JP2008228934A - Artery wall hardness evaluation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately evaluate the vascular hardness easily anytime at home by anyone without requiring professional knowledge. <P>SOLUTION: The artery wall hardness evaluation system is composed of a cuff to be attached to a part of a living body; a cuff pressure sensor for sensing the pressure inside the cuff; a cuff pressure control part for the control to pressurize or depressurize the cuff based on the value detected by the cuff pressure sensor; and a data processing part for computing the amplitude of the cuff pressure pulse waves and blood pressure pulse waves based on the pulse waves detected by the cuff pressure sensor, and evaluating the hardness of the artery wall based on the computed pulse wave amplitude. The hardness of the artery wall is evaluated by a pressure/diameter characteristic curve, which is the relation between the cross sectional area of the blood vessel and the inner/outer pressure difference applied to the vascular wall, and is estimated from the waveform and amplitude of the pulse waves detected by the cuff. Further, the hardness of the vascular wall is evaluated with the function with which the pressure/diameter characteristic curve is differentiated from the detected pulse waves with regard to the inner/outer pressure difference, and by using an arctangent function or sigmoid function. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an arterial wall hardness evaluation system that can easily evaluate the state of arterial wall hardness in a general home without using a large-scale apparatus or a complicated system installed in a hospital or the like. .

  Conventionally, as a technique for evaluating the degree of vascular wall hardening, there are a technique for measuring a pulse wave propagation velocity, and a technique for measuring interference between a traveling wave of a pulse wave passing through a blood vessel and a reflected wave. It is necessary to use a large-scale device for the measurement by these techniques, and actually it is necessary to receive a medical examination as a test in a specialized facility such as a hospital. In addition, specialized knowledge is required to operate these devices.

  On the other hand, in the invention disclosed in Japanese Patent Laid-Open Nos. 5-38331 and 5-38332, an arteriosclerosis evaluation apparatus using a cuff is proposed. However, these inventions merely evaluate the degree of change in the height of the amplitude of the pulse wave detected from the cuff pressure.

JP-A-2004-223046 and JP-A-7-124129 propose an arteriosclerosis evaluation apparatus using a cuff. The present invention proposes a method that considers the relationship between the difference between the internal and external forces applied to the artery wall and the artery diameter. The relationship between the internal / external pressure difference of the blood vessel wall and the blood vessel diameter is directly derived using the amplitude and blood pressure of the pulse wave detected by the cuff. According to this method, it is necessary to assume a certain function in advance as the relationship between the internal / external pressure difference of the blood vessel wall and the blood vessel diameter, and thus the obtained result necessarily depends on the assumed function. For this reason, there is a problem that the basis for whether this estimation method is valid is poor.
Japanese Patent Laid-Open No. 5-38331 JP-A-5-38332 JP 2004-223046 A JP 7-124129 A

  When it is desired to evaluate the blood vessel hardness by the conventional method, it is necessary to visit a facility such as a hospital and pay the price for each measurement. In addition, time constraints are inevitably generated due to the necessity of meeting the schedule of the apparatus and facility. For this reason, it cannot be said that anyone can always evaluate their own vascular hardness.

  Further, the techniques disclosed in Patent Documents 1 and 2 do not perform measurement in consideration of the characteristics of the blood vessel wall, and cannot be said to accurately evaluate the hardness of the blood vessel wall. Further, in the technique disclosed in Patent Document 3, there is a theoretical question as a method for evaluating the hardness of the blood vessel wall as described above, and it is a great question as to whether the hardness of the blood vessel wall is accurately evaluated. There is.

  Therefore, the present invention can easily evaluate vascular hardness at any time without requiring specialized knowledge in a general household, and can more accurately evaluate vascular hardness compared to conventional similar techniques. The purpose is to obtain a hardness evaluation system.

  In order to solve the above problems, an arterial wall hardness evaluation system according to the present invention is based on a cuff attached to a part of a living body, a cuff pressure sensor for detecting a pressure inside the cuff, and a detection value of the cuff pressure sensor. Cuff pressure control means for pressurizing and depressurizing the cuff to a predetermined value, and calculating the amplitude of the cuff pressure pulse wave and the blood pressure pulse wave based on the pulse wave detected by the cuff pressure sensor, and based on the pulse wave amplitude, the arterial wall And data processing means for evaluating the hardness of the steel.

  Further, another arterial wall hardness evaluation system according to the present invention is a relationship between a blood vessel cross-sectional area and an internal / external pressure difference applied to the blood vessel wall in the arterial wall hardness evaluation system. This is done by estimating the pressure characteristic curve. The evaluation of the arterial wall hardness is performed by estimating the shape and amplitude of the pulse wave detected by the cuff. The evaluation of the stiffness of the artery wall is performed by estimating a function obtained by differentiating the pressure characteristic curve with respect to the internal / external pressure difference from the detected pulse wave. In addition, the pressure characteristic curve is estimated by numerically integrating the differentiated pressure characteristic curve to evaluate the hardness of the artery wall. Further, a function that optimally fits the evaluation of the stiffness of the arterial wall to the estimated pressure characteristic curve is identified and evaluated using the parameter value determined at this time. Further, an arctangent function or a sigmoid function is used as the function. In addition, by using the method as described above, the evaluation of the arterial wall hardness is made robust against sudden fluctuations such as body movements.

  The present invention can easily evaluate blood vessel hardness at any time without requiring specialized knowledge in a general household, and can evaluate blood vessel hardness more accurately than conventional similar techniques. .

  That is, according to the present invention, blood vessel hardness can be easily evaluated at home by simply pressurizing and depressurizing the cuff wound around the upper arm as in blood pressure measurement. Therefore, anyone can easily evaluate brachial artery hardness anywhere and anytime to prevent arteriosclerosis leading to heart disease, cerebrovascular disorder, etc., and can provide an important technique from a preventive medical viewpoint.

  As described above, the present invention provides a cuff for attaching a part of a living body to the problem of enabling anyone to easily and accurately evaluate vascular hardness at any time without requiring specialized knowledge in a general household. A cuff pressure sensor for detecting the pressure inside the cuff, cuff pressure control means for pressurizing and depressurizing the cuff to a predetermined value based on a detection value of the cuff pressure sensor, and a pulse wave detected by the cuff pressure sensor And a data processing means for calculating the amplitude of the cuff pressure pulse wave and the blood pressure pulse wave and evaluating the stiffness of the arterial wall based on the pulse wave amplitude.

  For example, as shown in FIG. 1, the diameter of the blood vessel is determined by the difference between the pressure from the inside of the blood vessel to the outside and the pressure applied from the outside (internal / external pressure difference) and the material characteristics of the blood vessel. Here, the internal / external pressure difference = internal pressure−external pressure is defined. When the negative internal / external pressure difference, that is, when the external pressure is higher than the internal pressure, the blood vessel diameter becomes small, and conversely, when the positive internal / external pressure difference is positive, the blood vessel is expanded. Therefore, since the blood vessel diameter is determined when the internal / external pressure difference is determined, the blood vessel diameter can be expressed as a function of the internal / external pressure difference.

  There is a limit to the maximum value that the blood vessel diameter can take. Therefore, when the diameter of the blood vessel is drawn as a function of the internal / external pressure difference, for example, a sigmoid function curve as shown in FIG. 2 is obtained. Hereinafter, this function curve is referred to as a “blood vessel diameter characteristic curve”.

  The characteristics of the vascular wall tissue are reflected in the pressure characteristic curve of the blood vessel as described above. For example, as shown in FIG. 3, the curve of the characteristic curve becomes gentle if the tissue constituting the blood vessel wall is hard, and the curve becomes sharp if the tissue is soft. Therefore, in the present invention, the stiffness of the blood vessel is evaluated by estimating the pressure characteristic curve of the blood vessel, which is a characteristic point of the present invention.

  Various methods can be considered to estimate this characteristic curve, but it can also be estimated appropriately by the following procedure. That is, the method described below uses a cuff for measurement in order to estimate the characteristic curve. Cuff measurement has been widely used in ordinary homes, and has the advantage of being simple and non-invasive and inexpensive.

  A functional block diagram of a simplified arterial wall hardness evaluation system according to the present invention using a cuff is shown in FIG. As shown in the figure, the control unit that controls the entire system includes a cuff pressure control unit, and generates a cuff pressure pressurization / depressurization control signal according to information from a pressure sensor as described later. Based on the setting of the cuff pressure control unit, a pump that feeds air for compressing the cuff is controlled, and pressure control of the cuff that is attached to a part of the living body and pressurizes and depressurizes is performed. The pulse wave transmitted to this cuff is detected by a pressure sensor. The cuff pressure control is performed by the pressure sensor as described above, and the processing as described later is performed based on the pulse wave detected by the pressure sensor to calculate the pulse wave amplitude, evaluate the hardness of the blood vessel wall, and the like. I am doing so.

  When actually evaluating the arterial wall hardness using this system, a cuff is first attached to a part of the human body such as the upper arm of the human body. Thereafter, the pump is driven to gradually increase the internal pressure of the cuff, and the internal pressure of the cuff is sequentially measured. The sampling frequency at this time is about 1000 Hz, for example. While detecting the actual pressure with a pressure sensor, air is injected into the cuff and pressurized to a level slightly above the human maximum blood pressure. The target pressure at this time is about 200 mHg.

  After reaching the target pressure, the air in the cuff is evacuated and depressurized at a constant speed. The speed of depressurization is a speed at which a sufficient number of pulsations can be recorded during analysis. In practice, a pressure reduction rate of about 3 mmHg / second is a standard. FIG. 5 shows time-series data of the cuff internal pressure recording such pressurization and decompression operations.

  In the following, it is assumed that the cuff is mainly tightened as the external pressure applied to the blood vessel wall. Therefore, hereinafter, the internal / external pressure difference applied to the blood vessel wall is regarded as the difference between the blood pressure and the cuff pressure. When a band pass filter is applied to the cuff internal pressure time-series data recorded as described above to extract a pulse wave component, for example, cuff pulse wave data as shown in FIG. 6 is obtained. Here, the pass frequency band is about 0.5 Hz to 10 Hz. Hereinafter, this is referred to as “cuff pressure pulse wave time series”. Further, for example, in the cuff pressure pulse wave time series as shown in FIG. 7, a section from the local minimum value to the next local minimum value is referred to as one cuff pressure pulse wave. Therefore, the cuff pressure pulse wave time series is a series of a plurality of cuff pressure pulse waves.

  A low-pass filter is applied to the cuff internal pressure time-series data recorded as described above, and for example, a cuff pressure baseline as shown in FIG. 8 is extracted. At this time, the cutoff frequency is 0.5 Hz. Hereinafter, this is referred to as “cuff pressure baseline time series”. In the present invention, the pressure characteristic curve of the blood vessel is estimated using the cuff pressure pulse wave recorded in the cuff decompression process among the pulse wave components extracted in this way.

  As shown in FIG. 9, the cuff pressure pulse wave reflects the blood vessel diameter. If the blood pressure rises when the external pressure is constant, the internal / external pressure difference applied to the blood vessel wall increases in the positive direction, the blood vessel diameter increases, and the blood vessel volume increases. At this time, since the outside of the cuff is covered with a material that is difficult to expand and contract, the increase in the blood vessel volume as described above causes a reduction in the cuff volume, and the cuff internal pressure increases. Conversely, a decrease in blood pressure leads to a decrease in blood vessel diameter and a decrease in cuff pressure.

  The size / shape of the cuff pressure pulse wave and the internal / external pressure difference as described above can be related via a pressure characteristic curve of a blood vessel as shown in FIG. 10, for example. At this time, under different external pressures, even pulse waves with the same blood pressure change are measured as cuff pressure pulse waves of different magnitudes. For example, in FIG. 10, the blood pressure pulse wave 1 generated when the external pressure is large is measured as the cuff pressure pulse wave 1. The blood pressure pulse wave 2 generated when the external pressure is small is measured as the cuff pressure pulse wave 2.

  Here, only the blood pressure pulse wave and the cuff pressure pulse wave are measurable quantities, and the internal / external pressure difference is also known. However, since the pressure characteristic curve of the blood vessel is unknown, the position of each cuff pressure pulse wave in the vertical axis direction cannot be determined in FIG. Therefore, it is not possible to directly estimate the pressure characteristic curve of the blood vessel from the blood pressure pulse wave and the cuff pressure pulse wave.

  Therefore, in the present invention, for example, as shown in FIG. 11, it is proposed to take the following procedure in order to estimate the radial characteristic curve of the blood vessel using the cuff pressure pulse wave. First, a curve obtained by differentiating the pressure characteristic curve of the blood vessel with respect to the internal / external pressure difference is estimated from the cuff pressure pulse wave. Hereinafter, this curve is referred to as a differential pressure characteristic curve. Next, the differential pressure-intensity characteristic curve is numerically integrated to estimate the blood vessel pressure-intensity characteristic curve.

  As a method for estimating the differential pressure characteristic curve as described above, the following two methods are conceivable.

Method 1:
First, the amplitude of the extracted cuff pressure pulse wave is obtained. For example, as shown in FIG. 12, the height from the start point (local minimum value) of the cuff pressure pulse wave to the maximum value point is used as the amplitude. The ratio between the amplitude and pulse pressure (= difference between systolic blood pressure and diastolic blood pressure) of a certain cuff pressure pulse wave is an estimated value of the average slope in a certain section of the vascular pressure characteristic curve.

  FIG. 13 shows an example at that time. A blood pressure pulse wave 1 generated when a certain internal / external pressure difference is applied to the blood vessel is measured as a cuff pressure pulse wave 1 reflecting a pressure-diameter characteristic curve of the blood vessel. A line segment 1 is formed on the pressure characteristic curve using the amplitude and pulse pressure of the cuff pressure pulse wave. The slope of the line segment 1 matches the average slope of the radial characteristic curve in the section in which the line segment 1 is configured. Hereinafter, this section is referred to as a pulse wave section for this pulse wave. The width of each pulse wave section corresponds to the pulse pressure. Similarly, the average inclination of the pressure characteristic curve in the pulse wave section of each pulse wave is obtained.

  FIG. 14 shows the line segment corresponding to the line segment 1 of FIG. 13 of each pulse wave, with the start points of the line segments aligned on the X axis. The differential value of the pressure-diameter characteristic curve at an arbitrary internal / external pressure difference PmmHg is defined as an average value of an average slope of all pulse wave sections including the internal / external pressure difference P.

  As an example, FIG. 15 shows a case where the differential value of the pressure characteristic curve when the internal / external pressure difference is PmmHg is obtained. Here, the pulse wave sections 1, 2, and 3 are pulse wave sections including the internal / external pressure difference P. The differential value of the pressure-diameter characteristic curve at the internal / external pressure difference P is obtained as the average value of the slopes of the line segments 1, 2, and 3. Using the above-described method, differential values of the vascular pressure-diameter characteristic curve with respect to various internal and external pressure difference values are obtained. As a result, a differential pressure characteristic curve is estimated.

Method 2:
For example, as shown in FIG. 16, a section from the local minimum value to the maximum value that is the starting point of the extracted cuff pressure pulse wave is considered. This section corresponds to the process from the diastolic blood pressure to the systolic blood pressure of the blood pressure pulse wave. As shown in FIG. 17, the curve 1 is configured using the corresponding sections of the blood pressure pulse wave 1 and the cuff pressure pulse wave 1. Curve 1 can be considered as an estimate of a portion of the vascular pressure characteristic curve. FIG. 18 shows the line segments of each pulse wave corresponding to the curve 1 in FIG. 17 with the start points of the curves aligned on the X axis.

  The differential value of the radial characteristic curve at an arbitrary internal / external pressure difference PmmHg is obtained by the following method. First, the slope in the vicinity of P of the curve constituted by all pulse wave sections including the internal / external pressure difference P is calculated. Next, the average value of these slopes is calculated. The average value of the slope is set as the differential value of the pressure characteristic curve at the internal / external pressure difference P. An example of obtaining a differential value of the pressure characteristic curve when the internal / external pressure difference is PmmHg is shown in FIG.

In this example, there are three pulse wave sections including the internal / external pressure difference P, and the curves formed in each pulse wave section are curves 1, 2, and 3. The slopes of the curves 1, 2, and 3 in the internal / external pressure difference P are slopes 1, 2, and 3, respectively. The differential value of the pressure characteristic curve in the internal / external pressure difference P is obtained as an average value of the gradients 1, 2, and 3. The differential value of the vascular pressure-diameter characteristic curve with respect to other values of the internal / external pressure difference is similarly obtained by the above method. As a result, a differential pressure characteristic curve is estimated.
After the differential pressure characteristic curve is obtained in this way, the numerical integration is calculated to obtain the pressure characteristic curve. The pressure characteristic curve of the blood vessel can be estimated by the above method.

  In order to evaluate the hardness of the blood vessel wall from the pressure characteristic curve of the blood vessel as described above, in the present invention, a function that best fits the estimated blood pressure characteristic curve of the blood vessel is determined and identified at this time. Evaluate using the value of the selected parameter. As the method, the following two methods can be considered. However, similarly, a method using various functions can be considered.

である。 Method 1:
An arc tangent function that best fits the obtained blood vessel pressure characteristic curve is obtained as shown in FIG. The formula used at this time is

It is.

  The degree of arteriosclerosis is evaluated using the value of the parameter identified by the fitting of this function. In that case, for example, when B is small, it can be determined that the blood vessel wall is hard, and when B is large, it is soft.

である。この関数のフィッティングにより同定されたパラメータの値を用いて動脈硬化度を評価する。その際には例えばＢが小さいと血管壁は硬く、大きいと柔らかいと判断することができる。 Method 2:
For example, a sigmoid function that best fits the obtained blood pressure characteristic curve is obtained as shown in FIG. The formula used at this time is

It is. The degree of arteriosclerosis is evaluated using the value of the parameter identified by the fitting of this function. In that case, for example, when B is small, it can be determined that the blood vessel wall is hard, and when B is large, it is soft.

  The arterial wall hardness evaluation method proposed in the present invention is stable and robust with respect to sudden fluctuations such as body movement for the following three reasons. That is, the first reason is to integrate a plurality of pieces of pulse wave information when estimating the differential pressure characteristic curve. As a second reason, numerical integration calculation of the differential pressure characteristic curve performed for estimating the pressure characteristic curve serves as a low-pass filter. Furthermore, as a third reason, the calculation of the function fitting to the pressure-diameter characteristic curve performed for evaluating the hardness of the blood vessel wall contributes to the removal of noise elements.

  As described above, according to the present invention, the arterial wall hardness can be easily evaluated by using a cuff that has been widely used in blood pressure measurement conventionally, as shown in FIG. .

It is a figure explaining the internal and external pressure difference of the blood vessel. It is a figure which shows the example of the pressure diameter characteristic curve of the blood vessel. It is a figure which shows the example which a pressure-diameter characteristic curve changes with the hardness of the blood vessel. It is a system configuration diagram of the present invention. It is a figure which shows the cuff pressure time series data example. It is a figure which shows the cuff pressure pulse wave after passing the band pass filter about the time series cuff pressure. It is a figure which shows one cuff pressure pulse wave area in a cuff pressure pulse wave time series. It is a figure which shows the cuff pressure after applying a low-pass filter to cuff internal pressure time series data. It is a figure which shows the state in which the cuff pressure pulse wave reflects the vascular system. It is a conceptual diagram of the relationship between a blood pressure pulse wave and a cuff pressure pulse wave. It is a figure which shows the aspect which estimates the radial diameter characteristic curve of the blood vessel using a cuff pressure pulse wave. It is a figure which shows a cuff pressure pulse wave amplitude. It is a figure which shows that the ratio of the amplitude of a cuff pressure pulse wave and pulse pressure becomes an estimated value of the average inclination in a certain section of a vascular pressure-diameter characteristic curve. It is a figure which shows the aspect at the time of calculating | requiring the average inclination of the pressure characteristic curve in the vascular tube of each pulse wave. It is a figure which shows that the differential value of the pressure-diameter characteristic curve in arbitrary internal / external pressure difference is represented as a mean value of the average inclination of all the pulse wave sections including the internal / external pressure difference. It is a figure which shows the area from the local minimum value used as the starting point of the extracted cuff pressure pulse wave to the maximum value. It is a figure which shows the aspect which comprises the curve 1 using the applicable area of a blood pressure pulse wave and a cuff pressure pulse wave. It is a figure which shows the example which displayed the line segment equivalent to the said curve 1 with the starting point of each curve aligned on the X-axis. It is a figure which shows the case where the differential value of the diameter characteristic curve when an internal-external pressure difference is PmmHg is calculated | required. It is an example of an arc tangent function that best fits the obtained vascular pressure characteristic curve. It is an example of a sigmoid arc tangent function that best fits the obtained blood vessel pressure characteristic curve. It is a figure which shows the state of implementation of this invention.

Claims (8)

A cuff attached to a part of the living body,
A cuff pressure sensor for detecting the pressure inside the cuff;
Cuff pressure control means for pressurizing and depressurizing the cuff to a predetermined value based on a detection value of the cuff pressure sensor;
It comprises data processing means for calculating the amplitude of the cuff pressure pulse wave and the blood pressure pulse wave based on the pulse wave detected by the cuff pressure sensor and evaluating the hardness of the arterial wall based on the pulse wave amplitude. Arterial wall hardness evaluation system.   2. The arterial wall hardness according to claim 1, wherein the evaluation of the arterial wall hardness is performed by estimating a radial characteristic curve that is a relationship between a blood vessel cross-sectional area and an internal / external pressure difference applied to the blood vessel wall. Evaluation system.   2. The arterial wall hardness evaluation system according to claim 1, wherein the evaluation of the arterial wall hardness is performed by estimating from the shape and amplitude of the pulse wave detected by the cuff.   2. The arterial wall hardness evaluation system according to claim 1, wherein the evaluation of the arterial wall hardness is performed by estimating a function obtained by differentiating the pressure characteristic curve with respect to the internal / external pressure difference from the detected pulse wave. .   5. The arterial wall hardness evaluation system according to claim 4, wherein the evaluation of the hardness of the arterial wall is performed by estimating the pressure-diameter characteristic curve by numerically integrating the differentiated pressure-diameter characteristic curve.   The evaluation of the hardness of the arterial wall is performed by identifying a function that optimally fits the estimated pressure-diameter characteristic curve and using a parameter value determined at this time. Arterial wall hardness evaluation system.   The arterial wall hardness evaluation system according to claim 6, wherein the function is an arctangent function or a sigmoid function.   The evaluation of the stiffness of the arterial wall is based on the fact that the evaluation of the stiffness of the arterial wall is made robust against sudden fluctuations such as body movements by using the methods of claims 4, 5 and 6. The arterial wall hardness evaluation system according to claim 7, wherein:

Images