the point where the cuff pressure becomes equal to the average blood pressure. By taking advantage of the fact that the pulse wave amplitude gradually decreases after reaching the maximum amplitude, conventionally, the pulse wave amplitude is calculated relative to the relative level (X%, Y%) of the pulse wave amplitude calculated based on the maximum amplitude. ) Is determined as the systolic or diastolic pressure (diastolic pressure) (see FIG. 7), or the rate of increase in pulse wave amplitude increases or decreases rapidly. Cuff pressure at the time of
Blood pressure was calculated by the method of determining systolic pressure and diastolic pressure (see FIG. 8).

(C) Problems to be Solved by the Invention The behavior of the pulse wave amplitude originally has the property of greatly differing from individual to individual. Therefore, in the former method described above, the pulse wave amplitude at the true systolic pressure or the diastolic pressure is not always a fixed ratio with the maximum pulse wave amplitude. Also,
In the conventional latter method, the change point of the rate of increase or decrease of the pulse wave amplitude is often unclear. For the above reasons, there is a problem that a large measurement error often occurs when any of the conventional oscillometric methods is adopted.

The present invention has been made in view of the above-described problems, and has a high degree of accuracy and reliability using pulse parameters other than pulse wave amplitude, in which individual differences are small, and parameters with a distinct feature change, that is, pulse wave amplitudes. It is intended to provide an electronic sphygmomanometer employing a high oscillometric method.

(D) Means and Actions for Solving the Problems The electronic sphygmomanometer of the present invention measures the blood pressure while detecting the pulse wave and the cuff pressure. Means for calculating a value, means for calculating a pulse wave average ratio constituted by using the maximum value, minimum value and average value calculated by this means, and extraction of characteristic points of the pulse wave average ratio calculated by this means And a blood pressure determining means for determining a blood pressure value from the characteristic points extracted by this means and the corresponding cuff pressure.

Here, FIG. 1 illustrating the nature of the pulse wave average ratio R shows a change in the pulse wave average ratio R in the process of reducing the intra-armband pressure. This is clinical data obtained from 260 subjects, based on auscultation systolic pressure (SYS) and diastolic pressure (DI).
It is plotted on the pressure axis of the arm band normalized in A). The numerical value on the horizontal axis indicates a pressure difference when SYS-DIA is set to 100% and SYS is used as a reference. From this figure, during the depressurization process of the cuff, the pulse wave average ratio R tends to slightly decrease in the cuff internal pressure region higher than the systolic pressure, but the systolic pressure point (SYS in the figure)
Around the diastolic pressure point (DIA)
Point) increases almost monotonically. And about at diastolic pressure point
It has reached about 50% and tends to decrease again after that.
The nature of such a pulse wave average ratio R is shown in FIGS.
As shown in (c), the change is derived from a change in the pulse wave waveform in the cuff depressurization process, but is a stable change without variation among individuals, and a remarkable change in the feature amount corresponding to the blood pressure is observed. Thus, blood pressure measurement with high reproducibility is possible by using the pulse wave average ratio R. That is,
In this electronic sphygmomanometer, for example, the pulse wave component is extracted during the depressurization process of the cuff, the maximum value, the minimum value, and the average value of each pulse wave are calculated, and the pulse wave average ratio is calculated from the maximum value, the minimum value, and the average value. Is calculated, and the characteristic points of this pulse wave average ratio are extracted in the decompression process, and the systolic pressure and the diastolic pressure are calculated and determined from the extracted characteristic points. Although the change in the pulse wave average ratio is detected in the cuff depressurization process to calculate the blood pressure value in the cuff depressurization process, this may be performed in the slow speed pressurization process.

(E) Examples Hereinafter, the present invention will be described in more detail with reference to examples.

FIG. 3 is a block diagram showing a hardware configuration of an electronic sphygmomanometer according to the present invention.

In FIG. 1, a cuff (arm band) 1 is connected via a pipe 2 to an exhaust valve 3 having a slow exhaust function and a rapid exhaust function, a pressurizing pump 4, and a pressure sensor 5. Pressure pump 4
Is turned on / off by a command from the CPU 9, and the exhaust valve 3 is also configured so that the rapid exhaust function is turned on by a command signal a from the CPU 9. The pressure sensor 5 converts the pressure in the cuff 1 received through the pipe 2 into an electric signal, outputs the electric signal, amplifies it with an amplifier 6, converts it into a digital signal with an A / D converter 7, and takes it into the CPU 9. On the other hand, since the intra-armband pressure signal output from the amplifier 6 includes a pulse wave component, only the pulse wave component is derived by the band-pass filter 8 and is converted into a digital signal by the A / D converter 7. And import to CPU9. The CPU 9 executes a process for calculating blood pressure, which will be described later, and displays the measured value on the display device 10.

However, the hardware configuration of the electronic sphygmomanometer shown here is not particularly different from the configuration of the conventional oscillometric electronic sphygmomanometer. Therefore, the pressure sensor 5 may be a semiconductor pressure sensor or a combination of a bellows type sensor and an oscillator. The bandpass filter 8 is CP
It may be a digital filter configured by software in U9. The feature of the present invention is that the algorithm of the blood pressure calculation executed by the CPU 9 has a feature.

Next, referring to the flow charts shown in FIGS. 4 and 5,
The blood pressure measurement operation of the electronic blood pressure monitor will be described.

When a start switch (not shown) is turned on, the processing shown in FIG. 4 starts, and first, in step ST (hereinafter abbreviated as ST1) 1, variables used for blood pressure calculation are initialized. Here, when the functions of each variable are listed, t is the pulse wave data PW
(T) counter, n is a pulse counter (also a counter for the calculated pulse wave average ratio R), FLAG is a flag used when the pulse wave is divided into beats, and DIA is a variable (flag function that stores the minimum blood pressure). Is initialized because it has both), C _DIA
Is a counter indicating the position of the maximum point of the pulse wave average ratio R (indicating how many beats the maximum point is before the present), and R _MAX and R _MIN store the maximum value and the minimum value of the pulse wave average ratio R. Is a variable.

Following initialization, the pulse wave data PW (t) is read through the A / D converter 7 (ST2), the variable t is then incremented by 1 (ST3), and the pulse wave is divided into beats. (ST4). As shown in FIG. 6, the detection of the break point is realized by a process such as detecting an intersection between a pulse wave and a threshold value provided in the pulse wave data. Next, it is determined whether or not a breakpoint has been detected (ST5), and the processing from ST2 to ST5 is repeated until a breakpoint is detected, that is, data of the pulse wave data PW (t) is read. When the break point is detected, the determination in ST5 becomes YES, and the pulse wave average ratio R (n) is calculated here.

Details of the calculation process of the pulse wave average ratio R (n) will be described later.

Once the pulse wave average ratio R (n) is obtained, the variable n is set to 1
Increment and compare the variables R _MIN and R (n)
_MIN is newly stored if larger is than R (n) R a value of (n) to R _MIN, updates the R _MIN, the cuff pressure at that point in the variable SYS systolic pressure Memorize (ST9). ST8
When R (n) is larger than R _MIN , the determination is NO and the process skips ST9 and moves to ST10. Here, by the processing of ST8 to ST9,
The cuff pressure when the pulse wave average ratio R (n) is the minimum is stored in SYS as the systolic pressure.

Next, in ST10, the value of R (n) is determined whether greater than 40%, then returns to ST2 during an average value is less than 40%, goes to ST11 when the judgment YES, the variable R _MAX is It is determined whether it is smaller than the pulse wave average ratio R (n). At ST10
It is determined whether the pressure is greater than 40% because the cuff pressure at that time is not yet sufficiently close to the diastolic pressure, and the following diastolic pressure determination processing is performed, and the abnormal diastolic pressure is determined. This is to prevent the pressure from being calculated. In other words, if the cuff pressure has not yet been reduced to the vicinity of the diastolic pressure, the pulse wave average ratio R (n) continues to take a value smaller than 40%, and the process jumps from ST10 to ST2 to determine the systolic pressure. Repeatedly, but eventually, when the pressure reduction progressed sufficiently, the pulse wave average ratio R
(N) exceeds 40%, and the determination in ST10 is YES
Then, it will move to the processing after ST11.

If the variable R _MAX is smaller than the pulse wave average ratio R (n) in ST11, the cuff pressure is stored as the diastolic pressure variable DIA (ST1
6), the counter C _DIA to 0 (ST17), further current pulse wave average ratio R (n) is newly stored as R _MAX (ST18),
Return to ST2. Then, the processes of ST2 to ST11 and ST16 to ST18 are repeated. That is, in ST16 to ST18, the pulse wave average ratio R
The cuff pressure at the maximum value of (n) is updated every time by the variable DIA.

On the other hand, in ST11, the variable R _MAX is the pulse wave average ratio R (n).
If it is not less than, processing moves to ST12 and counter C _DIA
Is incremented by one. This counter _CDIA counts the number of beats after _RMAX is no longer updated after the pulse wave average ratio R (n) has already exceeded the maximum point. In the next process ST13, checks the value of the counter value, while a less than 3, the process returns to ST2, and repeats the processing of ST2 to ST13, but the value of this C _DIA is 3 or more, the ST13 When the determination is YES, that is, when a new maximum point does not appear even after three or more beats, it is determined that the maximum point is a reliable diastolic pressure point, and all the blood pressure determination processes are terminated. ST
After rapid evacuation at 14 to release the pressure on the arm girdle, the measured blood pressure value is displayed (ST15), and the measurement process ends.

Next, details of the calculation process of the pulse wave average ratio R (n) in ST6 will be described with reference to the flowchart shown in FIG.

First, in ST61, each variable is initialized. here,
t ′ is a time counter dedicated to the following average ratio calculation processing, T
_DEV is the value of the counter t at the breakpoint one beat before. Therefore, by substituting the value of the variable T _DEV for the variable t ′, a series of processing for calculating the average ratio is started from the break point one beat before. PW _MAX is a variable indicating the maximum value of the pulse wave data, and PW _MIN is a variable indicating the minimum value of the pulse wave data. In ST62, the pulse wave data PW (t ') value of is compared to the variable _{PW MAX, PW MAX <PW (} t' if), PW
(T ′) is set as a new PW _MAX , and the PW _MAX is updated (ST6).
3). That is, the maximum value of PW (t ') is stored in PW _MAX every time. Therefore, PW _MAX <PW
If not (t '), ST63 is skipped. next,
In ST64, the variable PW _MIN is compared with PW (t '), and PW _MIN >
If PW (t '), set PW (t') as a new PW _MIN ,
Update W _MIN (ST65). And in ST66, the variable TOTA
PW (t ') is sequentially added to L.

Next, at ST67, the counter t'is a variable t indicating the current time.
If t '= t, that is, if a series of processing has been performed up to the current break point, the process proceeds to ST69. On the other hand, if not t '= t, the process returns to ST62 and the process is repeated again. In ST69, the pulse wave average ratio R (n) is calculated as follows using the variable TOTAL, the counter t, the count value T _DEV at the previous breakpoint, PW _MAX , and PW _MIN .

Then, in preparation for the next average ratio calculation processing, the time t of the current break point is stored in the variable T _DEV , the processing ends, and the process returns to the main flow.

In the above embodiment, the pulse wave average ratio is determined in the process of decompressing the intra-arm band pressure at a very low speed, and the systolic pressure and the diastolic pressure are determined from the corresponding intra-arm band pressure by extracting the characteristic points. Alternatively, however, the pulse wave average ratio when the intra-arm band pressure is applied at a very low speed may be determined, and the characteristic points thereof may be similarly extracted to determine the diastolic pressure and the systolic pressure from the corresponding intra-arm band pressure.

(F) Effects of the Invention According to the present invention, the pulse wave component of the cuff internal pressure is extracted in the course of the slow change of the cuff internal pressure, the maximum value, the minimum value, and the average value of each pulse wave are obtained. Calculate the pulse wave average ratio from the minimum value and the average value, extract the characteristic point of this pulse wave average ratio, and determine the blood pressure value from the cuff internal pressure corresponding to this characteristic point. The correspondence between the characteristic point and the systolic pressure and the diastolic pressure is always maintained, and the measurement can be performed with higher accuracy than the conventional oscillometric electronic sphygmomanometer. Further, the relationship between pulse wave averaging and cuff internal pressure hardly differs between subjects, and correct measurement can be performed for a wide range of subjects.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the pressure inside the arm band and the average level of the pulse wave for explaining the concept of the pulse wave average ratio used in the present invention, and FIGS. 2 (a), (b) and (c) are the arm bands. FIG. 3 is a block diagram of an electronic sphygmomanometer embodying the present invention, and FIGS. 4 and 5 are flowcharts for explaining the operation of the electronic sphygmomanometer according to the present invention. 4 is a main flow diagram, FIG. 5 is a flow diagram showing the pulse wave average ratio calculation processing in the main flow diagram in detail, and FIG. 6 explains the division of the pulse wave for each beat. Figures, Figures 7 and 8
The figure is a diagram for explaining blood pressure determination in the conventional oscillometric method. 1: Armband, 3 exhaust valve, 4: Pressure pump, 5: Pressure sensor, 7: A / D converter, 8: Bandpass filter 9: CPU.

Claims (2)

(57) [Claims] An electronic sphygmomanometer for measuring blood pressure while detecting a pulse wave and a cuff pressure, comprising: means for calculating a maximum value, a minimum value, and an average value of a pulse wave for each beat; Means for calculating a pulse wave average ratio composed of values, minimum values and average values, means for extracting characteristic points of the pulse wave average ratio calculated by this means, and correspondence with the characteristic points extracted by this means. An electronic sphygmomanometer comprising: a blood pressure determining means for determining a blood pressure value based on the cuff pressure to be stored. 2. The electronic sphygmomanometer according to claim 1, wherein the characteristic point is a maximum value or a minimum value of a pulse wave average ratio.