JPH0480688B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application This invention relates to an electronic blood pressure monitor, particularly an electronic blood pressure monitor employing a vibration method.

(B) Conventional technology Generally, when a cuff is wrapped around the upper arm and the pressure is increased until it exceeds the systolic blood pressure, then the pressure is reduced, the cuff pressure produces regular continuous vibrations (pulse waves) in conjunction with the arterial pulsation. . During the decompression process, this pulse wave initially has a small amplitude, gradually increases, and after reaching its maximum amplitude,
This time it will gradually become smaller. There is a correlation between this cuff pressure and pulse wave amplitude; the cuff pressure corresponding to the maximum amplitude is the mean blood pressure, the cuff pressure at the point where the amplitude suddenly rises is the systolic blood pressure, and the cuff pressure at the point where the amplitude suddenly falls is the cuff pressure. It is known that this corresponds to the diastolic blood pressure, and an electronic blood pressure monitor using the vibration method uses this principle to measure blood pressure.

Therefore, in an electronic blood pressure monitor that uses the vibration method, it is first necessary to detect the pulse wave amplitude that changes during the process of reducing the cuff pressure that has been increased to a predetermined value.

Conventionally, to detect changes in pulse wave amplitude,
The amplitude (difference between maximum and minimum value) of each pulse wave is continuously detected. For this reason, an operation (pulse wave segmentation) has been performed in which the pulse wave signal is segmented into individual pulses. However, in the actual processing process of pulse wave segmentation, various inconveniences occur due to various factors, and special processing must be performed to avoid these inconveniences.
There was a problem with the number of programs on the ROM increasing.

Therefore, in order to solve this problem, the inventors of this application developed a method that uses the difference (parameter) between the maximum and minimum values of the pulse wave level within each certain time period to detect the pulse wave amplitude. , and created an electronic blood pressure monitor that approximates this parameter to the pulse wave amplitude for each beat.
No. 242054).

(c) Problems to be solved by the invention The electronic sphygmomanometer according to the earlier application mentioned above is easier to program than conventional ones, and has a ROM and RAM.
can now be realized with small capacity devices. However, since the pulse wave amplitude is approximated by the difference between the maximum value and the minimum value within a certain time interval,
If a high-quality exhaust valve is not used, the exhaust speed will not be constant, and a new problem has arisen: the correspondence between detected pulse waves (parameters) and cuff pressure will vary depending on the product, causing measurement errors. Furthermore, regardless of the quality of the exhaust valve, the exhaust speed may not be constant due to differences in arm circumference of the person to be measured, which also causes measurement errors. In other words, when the detected pulse wave and the corresponding cuff pressure value are plotted on a graph of the pressure corresponding to the pulse wave amplitude value, as shown in Fig. 9, the plot points will be dense in some places and sparse in others, and when determining blood pressure. When determining the corresponding cuff pressure as the systolic blood pressure (diastolic blood pressure) based on the pulse wave amplitude value, if the sparse portion corresponds to this, measurement errors will occur.

In view of the above, this invention is easy to program.
The objective is to provide a high-precision electronic blood pressure monitor that has a small ROM and RAM capacity and also has fewer measurement errors.

(d) Means for Solving the Problems The electronic blood pressure monitor of the present invention, as schematically shown in FIG. system 2, a pressure sensor 3 that converts cuff pressure into an electrical signal, a cuff pressure detection section 4 that obtains the output of this pressure sensor as a cuff pressure signal, and a pulse wave detection means that detects a pulse wave component of the output of the pressure sensor. 5, a cuff pressure change detection means 6 for detecting that the cuff pressure signal changes by a predetermined value, and a pulse wave detected by the pulse wave detection means within this cuff pressure section every time the cuff pressure changes by a predetermined value. A cuff pressure interval difference calculation means 7 calculates the difference between the highest and lowest levels, a difference storage means 8 sequentially stores the difference for each cuff pressure interval, and the highest difference value is extracted. It is comprised of a maximum difference value extracting means 9 and a blood pressure determining means 10 which takes the cuff pressure corresponding to the extracted maximum difference value as the blood pressure to be measured.

In this electronic blood pressure monitor, the cuff 1 is pressurized to a predetermined value by the pressure system 2, and in the process of being depressurized thereafter, the cuff pressure is detected by the cuff pressure detection unit 4 via the pressure sensor 3. Further, the pulse wave component included in the output of the pressure sensor 3 is detected by the pulse wave detection means 5. This pulse wave level detection is performed at a relatively fast cycle. In addition, the cuff pressure interval difference value calculation means 7
For each section of constant cuff pressure change (drop or rise) detected by the cuff pressure change detection means 6, the difference between the maximum and minimum pulse wave levels is calculated. As shown in Figure 2a, this section changes as W ₁ , W ₂ , W ₃ , etc. as time t passes, and one section is set to a drop (rise) of about 5 mmHg. be done. Then, the calculated difference values H( ₁ ), H( ₂ ), H( ₃ ), ... in each section W 1 , W 2 , W 3 , ... are obtained as the approximate pulse wave amplitude of the section [Second See Figure b],
This pulse wave amplitude is stored in the storage means 8. The relationship between the cuff pressure and the pulse wave amplitude (difference value) is as shown in FIG. The maximum difference value obtained by multiplying the maximum difference value and the cuff pressure corresponding to the difference value obtained by multiplying the maximum difference value by a predetermined value are extracted and calculated, and the blood pressure to be measured is determined.

(E) Examples The present invention will be explained in more detail below with reference to Examples.

FIG. 4 is a block diagram of an electronic blood pressure monitor in which the present invention is implemented. In the figure, a cuff 11 is a rubber bag to be wrapped around the arm, and is connected to an exhaust valve 13 and a pressure pump 14 that constitute a pressure system 12 through a rubber tube 15. Further, a pressure sensor 16 is also communicated with the cuff 11 through a rubber tube 15, and converts cuff pressure into an electrical signal. The pressure end of the pressure sensor 16 is connected to the input end of an amplifier 17, and the output electrical signal of the pressure sensor 16 is DC amplified by the amplifier 17. The output terminal of the amplifier 17 is connected to the A/D converter 1.
It is connected to one end of the input of the filter 8 and also to the input end of the bandpass filter 19 . The output end of the A/D converter 18 is connected to the MPU 20, and the output of the amplifier 17 and the output of the bandpass filter 19 are each converted into digital signals by the A/D converter 18.
It is now being incorporated into the MPU20.

The MPU 20 includes internal memory such as ROM and RAM, and according to the program stored in the ROM,
Detection of the difference between the highest and lowest pulse wave levels in each fixed interval as the cuff pressure changes, storage of the difference in each interval,
It has functions such as determining mean blood pressure, systolic blood pressure, and diastolic blood pressure. The determined blood pressure value is displayed on the display unit 21. The MPU 20 also has a control function of driving and stopping the pressurizing pump 14 using the signal a, and a function of controlling the exhaust valve 13 to switch between slow exhaust and rapid exhaust using the signal b. Furthermore, the pulse wave component from the amplifier 17 is read at a predetermined sampling period using signals c and d.

The blood pressure measurement principle of this electronic sphygmomanometer employs an amplitude method that uses pulse wave amplitude information, and the envelope curve of the pulse wave amplitude generally takes the shape shown in Figure 3 during the cuff decompression process, and the vibration The method uses this envelope curve to determine blood pressure. Although there are various algorithms for determining blood pressure using the vibration method, the electronic blood pressure monitor of this embodiment employs the following determination method.

Mean blood pressure: Cuff pressure at the time when the pulse wave amplitude is maximum.

Systolic blood pressure: The pulse wave amplitude reaches its maximum amplitude in the region where the cuff pressure is higher than the average blood pressure (increasing process of pulse wave amplitude)
Cuff pressure at 50%.

Diastolic blood pressure: Cuff pressure at the point where the pulse wave amplitude reaches 70% of the maximum amplitude value in the region where the cuff pressure is lower than the average blood pressure (falling process of pulse wave amplitude).

Next, the operation of the electronic blood pressure monitor of the above embodiment will be explained with reference to the flowchart shown in FIG.

First, when the measurement start key is pressed to start the operation, the pressurizing pump 14 starts operating in response to the signal a, and the cuff 11 starts pressurizing [Step ST
(hereinafter abbreviated as ST) 1]. Then, the cuff 11 is pressurized until the cuff pressure becomes sufficient for measurement (ST2). When the cuff pressure reaches a predetermined cuff pressure, the pressure pump 14
At the same time, the operation of the exhaust valve 13 is stopped and the pressurization is stopped (ST3), and the exhaust valve 13 becomes a slow exhaust due to the signal b.
Start decompression (ST4). Thereafter, the process moves to blood pressure measurement processing. First, in ST5, initial settings are made to calculate the pulse wave amplitude parameter, and then in ST6 a series of processes including reading the cuff pressure and pulse wave data, calculating the amplitude parameter H(i) (difference value), and determining the blood pressure are performed. ~Conducted in ST14. This series of processing is repeated after the mean blood pressure and systolic blood pressure are determined until it is determined that the diastolic blood pressure can be determined.

One pulse wave amplitude parameter is calculated each time the above-described iterative process is completed. Then, it is stored in RAM (memory) within the MPU 20.

Next, each step of the iterative process from ST6 to ST14 will be explained.

First, in ST6, cuff pressure data and pulse wave amplitude data are read and parameters H(i) are calculated. More specific processing contents of this routine will be described later.

In ST7, the pulse wave amplitude parameter H(i) obtained at that point in ST6 is compared with the maximum value Hmax among the previously obtained parameters H(1) to H(i-1), and if If H(i)>Hmax, then ST8~ST10
Move on to processing. That is, when the pulse wave amplitude envelope curve is in the rising process, ST8 to ST10 are executed, and when it is in the falling process, it jumps from ST7 to ST11.

In ST8, the current parameter H(i) is stored in the RAM of the MPU 20 as a new maximum value Hmax.
Then, based on this parameter H(i) [Hmax],
Calculate and determine the average blood pressure value (ST9). This determination method will be described later.

Furthermore, for all parameters H(1) to H(i-1) obtained so far, 50% of the value of Hmax
, and calculate and determine the systolic blood pressure from the number of the cuff pressure section (window) corresponding to that parameter (ST10). This determination method will also be described later.

In ST11, a non-updating counter is used to check whether the parameter H(i) is in the downward process.
Add 1 to COUNT1. Then, the process moves to ST12, where it is determined whether "(COUNT1)≧2?" If this determination is YES, it means that Hmax has not been updated more than once, which means that the parameter H(i) has entered a downward process. Therefore, if the judgment in ST12 is YES, the process moves to ST13 and H(i)<Hmax
×0.7, that is, the parameter H(i) is Hmax
A judgment is made as to whether it has become smaller than 70%. H
+1 to i as long as (i) does not become less than 70% of Hmax
(ST14), returns to ST6, and moves on to processing regarding the next parameter. As mentioned above, ST6~
The series of processing in ST14 is repeated until H(i)<Hmax×0.7, that is, until the diastolic blood pressure can be determined, so Hmax calculated in ST8 to ST10,
The mean blood pressure and systolic blood pressure are updated several times. However, when the envelope curve of pulse wave amplitude exceeds the maximum value,
H(i) becomes smaller than Hmax, and the judgment of ST6 is NO.
Since the process jumps to ST11, ST8 to ST10 are no longer executed, and the mean blood pressure and systolic blood pressure are finally determined.

Then, when the envelope curve of the pulse wave amplitude enters the descending process, the pulse wave amplitude parameter H(i) becomes Hmax in ST13.
It is determined whether or not it has become 70% or less, and if YES, the process moves to ST15 and exits from the series of repeated processing from ST6 to ST14. While the determination in ST13 is NO, that is, until the parameter H(i) becomes 70% or less of Hmax, the process returns from ST11 to ST6 via ST13 and ST14, and the series of processes from ST6 to ST14 are repeated.

When transitioning from ST13 to ST15, the cuff pressure at that point is taken as the diastolic blood pressure (ST15), and then the determined mean blood pressure, systolic blood pressure, and diastolic blood pressure are displayed on the display 21.
(ST16), and then by signal b, the exhaust valve 13 is switched to rapid exhaust (ST17), and the cuff 11 is
lower the pressure and end the blood pressure measurement.

Here, "calculation of parameter H(i)" in ST6 above
The processing will be explained in more detail.

FIG. 6 is a flowchart showing a subroutine for calculating the parameter H(i).

In this process, the difference between the maximum value and the minimum value of pulse wave data in an interval in which the cuff pressure drops constantly, that is, in each window, is calculated as a parameter and is stored in the memory of the MPU 20.
Note that reading of pulse wave data is assumed to be performed at regular intervals.

In the main flow of Figure 5, enter ST6,
When the parameter calculation routine is called, first,
In ST61, the cuff pressure value pr at that point is read and stored. Next, the maximum value pmax, minimum value within the window
Set pmin to 0, initialize each value, and set the pressure value pre at the end of the window in ST63 to the cuff pressure value pr obtained in ST61.
Set the value to 5mmHg lower than

Next, compare the magnitude relationship between the pulse wave data pw and pmin (ST65), and if pw is smaller, change pmin.
Update the minimum value pmin as pw (ST66). vice versa
If pmin is smaller, ST66 is skipped, and then pw and pmax are compared in magnitude (ST67). Here, if pw is larger, set pmax to pw and pmax
Update (ST68). Conversely, if pmax is larger, ST68 is skipped and the process moves to ST69.

In ST69, the current cuff pressure value pr is read, and then this cuff pressure value pr is compared with the set cuff pressure pre (ST70). Then, the cuff pressure value pr is the set cuff pressure
If less than pre, pmax and pmin in the window
Finish the search and proceed to ST71. If not, it means that the end of the window has not yet arrived, and we go back to ST64 and move from ST64 to ST70.
The processes up to this point are repeated, and the search for pmax and pmin continues.

In ST71, pmax-pmin is calculated, and the difference value between the maximum value and minimum value of the pulse wave data within the window is obtained. This value difference is the parameter H(i)
The addresses are stored in the memory of the MPU 20 in order of address.
This completes the parameter calculation subroutine processing and returns to the main routine.

Next, a method for determining the average blood pressure at ST9 in FIG. 5 will be explained. When the process enters ST9, the average blood pressure determination subroutine shown in Figure 7 is called,
The cuff pressure pr at that time is stored in the memory in the MPU 20 as the average blood pressure (ST72).

Next, the method for determining the systolic blood pressure at ST10 in FIG. 5 will be explained.

When the process enters ST10, the subroutine for determining the systolic blood pressure shown in FIG. 8 is called. First, ST81
Window number Nsys where H(i)≒0.5*Hmax
Search for (memory address). Then subtract Nsys from the number of the window that ended at that time,
The result is set as k (ST82). Next, the resulting value of adding k*5 (mmHg) to the cuff pressure pr at that time is stored in the memory in the MPU 20 as the systolic blood pressure (ST83). Then return to the main routine.

In the above embodiment, a high-pass filter is used to extract the pulse wave, but in this invention, a digital filter may be used instead, and the cuff pressure signal containing the pulse wave component is The cuff pressure signal and the pulse wave component may be separated by software processing different from the digital filter.

(F) Effects of the Invention According to the present invention, in pulse wave amplitude detection, the pulse wave amplitude for each beat is approximated by a parameter given by the difference between the maximum value and the minimum value for each constant cuff pressure change section. Therefore, since it is not approximated for each fixed time interval, measurement errors due to variations in the quality of the exhaust valve, variations in the arm circumference of the person to be measured, etc. can be reduced.

Furthermore, since it is possible to omit sequentially storing cuff pressure values corresponding to each parameter, an electronic blood pressure monitor can be realized with an MPU having an extremely small memory capacity RAM.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of this invention, and FIG.
The figures are diagrams for explaining difference value calculation in the present invention, in which Figure 2a shows the cuff pressure-pulse wave level, and Figure 2b shows the difference between the maximum and minimum values for each section. FIG. 3 is a diagram showing the envelope curve of pressure and pulse wave amplitude. FIG. 4 is a block diagram of an electronic blood pressure monitor showing an embodiment of the present invention. FIG. 5 is a diagram showing the electronic blood pressure monitor. FIG. 6 is a flowchart showing a subroutine for calculating parameters of the meter, FIG. 7 is a flowchart showing a subroutine for determining mean blood pressure, and FIG.
FIG. 9, a flowchart showing the subroutine for determining the systolic blood pressure, is a diagram showing an envelope pattern obtained by the conventional method of approximating pulse wave amplitude by time interval. 1... Cuff, 2... Pressure system, 3... Pressure sensor, 4... Cuff pressure detection section, 5... Pulse wave detection means,
6...Cuff pressure change detection means, 7...Cuff pressure interval difference value calculation means, 8...Difference value storage means, 9...Difference value maximum value extraction means, 10...Blood pressure determination means.

Claims (1)

[Claims] 1. A cuff, a pressure system connected to the cuff for pressurizing or depressurizing the cuff, a pressure sensor for converting cuff pressure into an electrical signal, and converting the output of the pressure sensor into a cuff pressure signal. a cuff pressure detection unit that detects a change in cuff pressure by a predetermined value; a pulse wave detection unit that detects a pulse wave component of the output of the pressure sensor; cuff pressure interval difference calculation means for calculating the difference between the highest and lowest pulse wave levels detected by the pulse wave detecting means within this cuff pressure interval each time the value changes; difference value storage means for sequentially storing the difference values; maximum difference value extraction means for extracting the highest value of the difference values; An electronic blood pressure monitor characterized by comprising: blood pressure determination means that uses cuff pressure as the blood pressure to be measured. 2. The blood pressure determining means includes an average blood pressure determining means that sets the cuff pressure at the time when the highest differential value is extracted as an average blood pressure, a storage address of the highest differential value, and a predetermined value for the highest differential value. systolic blood pressure determining means for calculating a systolic blood pressure from a memory address of the obtained difference value and a predetermined value corresponding to the cuff pressure section; 2. The electronic blood pressure monitor according to claim 1, further comprising a diastolic blood pressure determining means that determines the cuff pressure at the time when the cuff pressure is extracted as the diastolic blood pressure.