JP2000254104A - Arteriosclerosis level measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an arteriosclerosis level measurement device capable of easily and highly accurately measuring an arteriosclerosis level inside the living body. SOLUTION: By a maximum peak decision means 70, the maximum peak of a waveform indicated by a transmission function H(f) between upper arm arterial waves W1 and radius arterial waves W2 decided by a transmission function decision means 68 is decided. By an arteriosclerosis level decision means 72, the arteriosclerosis level of the living body is decided from the intensity of the maximum peak decided by the maximum peak decision means 70. That is, measurement is easily performed since the measurement is performed just by mounting two pulse wave sensors 27 and 46 to the prescribed part of the living body similarly to a conventional case and the accuracy of the arteriosclerosis level is improved since the arteriosclerosis level is measured based on the transmission function H(f).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arterial stiffness measuring device capable of measuring the arterial stiffness in a living body with high accuracy and ease.

[0002]

2. Description of the Related Art An arterial stiffness measuring apparatus for measuring the degree of arterial stiffness in a living body utilizes the fact that the pulse wave propagation speed at which a pulse wave propagates between predetermined portions of the living body reflects the arterial stiffness. Measuring devices have been proposed. That is, a first pulse wave sensor attached to a predetermined part of the living body, and a second pulse wave sensor attached to a downstream part of the first pulse wave sensor, the first pulse wave sensor detected by the first pulse wave sensor A portion (for example, one beat) of a second portion of the second pulse wave detected by the second pulse wave sensor from a predetermined portion (for example, a peak for each beat) generated in each cycle of the pulse wave. Calculate the propagation speed of the pulse wave based on the time difference up to each peak)
An arterial stiffness measuring device that measures the arterial stiffness of a living body from the actually calculated pulse wave velocities by using a predetermined relationship between the pulse wave velocities and the arterial stiffness has been proposed. According to the arteriosclerosis measuring device, a predetermined 2
The arterial stiffness can be measured simply by attaching the pulse wave sensor to the site, so that the arterial stiffness can be easily measured.

[0003]

As described above, the arteriosclerosis measuring device for measuring the degree of arteriosclerosis of a living body based on the pulse wave velocity is used to determine the pulse wave velocity. It is necessary to determine the length of the blood vessel between the wave sensor and the second pulse wave sensor and to determine the time difference.
However, it is difficult to accurately determine the length of a blood vessel. In addition, in order to accurately determine the time difference, it is necessary to accurately detect a predetermined portion of the pulse wave, but when viewed locally, the change in the pulse wave is gentle, and furthermore, since artifacts are mixed in It is difficult to accurately detect a predetermined part of the pulse wave. Therefore, it has been difficult to accurately determine the time difference. Therefore, the degree of arteriosclerosis measured based on the pulse wave velocity was relatively low in accuracy.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an arterial stiffness measuring device capable of simply and highly accurately measuring the arterial stiffness in a living body. To provide.

[0005]

The inventor of the present invention has made various studies on the background described above, and as a result, the first pulse wave detected by the first pulse wave sensor and the second pulse wave detected by the second pulse wave sensor. It has been found that the magnitude of the maximum peak of the waveform represented by the transfer function between the second pulse wave and the second pulse wave increases as the blood vessel becomes harder. This is probably because the harder the blood vessel, the less the attenuation of the pulse wave. The present invention has been made based on such findings.

That is, the gist of the present invention is as follows.
A first pulse wave sensor that is attached to a predetermined portion of the living body and detects a first pulse wave that propagates in the artery of the living body; and a first pulse wave sensor that is attached to a downstream portion of the first pulse wave sensor and propagates in the artery. A second pulse wave sensor for detecting two pulse waves, and an arteriosclerosis measuring device for measuring the arteriosclerosis of the living body based on the pulse waves detected by the first pulse wave sensor and the second pulse wave sensor And (a) a transfer function including a frequency as a variable between a first pulse wave detected by the first pulse wave sensor and a second pulse wave detected by the second pulse wave sensor. Transfer function determining means for determining, (b) maximum peak determining means for determining the maximum peak on the frequency axis of the transfer function determined by the transfer function determining means, and (c) determined by the maximum peak determining means Determine the degree of arteriosclerosis of the living body based on the maximum peak A degree of arteriosclerosis determining unit that is to contain.

[0007]

According to this configuration, the maximum peak determining means determines the maximum waveform on the frequency axis of the waveform represented by the transfer function between the first pulse wave and the second pulse wave determined by the transfer function determining means. The peak is determined, and the arteriosclerosis degree determining means
Since the degree of arteriosclerosis of the living body is determined based on the maximum peak determined by the maximum peak determining means, the degree of arteriosclerosis can be measured easily and with high accuracy. That is,
As in the past, measurement can be performed simply by attaching two pulse wave sensors to a predetermined part of the living body, so that measurement can be easily performed, and the degree of arteriosclerosis can be measured based on the transfer function between the two pulse waves. The accuracy of the degree is improved.

[0008]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram illustrating the configuration of an arteriosclerosis measuring device 8 according to the present invention. In FIG. 1, an arteriosclerosis measuring device 8 has a rubber bag in a cloth band-shaped bag, for example, a cuff 10 wound around the upper arm 12 of the other arm of the patient, and a pipe 20 connected to the cuff 10. , A pressure sensor 14, a switching valve 16, and an air pump 18 which are connected to each other. The switching valve 16 is provided with the cuff 10
It is configured to be able to switch between three states: a pressure supply state in which the supply of pressure into the cuff is allowed, a slow discharge state in which the cuff 10 is gradually discharged, and a rapid discharge state in which the cuff 10 is rapidly discharged. Have been.

The pressure sensor 14 detects the pressure in the cuff 10 and outputs a pressure signal SP representing the pressure to the static pressure discriminating circuit 2.
2 and the pulse wave discrimination circuit 24. The static pressure discriminating circuit 22 has a low-pass filter, discriminates a cuff pressure signal SK representing a steady pressure included in the pressure signal SP, that is, a cuff pressure, and converts the cuff pressure signal SK into an A / D converter 26.
To the electronic control unit 28 via the Pulse wave discrimination circuit 2
Reference numeral 4 denotes a band pass filter, which discriminates a pulse wave signal SM ₁ which is a vibration component of the pressure signal SP in frequency, and converts the pulse wave signal SM ₁ via the A / D converter 30 into the electronic control unit 2.
8 The cuff pulse wave represented by the pulse wave signal SM ₁ is
This is a brachial artery wave generated from a brachial artery (not shown) and transmitted to the cuff 10 in synchronization with the heartbeat of the patient. In this embodiment, the cuff 10 is attached to the upper arm 12 of the living body, and the cuff 10 in the cuff 10 the pressure sensor 14 for detecting the pressure functions as a first pulse wave sensor 27, brachial artery pulse wave represented by the pulse-wave signal SM ₁ is the first pulse wave W1 (t).

The electronic control unit 28 includes a CPU 29, R
The microcomputer 29 includes a so-called microcomputer including an OM 31, a RAM 33, an I / O port (not shown), and the like. The CPU 29 executes signal processing using a storage function of the RAM 33 according to a program stored in the ROM 31 in advance. Thereby, a drive signal is output from the I / O port to control the switching valve 16 and the air pump 18 and also to control the display contents of the display 32.

The pressure pulse wave detecting device 34 is mounted on the wrist 42 on the downstream side of the upper arm 12 on which the cuff 10 is mounted, with the open end of the housing 36 having a container shape facing the body surface, that is, the skin 38. The band 40 detachably attaches to the wrist 42. Inside the housing 36, a pressure pulse wave sensor 46 functioning as a second pulse wave sensor is provided via a diaphragm 44 so as to be relatively movable and protrudable from an open end of the housing 36. The housing 36 and the diaphragm 4
The pressure chamber 48 is formed by 4 or the like. The pressure chamber 48 is supplied with pressurized air from an air pump 50 via a pressure regulating valve 52, whereby the pressure pulse wave sensor 46 applies a pressing force P corresponding to the pressure in the pressure chamber 48. _HD
Is pressed against the body surface 38. Therefore, the housing 36, the diaphragm 44, and the like that constitute the pressure chamber 48 function as a pressing device for the pressure pulse wave sensor 46.

The pressure pulse wave sensor 46 has a flat pressing surface 54 of a semiconductor chip made of, for example, single crystal silicon or the like.
In addition, a number of semiconductor pressure sensitive elements (not shown)
Are arranged at intervals of, for example, about 0.2 _mm in the direction crossing the wrist 42, and are generated from the radial artery 56 by being pressed onto the radial artery 56 on the body surface 38 of the wrist 42. A pressure vibration wave, ie, a pressure pulse wave, transmitted to the surface 38 is detected, and a pressure pulse wave signal SM ₂ representing the pressure pulse wave is converted to an A / D signal.
The signal is supplied to the electronic control unit 28 via the converter 58. The pressure pulse wave sensor 46 moves the diaphragm 44 until the part of the wall of the radial artery 56 becomes flat due to the flat pressing surface 54.
While being pressed by, the detecting the pressure pulse wave from the radial artery 56, the influence of the tension of the tube wall of the radial artery 56 is removed, PPW signal SM ₂ is the radial artery 56 Is a radial artery wave that schematically indicates the pressure in the
Since 6 is an artery downstream of the brachial artery, the radial artery wave is the second pulse wave W2 (t).

The CPU 29 of the electronic control unit 28
According to a program stored in the ROM 31 in advance.
A drive signal is output to the air pump 50 and the pressure regulating valve 52,
The pressure in the pressure chamber 48, that is, the pressing force of the pressure pulse wave sensor 46 on the skin is adjusted. That is, the optimum pressing force P _HDPO of the pressure pulse wave sensor 46 is determined based on the pressure pulse waves sequentially obtained in the pressure change process in the pressure chamber 48, and the pressure pulse wave sensor 4
The pressure regulating valve 52 is controlled so as to maintain the optimum pressing force P _HDPO of _No. 6.

FIG. 2 is a functional block diagram illustrating a main part of the control function of the arithmetic and control unit 28 in the arterial stiffness measuring device 8 configured as described above. The cuff pressure control means 60 controls the air pump 18 and the switching valve 16,
The compression pressure of the cuff 10 is controlled to a preset pressure.
The preset pressure is sufficiently lower than the average blood pressure value, and a pulse wave from the brachial artery (not shown)
Pressure enough to transmit to 0, for example, 20-30 mmHg
Is set to

The optimum pressing force control means 64 continuously changes the pressing force of the pressure pulse wave sensor 46, and based on the pressure pulse wave obtained in the change process, a part of the tube wall of the radial artery 56 is The optimal pressing force P _HDPO is determined so as to be flat, and the pressure pulse wave sensor 4
6 is pressed by the optimum pressing force P _HDPO .

The coefficient determining means 66 sets the predetermined section of the brachial artery wave W1 detected by the pressure sensor 14 and the predetermined section of the radial artery wave W2 detected by the pressure pulse wave sensor 46 to a predetermined section of the brachial artery wave W1. Based on the later predetermined section, a coefficient of an autoregressive model that uses the brachial artery wave W1 as an input signal and the radial artery wave W2 as an output signal is determined. Since the sequentially detected pulse waves are affected by previous pulse waves, the relationship can be represented by a well-known autoregressive model. Equation 1 is an example of the autoregressive model. In Equation 1, W1 (m) and W2 (n)
Is a brachial artery wave and a radial artery wave sequentially sampled. For example, m is 14 and n is 12. Also,
a (n) and b (m) are coefficients, and c is an error.

[0018]

[Formula 1] a (1) W2 (1) + a (2) W2 (2) +... + A (n) w2 (n) = b (1) W1 (1) + b (2) W1 (2) +… + B (m) w1 (m) + c

Here, the output signal of the radial artery wave W2
(1) to W2 (n) are input signals {W1 (1) to W1
(N) It must be a section after the section corresponding to｝. Brachial artery wave W1 and radial artery wave W sequentially input
3 is a series of points sampled at predetermined intervals of several milliseconds or tens of milliseconds, as shown in FIG. 3, so that six points up to the peak P1 of the brachial artery wave W1 are used as input signals. For example, as an output signal,
Three points immediately after the peak P2 corresponding to the peak P1 are used. (Note that the score uses a relatively small numerical value for the sake of explanation.) Further, by moving both the section of the input signal and the section of the output signal, another set of the input signal and the output signal is formed. can get. By substituting a large number of sets of signals obtained in this way into Equation 1, a plurality of relational expressions between the coefficient a (n) and the coefficient b (n) are obtained. Then, from the plurality of relational expressions, the coefficient of Expression 1 is determined by the least square method so that the error c is minimized. Therefore, the brachial artery wave W1 in the coefficient determining means 66
And the predetermined section of the radial artery wave W2 are set in advance as sections in which a set of input signals and output signals required for determining the coefficients a (n) and b (n) is sufficiently obtained. Is done.

The transfer function determining means 68 includes a coefficient determining means 6
The transfer functions H (z) and H (f) between the brachial artery wave W1 and the radial artery wave W2 are determined from the autoregressive model whose coefficients have been determined according to 6. The autoregressive model is calculated using the above equation
In this case, the transfer function H (z) can be expressed as in Equation 2. Note that the transfer function is expressed as a Z-transformed function as shown in Expression 2. In this equation 2, the coefficient a determined by the coefficient determining means 66
By substituting (n), the transfer function H (z) can be determined.

[0021]

(Equation 2)

Further, a sampling period (sampling interval)
Is Δt, the relationship between Z and frequency f can be expressed as Expression 3, and thus Expression 2 can be expressed as Expression 4 as a function of frequency f.

[0023]

## EQU3 ## z = exp (j2πfΔt)

(Equation 4)

The maximum peak determining means 70 determines the maximum peak of the waveform represented by the transfer function H (f) determined by the transfer function determining means 68. FIG. 4 is a diagram showing an example of a waveform represented by the transfer function H (f) determined by the transfer function determining means 68. In the waveform shown in FIG. 4, P3 is determined to be the maximum peak.

The arteriosclerosis determining means 72 determines the arteriosclerosis of the living body based on the maximum peak determined by the maximum peak determining means 70. The intensity of this maximum peak is
It reflects the degree of arteriosclerosis.
The intensity of the maximum peak increases. FIG. 5 is a diagram showing waveforms of ten types of transfer functions H (f) determined from different living bodies, and the intensity of the maximum peak is represented by the transfer function H (f).
(F) It differs for each. This is probably because the greater the degree of arteriosclerosis, that is, the harder the artery, the less the attenuation of the pulse wave propagating in the artery. Therefore, the arteriosclerosis determining means 72 determines the degree of arteriosclerosis from the intensity of the maximum peak determined by the maximum peak determining means 70 using, for example, a preset relationship between the peak intensity and the arterial stiffness shown in FIG. decide.

The display means 74 includes an arterial stiffness determination means 70
Is displayed on the display 32.

FIG. 7 is a flowchart for explaining the main part of the control operation of the arithmetic and control unit 28. This flowchart is executed when a start switch (not shown) is turned on.

In FIG. 7, first, in steps S1 (hereinafter, the steps are omitted) and S2, the cuff 1 is used to detect the brachial artery wave W1 and the radial artery wave W2.
The pressure in 0 and the pressure in the pressure chamber 48 are controlled. That is, in S1 corresponding to the cuff pressure control means 60, the air pump 18 and the switching valve 16 are controlled so that the compression pressure of the cuff 10 is controlled to a predetermined pressure of 20 to 30 mmHg. In step S2, in the process of continuously increasing the pressing force of the pressure pulse wave sensor 46, the pressure when the amplitude of the pressure pulse wave detected by the pressure detecting element located immediately above the radial artery 56 is maximized. The pressure is determined as the optimum pressing force P _HDPO , and the pressing force of the pressure pulse wave sensor 46 is held at the optimum pressing force P _HDPO .

[0029] In subsequent S3, with the pulse wave signal SM ₁ That brachial wave W1 which is discriminated by the pulse-wave filter circuit 24 is read, stored in a predetermined storage area in the RAM 33, the subsequent S4, PPW with pressure-pulse-wave signal SM ₂ i.e. the radial artery wave W2 supplied from the sensor 46 is read and stored in a predetermined storage area in the RAM 33.

In the following S5, the brachial artery wave W1 required for determining the coefficient of the mathematical expression 2 in S7 described later.
It is determined whether or not a preset predetermined section of the (input signal) and the radial artery wave W2 (output signal) has been read. If this determination is denied, S3 and subsequent steps are repeated.

However, if the determination in S5 is affirmative, S6 and S7 corresponding to the subsequent coefficient determining means 66 are executed. First, in S6, a plurality of sets of data described in detail below are substituted from the brachial artery wave W1 and the radial artery wave W2 stored in the RAM 33 into the autoregressive model shown in Expression 2, and a coefficient a ( A plurality of relational expressions for n) and b (m) are obtained.

The above-mentioned plural sets will be described in more detail with reference to FIG. 3. For example, when there are six input signals and three output signals, the peak P1 of the brachial artery wave W1 is obtained.
Up to six points (input signals) and three points (output signals) immediately after the peak P2 of the radial artery wave W2 constitute one set. Then, the next set is obtained by moving the sections of the brachial artery wave W1 and the radial artery wave W2. That is, five points to the peak P1 of the brachial artery wave W1 and six points of the circle immediately after the peak P1 (input signal), two circles of the radial artery wave W2, and one circle (output signal) following the circle are output. Become a set. Similarly, a plurality of sets of signals are obtained by sequentially moving the sections of the brachial artery W1 and the radial artery W2.

In the following S7, the coefficients a (n) and b (m) obtained in S6 are obtained from the relational expression of the coefficients a (n) and b (m) by the least square method so that the error c is minimized.
(N) and b (m) are determined.

Next, S corresponding to the transfer function determining means 68
8 to S9 are executed. First, in S8, the transfer function H (z) is obtained by substituting the coefficient a (n) determined in S7 into Equation 2. And the following S9
Then, by substituting Equation 3 into the transfer function H (z), the transfer function H (f) shown in Equation 4 is obtained as a function of the frequency f.

S corresponding to the following maximum peak determining means 70
In 10, the peak indicating the maximum intensity of the waveform represented by the transfer function H (f) determined in S9 is determined, and in S11 corresponding to the arteriosclerosis degree determining means 72, the intensity of the maximum peak determined in S10 is determined. Thus, the degree of arteriosclerosis is determined using the relationship shown in FIG. And the following display means 7
In S12 corresponding to 4, the degree of arteriosclerosis determined in S11 is displayed on the display 32.

Then, in S13, it is determined whether a start switch (not shown) has been turned off.
If this determination is denied, the arteriosclerosis degree is continuously determined by repeatedly executing the above S3 and the following steps. If the determination in S13 is affirmed, the present routine is terminated.

As described above, according to this embodiment, the brachial artery wave W determined by the transfer function determining means 68 (S8 to S9) is determined by the maximum peak determining means 70 (S10).
1 and the maximum peak of the waveform represented by the transfer function H (f) between the radial artery wave W2 is determined.
By (S11), the maximum peak determining means 70 (S10)
The degree of arteriosclerosis of the living body is determined from the intensity of the maximum peak determined by the above. That is, since the measurement can be performed simply by attaching the two pulse wave sensors 27 and 46 to a predetermined part of the living body as in the related art, the measurement can be easily performed, and the arteriosclerosis degree can be measured based on the transfer function H (f). The accuracy of arteriosclerosis is improved.

Although one embodiment of the present invention has been described with reference to the drawings, the present invention can be applied to other embodiments.

For example, in the above-described embodiment, the arteriosclerosis determining means 72 determines the degree of arteriosclerosis from the intensity of the maximum peak determined by the maximum peak determining means 70. The arterial stiffness may be determined from an area within a certain range (for example, ± 2 Hz) centered on the determined maximum peak. In this case, there is provided normalization means for normalizing the transfer function (f) with respect to the frequency based on the maximum peak determined by the maximum peak determination means 70, and the transmission after the frequency normalization means normalizes the transfer function (f). The arterial stiffness may be determined from a certain area around the maximum peak of the function (f).

In the above-described embodiment, the optimum pressing force control means 64 continuously changes the pressing force of the pressure pulse wave sensor 46 so that a part of the tube wall of the radial artery 56 becomes flat. The pressing force P _HDPO is determined, and the pressure pulse wave sensor 46 is pressed with the optimum pressing force P _HDPO . However, when the degree of arteriosclerosis determined by the degree of arteriosclerosis determination means 72 does not require an absolute value and is intended only for relative comparison,
Since the intensity of the waveform represented by the transfer function (f) does not matter, in this case, the optimal pressing force control means 64 is not provided.
The pressure pulse wave sensor 46 may be pressed with a predetermined pressing force so that a pressure pulse wave can be detected from the radial artery 56.

In the above-described embodiment, the first pulse wave sensor 27 is mounted on the upper arm, and the pressure pulse wave sensor 46 is mounted on the wrist 42 of the arm. Therefore, the first pulse wave sensor 2
Although the pressure pulse wave sensor 7 and the pressure pulse wave sensor 46 have a direct upstream and downstream relationship, the present invention can be applied without a direct upstream and downstream relationship. For example, the combination of the parts where the first pulse wave sensor and the second pulse wave sensor are mounted may be the carotid artery and the upper arm, or the upper arm and the back of the foot.

In the above embodiment, the coefficient determining means 6
6, the brachial artery wave W1 and the radial artery wave W2 are substituted into the autoregressive model equation (Formula 1) to determine the coefficient a (n).
(N) is substituted into Equation 2 to determine the transfer function H (z), but the brachial artery wave W1 (t) and the radial artery wave W
2 (t) is first Z-transformed to obtain a function W1
(Z) and the ratio of W2 (z) (= W2 (z) / W1
(Z)) may be determined as the transfer function H (z).

In addition, the present invention can be variously modified without departing from the gist thereof.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an arteriosclerosis degree measuring apparatus according to one embodiment of the present invention.

FIG. 2 is a functional block diagram illustrating a main part of a control function of the arithmetic and control unit according to the embodiment of FIG. 1;

FIG. 3 shows a sequentially detected brachial artery wave W1 and radial artery wave W
FIG. 2 is a diagram showing an example of the second example.

FIG. 4 is a diagram illustrating an example of a waveform represented by a transfer function H (f).

FIG. 5 is a diagram showing H (f) waveforms relating to ten types of transmission determined from different living bodies.

FIG. 6 is a diagram illustrating an example of a preset relationship between a peak intensity and an arteriosclerosis degree.

FIG. 7 is a flowchart illustrating a main part of a control operation of the arithmetic and control unit according to the embodiment of FIG. 1;

[Explanation of symbols]

 8: Arteriosclerosis measuring device 27: First pulse wave sensor 46: Pressure pulse wave sensor (second pulse wave sensor) 68: Transfer function determining means 70: Maximum peak determining means 72: Arteriosclerotic determining means

Claims (1)

[Claims] A first pulse wave sensor attached to a predetermined part of a living body and detecting a first pulse wave propagating in an artery of the living body;
A second pulse wave sensor attached to a downstream portion of the first pulse wave sensor and detecting a second pulse wave propagating in the artery, wherein the second pulse wave sensor is detected by the first pulse wave sensor and the second pulse wave sensor. An arterial stiffness measuring device for measuring the degree of arteriosclerosis of the living body based on a pulse wave, wherein the first pulse wave detected by the first pulse wave sensor and the second pulse wave sensor are detected by the second pulse wave sensor Transfer function determining means for determining a transfer function including frequency as a variable between the second pulse wave, and maximum peak determining means for determining a maximum peak on the frequency axis of the transfer function determined by the transfer function determining means An arterial stiffness measuring device, comprising: an arteriosclerosis determining means for determining an arteriosclerosis of the living body based on the maximum peak determined by the maximum peak determining means.