WO2010024417A1

WO2010024417A1 - Arteriosclerosis evaluating apparatus

Info

Publication number: WO2010024417A1
Application number: PCT/JP2009/065124
Authority: WO
Inventors: 真美松川; 好章渡辺; 雅史齋藤; 隆昭浅田; 未央古谷
Original assignee: 学校法人同志社; 株式会社村田製作所
Priority date: 2008-09-01
Filing date: 2009-08-29
Publication date: 2010-03-04
Also published as: JP5016717B2; JPWO2010024417A1

Abstract

Provided is an arteriosclerosis evaluating apparatus capable of accurately separating incident waves and reflected waves and precisely evaluating the degree of arteriosclerosis due to an individual difference. A first detection means (1) detects, as a displacement signal, pulse waves transmitting through an artery at one point of a live body, and a second detection means (2) measures blood flow rate of the artery at the same point of the live body. The blood flow rate obtained by the second detection means is converted to a displacement signal to obtain incident waves, after which reflected waves are obtained by subtracting the incident waves from the displacement signal detected by the first detection means. A blood vessel function of the live body is evaluated from the amplitude intensities of the incident and reflected waves.

Description

Atherosclerosis evaluation device

The present invention relates to an apparatus for evaluating vascular functions such as arteriosclerosis.

In the modern society, cardiovascular diseases caused by arteriosclerosis are increasing with changes in lifestyle and aging. However, the medical system for early detection of these is uncertain. Evaluation of the flexibility of the blood vessel wall is very important for arteriosclerosis, and current diagnostic apparatuses generally use image diagnosis based on MRI and X-ray CT and a pulse wave velocity method. However, MRI and X-ray CT have high inspection costs and are not suitable for daily monitoring. In addition, a technique called pulse wave velocity method is based on the fact that the pulse wave velocity changes according to the hardness of the blood vessel wall. However, the relationship between age and pulse wave velocity is unclear, and its diagnostic accuracy is low especially considering the viewpoint of prevention and individual differences.

Patent Document 1 includes a pulse wave detection device attached to a predetermined part of a living body, and a compression device that is attached to the downstream side of the pulse wave detection device and suppresses blood flow by compressing the part. A device that evaluates the degree of arteriosclerosis based on the peak of the traveling wave component and the peak of the reflected wave component detected by the pulse wave detection device while the blood flow is suppressed by the compression device has been proposed. ing. Specifically, a cuff that is integrally provided with a first compression bag and a second compression bag is attached to the upper arm, and the brachial pulse wave is generated by the first compression bag in a state where the attachment site by the second compression bag is hemostatic. When detected, this brachial pulse wave is a composite wave of the traveling wave and the reflected wave generated at the wearing site of the second compression bag. Since the reflected wave becomes larger and faster as the artery becomes harder, the time difference and intensity ratio between the peak of the traveling wave component and the peak of the reflected wave component are calculated by the arteriosclerosis information calculation means. Since it changes depending on the degree of arteriosclerosis, it is said that the degree of arteriosclerosis can be evaluated.

In the case of Patent Document 1, as a means for separating a traveling wave and a reflected wave, a pulse wave is detected in a state where the artery is stopped using a second compression bag and the blood flow is suppressed. If such a method is used, two types of configurations, the first compression bag (measurement unit) and the second compression bag (hemostatic unit) are indispensable. Since the traveling wave and the reflected wave are separated, it is affected by the distance variation between the two devices. Moreover, the influence on the pulsation by using the second compression bag is not taken into consideration, and the amplitude intensity of the reflected wave component varies depending on the suppression force of the second compression bag. Furthermore, since there are individual differences in subcutaneous fat and the like, it is difficult to control the compression force, and this is insufficient as a method for identifying individual differences.
JP 2004-113593 A Tomoki Kitawaki, et al., "Analysis of brachial artery pressure pulse waveform in biological circulatory system using one-dimensional numerical calculation model", 18th Numerical Fluid Dynamics Symposium, C2-1, 2004

An object of the present invention is to provide an arteriosclerosis evaluation apparatus capable of accurately separating incident waves and reflected waves and accurately evaluating the degree of arteriosclerosis due to individual differences.

In order to achieve the above object, the present invention provides a first detecting means for detecting a pulse wave transmitted through an artery in one place of a living body, a second detecting means for measuring a blood flow velocity of an artery of the living body, First waveform specifying means for specifying the first waveform based on the blood flow velocity obtained by the second detection means, and subtracting the first waveform from the pulse wave detected by the first detection means. An arteriosclerosis evaluation apparatus comprising: a second waveform determination unit that obtains a second waveform; and an evaluation unit that evaluates the degree of arteriosclerosis from the amplitude intensity of the first waveform and the second waveform. provide.

A pulse wave is a pressure wave propagating in a blood vessel that appears as a displacement on the body surface. This displacement consists of the incident wave component due to the forward wave generated by the ejection of blood from the heart and the reflected wave component that is generated as it propagates through the blood vessel and is reflected at the periphery (hereinafter, each component is referred to as the incident wave and the reflected wave). Call). Since the reflected wave propagates to the periphery, it strongly depends on the viscoelastic properties of the blood vessel wall and changes significantly due to the hardening of the blood vessel wall. Therefore, if the incident wave and the reflected wave are separated and the reflected wave is evaluated, it is considered possible to determine the hardening state of the blood vessel.

In the present invention, first, a first detection means detects a pulse wave transmitted through an artery in one place of a living body. For example, a pulse wave is detected as a displacement signal. As this detection means, a known pulse wave sensor of displacement output may be used, or a piezoelectric transducer may be used. In the case of a piezoelectric transducer with velocity output, a displacement signal can be obtained by integrating the output with time. The piezoelectric transducer can detect a pulse wave by either a velocity signal or a displacement signal, but it is preferable to detect it as a velocity signal. In order to measure minute displacements of the skin surface such as pulse waves, it is necessary to amplify the measured displacement. On the other hand, even if the skin surface is at rest, fine noise is generated due to breathing and fluctuations in the body. Likely to happen. By detecting the pulse wave as a velocity signal, there is an advantage that it is resistant to noise and DC fluctuation can be cut, so that a measurement error hardly occurs. The pulse wave detected in this way is a composite wave including an incident wave and a reflected wave.

On the other hand, the blood flow velocity of the living artery is measured by the second detection means. This artery is preferably the same as the artery that detects the pulse wave by the first detection means, but it is not necessarily the same as the artery that detects the pulse wave by the first detection means. The blood flow velocity can be measured using, for example, the Doppler function of an ultrasonic diagnostic apparatus. Note that the measurement locations of the first detection means and the second detection means do not need to be at the same position, and there may be some difference in position as long as the same blood flow flowing through the artery can be measured. Next, the measured blood flow velocity is converted into a displacement signal, for example, and estimated as an incident wave. In the conversion, first, the blood flow velocity is converted into an internal pressure waveform (a time waveform of intravascular pressure). The conversion to the internal pressure waveform can be calculated using a continuous equation of a one-dimensional fluid model, a motion equation, and the like known from Non-Patent Document 1 and the like. Next, the converted internal pressure waveform is converted into a displacement signal on the skin surface using the complex elastic modulus. For example, a Voigt model or a generalized Voigt model can be used as a model representing the complex elastic modulus. The displacement signal thus converted is considered to represent an incident wave among pulse waves generated by the blood flow ejection of the actual subject's heart. The reason is that in arteries, blood flows in almost one direction from the heart to the periphery of the artery. This is because it is considered that the displacement information obtained from the blood flow flowing in one direction approximates the displacement information of the incident wave component of the pulse wave generated from the heart like the blood flow. The incident wave is the first waveform having the largest amplitude intensity among the pulse waves, and this is called the first waveform.

Since the pulse wave (synthetic wave) including the incident wave and the reflected wave is detected by the first detection means, the first waveform (incident wave) is subtracted from the synthesized wave to obtain the second waveform (reflected wave). ) That is, the reflected wave is estimated from the difference between the combined wave and the incident wave. Since the incident wave and the synthesized wave are waveforms detected by different detection means, it is preferable to fit the first waveform to the first peak waveform of the synthesized wave before taking the difference. The degree of arteriosclerosis of the blood vessel is evaluated from a comparison of amplitude intensity (peak intensity) between the first waveform (incident wave) and the second waveform (reflected wave) estimated as described above. For example, the difference or ratio of the amplitude intensity between the reflected wave and the incident wave is obtained, and the degree of arteriosclerosis can be evaluated from this difference or ratio. In general, as arteriosclerosis progresses, the viscoelasticity of the blood vessels decreases and the amplitude intensity of the reflected wave tends to increase. Therefore, the degree of arteriosclerosis can be evaluated from the amplitude intensity ratio between the reflected wave and the incident wave. If the amplitude of the incident wave is standardized when fitting the incident wave, the amplitude of the reflected wave obtained after the fitting is a ratio to the amplitude of the incident wave. By comparing, the degree of arteriosclerosis can be easily evaluated.

Decomposition means for decomposing the second waveform into a plurality of developed waveforms by fitting with the fit function may be further included. As the fitting function, a known nonlinear fitting function such as an ExponentialonGaussian function, a Gauss function, a Voigt function, a Log-Normal function, a Lorentz function, or the like can be used depending on the waveform shape. By disassembling the second waveform estimated as a reflected wave into a plurality of waveforms, it is possible to grasp the arteriosclerosis degree information in more detail.

The first detection means may be anything as long as it can detect a pulse wave. For example, a piezoelectric transducer can be used. Piezoelectric transducers are small and inexpensive detectors compared to medical pulse wave sensors, and can detect pulse waves simply by making contact with the skin surface of a human body. Further, since the pulse pressure is not directly measured as in the conventional pulse wave meter, but the vibration (displacement information) of the pulse wave is directly measured, the pulse wave can be measured more easily and accurately. On the other hand, the second detection means is not limited to the ultrasonic diagnostic apparatus as long as it can measure the blood flow velocity.

Effects of preferred embodiments of the invention

As described above, according to the present invention, the pulse wave (synthetic wave) is detected by the first detection unit, and the incident wave (first waveform) is estimated from the blood flow velocity measured by the second detection unit. Since the reflected wave (second waveform) is obtained by subtracting the incident wave from the pulse wave detected by the first detection means, the incident wave and the reflected wave are not affected by the measurement variation as in the prior art. Can be accurately measured separately. By evaluating the blood vessel function from the amplitude intensity of the incident wave and the reflected wave separated in this way, the degree of arteriosclerosis due to individual differences can be accurately evaluated.

1 is a system diagram of a first embodiment of an arteriosclerosis evaluation apparatus according to the present invention. It is a schematic structure figure of an example of a piezoelectric transducer. It is an internal circuit diagram of the evaluation apparatus which concerns on this invention. It is a blood-flow velocity waveform figure in the carotid artery of the test subject in the 20s and the test subject in the 60s obtained by the ultrasonic diagnostic apparatus. FIG. 5 is an internal pressure waveform diagram of subjects in their 20s and subjects in their 60s obtained by converting the blood flow waveform in FIG. 4. FIG. 6 is a waveform diagram of a displacement signal (incident wave) on the skin surface obtained by converting the internal pressure waveform of FIG. 5 using a generalized Voigt model. It is a pulse-wave waveform diagram in a subject's carotid artery obtained by a pulse wave detector. It is a wave form diagram which shows the result of having isolate | separated the incident wave and the reflected wave from the pulse wave waveform shown in FIG.

Hereinafter, preferred embodiments of the present invention will be described based on examples.

-First Example-
FIG. 1 shows an example of an arteriosclerosis evaluation method according to the present invention. In this example, arteriosclerosis is evaluated by measuring the pulse wave and blood flow velocity of the cervical artery of a human body. While contacting the piezoelectric transducer 1 with the neck of the subject H and at the same time or before / after that, the subject for the superficial tissue probe (PLT-1204AT center frequency 12 MHz) 3 of the ultrasonic diagnostic apparatus (TOSHIBA Aplio SSA-700A) 2 Touch the same part of the neck of H. The ultrasonic diagnostic apparatus 2 obtains an image of blood flow waveform and blood flow velocity information of the subject H's artery by the Doppler function, and the image signal is sent to the arteriosclerosis diagnostic apparatus 4 through wiring. The piezoelectric transducer 1 is a kind of acoustic sensor that converts a pulse wave transmitted through an artery into a velocity signal. The piezoelectric transducer 1 is connected to the arteriosclerosis evaluation apparatus main body 4 via wiring. The arteriosclerosis evaluation apparatus main body 4 is provided with a display unit 4a for displaying the evaluation result. On the display unit 4a, the degree of arteriosclerosis of the subject is displayed by numerical values, symbols, graphs, and the like. The measurement location is not limited to the cervix, and may be any site such as a wrist, ankle, or thigh as long as the pulse wave and blood flow velocity of the same artery can be measured. An electrocardiograph output signal for measuring the electrical waveform of the heart beat can be connected to the arteriosclerosis evaluation apparatus body 4 to synchronize the pulse wave and blood flow velocity waveform with the heart beat.

FIG. 2 shows an example of the structure of the piezoelectric transducer 1. The transducer 1 has a piezoelectric unimorph structure, a bottom portion 11 of a bottomed cylindrical case 10 is configured as a vibration surface, and a piezoelectric ceramic element 12 is fixed to the inner surface of the bottom portion 11. The outer surface of the bottom 11 is brought into contact with the skin of the subject H. The opening of the case 10 is closed by a sealing material 13, and a lead wire 14 is drawn through the sealing material 13. Needless to say, the piezoelectric transducer 1 is not limited to the structure shown in FIG.

FIG. 3 shows an internal circuit configuration of the arteriosclerosis evaluation apparatus main body 4. The pulse wave (velocity signal) detected by the piezoelectric transducer 1 is amplified by the amplifier 40 and then input to the block 41. The input velocity signal is time integrated in block 41 and converted into a displacement signal. This displacement signal is a composite wave including an incident wave and a reflected wave in the pulse wave. A known medical pulse wave sensor may be used in place of the piezoelectric transducer 1.

On the other hand, the blood flow velocity waveform obtained by the ultrasonic diagnostic apparatus 2 is sent to the block 43 in the arteriosclerosis evaluation apparatus main body 4. In block 43, the blood flow velocity waveform is converted into an internal pressure waveform (temporal waveform of intravascular pressure). The conversion to the internal pressure waveform can be calculated from the continuous equation and equation of motion of a one-dimensional fluid model known from Non-Patent Document 1 and the like. Specifically, the time change of the blood vessel cross-sectional area is estimated from the blood flow velocity, and the time waveform of the internal pressure is estimated from the relationship between the time change of the blood vessel cross-sectional area and the intravascular pressure. Next, the temporal waveform of the intravascular pressure is sent to the block 44, and the temporal waveform of the intravascular pressure p is converted into a displacement signal ε on the skin surface using the generalized Voigt model shown in equations (1) and (2). The displacement signal ε thus converted is the displacement of the body surface estimated from the blood flow waveform, and is considered to represent the incident wave of the pulse wave generated by the blood flow ejection of the subject H's heart.

However, the shear elastic constant γ and shear viscosity coefficient η vary depending on the age of the subject, for example, γ for young people can be 5.6 kPa to 16.0 kPa, and γ for elderly people can be 14.0 kPa to 40.0 kPa. . In addition, η can be 230,000 Pa · s to 1,100 Pa · s for both young and elderly people. Note that the generalized Voigt model is used here as a model representing the complex elastic modulus for converting the intravascular pressure into a displacement signal on the skin surface, but a Voigt model or another model may be used.

The displacement signal obtained in block 41 and the displacement signal obtained in block 44 are sent to block 45 where the difference is calculated. That is, the reflected wave is calculated by subtracting the displacement signal (incident wave) in block 44 from the displacement signal (combined wave) in block 41. In block 46, the amplitude intensity of the incident wave and the reflected wave is compared. For example, the ratio between the peak intensity of the reflected wave and the peak intensity of the incident wave is calculated. When arteriosclerosis is advanced, the peak intensity of the reflected wave is considered to be relatively large, so that the peak ratio is also increased. The compared peak intensity is sent to block 47 where the degree of arteriosclerosis is evaluated or diagnosed.

-Experimental result-
Next, the results of evaluating two subjects A and B using this evaluation apparatus will be described. Here, subject A is a healthy male in his 20s and subject B is in his 60s. 4A and 4B are blood flow waveforms in the carotid arteries of the subject A and the subject B obtained by the ultrasonic diagnostic apparatus 2. FIG. 5A and 5B are internal pressure waveforms of the subject A and the subject B obtained by converting the blood flow waveform of FIG. 6A and 6B are skin surface displacement signals (incident waves) obtained by converting the internal pressure waveform of FIG. 5 using a generalized Voigt model. There is a slight difference in the rear part of the peak waveform of the incident wave between the subject A (20's) and the subject B (60's).

(A), (b) of FIG. 7 is a pulse wave waveform (the velocity signal is time-integrated and converted into a displacement) in the carotid arteries of the subject A and the subject B obtained by the piezoelectric transducer 1. It can be seen that the waveforms of both are greatly different. These pulse wave waveforms are combined waves of incident waves and reflected waves.

8A and 8B show the results of separating the reflected wave by subtracting the incident wave obtained in FIG. 6 from the pulse wave waveform shown in FIG. In separating the reflected wave, the incident wave was fitted to the first peak waveform of the pulse wave waveform. In the case of a pulse wave waveform in the 60s, the maximum peak is not the peak of the incident wave, so the fitting of the incident wave was performed at the inflection point starting from the rise of the waveform. In FIG. 8, after separating the pulse wave into an incident wave and a reflected wave, each waveform is normalized by setting the maximum amplitude of the incident wave to 1, so the amplitude intensity of the reflected wave is an amplitude intensity ratio with respect to the incident wave. If necessary, the separated reflected wave may be smoothed so that the peak can be easily obtained. In FIG. 8, the reflected wave before the smoothing process is represented by dots, and the reflected wave after the smoothing process is represented by a solid line.

As is clear from FIG. 8, in the case of the subject A in the 20s, the peak intensity (ratio) of the reflected wave is about 0.2 as shown in (a), whereas in the case of the subject B in the 60s, ( As shown in b), it can be seen that the peak intensity (ratio) of the reflected wave is as large as about 0.8. From this result, the timing at which the reflected wave arrives at the measurement site is almost the same, but the amplitude of the reflected wave is larger in the elderly than in the young, and a characteristic difference can be confirmed particularly in the amplitude of the late systole of the heart. It was. This is considered to be because the attenuation of reflected waves was less because the blood vessel walls of elderly people were generally harder. The degree of arteriosclerosis can be evaluated with higher accuracy by digitizing and statistically evaluating the amplitude intensity ratio of the reflected wave / incident wave.

In the above embodiment, both the first detection means and the second detection means are converted into displacement signals and compared, but it is also possible to make comparisons using speed signals. That is, when the first detection unit detects a pulse wave as a velocity signal, the velocity signal (incident wave) on the skin surface is estimated from the blood flow velocity waveform detected by the second detection unit, and the incident wave is converted into the pulse wave. The reflected wave may be separated by fitting to. In addition to evaluating the degree of arteriosclerosis based on the amplitude intensity ratio between the reflected wave and the incident wave, frequency analysis of the reflected wave and the incident wave is performed, and the degree of arteriosclerosis is evaluated by comparing the amplitude by applying frequency analysis. It is also possible. For example, the waveform of the reflected wave may be subjected to frequency analysis, and the amplitude of a specific frequency may be extracted and evaluated.

DESCRIPTION OF SYMBOLS 1 Piezoelectric transducer 2 Ultrasonic diagnostic apparatus 3 Probe 4 Arteriosclerosis evaluation apparatus main body 40 Amplification block 41 Integration block 43 Internal pressure conversion block 44 Displacement conversion block 45 Difference block 46 Amplitude intensity comparison block 47 Evaluation block

Claims

First detection means for detecting a pulse wave transmitted through an artery in one place of a living body;
Second detection means for measuring a blood flow velocity of the living artery;
First waveform specifying means for specifying a first waveform based on the blood flow velocity obtained by the second detection means;
Second waveform determining means for subtracting the first waveform from the pulse wave detected by the first detecting means to obtain a second waveform;
An arteriosclerosis evaluation apparatus comprising: evaluation means for evaluating the degree of arteriosclerosis from the amplitude intensity of the first waveform and the second waveform.
The first detection means detects the pulse wave as a displacement signal,
The first waveform specifying means converts the blood flow velocity obtained by the second detection means into a displacement signal, specifies an incident wave as a first waveform,
2. The arteriosclerosis evaluation according to claim 1, wherein the second waveform determination unit obtains a reflected wave as a second waveform by subtracting the incident wave from the displacement signal detected by the first detection unit. apparatus.
The first waveform specifying means includes first conversion means for converting the blood flow velocity into a time waveform of intravascular pressure, and second conversion for converting the converted time waveform of intravascular pressure into a displacement signal using a complex elastic modulus. The arteriosclerosis evaluation apparatus according to claim 2, further comprising: means.
The first conversion means estimates a time change of a blood vessel cross-sectional area from a blood flow velocity, and estimates a time waveform of the blood vessel internal pressure from a relationship between the time change of the blood vessel cross-sectional area and the blood pressure in the blood vessel. The arteriosclerosis evaluation apparatus according to 1.
The arteriosclerosis evaluation apparatus according to claim 3 or 4, wherein the model representing the complex elastic modulus in the second conversion means is a Voigt model or a generalized Voigt model.
The arteriosclerosis evaluation apparatus according to any one of claims 1 to 5, further comprising a decomposing unit that decomposes the second waveform into a plurality of developed waveforms by fitting with a fit function.
The arteriosclerosis evaluation apparatus according to claim 1, wherein the first detection unit includes a piezoelectric transducer that detects the pulse wave as a velocity signal.
The arteriosclerosis evaluation apparatus according to claim 7, wherein the first detection unit includes an integrator that time-integrates the detection output of the piezoelectric transducer.