Method and device for predicting blood pressure change by changing finger tip photoelectric signal

Abstract

The invention provides a method and a device for predicting blood pressure change by changing a finger tip photoelectric signal, and belongs to the technical field of medical information. The method for predicting the blood pressure change comprises the following steps: firstly, collecting waveforms of photoelectric signals from non-pressurization to pressurization of a fingertip, then obtaining average arterial pressure and systolic pressure in a fingertip artery according to key feature points of waveform change, and further predicting the average arterial pressure and systolic pressure of a brachial artery; wherein the conversion coefficient between the intravascular pressure values between the fingertip artery and the brachial artery of the organism is kept constant within a relatively long time range, so that the pressure change of the brachial artery of the organism can be predicted through the change of the pressure of the fingertip artery, and the change condition of the brachial artery of the organism, namely the standard blood pressure, is judged; meanwhile, during detection, the blood pressure can be measured only by putting the fingertip into the finger pressing device, and compared with a traditional upper arm cuff measuring method, the method is more convenient, and the measuring device is smaller and more exquisite and convenient to carry.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of medical information technology, and in particular to a method and device for predicting blood pressure changes by changing the photoplethysmogram signal of the fingertips. BACKGROUND

[0002] Human blood pressure refers to the pressure perpendicular to the arterial wall generated by the pulsating blood flow in the artery, wherein the peak value of the pressure is the systolic pressure, which is commonly referred to as high pressure, and the valley value of the pressure is the diastolic pressure, which is commonly referred to as low pressure. The arterial blood pressure of different parts of the human body is different, and the standard blood pressure of the human body in medicine is the blood pressure value of the brachial artery of the upper arm for standardization. Blood pressure is an important indicator of health monitoring. It can reflect the health status of the human body. In recent years, with the gradual attention to the prevention, diagnosis and treatment of cardiovascular and cerebrovascular diseases, blood pressure monitoring and management have become the close attention indicators of the middle-aged and elderly population, especially for hypertensive patients.

[0003] The photoplethysmogram signal is measured by an optical sensor (such as LED light) to measure the change in the intensity of the attenuated light reflected or projected through the human blood vessels and tissues, and to record the pulsatile state of the arterial vessels. By converting the optical signal into an electrical signal, the change in the absorption of light by the arterial pulsation is converted into a change in the electrical signal, and the obtained signal can reflect the characteristics of blood flow. This technology is also named as photoplethysmography.

[0004] Most of the electronic blood pressure meters on the market are designed based on the oscillometric method. The oscillometric method is based on the principle of arterial pulsation. By applying external pressure to block the pulsation of the brachial artery and gradually reducing the pressure to make the blood flow again, the pressure fluctuation synchronized with the arterial pulsation is obtained and recorded. The blood pressure is calculated according to the amplitude of the pressure fluctuation. The oscillometric method brings obvious discomfort to the measurer during measurement. Moreover, the measurement equipment is relatively large and inconvenient to carry. The measured population needs to roll up their sleeves during testing, and the measurement process is complex. Meanwhile, there is an artery in the fingertips of the human body, and the compliance of the fingertip artery does not change significantly over a long period of time. In addition, the internal pressure of the fingertip artery is greater than the retraction tension of the fingertip tissue itself in order to maintain normal blood flow. Therefore, the pressure value applied externally can reflect the state of the fingertip artery lumen under pressure. However, the pulsation of the fingertip artery is relatively weak, and it is difficult to accurately measure the outward conduction pressure of the fingertip artery itself after being pressed. Therefore, the photoplethysmogram signal of the fingertip artery can be collected to achieve the prediction of blood pressure. SUMMARY

[0005] One technical problem to be solved by the present disclosure is how to accurately collect the pulsatile state of the fingertip artery after being pressed to achieve the prediction of blood pressure.

[0006] To solve the above technical problems, the present disclosure provides a method for predicting blood pressure changes by changing the photoplethysmography signal at the fingertip, which comprises:

[0007] Step one, place the fingertip into the finger pressing device without any pressure operation, and collect the amplitude value of the pulsation in the photoplethysmography signal waveform at this time, and take the average value of the amplitude value in unit time as the initial amplitude value;

[0008] Step two, the finger pressing device applies pressure to the fingertip according to the preset pressure, stops after reaching the preset pressure, and the photoplethysmography signal waveform after pressure can be obtained, the photoplethysmography signal waveform after pressure is collected and the characteristic points are extracted, and the mean arterial pressure and systolic pressure corresponding to the fingertip artery are measured according to the characteristic points;

[0009] Step three, the finger pressing device releases the preset pressure on the fingertip, so that the photoplethysmography signal waveform of the fingertip returns to the pulsation state without pressure, so as to prevent the fingertip from being in ischemic state caused by long-term pressure of the finger pressing device.

[0010] In a specific embodiment, the aforementioned method for predicting blood pressure changes by changing the photoplethysmography signal at the fingertip, wherein the method for measuring the mean arterial pressure and systolic pressure of the fingertip artery comprises: removing the baseline drift and high-frequency noise in the photoplethysmography signal waveform in steps one and two by band-pass filtering; collecting the filtered photoplethysmography signal waveform and obtaining the amplitude value of each pulsation; selecting the point with the maximum amplitude value as the first characteristic point, and the pressure value corresponding to the first characteristic point is the measured mean arterial pressure corresponding to the fingertip artery; selecting the point with an amplitude value of one third of the initial amplitude value as the second characteristic point, and the pressure value corresponding to the second characteristic point is the measured systolic pressure corresponding to the fingertip artery; and obtaining the diastolic pressure according to the conversion formula of the mean arterial pressure and the systolic pressure.

[0011] The second aspect of the present application provides a blood pressure prediction device based on changing the photoplethysmography signal at the fingertip, comprising: a finger clamp cover, the finger clamp cover comprising an automatic pressure device, an upper finger clamp and a lower finger clamp, the upper finger clamp and the lower finger clamp forming a half-open shape to receive the fingertip, and the automatic pressure device being connected with the upper finger clamp and the lower finger clamp to drive the upper finger clamp and the lower finger clamp to pressurize the fingertip;

[0012] A laser emission tube is located inside the upper finger clamp to emit red light or infrared light;

[0013] A photoreceiver tube is located inside the lower finger clamp corresponding to the position of the laser emission tube to receive red light or infrared light;

[0014] A baroreceptor is located inside the lower finger clamp, and the baroreceptor is used to receive the size of the fingertip pressure value in real time;

[0015] The central processor is connected with the finger clamp, collects the pressure value and the photoelectric signal of the finger clamp, and uses the aforementioned finger pressure type blood pressure prediction method based on the change of the photoelectric signal to predict the blood pressure.

[0016] Through the technical scheme, the method for predicting blood pressure change based on the change of the photoelectric signal of the finger end provided by the application first collects the initial pulsation amplitude of the inserted finger tip by the finger pressure device and obtains the pulsation average value of the collected data as the standard for judging the mean arterial pressure and the systolic pressure later, then the finger pressure device pressurizes the finger tip until the preset pressure is reached and stops, collects the photoelectric signal waveform in the whole process, analyzes the photoelectric signal waveform in this stage, and the mean arterial pressure and the systolic pressure corresponding to the finger tip artery can be obtained, and meanwhile, the detection of the blood pressure can be performed only by inserting the finger tip into the finger pressure device, which is more convenient than the traditional sleeve method which needs to raise the sleeve, and the blood pressure collection from the finger tip will not cause discomfort of the measured people, in addition, the application realizes the prediction by the cooperation of the photoelectric signal, the pressure size and the blood pressure, and finally the mean arterial pressure and the systolic pressure are judged by observing the change of the photoelectric signal waveform, and the diastolic pressure can be calculated by the mean arterial pressure and the systolic pressure through the empirical formula. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, brief introductions will be given to the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative labor.

[0018] Figure 1 is a change relation diagram of the pressure value and the photoelectric value of a blood pressure prediction device based on the change of the photoelectric signal of the finger end disclosed by the embodiments of the present disclosure;

[0019] Figure 2 is a connection diagram of an implementation device of a blood pressure prediction device based on the change of the photoelectric signal of the finger end disclosed by the embodiments of the present disclosure;

[0020] Figure 3 is a perspective view of an implementation device of a blood pressure prediction device based on the change of the photoelectric signal of the finger end disclosed by the embodiments of the present disclosure.

[0021] Explanation of reference signs:

[0022] 1, automatic pressure device; 2, upper finger clamp; 3, lower finger clamp; 4, laser emitting tube; 5, photoelectric receiving tube; 6, pressure receptor; 7, central processor. DETAILED DESCRIPTION

[0023] The embodiments of the present disclosure will be further described in detail below with reference to the drawings and examples. The detailed description and drawings of the following examples are used to exemplarily illustrate the principles of the present disclosure, but cannot be used to limit the scope of the present disclosure, and the present disclosure can be implemented in many different forms, not limited to the specific examples disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0024] Embodiment one

[0025] Step one, put the fingertip into the finger pressing device without any pressure operation, and collect the amplitude value of the pulsatile waveform of the photoelectric signal at this time, and take the average value of the amplitude value in unit time as the initial amplitude value;

[0026] Step two, the finger pressing device applies pressure to the fingertip according to the preset pressure, stops after reaching the preset pressure, and finally obtains the photoelectric signal waveform after pressure, collects the photoelectric signal waveform after pressure and extracts the feature points, and measures the mean arterial pressure and systolic pressure corresponding to the fingertip artery according to the feature points;

[0027] Step three, the finger pressing device releases the preset pressure on the fingertip, so that the photoelectric signal waveform of the fingertip returns to the pulsatile state without pressure, to prevent ischemic necrosis of the fingertip caused by long-term pressure of the finger pressing device.

[0028] Specifically, in order to solve the existing problem of how to accurately collect the pulsation of the fingertip artery to achieve blood pressure prediction, while avoiding discomfort to the measured population and inconvenience of carrying the device, the detection method provided in the embodiment only collects the photoelectric signal waveform from no pressure operation to pressure to the predetermined pressure, extracts the feature points from the obtained photoelectric signal waveform to measure the mean arterial pressure and systolic pressure, and the finger pressing device only acts on the fingertip of the measured population. Therefore, the discomfort of the measured population during the measurement is small, and the device can be miniaturized for convenient carrying. According to the physiological structure of the human body, in order to maintain the flow of blood, the elasticity of the fingertip artery is greater than the retraction tension of other tissues of the fingertip. When external pressure is applied, the degree of compression of the fingertip artery can reflect the size of the external pressure, and the degree of compression of the fingertip artery can be detected by the change of the photoelectric signal. The blood pressure can be predicted by collecting the photoelectric signal waveform of the fingertip artery and combining the pressure received by the fingertip, and the final blood pressure prediction can be obtained by the conversion coefficient of the brachial artery.

[0029] When detecting, first put the fingertip of the measured population into the finger pressing device without pressure, and observe the pulsatile morphology of the photoelectric signal waveform without pressure. Usually, the photoelectric signal appears 3-5 times in the complete pulsatile wave, and the baseline and amplitude do not change obviously, which can be considered as completed collection. At this time, step one is completed (see Figure 1In the middle: step one of the unpressurized waveform), after filtering, the amplitude of each beat is calculated and averaged as the initial amplitude value. Then the finger pressure device starts to press from zero pressure value until the preset pressure value, at this time the photoelectric signal waveform will appear baseline constantly moving up and amplitude from small to large and then from large to small until disappear (see Figure 1 In the middle: step two of the pressurized waveform); at this time the pressure device stops pressing and returns to the unpressurized state, at this time the photoelectric signal waveform will appear baseline rapidly drop and return to the unpressurized beat state (see Figure 1 In the middle: step three of the recovery waveform). For the accuracy of measurement, step two generally needs 8-12 complete beat waveforms, which can be controlled by adjusting the pressurization time.

[0030] Specifically, the first fingertip of the index finger can be placed in the finger pressure device to collect the initial amplitude, and the finger pressure device does not apply pressure to the fingertip placed in the device. At this time, the photoelectric signal waveform can be observed to be normally pulsating, and the amplitude of each pulsating wave is stable, and the size of the wave crest and trough is basically the same without obvious changes. Then the central processing unit obtains the amplitude of each pulsating wave, and calculates the average value of 3-5 complete pulsating wave amplitudes as the initial amplitude value, which will be used as the basis for subsequent determination of systolic pressure. It can be understood that the initial amplitude value can indicate the initial expansion degree of the fingertip artery, which can be used as a standard for judging the change of pulsating amplitude caused by external pressure on the fingertip artery. Therefore, the initial amplitude value needs to be considered when determining the systolic pressure.

[0031] Secondly, the finger pressure device pressurizes the fingertip, and the photoelectric signal waveform baseline rises continuously with the continuous pressure. The photoelectric signal waveform baseline is usually defined as the connecting line of the trough points in adjacent pulsations. It can be understood that the pressure of the finger pressure device will squeeze the venous vessels and arterial vessels in the fingertip at the same time. Since the pressure in the venous vessels is lower than that in the arterial vessels, the venous vessel lumen is continuously squeezed and reduced until it is completely closed during the pressure increase, while the arterial vessel wall still maintains pulsation, but it lacks venous blood compared with normal pulsation. Therefore, the photoelectric signal waveform will continuously rise with time and pressure, and the baseline will move up.

[0032] In addition, since the flow in the arterial vessels includes pulsating flow and non-pulsating flow, as the pressure of the finger pressure device increases, when the pressurization pressure is greater than the diastolic pressure of the fingertip artery, the non-pulsating flow in the arterial vessels will resist the action of the arterial vessel's own elasticity. When the non-pulsating flow and pulsating flow in the arterial vessels resist the external pressure and the elasticity of the arterial vessels, the photoelectric signal waveform will appear baseline constantly moving up and pulsating amplitude gradually increasing. Therefore, when the amplitude value is maximum, the pressure value corresponding to the wave crest point in the corresponding wave band is the mean arterial pressure of the fingertip artery, which is the first characteristic point of the photoelectric signal.Figure 1 The position of the first feature point corresponds to the mean arterial pressure in the fingertip artery. Because the conversion coefficient between the fingertip artery and the brachial artery remains stable for a long time, the mean arterial pressure of the brachial artery of the measured population can be predicted based on this.

[0033] Then, as the pressure of the finger pressing device increases, the baseline of the photoelectric signal waveform continues to rise and the pulsation amplitude gradually decreases. It can be understood that, as the pressure exceeds the mean arterial pressure of the fingertip and approaches the systolic pressure, the pressure of the blood flow in the fingertip artery cannot resist the external pressure and the self-rebound pressure of the blood vessel, so the pulsation amplitude gradually decreases until the fingertip artery is completely closed and no blood flows, and therefore the photoelectric signal waveform does not have a pulsation waveform, which corresponds to the systolic pressure of the fingertip artery, that is, the second feature point of the photoelectric signal. Similarly, the measured systolic pressure can be converted by the pressure conversion coefficient to predict the systolic pressure of the brachial artery of the measured population.

[0034] In actual measurement, the photoelectric signal collected will be mixed with many interference signals due to the influence of the surrounding environment when the finger pressing device detects the fingertip. The baseline drift in the photoelectric signal waveform and the high-frequency noise in the photoelectric signal are removed by band-pass filtering to remove the interference signals and improve the quality of the photoelectric signal.

[0035] In actual measurement, the systolic pressure is the maximum pressure of the arterial blood flow on the blood vessel wall. In theory, when the external pressure is equal to the systolic pressure of the fingertip artery, the fingertip artery will have no blood flow, and the photoelectric signal waveform will not have a pulsation amplitude signal. However, in actual testing, it is found that the interference from the external environment light and electromagnetic is difficult to completely filter out, and therefore the normal pulsation amplitude of the arterial blood vessel under the condition of no pressure on the fingertip, that is, the initial amplitude value, is selected as the basis for judgment, and the pressure value corresponding to the point where the amplitude decreases from the maximum to one-third of the initial amplitude value is selected as the systolic pressure for offsetting the external interference in actual application.

[0036] The relationship between the mean arterial pressure, the diastolic pressure and the systolic pressure is:

[0037] Mean arterial pressure = diastolic pressure + 1 / 3(systolic pressure - diastolic pressure)

[0038] Therefore, the diastolic pressure can be calculated from the mean arterial pressure and the systolic pressure obtained from the photoelectric signal.

[0039] Specifically, in order to ensure the accuracy and precision of the measurement, preferably, the second detection and the third repeated detection are carried out, and three groups of corresponding values of mean arterial pressure, systolic pressure and diastolic pressure are collected respectively for comparison and averaging. The blood pressure measurement by the method is compared with the blood pressure measurement by the traditional cuff. The detection method is correlated with the blood pressure value of the traditional cuff, and the pearson correlation coefficient can reach 0.962. The detection method is convenient, and only needs to put the fingertips of the measured person into the finger pressure device to obtain the final diastolic pressure and systolic pressure values of the measured person.

[0040] In another aspect, the application also provides a finger pressure type blood pressure prediction device based on changing PPG signal, comprising: a finger sleeve, a laser emitting tube 4, a photoelectric receiving tube 5, a pressure receptor 6, a collection processor 7. It can be understood that when testing, the measured person puts any fingertip into the inside of the finger sleeve. The finger sleeve comprises an automatic pressure device 1, an upper finger clamp 2 and a lower finger clamp 3. The automatic pressure device 1 is built-in motor which can drive the upper finger clamp 2 to rotate, cooperating with the lower finger clamp 3 to clamp the fingertip. The upper finger clamp 2 and the lower finger clamp 3 form a half-open shape. At the same time, the laser emitter 4 is located in the inside of the upper finger clamp 2, and the photoelectric receiver 5 is located in the inside of the lower finger clamp 3. Specifically, the laser emitting tube 4 can emit red light or infrared light. The red light or infrared light can transmit the photoelectric signal to the photoelectric receiving tube 5 through the skin tissue and the arterial blood. The combination of the laser emitting tube 4 and the photoelectric receiving tube 5 can be but not limited to Matsushita PSV-SR25. Finally, the photoelectric receiving tube 5 transmits the collected real-time information to the inside of the collection processor 7. The collection processor 7 can amplify, filter and digitize the collected information to obtain the photoelectric signal waveform, and pre-process the photoelectric signal waveform. At the same time, the specific numerical value of each wave crest value, wave trough value and peak valley difference of the photoelectric signal waveform is displayed separately. Therefore, the data can be quickly obtained for comparison, saving the time of obtaining mean arterial pressure and systolic pressure. At the same time, the lower finger clamp 3 also has a pressure receptor 6. The pressure receptor 6 is used for real-time monitoring of the actual pressure received by the fingertip. The pressure receptor 6 can transmit the actual pressure received by the fingertip to the collection processor 7 through the conversion coefficient to obtain the predicted blood pressure. Combined with the collected photoelectric signal waveform, the photoelectric signal-predicted pressure-time curve can be obtained. Through the curve, the mean arterial pressure and systolic pressure can be obtained by using the python language to write code, and finally the rapid prediction of the brachial blood pressure is completed.

Claims

1. A method for predicting blood pressure changes based on changing finger tip photoelectric signals, characterized by, It comprises: Step 1: Put the fingertip into the finger pressing device without any pressure operation, collect the amplitude value of the pulsating waveform of the photoelectric signal at this time, and take the average value of the amplitude value in unit time as the initial amplitude value; Step 2: The finger pressing device applies pressure to the fingertip according to the preset pressure, stops after reaching the preset pressure, and obtains the photoelectric signal waveform during the pressure process. Collect the photoelectric signal waveform and extract the characteristic points. According to the characteristic points and combined with the pressure value of the pressure, the average arterial pressure and systolic pressure corresponding to the fingertip artery are obtained; Step 3: The finger pressing device releases the preset pressure on the fingertip, so that the photoelectric signal waveform of the fingertip returns to the pulsating state without pressure, preventing the fingertip from being ischemic due to the pressure of the finger pressing device.

2. The method for predicting blood pressure changes by changing the photoelectric signal of the fingertip according to claim 1, wherein The method for measuring the average arterial pressure and systolic pressure of the fingertip artery comprises: removing the baseline drift and high-frequency noise in the photoelectric signal waveform in steps 1 and 2 by band-pass filtering method; collecting the filtered photoelectric signal waveform and obtaining the amplitude value of each pulsation; selecting the point with the maximum amplitude value as the first characteristic point, and the pressure value corresponding to the first characteristic point is the measured average arterial pressure of the fingertip artery; selecting the point with an amplitude value of one-third of the initial amplitude value as the second characteristic point, and the pressure value corresponding to the second characteristic point is the measured systolic pressure of the fingertip artery; and calculating the diastolic pressure according to the conversion formula of the average arterial pressure and the systolic pressure.

3. A blood pressure prediction device based on changing the finger photoplethysmographic signal, characterized by, It comprises: A finger clamp cover, the finger clamp cover comprises an automatic pressure device (1), an upper finger clamp (2) and a lower finger clamp (3), the upper finger clamp (2) and the lower finger clamp (3) form a half-open shape to receive the fingertip, the automatic pressure device (1) is connected with the upper finger clamp (2) and the lower finger clamp (3) to drive the upper finger clamp (2) or the lower finger clamp (3) to pressurize the fingertip; A laser emitting tube (4) is located inside the upper finger clamp (2) to emit red light or infrared light; A photoelectric receiving tube (5) is located inside the lower finger clamp (3) corresponding to the position of the laser emitting tube (4) to receive red light or infrared light; A pressure receptor (6) is located inside the lower finger clamp (3), and the pressure receptor (6) is used to receive the size of the fingertip pressure value in real time; A central processing unit (7) is connected with the finger clamp cover, the collection processor is used to collect the finger clamp pressure value and the photoelectric signal, and the blood pressure is predicted by the method for predicting blood pressure changes by changing the photoelectric signal of the fingertip according to claim 1 or 2.

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