A method for measuring arterial elasticity based on cuff pressure maintenance

Abstract

The present invention is a method for measuring arterial elasticity under a cuff pressure-maintaining state, comprising step 1: adjusting a linear deflation valve to keep the air pressure of the cuff stable; step 2: collecting pulse waves under the cuff pressure-maintaining state; step 3: using FIR high-pass and low-pass filters to filter the signal, with passbands of 0.05HZ and 30HZ respectively; step 4: screening the obtained pulse wave signal, and eliminating the waveform under the state of body misoperation according to the width and amplitude of the pulse wave; step 5: using a linear function to eliminate the baseline; step 6: normalizing a single pulse; step 7: finding the starting point of the reflected wave; step 8: calculating the intensity of the reflected wave; step 9: screening the calculation results of multiple pulse waves. The present invention reduces the baseline rebound in the initial stage of pressure maintenance by adjusting the linear deflation valve, so that the useful pulse wave signal is more complete, and the use of a single airbag not only solves the problem of inconvenient measurement, but also can better reflect the degree of arteriosclerosis of the human body by measuring the elastic coefficient of the artery.

Description

Technical Field

[0001] The invention belongs to the technical field of non-invasive detection of human arterial elasticity function, and in particular relates to a method for measuring arterial elasticity under a cuff-maintained pressure state. Background Art

[0002] Cardiovascular disease is a hidden and serious disease that seriously endangers human health, and most cardiovascular emergencies are often accompanied by arteriosclerosis in the early stages. According to statistics from the World Health Organization (WHO), in recent years, the number of people who die from cardiovascular disease each year has reached 20 million worldwide.

[0003] Arteriosclerosis in any part of the body may lead to ischemic function in the corresponding area. Arteriosclerosis is the pathophysiological basis of many cardiovascular diseases, such as coronary heart disease, stroke, hypertension, acute myocardial infarction, cerebral stroke, etc. At the same time, the early stage of arteriosclerosis is often accompanied by a decrease in the elasticity of the arterial blood cavity.

[0004] For a long time, the main means of clinically detecting arteriosclerosis has been arteriography. However, the equipment based on arteriography is an invasive operation, which is complicated to detect, expensive, and may cause discomfort to the person being tested. At present, the main means of non-invasively detecting arteriosclerosis is to measure the pulse wave velocity (PWV). This method calculates the conduction velocity of the pulse in the human body by measuring the time difference between the pulse of the upper arm and the lower limb. However, the distance from the upper limb and the lower limb to the heart is an empirical value, which is related to other physical differences such as personal height and weight, and the accuracy of the individual is difficult to guarantee.

[0005] In summary, the existing method of calculating the pulse by the time difference between the pulses of the upper arm and the lower limbs has the problem of poor accuracy due to limitations such as individual physical differences. Summary of the invention

[0006] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification summary and invention title of the present invention to avoid blurring the purpose of this section, specification summary and invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0007] Therefore, the purpose of the present invention is to provide a method for measuring arterial elasticity based on the cuff holding pressure state, which can solve the problem that the existing method of calculating the pulse by the time difference between the pulse of the upper arm and the lower limb is limited by factors such as individual physical differences and has poor accuracy. The present invention provides a method for measuring arterial elasticity based on the cuff holding pressure state, and the method for measuring arterial elasticity based on the cuff holding pressure state includes the following steps: Step 1: When the cuff pressure is close to 40 mmHg, the deflation speed of the programmable deflation valve is adjusted by software and the airbag is deflated slowly by coordinating with the PID algorithm control; Step 2: Completely close the deflation valve. The MCU samples the air pressure value every 5ms. The whole process lasts for 12 seconds. When the time is up, stop sampling and deflate. Step 3: Perform high-pass filtering on the original signal through the finite FIR digital filtering method to remove baseline drift, and then perform low-pass filtering on the original signal to remove high-frequency jitter; Step 4: Preliminary screening of the pulse signal under the cuff pressure holding state; Step 5: Find the starting point of each pulse wave, and then use function calculation to subtract the influence of baseline drift from the waveforms between adjacent starting points; Step 6: Perform signal normalization processing on each useful pulse wave; Step 7: Find the starting point of the reflected wave in each pulse wave; Step 8: Evaluate the intensity of the reflection of the pulse wave from the starting point of the reflection wave to the 200th point; Step 9: Filter all the pulse wave calculation results to obtain the arterial elasticity coefficient.

[0008] Optionally, the cut-off frequency for removing baseline drift in step 3 is 0.05 Hz, and the cut-off frequency for removing high-frequency jitter is 30 Hz.

[0009] Optionally, the function calculation of step 5 is a linear function y=kx+b to obtain k and b, and then all points between the two starting points are substituted into the function.

[0010] Optionally, the normalization process in step 6 is to normalize the peak height to 1, and adjust the sampling length of a single pulse to 200.

[0011] Optionally, the method for finding the starting point of the reflected wave in step 7 is as follows: starting from the wave crest, find the minimum point by taking the first-order derivative; if there is a minimum point, it is the starting point of the reflected wave; if there is no minimum point, take the derivative of the first-order derivative to obtain the second-order derivative; the first minimum point of the first-order derivative is the starting point of the reflected wave.

[0012] Optionally, the measurement method described in step 8 is as follows: connect the straight line between the starting point and the end point of the reflected wave, calculate the maximum and minimum values ​​of the pulse wave relative to the straight line, and the difference between the maximum and minimum values ​​is the fluctuation size of the pulse reflected wave; then divide the fluctuation size of the algorithm by a fixed constant K=10.

[0013] Optionally, the arterial elasticity coefficient in step 9 is the median of all pulse wave results.

[0014] In summary, the present invention includes at least one of the following beneficial effects: The present invention adopts a single air bag to solve the problem of inconvenient measurement, and at the same time can better reflect the degree of arteriosclerosis of the human body by measuring the elastic coefficient of the artery, so that the present invention has the characteristics of portability and reliability.

[0015] The present invention slowly deflates the airbag by adjusting the programmable deflation valve when the cuff pressure approaches 40 mmHg, with the aim of reducing the baseline rebound at the initial stage of pressure maintenance, thereby making the useful pulse wave signal more complete and ensuring the accuracy of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 It is a flow chart of calculating arterial elasticity coefficient based on a method for measuring arterial elasticity under a cuff pressure-maintaining state according to the present invention; Figure 2 It is a schematic diagram of the original pressure waveform of a method for measuring arterial elasticity based on the cuff-maintained pressure state of the present invention; Figure 3 A schematic diagram of the original pressure waveform of a method for measuring arterial elasticity based on the cuff holding pressure state of the present invention; Figure 4 A schematic diagram of a normalized waveform of a method for measuring arterial elasticity based on a cuff-maintained pressure state according to the present invention; Figure 5 A schematic diagram of a starting point of a reflected wave found by calculating the second-order derivative of a connection group of a method for measuring arterial elasticity under a cuff-maintained pressure state according to the present invention; Figure 6 This is a pulse fluctuation effect diagram of a method for measuring arterial elasticity based on the cuff holding pressure state of the present invention. DETAILED DESCRIPTION

[0018] The following is combined with Figure 1-6 The present invention is described in further detail.

[0019] Embodiment 1, refer to Figure 1-6In order to solve the problem of poor accuracy caused by factors such as individual physical differences in the existing method of calculating pulse by the time difference between the pulse of the upper arm and the lower limb, the present invention discloses a method for measuring arterial elasticity under the state of cuff holding pressure, including the following steps: Step 1: When the cuff pressure is close to 40 mmHg, the deflation speed of the programmable deflation valve is adjusted by software and the airbag is deflated slowly in conjunction with the PID algorithm control. This can reduce the elastic rise of the baseline air pressure at the moment the deflation valve is closed, thereby making the useful pulse wave signal more complete.

[0020] Step 2: Close the deflation valve completely. The MCU samples the air pressure value every 5ms. The whole process lasts for 12 seconds. After the time is up, the sampling stops and the air is deflated. The obtained air pressure waveform is as follows: Figure 2 The original pressure waveform.

[0021] Step 3: Use the finite FIR digital filtering method to perform high-pass filtering on the original signal to remove baseline drift, with a cutoff frequency of 0.05 Hz; then perform low-pass filtering on the original signal to remove high-frequency jitter, with a cutoff frequency of 30 Hz.

[0022] Step 4: Perform preliminary screening of the pulse signal when the cuff is in the pressure-maintaining state, mainly to eliminate pulse waves that are significantly affected by baseline drift, human body malfunction, arrhythmia and other factors.

[0023] Step 5: Find the starting point of each pulse wave, and then use the function y=kx+b to find k and b for the waveform between adjacent starting points. Then, bring all points between the two starting points into the function. This will completely eliminate the influence of baseline drift, and the resulting waveform is as follows: Figure 3 The original pressure waveform.

[0024] Step 6: Perform signal normalization processing on each useful pulse wave: the peak height is normalized to 1, and the sampling length of a single pulse is adjusted to 200, so that the peak value and number of sampling points of each single pulse are the same.

[0025] Step 7: Find the starting point of the reflected wave in each pulse wave. The method for finding the starting point of the reflected wave is as follows: starting from the peak, find the minimum point by taking the first-order derivative. If there is a minimum point, then this point is the starting point of the reflected wave. Figure 4 The starting point of the reflected wave of the normalized waveform is around the 76th point; if there is no minimum point, continue to derive the result of the first-order derivative to obtain the second-order derivative, so that the first minimum point of the first-order derivative can be found, and this point is the starting point of the reflected wave. Figure 5 The starting point of the reflected wave found by taking the second-order derivative is shown below.

[0026] Step 8: Evaluate the intensity of the pulse wave reflection from the starting point to the 200th point as follows: Connect the straight line between the starting point and the end point of the reflected wave, calculate the maximum and minimum values ​​of the pulse wave relative to the straight line, and the difference between the maximum and minimum values ​​is the fluctuation size of the pulse reflected wave. Then divide the fluctuation size of the algorithm by a fixed constant K = 10, indicating that the larger the fluctuation value, the smaller the calculation result and the better the elasticity, such as Figure 6 shown.

[0027] Step 9: Filter all the results obtained from the pulse wave calculations and select the median of all the pulse wave results to obtain the arterial elasticity coefficient.

[0028] Specific implementation principle: The pulse wave of the subject's upper arm is collected for 12 seconds while the cuff airbag is maintained at 40 mmHg. The ratio of the reflected wave to the main wave in a single pulse wave is calculated respectively, and then the calculated results of multiple pulse waves are sorted and screened to obtain the subject's arterial elasticity coefficient.

[0029] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made according to the structure, shape, principle, and method of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring arterial elasticity based on the cuff holding pressure state, characterized in that: The steps include: Step 1: When the cuff pressure is close to 40 mmHg, the deflation speed of the programmable deflation valve is adjusted by software and the airbag is deflated slowly by coordinating with the PID algorithm control; Step 2: Completely close the deflation valve, and the MCU samples the air pressure value every 5ms. The whole process lasts for 12 seconds. After the time is up, the sampling stops and the air is deflated. Step 3: Perform high-pass filtering on the original signal through the finite FIR digital filtering method to remove baseline drift, and then perform low-pass filtering on the original signal to remove high-frequency jitter; Step 4: Preliminary screening of the pulse signal under the cuff pressure holding state; Step 5: Find the starting point of each pulse wave, and then use function calculation to subtract the influence of baseline drift from the waveforms between adjacent starting points; Step 6: Perform signal normalization processing on each useful pulse wave; Step 7: Find the starting point of the reflected wave in each pulse wave; Step 8: Evaluate the intensity of the reflection of the pulse wave from the starting point of the reflection wave to the 200th point; Step 9: Filter all the pulse wave calculation results to obtain the arterial elasticity coefficient.

2. The method for measuring arterial elasticity based on the cuff holding pressure state according to claim 1, characterized in that: The cut-off frequency for removing baseline drift in step 3 is 0.05 Hz, and the cut-off frequency for removing high-frequency jitter is 30 Hz.

3. The method for measuring arterial elasticity based on the cuff holding pressure state according to claim 1, characterized in that: The function calculation of step 5 is a linear function y=kx+b to find k and b, and then all points between the two starting points are substituted into the function.

4. The method for measuring arterial elasticity based on the cuff holding pressure state according to claim 1, characterized in that: The normalization process in step 6 is to normalize the peak height to 1, and adjust the sampling length of a single pulse to 200.

5. The method for measuring arterial elasticity based on the cuff holding pressure state according to claim 1, characterized in that: The method for finding the starting point of the reflected wave in step 7 is as follows: starting from the wave crest, find the minimum point by taking the first-order derivative. If there is a minimum point, it is the starting point of the reflected wave. If there is no minimum point, take the derivative of the first-order derivative to get the second-order derivative. The first minimum point of the first-order derivative is the starting point of the reflected wave.

6. The method for measuring arterial elasticity based on the cuff holding pressure state according to claim 1, characterized in that: The measurement method described in step 8 is as follows: connect the straight line between the starting point and the end point of the reflected wave, calculate the maximum and minimum values ​​of the pulse wave relative to the straight line, and the difference between the maximum and minimum values ​​is the fluctuation size of the pulse reflected wave; then divide the fluctuation size of the algorithm by a fixed constant K = 10.

7. The method for measuring arterial elasticity based on the cuff holding pressure state according to claim 1, characterized in that: The arterial elasticity coefficient in step 9 is the median of all pulse wave results.

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