JPH07255684A - Sphygmomanometer by photoelectric volume pulse wave - Google Patents

Abstract

PURPOSE:To enhance the accuracy in measuring the blood pressure by inferring a cuff pressure from the first pulse wave component having an amplitude between the max. and standard amplitudes and the second pulse wave component having an amplitude smaller than that of the first pulse wave component but larger than the standard amplitude, which are extracted out of a photoelectric volume pulse wave. CONSTITUTION:For use as a finger sphygnomanometer, this instrument is provided with a cuff 10 for inserting a finger of the examined, a bladder 12 for pressing the arteries of the finger, a near infrared radiation LED 14 and a phototransistor 16. The cuff pressure is detected by a pressure sensor 22, the output from which is transmitted to a microprocessor 20 to detect a photoelectric volume pulse wave of the arteries of the examined by controlling variably the cuff pressure. The first pulse wave component having the first amplitude between the max. and standard amplitudes and the second pulse wave component having an amplitude smaller than the first amplitude of the first pulse wave component are extracted out of said photoelectric volume pulse wave to infer a cuff pressure when the amplitude of the photoelectric volume pulse wave is equal to the standard amplitude; the max. blood pressure is determined on the basis of such cuff pressure.

Description

Detailed Description of the Invention

[0001]

[Object of the Invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sphygmomanometer based on the photoelectric plethysmography method which measures blood pressure by photoelectrically detecting plethysmograms of human arteries.

[0002]

As is well known, the traditional blood pressure measurement method is
The cuff (manchette) equipped with an air bladder (manchette) interrupts the arteries of the arm, and detects the Korotkoff sound using a stethoscope while slowly reducing the cuff pressure. In this method, the blood pressure when the Korotkoff sound is generated is the maximum blood pressure (blood pressure in the systole of the heart), and the blood pressure when the Korotkoff sound disappears is the minimum blood pressure (blood pressure in the diastole).

In recent years, in place of the traditional Korotkoff method, a sphygmomanometer based on the photoelectric plethysmography method (also called volume oscillation method) capable of electrically measuring blood pressure has been developed (Kenichi Yamakoshi). "Study on non-invasive arterial blood pressure measurement using photoplethysmography," Waseda University, Showa 5
November 6th).

In the plethysmography, near infrared light is applied to a part such as a finger or arm of a human body while changing the cuff pressure, and transmitted light is detected by a photoelectric sensor such as a phototransistor. The photoplethysmogram of the artery is recorded. FIG. 1 shows a representative example of the volume pulse wave. In the volume pulse wave method, when the volume pulse wave is recorded in the process of increasing the cuff pressure as in the case of FIG. 1, the blood pressure at the time when the volume pulse wave disappears corresponds to the systolic blood pressure of the Korotkoff method. Alternatively, as disclosed in JP-A-61-257626, when the volume pulse wave is recorded in the process of decreasing the cuff pressure, the blood pressure at the time when the volume pulse wave appears corresponds to the systolic blood pressure.

However, since it is difficult to accurately identify the disappearance or appearance of the plethysmogram, in practice, in the plethysmography, the maximum amplitude of the plethysmogram (corresponding to the mean blood pressure) is first determined. It is common to detect and detect the blood pressure when the amplitude of the plethysmogram becomes a fraction of this maximum amplitude (that is, the reference amplitude) as the systolic blood pressure. That is, for example, when the volume pulse wave is detected in the process of increasing the cuff pressure as shown in FIG. 1, the amplitude of about 1/4 of the maximum amplitude (PG _MAX ) of the volume pulse wave is set as the reference amplitude, The blood pressure when the pulse wave amplitude becomes smaller than this reference amplitude is the maximum blood pressure (SBP)
It is known from experience that good to say is. Alternatively, in a sphygmomanometer that records a volume pulse wave in the process of decreasing the cuff pressure, like the sphygmomanometer of JP-A-61-257626, one-fifth of the maximum amplitude is adopted as the reference amplitude. In each case, the reference amplitude is empirically determined so that there is a good correspondence between the systolic blood pressure measured by the plethysmography and the systolic blood pressure measured by the traditional Korotkoff method. Preferably.

[0006]

Ideally, the amplitude of the plethysmographic wave increases or decreases fairly smoothly or linearly with the change of the cuff pressure as in the example shown in the center graph of FIG. Specifically, the systolic blood pressure (SBP) is detected with sufficient accuracy by finding the intersection of the envelope of each peak of the volume pulse wave and the reference amplitude (1 / 4PG _{MAX in} the example shown in FIG. 1). can do.

However, when elasticity of the artery of the subject is lost due to aging or arteriosclerosis, or during cold weather when the blood vessel is contracting, the blood vessel cannot pulsate minutely under high cuff pressure. As shown in the graph below 1, the amplitude of the volume pulse wave sharply decreases before and after the reference amplitude. The same phenomenon is observed when the subject's arterial blood vessels are thin. As a result, systolic blood pressure is measured lower than it actually is. On the contrary, when detecting the plethysmogram in the process of decreasing the cuff pressure, the systolic blood pressure is measured higher than it actually is.

An object of the present invention is to provide a sphygmomanometer based on the photoplethysmography capable of measuring blood pressure with higher accuracy.

Another object of the present invention is to use the photoplethysmography method capable of measuring blood pressure with high accuracy even when the subject's artery has poor elasticity, the blood vessel is thin, or in cold weather. To provide a blood pressure monitor.

[0010]

[Constitution of the invention]

SUMMARY OF THE INVENTION Means for Solving the Problems and the Outline of Action The present invention relates to a sphygmomanometer based on the photoelectric volumetric pulse method, in which the amplitude between the maximum amplitude and the reference amplitude (preferably the maximum amplitude A first pulse wave component having an amplitude of about ½ and an amplitude smaller than the amplitude of the first pulse wave component and larger than the reference amplitude (for example, a minimum larger than about one third of the maximum amplitude). Of the first pulse wave component and the amplitude of the second pulse wave component are extracted based on the amplitude of the first pulse wave component and the amplitude of the second pulse wave component. The cuff pressure when the amplitude of the wave becomes equal to the reference amplitude is estimated, and the cuff pressure is determined as the systolic blood pressure of the subject.

In another aspect of the present invention, a sphygmomanometer of the present invention comprises a cuff for compressing an artery of a subject, an air pump for supplying pressurized air to the cuff, and a pressure sensor for detecting the cuff pressure. It has a pulse wave detecting means such as a photoelectric sensor for detecting a photoelectric volume pulse wave of an artery of a subject, and a control arithmetic unit. The control arithmetic unit can be realized by a programmed microprocessor. The microprocessor controls the cuff pressure and records the amplitude of each pulse wave component of the photoplethysmograph in relation to the cuff pressure. The microprocessor calculates the maximum amplitude of the photoplethysmogram and sets a reference amplitude equal to a predetermined fraction of this maximum amplitude (eg, 1/4 to 1/5). The microprocessor includes a first pulse wave component having an amplitude between the maximum amplitude and the reference amplitude, and a second pulse wave component having an amplitude smaller than the amplitude of the first pulse wave component and larger than the reference amplitude. Component from the photoplethysmographic pulse wave, and the amplitude of the first pulse wave component and the second pulse wave component
Based on the amplitude of the pulse wave component, the cuff pressure when the amplitude of the photoelectric volume pulse wave becomes equal to the reference amplitude on the higher cuff pressure side than the maximum amplitude is estimated. This cuff pressure is determined as the subject's systolic blood pressure.

[0012]

EXAMPLE FIG. 2 shows an example in which the present invention is applied to a finger sphygmomanometer. With reference to FIG. 2, this finger sphygmomanometer has a cuff 10 adapted to be inserted through the finger of a subject. As in the prior art, the cuff includes an air bag (bladder) 12 for compressing the finger arteries of the subject, a light projecting element such as a near infrared light emitting diode (iRED) 14, and a phototransistor 16. Such a light receiving element can be provided. The cuff 10 is supplied with pressurized air from an air pump 18 such as a motor driven diaphragm pump, and the rate of pressurization of the air pump is controlled by a microprocessor 20 which is a programmed digital microcomputer. The cuff pressure is detected by the pressure sensor 22,
The analog output signal is amplified by the amplifier 24, converted into a digital signal by the A / D converter 26, and sent to the microprocessor 20. After blood pressure measurement, the cuff pressure is released by opening the exhaust valve 28, which is controlled by the microprocessor 20.

In order to reduce the light emission time and heat generation of the near infrared light emitting diode (iRED) 14 and extend its life,
The iRED 14 is controlled by the pulse lighting circuit 30 instructed by the microprocessor 20 so that the iRED 14 has a frequency of, for example, 300 Hz.
It can be turned on for a period of 00 μsec. iRE
The voltage applied to D14 is controlled by the light quantity control 32. The transmitted light is converted into an electric signal by the phototransistor 16, and the output signal thereof is sent to the operational amplifier 36 via the sampling circuit 34 driven in synchronization with the pulse lighting circuit 30. This operational amplifier 36 has an amplifying function, a differentiating function, and a half-wave rectifying function, and the obtained photoelectric volume pulse wave (plethysmogram) is converted into a digital signal by the A / D converter 26 and input to the microprocessor 20. It

The sphygmomanometer can further be provided with an operation section 38 having a measurement start button, a liquid crystal display section 40 for displaying a blood pressure measurement result and a trend, and a printer 42 for printing the measurement result and the trend.

To explain the operation of the sphygmomanometer with reference to the flow charts of FIGS. 3 to 5, when the power is turned on and the initialization of the microprocessor 20 is completed, the microprocessor 20 causes the subject to press the blood pressure measurement start button 38. After waiting for (S101), light emission and light reception are started, and A / D conversion of the output of the phototransistor 16 is started (S10).
2), A / D conversion of the output of the pressure sensor 22 is started (S103). The microprocessor determines based on the output of the phototransistor 16 whether or not the subject has put his / her finger through the cuff 10 (S104). If a finger is detected, the exhaust valve 28 is closed (S105), and the air pump 1
The air bag 12 of the cuff 10 is rapidly pressurized by fully rotating the motor 8 (S106).

For rapid pressurization, the cuff pressure is, for example, 60 mmHg.
Is continued until (S107). Cuff pressure is 60m
When it becomes mHg and the air bag 12 of the cuff 10 comes into close contact with the finger of the subject, the air pump is temporarily stopped (S10
8) Then, the light amount control 32 adjusts the voltage applied to the iRED 14 to adjust the light emitting / receiving amount (S109). Next, the air pump is rotated at a slow speed (S110), and the cuff is pressurized at a slow speed.

During the slow pressurization, the phototransistor 16
Output signal is subjected to amplification, differentiation, and half-wave rectification processing by the operational amplifier 34, and the obtained photoelectric volume pulse wave is A / D.
It is converted into a digital value by the converter 26. The microprocessor 20 detects the peak of each pulse wave component of the photoelectric volume pulse wave and records the amplitude of each peak and the cuff pressure in the buffer memory of the microprocessor 20 as digital values (S111). As an example, in the case of the subject shown in the lower graph of FIG. 1, the digital value of the amplitude of the pulse wave component of the photoplethysmograph will fluctuate as shown in the graph of FIG.

The microprocessor waits for, for example, 2 seconds to elapse from the detection of each peak (S112), and before 2 seconds elapses, the average value of the five peaks before and after the current phase is continuous. 1 / maximum of 5 peaks before and after
The peak detection is repeated until it becomes smaller than 5 (S1
13). As a result, the maximum amplitude PG _MAX of the volume pulse wave becomes 1
All peaks with an amplitude equal to / 5 will be detected.

When no new peak is detected within 2 seconds from the previous peak detection (S112), or when the average value of the five peaks becomes smaller than ⅕ of the maximum amplitude PG _MAX ( S113), the cuff pressure is 120mmH
In the case of g (S114), the air pump is stopped (S
115). If the cuff pressure is 120 mmHg or less,
Continue to drive the air pump and the cuff pressure is 120mmHg
Wait until the above is reached and stop the air pump. this is,
In any case, the purpose is to pressurize the cuff until the pressure reaches 120 mmHg.

When the pressurization is completed (S115), the light projecting and receiving light is completed (S116), the exhaust valve 28 is opened to release the cuff pressure (S117), and the subject can remove his / her finger from the cuff 10. Next, the systolic blood pressure is calculated (S11
8), output to the liquid crystal display unit 40 or the printer 38 (S
119).

The calculation of the systolic blood pressure (S118) is performed as shown in the flowchart of FIG. 5 and the graph of FIG.
First, from the buffer memory of the microprocessor, as shown in FIG.
The amplitude of the peak of the pulse wave component shown in the graph of is called, and the maximum amplitude PG _MAX (FIG. 6) of the pulse wave is calculated (S
201). The maximum amplitude PG _MAX can be obtained by interpolation calculation. Next, a reference amplitude equal to a predetermined fraction of the maximum amplitude PG _MAX is obtained (S202). The reference amplitude can be set to, for example, 1/4 of the maximum amplitude PG _MAX .

Next, from the data in the buffer memory, the minimum amplitude (1/2 of the maximum amplitude PG _MAX ) (point PG in FIG. 6) is obtained.
The first pulse wave component having 1) is extracted (S20
3) The second pulse wave component having the minimum amplitude (point PG2 in FIG. 6) which is equal to or larger than the reference amplitude (1/4 PG _MAX ) is extracted (S204). Next, the intersection of the straight line passing through the points PG1 and PG2 and the reference amplitude (1 / 4PG _MAX ) (point PG in FIG. 6)
3) is obtained (S205), and the cuff pressure at the intersection is calculated.
Assuming that the cuff pressure at the point PG1 of the first pulse wave component is PC1 (FIG. 6) and the cuff pressure at the point PG2 of the second pulse wave component is PC2, the cuff pressure PC3 at the intersection point PG3 is obtained by, for example, the following equation. be able to.

PC3 = PC1 + {(PG1-1 / 4 ・ PG _MAX ) × (PC2
−PC1) ÷ (PG1−PG2)} Finally, the cuff pressure (PC3) at the intersection is determined as the systolic blood pressure, and is output to the liquid crystal display unit or the printer (S20).
7).

Although specific embodiments of the invention have been described above, the invention is not limited thereto. For example, the present invention can be applied not only to a finger sphygmomanometer, but also to a wristband sphygmomanometer. It can also be applied to a sphygmomanometer in which blood pressure is measured while the blood in the artery is once blocked and the air in the cuff is exhausted at a very low speed. Further, the reference amplitude is not limited to 1/4 of the maximum amplitude and can be changed as appropriate.

[0025]

As can be easily understood by comparing the volume pulse wave shown in the lower graph of FIG. 1 with the graph of FIG. 6, according to the blood pressure monitor of the present invention, the pulsation of arterial blood vessels is more active. The peaks of the pulse wave component (PG1 and PG2 in FIG. 6) at a low cuff pressure are detected, and the systolic blood pressure is determined based on these peaks. Contraction, or because the subject's arterial blood vessel is too thin, micropulsation of the arterial blood vessel under high cuff pressure is blocked, and as a result, the conventional method does not accurately measure the photoplethysmogram before and after the reference amplitude. Even if it is difficult to detect the blood pressure accurately, the blood pressure can be measured with high accuracy.

[Brief description of drawings]

1 is a graph showing a representative example of plethysmogram in relation to cuff pressure, the middle graph shows plethysmogram of a normal subject, and the lower graph shows arterial blood vessels under high cuff pressure. 2 shows a plethysmogram of a subject in which the minute pulsation of is disturbed.

FIG. 2 is a block diagram of a sphygmomanometer of the present invention.

FIG. 3 is a part of a flowchart showing the operation of the sphygmomanometer of the present invention.

FIG. 4 shows a continuation of the flowchart of FIG.

5 is a flowchart showing details of a systolic blood pressure calculation routine of the flowchart of FIG.

FIG. 6 is a graph showing the principle of determining the systolic blood pressure in the sphygmomanometer of the present invention.

[Explanation of symbols]

 10: Cuff 16: Light receiving element (photoelectric volume pulse wave detection means) 16/34/20: Volume pulse wave recording means 18: Air pump 20: Microprocessor (control calculation means) 22: Pressure sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiki Echida 2-1-1 Nakajima, Kokurakita-ku, Kitakyushu, Fukuoka Prefecture Totoki Kikai Co., Ltd. (72) Kentaro Todoroki, Nakajima, Kitakyushu, Kitakyushu, Fukuoka 2 1-chome 1-1 Totoki Kiki Co., Ltd. (72) Keisuke Kanzaki 2-1-1 1-1 Nakajima, Kokurakita-ku, Kitakyushu-shi, Kitakyushu, Fukuoka (72) Inventor Masafumi Sengoku Yushima, Bunkyo-ku, Tokyo 2-17-4, Ueda Manufacturing Co., Ltd. (72) Inventor Takahiro Yamaguchi 2-17-4, Yushima, Bunkyo-ku, Tokyo Tokyo Ueda Manufacturing Co., Ltd.

Claims (5)

[Claims] 1. A photoelectric volume pulse wave of an artery of a subject is detected in association with the cuff pressure while variably controlling the cuff pressure, and a maximum amplitude of the detected photoelectric volume pulse wave and a reference amplitude equal to a predetermined fraction thereof are set. Obtained, in the sphygmomanometer by the photoelectric volume pulse method that came to determine the cuff pressure when the amplitude of the photoelectric volume pulse wave becomes equal to the reference amplitude on the higher cuff pressure side than the maximum amplitude, as the systolic blood pressure of the subject: A first pulse wave component having a first amplitude between the maximum amplitude and the reference amplitude and a first amplitude smaller than the first amplitude of the first pulse wave component from the photoelectric volume pulse wave and larger than the reference amplitude. A second pulse wave component having a second amplitude is extracted, and the amplitude of the photoelectric volume pulse wave is equal to the reference amplitude based on the amplitudes of the first pulse wave component and the second pulse wave component. The cuff pressure at which A sphygmomanometer characterized in that it is determined as the examinee's highest blood pressure. 2. The sphygmomanometer according to claim 1, wherein the second pulse wave component is a pulse wave component having a minimum amplitude larger than the reference amplitude. 3. The sphygmomanometer according to claim 1, wherein the first amplitude of the first pulse wave component is about one half of the maximum amplitude. 4. The sphygmomanometer according to claim 1, wherein the second pulse wave component is a pulse wave component having a minimum amplitude greater than about one third of the maximum amplitude. 5. A cuff for compressing an artery of a subject with pressurized air, an air supply unit for applying variable pressure pressurized air to the cuff, a pressure detection unit for detecting an air pressure of the cuff, and Pulse wave detecting means for detecting the photoelectric volume pulse wave, recording means for recording the amplitude of each pulse wave component of the photoelectric volume pulse wave in association with the cuff pressure, and maximum amplitude calculating means for calculating the maximum amplitude of the photoelectric volume pulse wave And a reference amplitude calculating means for calculating a reference amplitude equal to a predetermined fraction of the maximum amplitude, and a first pulse wave component having a first amplitude between the maximum amplitude and the reference amplitude from the photoelectric volume pulse wave. Means for extracting a second pulse wave component having a second amplitude smaller than the first amplitude of the first pulse wave component and larger than the reference amplitude from the photoelectric volume pulse wave; Based on the amplitude of the first pulse wave component and the amplitude of the second pulse wave component Estimating means for estimating the cuff pressure when the amplitude of the photoplethysmogram becomes equal to the reference amplitude on the higher cuff pressure side than the maximum amplitude, and the output for outputting the cuff pressure estimated by the estimating means as the systolic blood pressure of the subject. A sphygmomanometer according to the photoelectric plethysmography method, which comprises: