JP2958471B2 - Non-invasive blood pressure measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-invasive blood pressure measuring device for non-invasively measuring the blood pressure of a subject in a weak blood pressure state.

[0002]

2. Description of the Related Art Conventionally, as a method for non-invasively measuring a blood pressure value of a subject, for example, a photoelectric volume oscillation method is known. In this photoelectric volume oscillation method, when the pressure of a cuff wound on a finger is increased or decreased, a change in a weak vibration caused by blood pressure, that is, a change in the volume of a blood vessel, is received by a light-receiving element that receives transmitted light from a light-emitting element. The blood pressure value is measured from the amplitude and the cuff pressure of the photoelectric volume pulse wave signal, which is the AC component of the light receiving signal output from the light receiving element. FIG. 7 shows the relationship between the photoplethysmogram and the cuff pressure obtained when the cuff pressure is increased linearly. In the volume oscillation method, the plethysmogram reaches the maximum amplitude value L. The average blood pressure value Pm can be obtained from the cuff pressure at the time of
The cuff pressure is further increased to, for example, 20% of the maximum amplitude value L.
Can be measured as the maximum blood pressure value Ps. In addition, the minimum blood pressure value Pd is obtained by setting the cuff pressure to 0 mm.
It can be obtained from the cuff pressure at the inflection point M of the envelope of the volume pulse wave observed in the process of rising from Hg.
The details of such blood pressure measurement using the photoelectric volume oscillation method are described in “Clinical Monitor Vol13 No1 1990” published by the Clinical Monitor Study Group.

When a subject is in a shock state due to a ventricular fibrillation state or in an extremely low blood pressure state due to a large amount of bleeding, the conventional non-invasive sphygmomanometer may not be able to measure. Was. Therefore, in order to obtain some kind of blood pressure information from a subject in such a shock state, the cuff pressure is set to a constant value of, for example, 60 mmHg, and a volume pulse wave signal from the light receiving element is observed. A sphygmomanometer has been proposed that can determine whether or not a subject is in a weak blood pressure state of 60 mmHg or less (or a state in which pulsation is stopped) based on whether or not a plethysmogram is detected.

[0004]

However, a cuff pressure of 60
The measurement of blood pressure in a state set to a constant value such as mmHg can only determine the weak blood pressure state of a subject at a certain constant pressure. In such a method, the blood pressure of the subject in a shock state or the like can be determined. The value could not be measured. In the current situation where the importance of prompt emergency treatment is called for, the ability to measure blood pressure immediately after bringing a subject in a shocked state into an ambulance is an important part of emergency medical treatment. Is important.

[0005] The present invention has been proposed to solve the problems of the prior art, and it is possible to determine whether or not the subject is in a weak blood pressure state and to determine whether the subject is in a weak blood pressure state. It is an object of the present invention to provide a non-invasive blood pressure measurement device capable of easily measuring a blood pressure value.

[0006]

In order to achieve this object, a non-invasive blood pressure measuring device according to the present invention comprises a cuff attached to a part of a subject's body and a cuff pressurized on the subject by the cuff. A pressure detector for detecting pressure, a pressurizing means for pressurizing the cuff by an input pressure control signal, or a cuff pressure drop by inputting a depressurization control signal, and irradiating light to a pressurized portion of the body by the cuff A light emitting unit, a light receiving unit that detects a transmitted light amount or a reflected light amount of light incident on the body from the light emitting unit, and a pulse wave detecting unit that separates a pulse wave component in a light receiving signal obtained from the light receiving unit, When it is determined based on the detection output from the pulse wave detecting means that no pulse wave component is detected before the cuff pressure is applied, the pressure increasing control signal is received while receiving the detection output from the pressure detector. Output or rise once Cuff pressure control means for outputting a decompression control signal for lowering the cuff pressure to the pressurizing means, and a process in which the cuff pressure is increased or reduced by the cuff pressure by the cuff pressure control means. Blood pressure value measuring means for detecting an inflection point of the received light signal, receiving a detection output from the pressure detector, and outputting a cuff pressure at the inflection point as an average blood pressure value of the subject in a weak blood pressure state. I have.

Further, the non-invasive blood pressure measuring device according to the present invention is configured such that light of a plurality of wavelengths is emitted from the light emitting section in a time-division manner, and the blood pressure value measuring means detects light receiving signals of a plurality of wavelengths. When an inflection point exists at any of the points, the cuff pressure at this inflection point can be output as an average blood pressure value.

Next, the basic concept of the present invention will be described. If the pulse wave component is not detected in the measurement signal from the subject before the cuff pressure is applied, it can be determined that the subject is in a weak blood pressure state. When the cuff pressure of the subject in such a state is increased linearly as shown in FIG. 3B, a part of the subject's body, for example, a finger is pressed by the cuff 4. As shown in FIG. 3 (a), the biological tissue 7 sandwiched between the light emitting unit 5 and the light receiving unit 6A (see FIG. 1) has a tissue portion 7a that does not contain blood, while the thickness thereof is kept constant. The venous blood 7c is gradually eliminated. As a result, the light intensity of the transmitted light detected by the light receiving unit 6A gradually increases due to the decrease in the dimming elements (arterial blood and venous blood) accompanying the increase in the cuff pressure, and the cuff pressure becomes higher than the arterial pressure.
When all the blood is removed and only the tissue portion 7a is left, the change in the light intensity becomes substantially constant. When the arterial blood is completely eliminated in this way, a large change appears in the slope of the light intensity as shown in FIG. 3 (c). Therefore, this inflection point a is detected, and the cuff pressure at this point can be read. For example, the average blood pressure value of a subject in a weak blood pressure state can be measured.

On the other hand, when the cuff 4 is worn on the upper arm of the subject, since the transmitted light cannot be detected, the light emitting unit 5 and the light receiving unit 6B are arranged at a fixed distance on the same surface as shown in FIG. The reflected light after the light emitted from the light emitting unit 5 is attenuated by the living tissue 7 is detected by the light receiving unit 6B. In this case, after it is determined that the subject is in a weak blood pressure state,
As shown in FIG. 5 (b), when the cuff pressure is increased linearly, the optical path length D, which is the distance between the light emitting unit 5 and the light receiving unit 6B, is kept constant, but the arterial blood 7b and the venous blood 7c are reduced. Since the light is gradually removed, the light intensity of the reflected light detected by the light receiving unit 6B gradually increases. When the cuff pressure exceeds the arterial pressure, all the blood is eliminated and only the tissue portion 7a is removed.
As shown in (c), the gradient of the light intensity of the reflected light greatly changes, and thereafter, the change with respect to the cuff pressure becomes extremely small.
By detecting the inflection point a and reading the cuff pressure at this point, the average blood pressure value of the subject in the weak blood pressure state can be measured.

By the way, depending on the oxygen concentration in the blood of the subject, there are wavelengths at which the tissue portion 7a, the arterial blood 7b, and the venous blood 7c, which do not contain blood, exhibit the same light absorption characteristics. FIG. 6 shows three wavelengths λ1, λ2, λ
3 shows an example in which the absorbance at a certain wavelength λ2 is the same in the tissue part (shown by the light absorption characteristic G3), the arterial blood (the light absorption characteristic G1), and the venous blood (the light absorption characteristic G2). If it is attempted to measure the blood pressure using a wavelength at which the absorbance is equal in the tissue portion, the arterial blood, and the venous blood, the measurement becomes difficult, especially in the case of measurement performed by receiving reflected light. Therefore, if light of a plurality of wavelengths, for example, light of three wavelengths is sequentially emitted from the light emitting unit 5, a case where light absorption characteristics of light of all wavelengths coincide cannot occur. Using the light of the wavelength, it is possible to determine whether or not the subject is in a weak blood pressure state and, if so, to measure the average blood pressure value. Also, in the measurement performed by detecting the transmitted light, the use of a plurality of wavelengths can give the measurement reliability and improve the measurement accuracy.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of the non-invasive blood pressure measuring device according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the blood pressure measuring device. In this figure, a light emitting unit 5 for irradiating a living tissue 7 of a subject with light is provided on a part of the body of the subject, for example, a cuff 4 attached to a finger, and a living tissue 7 is provided on the opposite side of the light emitting unit 5. And a light-receiving unit 6A disposed therebetween.
Here, it is assumed that the living tissue 7 is composed of a tissue portion 7a containing no blood, arterial blood 7b, and venous blood 7c (FIG. 3).
(A)). In this embodiment, the light emitting section 5 is constituted by light emitting elements that emit light of three different wavelengths, for example, three light emitting diodes 5a, 5b, and 5c. From each of the light emitting diodes 5a, 5b, 5c, a first wavelength of 6
A light having a wavelength of 60 nm, a second wavelength of 805 nm, and a third wavelength of 940 nm are emitted. In addition, 3
Instead of using individual light-emitting diodes, a configuration in which light of three wavelengths is emitted by switching filters of each color arranged on the front surface of the light source is also possible. Light receiving section 6A
Is constituted by a light receiving element such as a phototransistor, for example, and the amount of transmitted light after light emitted from the light emitting unit 5 has passed through the living tissue 7 is detected by the light receiving unit 6A.

The cuff 4 is connected by an air tube 8a to a cuff pressure control pump 8 including a drive circuit, and is controlled by a central processing unit 1 (hereinafter referred to as CPU 1) to the pump 8 serving as a pressurizing means. When the signal is input, the cuff pressure is increased or reduced, the cuff pressure is released, and the like. The cuff pressure when the living tissue 7 is pressurized by the cuff 4 is determined by a pressure detector 9.
After the output of the pressure detector 9 is converted into a digital signal by the A / D converter,
It is taken into PU1. Further, from the timing generation circuit 2 under the control of the CPU 1, each light emitting diode 5a,
A pulse signal for determining the timing for sequentially emitting light in a time-division manner is provided to each buffer 3 of the driver circuit 3.
a, 3b, and 3c, and a timing signal for separating the light receiving signal for each wavelength from the output signal of the light receiving unit 6A is output to the demodulation circuit 11. Each buffer 3
a, 3b and 3c sequentially amplify the input timing pulse signal to drive the light emitting diodes 5a, 5b and 5c. Thereby, each light emitting diode 5a, 5b, 5c
From there, light of the first to third wavelengths is sequentially applied to the living tissue 7. In the light receiving section 6A, each light emitting diode 5
The amount of transmitted light after the light emitted from a, 5b, and 5c is attenuated by passing through the living tissue 7 is detected, and this light reception output signal is supplied to the demodulation circuit 11 after being amplified by the input amplifier 10. Is done. The demodulation circuit 11 separates the input signal into light receiving signals for each wavelength based on the timing signal, and separates each light receiving signal into a DC component and a pulse wave component. Each signal component output from the demodulation circuit 11 is converted into a digital signal by the A / D converter 12 and then taken into the CPU 1. Here, the demodulation circuit 11 constitutes a pulse wave detecting means, and the CPU 1 constitutes a cuff pressure control means and a blood pressure value measuring means.

Next, the operation of the thus configured non-invasive blood pressure measuring device will be described with reference to the operation flowchart of FIG. First, at the start of measurement, the cuff is in a non-pressurized state,
The cuff pressure is kept at 0 mmHg (step S1).
In this state, each light emitting diode 5a, 5b,
From 5c, light of each wavelength is sequentially emitted toward the living tissue 7, and the amount of transmitted light is detected by the light receiving unit 6A. This light receiving output signal is separated into a DC component and a pulse wave component in the demodulation circuit 11 and is taken into the CPU 1 (step S).
2). The CPU 1 determines whether or not a pulse wave component is included in the received light signal (step S3). If the pulse wave component is detected, the average blood pressure value Pm and the systolic blood pressure of the subject are measured using the photoelectric volume oscillation method. A series of processes for measuring the value Ps and the diastolic blood pressure value Pd are performed (step S4). On the other hand, if no pulse wave component is detected, it can be determined that the subject is in a weak blood pressure state. In this case, the CPU 1 outputs a boost control signal to the cuff pressure control pump 8. Thereby, the pressure of the cuff 4 is increased linearly by the pump 8 (step S5). During the process of increasing the cuff pressure, the CPU 1
The light intensity of the transmitted light of three wavelengths is sequentially measured, and the difference from the light intensity before the cuff pressure rise is calculated (steps S6 to S7). CP
In U1, it is determined whether or not any of the three wavelengths has an inflection point a at which the gradient of the change in the transmitted light intensity changes greatly based on the calculated value. If no inflection point is found, the cuff pressure is set to the maximum value, for example, 180 mmHg.
Is determined, and if the maximum cuff pressure has not been reached, the process returns to step S5, and the same processing is repeated. If the inflection point a is found in the light receiving signal of any of the three wavelengths in step S8, the cuff pressure at this inflection point a is detected and displayed as an average blood pressure value (step S10). At the same time, a cuff pressure release signal is sent to the cuff pressure control pump 8 to release the cuff pressure (step S).
11). If it is determined in step S9 that the maximum cuff pressure has been reached, the cuff pressure is released and re-measurement is performed, or measurement disable processing is performed (steps S12 to S1).
3).

After the cuff pressure reaches the maximum pressure, C
In the process of sending a pressure reduction control signal from the PU 1 to the cuff pressure control pump 8 and linearly lowering the cuff pressure, a process of detecting the inflection point a and measuring the average blood pressure value again is performed. Then, more accurate measurement is possible.

Next, a description will be given of an embodiment in which the cuff 4 is mounted on the upper arm of the subject for measurement. In this example,
As shown by a broken line in FIG. 1, a light emitting unit 5 and a light receiving unit 6B are attached to the inner surface of the cuff 4 at a constant distance on a straight line. This fixed distance is the optical path length D separating the light emitting unit 5 and the light receiving unit 6B. In this case, light of three wavelengths is sequentially emitted from the light emitting diodes 5a, 5b, and 5c of the light emitting unit 5 toward the living tissue 7, and the amount of reflected light after being reduced in the living tissue 7 is the light receiving unit 6B. Is detected by The procedure for measuring the blood pressure in this case can be performed based on the flowchart of FIG.

In the above two embodiments, the light emitting unit 5 is used.
To three light emitting diodes 5a emitting light of different wavelengths.
Although composed of 5b and 5c, the light emitted from the light emitting unit 5 is not limited to three wavelengths, but may be, for example, two wavelengths. In particular, when measurement is performed on the fingers, since transmitted light is detected instead of reflected light,
The measurement can be performed even when the light emitting unit 5 emits one wavelength of light.

[0017]

As described above, according to the present invention, even a subject placed in a shock state or an extremely low blood pressure state, which has been difficult to measure by the conventional volume vibration method, can be placed in a weak blood pressure state. Since it is possible to determine whether or not the subject is present, and if the subject is in a weak blood pressure state, the blood pressure value of the subject can be measured, it is highly effective in a clinical setting, especially in an emergency medical setting.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a non-invasive blood pressure measuring device according to the present invention.

FIG. 2 is a flowchart showing an operation procedure of the blood pressure measurement device of FIG.

3A is a schematic diagram of a living tissue when a transmitted light is detected to measure a blood pressure value, FIG. 3B is a diagram showing a change in the cuff pressure at the time of measurement, and FIG. FIG. 4 is a diagram showing the light intensity of a received light signal.

FIG. 4 is an explanatory diagram showing how reflected light after passing through living tissue is received by a light receiving unit.

5A is a schematic diagram of a living tissue when a blood pressure value is measured by detecting reflected light, FIG. 5B is a diagram showing a change in the cuff pressure at the time of measurement, and FIG. FIG. 4 is a diagram showing the light intensity of a received light signal.

FIG. 6 is a characteristic diagram illustrating an example in which the absorbances of tissue, arterial blood, and venous blood match according to wavelength.

FIG. 7 is a waveform diagram showing a relationship between cuff pressure and amplitude of a volume pulse wave in the volume vibration method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CPU 2 Timing generation circuit 3 Driver circuit 4 Cuff 5 Light-emitting part 6A, 6B Light-receiving part 7 Living tissue 8 Cuff pressure control pump 9 Pressure detector 10 Input amplifier 11 Demodulation circuit 12 A / D converter Pm Mean blood pressure value Ps Maximum blood pressure Value Pc Minimum blood pressure value

Claims (2)

(57) [Claims] 1. A cuff attached to a part of a subject's body, a pressure detector for detecting a cuff pressure applied to the subject's body by the cuff, and a cuff detected by an input pressure control signal. Pressurizing means for pressurizing or lowering the cuff pressure by inputting a decompression control signal; a light emitting unit for irradiating light to a pressurized portion of the body by the cuff; and a transmitted light amount of light incident on the body from the light emitting unit Or, a light receiving section for detecting the amount of reflected light, pulse wave detecting means for separating a pulse wave component in a light receiving signal obtained from the light receiving section, and based on a detection output from the pulse wave detecting means, before the cuff pressure is applied. If it is determined that a pulse wave component is not detected, a pressure control signal is output to the pressurizing means while receiving a detection output from the pressure detector, or a pressure control signal for lowering the cuff pressure once boosted is output. Output to pressurizing means A cuff pressure control means for detecting an inflection point of a light receiving signal from the light receiving section in a process of increasing or decreasing the cuff pressure by the cuff pressure controlling means; A non-invasive blood pressure measuring device, comprising: a blood pressure value measuring unit that receives a detection output and outputs a cuff pressure at the inflection point as an average blood pressure value of a subject in a weak blood pressure state. 2. The light emitting unit is configured to emit light of a plurality of wavelengths in a time-division manner, and the blood pressure value measuring means is configured to detect an inflection point in any of the light receiving signals of the plurality of wavelengths. 2. The non-invasive blood pressure measurement device according to claim 1, wherein the cuff pressure at the inflection point is output as an average blood pressure value.