JPH0779800B2 - Electronic blood pressure monitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electronic blood pressure type.

(B) Conventional Technique In general, some electronic blood pressure monitors detect a Korotkoff sound (K sound) by a microphone (K sound sensor) to determine the maximum and minimum blood pressure values. In the electronic blood pressure type using this microphone, the blood pressure can be determined by capturing the time point at which the K sound is emitted and the time point at which the K sound is interrupted, but a microphone for detecting the K sound is required and the blood pressure is accurately measured. Therefore, there is a problem in that the microphone must be correctly applied to the living body, and skill is required in applying the microphone.

On the other hand, for example, as an electronic blood pressure monitor for a finger, a finger is pressed with a cuff for the finger, and a photoelectric pulse wave sensor attached to the cuff for the finger is used to detect a change in the arterial volume by finger compression, It is known that the pressure in the cuff (hereinafter referred to as the cuff pressure) is detected by a pressure sensor, and the blood pressure value is determined by the pulse wave and the cuff pressure obtained in the process of reducing the cuff pressure. This type of electronic sphygmomanometer does not require a microphone, so that the above inconvenience does not occur and it is convenient, but on the other hand, it is necessary to correctly detect the pulse wave for each cycle as shown below.

That is, as shown in FIG. 6, the pulse wave is gradually generated as the cuff pressure is reduced, takes a maximum amplitude value, and then attenuates. At this time, the cuff pressure in the vicinity of point S in FIG. 6 (around the time when the pulse wave starts to be generated) responds to the systolic blood pressure, and in the vicinity of a point M (a time near the maximum amplitude of the pulse wave is observed). It has been clinically confirmed that the cuff pressure that responds to the mean blood pressure and the cuff pressure that responds to the vicinity of point D (near the start point of attenuation of the pulse wave) become the minimum blood pressure.

In the above-mentioned conventional electronic blood pressure monitor for a finger, with respect to the pulse wave, the S point, the M point, and the
The maximum blood pressure etc. is determined by specifying points etc. Therefore, in order to calculate the pulse wave amplitude value for each pulse wave (every one cycle), it is necessary to accurately capture one cycle of the pulse wave. As a means for capturing one cycle of a pulse wave, that is, a pulse wave recognition means, when the time derivative (hereinafter referred to as pulse wave derivative) of the pulse wave obtained by the pulse wave differentiating means exceeds a predetermined threshold value. It is assumed that the pulse wave appears, and the pulse wave recognition means for recognizing one cycle is adopted by grasping the appearance time of each pulse wave.

(C) Problems to be Solved by the Invention Problems with the conventional electronic blood pressure monitor for a finger will be described below with reference to FIGS. 5 (a) and 5 (b).

FIG. 5 (a) shows the waveform of the pulse wave. In the left half, near the point S in FIG. 6, that is, the cuff pressure is the systolic blood pressure (hereinafter referred to as SY).
The pulse wave before and after the time point corresponding to
In the figure, the pulse wave around the point D, that is, before and after the time point when the cuff pressure corresponds to the minimum blood pressure (hereinafter referred to as DIA), is shown with the horizontal axis representing time. Here, the waveform of the pulse wave A at the left end of the pulse wave waveforms in the vicinity of SYS indicates a state in which the pulse wave is disturbed by an artifact (disturbance of the pulse wave caused by moving a finger or an arm during blood pressure measurement). ing.

On the other hand, FIG. 5 (b) shows the waveform of the pulse wave differential of the pulse wave shown in FIG. 5 (a), and SYS is displayed in the left half part as in FIG. 5 (a).
The pulse wave derivative in the vicinity and the waveform of the pulse wave derivative in the vicinity of DIA are shown in the right half. A'in FIG. 5 (b)
Is the pulse wave derivative of the pulse wave A disturbed by artifacts.

Now, assuming that the threshold value for the pulse wave differential for detecting the appearance of the pulse wave is set to xa as shown in FIG. 5 (b), the pulse wave near SYS is The appearance time can be detected without any problem, but the level of the pulse wave derivative near DIA is SYS.
Since it is smaller than the level of the pulse wave derivative in the vicinity, the appearance of the pulse wave may not be detected in the vicinity of DIA and may not be recognized as the pulse wave. There was the inconvenience that accurate blood pressure measurement was not performed.

Therefore, if the threshold value is set to xb, which is smaller than xa, the pulse wave differential A ′ disturbed by artifacts is also falsely detected and recognized as a pulse wave, and the pulse wave amplitude value data for blood pressure determination is detected. Data with a large error is mixed in, and the problem that accurate blood pressure cannot be measured also occurs.

The present invention has been made in view of the above inconvenience, and an object of the present invention is to provide an electronic sphygmomanometer that accurately recognizes a pulse wave, prevents erroneous recognition of a pulse wave disturbed by an artifact or the like, and enables accurate blood pressure determination. I am trying.

(D) Means for Solving Problems As shown in the schematic configuration of FIG. 1, the electronic sphygmomanometer of the present invention has a pulse wave obtained from the living body when the cuff 1 is decompressed and the pressure of the cuff 1 by the pressure sensor 4. And a pulse wave differentiating means 6 for calculating the time differential of the pulse wave, and an output signal of the pulse wave differentiating means 6 is compared with a predetermined threshold value for one cycle. The pulse wave recognition means 7 for recognizing each pulse wave, the pulse wave amplitude decrease detection means for detecting a decrease in the pulse wave amplitude, and the pulse wave amplitude decrease detection means for responding to the detection of the decrease in the pulse wave amplitude. Threshold value changing means 9 for changing the threshold value to a value smaller than the predetermined threshold value.

(E) Action The threshold value in the pulse wave recognition means 7 of the electronic sphygmomanometer of the present invention is, for example, at a high value xa shown in FIG. 5 (b) when the level of the pulse wave derivative near SYS is relatively high. Set, do not detect the current time of the pulse wave disturbed by artifacts,
The disturbed pulse wave is prevented from being recognized as a pulse wave. On the other hand, when the level of the pulse wave differentiation is relatively low near DIA, the threshold value setting variable means 9 sets the threshold value set in the pulse wave recognition means 7 to xb which is smaller than xa, for example. Each pulse wave is recognized one by one by changing it stepwise or continuously and surely detecting the time point at which the pulse wave emerges from the pulse wave derivative near the low level DIA.

(F) Embodiment An embodiment of the present invention will be described below with reference to FIGS. 2 to 4.

FIG. 2 is an external perspective view of a finger electronic sphygmomanometer in which the present invention is implemented. The finger electronic sphygmomanometer is composed of a main body 11 and a cuff housing portion 12, which are connected by a cord wire 13. Has been done.

On the case surface of the main body 11, a display 14 for displaying the maximum blood pressure, the minimum blood pressure, etc., a pressurization value setting device 15 for selecting a pressurization set value, a clear key 16, a start key 17, and a power key 18 are provided. Has been.

A cuff rubber bag 19 having a cylindrical outer shape is stored in the case of the cuff storage portion 12. Although not shown in the figure, the cuff rubber bag 19 is provided with a pulse wave sensor for detecting a finger pulse wave. The electric signal line connecting the pulse wave sensor and the main body 11 and the cuff rubber bag 19 and the main body are provided. The rubber tubes connecting 11 and 11 are bundled and connected as a cord wire 13 between them.

FIG. 3 shows a circuit block diagram of the electronic blood pressure monitor for the finger. In the figure, pressurization value setting switch 15a, clear switch 16a, start switch 17a and power switch
18a respectively correspond to the pressurization value setting device 15, the clear key 16, the start key 17, and the power key 18, and are turned on when these keys are operated. The on / off signals and setting signals of these switches are input to the CPU 20.

The motor drive circuit 21 is adapted to turn on / off a motor (pressurizing means) 22 of a pressurizing pump in response to a command from the CPU 20. The cuff rubber bag 19 is pressurized by the start of the motor 22.

The quick exhaust valve drive circuit 23 is configured to open / close the valve (pressure reducing means) 24 in response to a command from the CPU 20.

By driving the motor 22, air pressure is supplied to the cuff rubber bag 19 via the air tank 25, and the pressure of the cuff rubber bag 19 is converted into an electric signal by the semiconductor pressure sensor 26 and passed through the amplifier circuit 27 to the A / D converter. Converted to digital signal at 28, CPU
It is designed to be incorporated into 20.

Furthermore, the LED driving cuff 29 drives the light emitting element 30 attached to the cuff rubber bag 19 in response to a command from the CPU 20, while the signal received by the light receiving element 31 is passed through the filter 32 and the amplification circuit 33. , A / D converter 28 performs digital conversion and is also taken in by the CPU 20. The light emitting element 30 and the light receiving element 31 constitute a pulse wave sensor.

Display data from the CPU 20 is displayed on the display (LCD) 14 via the LCD drive circuit 34. Further, in order to notify an error or the like, the buzzer 36 is driven via the buzzer drive circuit 35 by a command from the CPU 20. Reference numeral 37 is a slow speed exhaust valve (pressure reducing means).

The CPU 20 executes various functions according to the program of the flowchart described later, and the above-mentioned constituent circuits execute the blood pressure measurement operation under the control of the CPU 20.

Next, the operation of the electronic blood pressure monitor for a finger according to this embodiment will be described in a fourth step.
A description will be given below with reference to the drawings.

First, when the measurer presses the power key 18 and turns on the power switch 18a, the input / output and the display of the LCD 14 are initialized [step (hereinafter referred to as ST) 1], and the start switch 17
Wait in ST2 until a is turned on.

Next, when the measurer inserts a finger (for example, the index finger of the left hand) into the cuff rubber bag 19 of the cuff storage unit 12, presses the start key 17 and turns on the start switch 17a, the process proceeds from ST2 to ST3, and the CPU 20 causes the motor drive circuit. 21 command, motor 2
2 is driven, the cuff rubber bag 19 is pressurized to the set value selected by the pressurization value setting switch 15a, and the finger of the measurer is pressed.

In ST3, when the cuff rubber bag 19 is pressurized to the set value, the process proceeds to ST4, the motor 22 is stopped, the slow exhaust valve 37 starts the slow exhaust, and in the next ST5, the threshold for pulse wave recognition. Value xt
Set h to xt ₁ .

In ST6, the CPU 20 calculates the pulse wave derivative based on the sampled pulse wave level taken in from the A / D converter 28, and the time point at which the value of this pulse wave derivative exceeds x th is regarded as the pulse wave output current time. Detects, recognizes one cycle of the pulse wave, calculates the pulse wave amplitude value from the pulse wave level data that is sampled and stored during one cycle of this pulse wave, and determines the temporal transition of this pulse wave amplitude value. Based on this, the maximum blood pressure, the average blood pressure, and the minimum blood pressure (the number of pulse nights if necessary) are calculated.

There are various algorithms for calculating the above-mentioned maximum blood pressure, average blood pressure, and minimum blood pressure. For example, the systolic blood pressure is the cuff pressure when the pulse wave amplitude value of the pulse wave detected by the pulse wave sensor exceeds a predetermined level, and the cuff pressure at the maximum pulse wave amplitude value is the average blood pressure. And the mean blood pressure is calculated as (3 x mean blood pressure-maximum blood pressure) / 2, the minimum blood pressure. However, in the present invention, the blood pressure determination process is not a main part, and thus details thereof will be omitted.

In ST6, the process is temporarily interrupted every time a predetermined number of pulse wave amplitude values of 1 or 6 or more is calculated, and the process proceeds to ST7. In ST7, it is determined whether or not the systolic blood pressure, the average blood pressure, and the like have been determined. If these values have not yet been determined, the process proceeds to ST10, and it is determined whether or not the pulse wave amplitude value is currently decreasing. The pulse wave amplitude value begins to decrease when it exceeds the point M in the pulse wave shown in FIG. 6 and approaches the point D. The level of the pulse wave differential is shown in FIG. 5 (b). As shown, it is smaller than the level of the pulse wave derivative near SYS. Therefore, ST10
If it is determined that the pulse wave amplitude value has decreased in ST, proceed to ST11 and set the threshold x th to a value xt ₂ (<xt ₁ ) that is smaller than the previously set value xt _1. In addition, by detecting the appearance of the pulse wave, it is easy to recognize each pulse wave, ST6
Then, the blood pressure determination process is continued. On the other hand, if it is determined in ST10 that the pulse wave amplitude value is not decreasing, the level of the pulse wave differential is still relatively high, so the threshold value x th is not changed and the process returns to ST6. The blood pressure determination process is continued.

Until the maximum blood pressure, average blood pressure and minimum blood pressure are determined
The processing of ST6, ST7, ST10 (ST11) is repeated. If it is determined in ST7 that the systolic blood pressure has been determined,
In step ST8, the CPU 20 causes the LCD drive circuit 34 to display on the LCD 14 the systolic blood pressure, the diastolic blood pressure, etc. (and the pulse rate when the pulse rate is calculated) obtained as a result of the measurement. Finally, CPU20
Gives a command to the quick exhaust valve drive circuit 23, opens the valve 24, and performs quick exhaust (ST9) to end one blood pressure measurement.

In the above embodiment, the threshold value x th is set to xt ₁ , x
Although it is configured to switch to two stages of t ₂ (xt ₁ > xt ₂ ), it is possible to change it by dividing it into three or more multistage or continuously changing it. The process of threshold change does not necessarily need to be monotonically decreasing.

Further, in the above embodiment, the threshold value x th is set to be smaller than xt ₁ .
The determination of the time point of changing to xt ₂ is made based on whether or not the pulse wave amplitude value has started to decrease, but it can also be made by, for example, a timer that starts timing from the time when the start switch 17a is turned on. Yes, the design can be changed as appropriate.

(G) Effect of the Invention In the electronic sphygmomanometer of the present invention, the threshold value in the pulse wave recognition means is set to a value smaller than this threshold value when the pulse wave amplitude decrease detection means detects a decrease in the pulse wave amplitude. Since it is changed by the value varying means, the threshold value is changed so as to match the difference in the level of the pulse wave differentiation, each pulse wave is accurately recognized, and the pulse wave is disturbed by artifacts. This has the advantage of eliminating the effect of (1) and enabling blood pressure measurement with less error.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a schematic configuration of the present invention, FIG. 2 is an external perspective view of an electronic blood pressure monitor for a finger according to an embodiment of the present invention, and FIG. 3 is an electronic blood pressure monitor for the finger. Circuit block diagram,
FIG. 4 is a flow chart for explaining the operation of the electronic blood pressure monitor for the finger, FIG. 5 (a) is a diagram showing the waveform of a pulse wave, and FIG. 5 (b) is a waveform of the time derivative of the pulse wave. Fig. 6 shows
It is a figure which shows the time transition of a pulse wave. 1: cuff, 2: pressurizing means, 3: depressurizing means, 4: pressure sensor, 5: pulse wave sensor, 6: pulse wave differentiating means, 7: pulse wave recognizing means, 8: blood pressure determining means, 9: threshold Value change means.

Claims (1)

[Claims] 1. An electronic sphygmomanometer for determining a blood pressure by utilizing a pulse wave obtained from a living body and a pressure value of the cuff by a pressure sensor when the cuff is decompressed, and a pulse wave differentiating means for calculating a time derivative of the pulse wave. Pulse wave recognition means for recognizing a pulse wave for each cycle by comparing the output signal of the pulse wave differentiating means with a predetermined threshold value, and pulse wave amplitude decrease detecting means for detecting a decrease in pulse wave amplitude. A threshold value changing means for changing the threshold value to a value smaller than the predetermined threshold value in response to the pulse wave amplitude decrease detecting means detecting the decrease of the pulse wave amplitude. A characteristic electronic blood pressure monitor.