Systolic Blood Pressure Measuring Device and Method Based on Real-Time Pulse Wave Signal

Abstract

The present invention relates to the field of medical electronic information technology of electronic sphygmomanometers, and particularly to a systolic blood pressure measuring device and method based on real-time pulse wave signals. The systolic blood pressure measuring device based on real-time pulse wave signals of the present invention comprises: a data acquisition and processing center and a measuring accessory. The data acquisition and processing center mainly consists of a main control MCU, a high-precision AD acquisition module, a pressure sensor, an air pump, a linear valve, and a display module; the measuring accessory includes: one cuff and one pulse wave sensor. The device and corresponding method of the present invention can achieve personalized measurement, real-time measurement, and improved measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the medical electronic information technology field of electronic sphygmomanometers, and particularly relates to a systolic blood pressure measurement device and method based on real-time pulse wave signals. Background Art

[0002] Relevant investigation reports of the World Health Organization point out that cardiovascular and cerebrovascular diseases rank first among the world's leading causes of death. With the development of the domestic economic level, the prevalence of cardiovascular and cerebrovascular diseases among Chinese residents remains high, and hypertension and arteriosclerosis are common diseases. Blood pressure, as an indicator for detecting vital signs, can reflect cardiovascular function. Therefore, it is of great significance to realize daily blood pressure monitoring. Arterial blood pressure is divided into systolic pressure (SP) and diastolic pressure (DP). SP refers to the maximum value that the arterial blood pressure can reach during the ejection of the left ventricle in a cardiac cycle; DP refers to the minimum value that the arterial blood pressure drops at the end of diastole of the left ventricle.

[0003] Currently, blood pressure measurement mainly includes two categories: invasive methods and non-invasive methods. Invasive measurement methods involve inserting a pressure sensor into a human artery to directly and continuously detect the pressure inside the blood vessel. This method can obtain the real pressure inside the measured blood vessel and has high accuracy. However, due to the need for professional surgery, it is destructive to blood vessels, and there is also a risk of wound infection, so its application is not extensive. Non-invasive measurement methods are divided into intermittent measurement and continuous measurement.

[0004] Intermittent measurement methods include the auscultatory method of Korotkoff sounds and the oscillometric method. Both methods measure blood pressure values during the deflation process of an inflated cuff and can better reflect the measurement results. They are commonly used standards for clinical and scientific research references, but there is a poor consistency. Especially for the auscultatory method, its disadvantage is that there are many human influencing factors. Affected by factors such as experience and hearing of different operators, the measurement results may vary greatly. Continuous measurement methods mainly involve placing sensors at corresponding positions on the human body surface to measure the changes in surface physiological signals caused by blood pressure changes inside the blood vessels. Through specific mathematical derivation models, specific parameters are determined based on statistics to calculate the pressure value inside the blood vessel. Common methods include the arterial tonometry method, the volume compensation method, the pulse wave characteristic parameter measurement method, and the pulse wave velocity method, etc. However, these methods have deficiencies in terms of measurement accuracy, complexity of measurement equipment, and wearing comfort.

[0005] The currently widely used electronic sphygmomanometers adopt the continuous measurement method. By placing sensors at specific positions on the human body surface, the physiological signal changes on the body surface brought about by blood pressure changes in blood vessels are measured, and different physiological signals of the subject are analyzed to measure the systolic blood pressure. The physiological signals of different subjects are affected by multiple factors such as age, gender, height, and health status, but the influencing factors of each factor are still unknown. For some sphygmomanometers that measure systolic blood pressure based on pulse wave signals, most use the pulse wave signal at the radial artery to calculate the systolic blood pressure. However, there is a conduction time from the pulse wave at the brachial artery to the pulse wave at the radial artery. The pulse wave signal is affected by multiple factors of the subject's physiological characteristics, and the pulse wave signal acquisition process is easily affected by the measurement environment. There are many noise points and drifts in the pulse wave signal, resulting in the inability to better represent the differences in conduction time among different subjects. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: to improve the accuracy and reliability of SP test results, reduce the factors of human operation errors, and the influence of inaccurate individual characteristics caused by blood pressure calculation based on statistical models, and achieve accurate and personalized measurement of SP.

[0007] The systolic blood pressure measurement device based on real-time pulse wave signals of the present invention includes: a data acquisition and processing center and a measurement accessory. The data acquisition and processing center mainly consists of a main control MCU, a high-precision AD acquisition module, a pressure sensor, an air pump, a linear valve, and a display module; the measurement accessory includes: 1 cuff and 1 pulse wave sensor.

[0008] The cuff is used to apply pressure to the human blood vessels, the pulse sensor is used to collect the human pulse signal, the pressure sensor is used to convert the real-time pressure in the cuff into an electrical signal, the air pump is used to inflate the airbag in the cuff, the linear valve is used to linearly deflate the cuff, the high-precision AD acquisition module is used to collect the electrical signals of the pressure sensor and the pulse wave sensor, the main control MCU is used to control and detect the working states of each hardware component, including controlling the air pump to inflate, controlling the linear valve to deflate, and reading the digital quantity from the high-precision AD acquisition module in real time. At the same time, it is also responsible for real-time processing of the data collected by the hardware system, obtaining the final SP according to the characteristics of the data, and dynamically determining the test process to complete the test process.

[0009] The method for measuring systolic blood pressure using the measurement device of the present invention is as follows:

[0010] (1) System initialization: After the system is powered on, the initialization program is called to complete the routine detection of the system hardware and the setting of the normal working state. After shaking hands with the host computer, it enters the main program and waits for commands;

[0011] (2) Information entry: Enter the gender, age, height, and weight information of the subject;

[0012] The subject is in a sitting state, lying flat, or other standard body positions and states for blood pressure measurement. During the entire test process, the subject should maintain a stable body posture and even breathing, and avoid stimuli that may cause an unstable heartbeat.

[0013] (3) Fix the cuff and pulse wave sensor: Place the cuff flat on the brachial artery of the subject's upper arm, and fix the pulse wave sensor on the radial artery of the subject.

[0014] (4) Acquisition of pulse wave characteristic signals:

[0015] (4-1) After the system starts measuring, let the air pump continuously inflate and pressurize the cuff. The airbag in the cuff gradually expands and gradually compresses the subject's blood vessels. When the blood vessels are completely clamped and blood no longer flows from the upper arm artery to the radial artery, the pulse wave characteristic signal disappears at this time, as Figure 3 shown. At this time, the air pump stops inflating the cuff.

[0016] (4-2) Slowly deflate the airbag. As the air pressure in the cuff gradually decreases, the flow of a small amount of blood will generate a detectable pulse wave signal, thus forming the first detectable pulse wave characteristic signal, as Figure 4 shown. Collect and record this first pulse wave characteristic signal.

[0017] (5) Processing of pulse wave characteristic signals:

[0018] Collect the pulse wave signal and perform smoothing processing to obtain a stable pulse wave signal.

[0019] (5-1) Starting from the first sampling point, use the moving average method to calculate the average of each sampling point and the two adjacent sampling points on the left and right as the smoothed value of this point; at the same time, detect whether the sampling point is a mutation point, that is, calculate whether the difference between the values of two adjacent sampling points is greater than a given threshold. If it is greater than the set threshold, then this sampling point is a mutation point; use a cubic polynomial to perform fitting interpolation on the existing sampling points. Figure 5 is a schematic diagram of the pulse wave signal within one heartbeat cycle.

[0020] Since there is a propagation time difference for blood from the brachial artery to the radial artery, in order to accurately represent the SP at the brachial artery, the pulse wave conduction time from the brachial artery to the radial artery is calculated, and the number of sampling points N corresponding to this period of time is calculated using the sampling frequency. Move the first detectable pulse wave characteristic signal forward by N sampling points, and use the airbag pressure value corresponding at this time as the SP.

[0021] Among them, the calculation formula for the pulse wave conduction time PWTT from the brachial artery to the radial artery is:

[0022]

[0023] Among them, C is the pulse wave propagation velocity, and S is the pulse wave propagation distance.

[0024] The calculation formula for the pulse wave propagation velocity C is:

[0025]

[0026] Among them, h is the blood vessel wall thickness, D is the blood vessel inner diameter, E is the Young's elastic modulus of the blood vessel, ρ is the blood density, K is the Moens constant, and for the human aorta, the K value is 0.8.

[0027] (6) Calculate the heartbeat period: Take the first-order differential of the pulse wave signal. As Figure 6 shown, identify the wave peaks through the adaptive threshold method. This wave peak value is the starting point of a heartbeat period. Calculate the number of sampling points between two wave peaks, which is the heartbeat period.

[0028] (7) During the process of gradually reducing the pressure of the cuff, find the first detectable point after the pulse wave signal recovers, specifically as follows: Take its first-order differential. As Figure 6 shown, judge one by one whether the differential value of the previous sampling point of each sampling point is less than 0 and whether the differential value of the next sampling point is greater than 0. If this condition is met, then judge whether the signal values of the next 8 consecutive sampling points show an upward trend. If this condition is met, within the heartbeat period obtained in (6), repeat the above judgment to see if there is another sampling point that meets the above conditions. If there is, then this point is the first detectable point of the pulse wave signal sought, denoted as P, as Figure 4 shown.

[0029] (8) According to the "Chinese Adult Human Body Dimensions" table, use the age and height of the subject to find the corresponding upper arm length and forearm length and sum them up. The value is the pulse wave propagation distance S; use the pulse wave propagation velocity calculation formula to find the pulse wave propagation velocity C, substitute it into the pulse wave conduction time calculation formula to find the propagation time difference T from the brachial artery to the radial artery, use the sampling frequency (256HZ) to calculate the number of sampling points N corresponding to T, and find the (N)th previous pulse wave signal sampling point of the first detectable point P of the pulse wave signal, denoted as RealP, as Figure 7 shown.

[0030] (9) On the pressure waveform, find the pressure value corresponding to RealP, which is SP, as Figure 8 shown.

[0031] To verify the effectiveness of this measurement method, several subjects with diverse demographic information (age, height, weight, upper arm circumference, gender, etc.) were selected. Under the same measurement environment, according to the standard blood pressure measurement method, the systolic blood pressure of the subjects was measured using a binaural stethoscope and the method proposed in the present invention respectively.

[0032] According to relevant clinical guidelines, systolic blood pressure is significantly affected by age factors. Therefore, the subjects were grouped by age, and the standard deviation of the difference between the measured values of the method proposed in the present invention and the measured values of the binaural stethoscope was compared for each age group.

[0033] The basic information of the subjects aged 20 - 29 is shown in Figure 9 As shown, there are 10 male and 10 female subjects respectively, and the measurement results are as Figure 10 shown. Combining Figure 9 and Figure 10 , the standard deviation of the difference between the measurement method described in the present invention and the binaural stethoscope in the subjects aged 20 - 29 is 3.54. The basic information of the subjects aged 30 - 39 is shown in Figure 11 As shown, there are 10 male and 10 female subjects respectively, and the measurement results are as Figure 12 shown. Combining Figure 11 and Figure 12 , the standard deviation of the difference between the measurement method described in the present invention and the binaural stethoscope in the subjects aged 30 - 39 is 1.42. The basic information of the subjects aged 40 - 49 is shown in Figure 13 As shown, there are 10 male and 10 female subjects respectively, and the measurement results are as Figure 14 shown. Combining Figure 13 and Figure 14 , the standard deviation of the difference between the measurement method described in the present invention and the binaural stethoscope in the subjects aged 40 - 49 is 3.26. The basic information of the subjects aged 50 - 59 is shown in Figure 15 As shown, there are 10 male and 10 female subjects respectively, and the measurement results are as Figure 16 shown. Combining Figure 15 and Figure 16 , the standard deviation of the difference between the measurement method described in the present invention and the binaural stethoscope in the subjects aged 50 - 59 is 2.59. The basic information of the subjects aged 60 - 69 is shown in Figure 17 As shown, there are 10 male and 10 female subjects respectively, and the measurement results are as Figure 18 shown. Combining Figure 17 and Figure 18 , the standard deviation of the difference between the measurement method described in the present invention and the binaural stethoscope in the subjects aged 60 - 69 is 2.71.

[0034] The beneficial effects of the present invention compared with the prior art are:

[0035] (1) The device and corresponding method of the present invention can achieve personalized measurement. During the measurement process, the subject wears a cuff and a pulse wave sensor. The determination of the SP value is only related to the individual pulse wave waveform change, cuff pressure change and measurement time, without referring to the parameters of the general statistical model, and can fully reflect the influence of the physiological electrical signal characteristics of the subject on the SP.

[0036] (2) The device and corresponding method of the present invention can achieve real-time measurement. During the measurement process, the pressure change in the cuff and the change in the corresponding pulse wave characteristic signal are continuously collected in real time, and the SP of the tested individual is calculated synchronously.

[0037] (3) The device and corresponding method of the present invention improve the measurement accuracy. By signal processing, a stable pulse wave signal is collected, and the first detectable pulse wave signal is determined through multiple condition screening to ensure its accuracy; when determining the SP value, the pulse wave conduction time from the brachial artery to the radial artery is considered, and the SP measurement method is corrected to accurately reflect the SP value at the brachial artery; compared with the "gold standard" Korotkoff sound method for non-invasive blood pressure measurement internationally, it can accurately determine the time of the impact sound synchronized with the pulse after the blood flow reopens the blood vessel, avoiding the errors caused by the different hearing, reaction ability, proficiency, and technical level of the measurement personnel. Specifically, the present invention uses the age and height of the subject to find the corresponding arm length as the pulse wave propagation distance, calculates the pulse wave propagation speed at the same time, obtains the pulse wave conduction time from the brachial artery to the radial artery, and traces back the corresponding sampling points of this part from the first detectable pulse wave characteristic signal, correcting the calculation error of using the radial artery pulse wave to measure systolic blood pressure and strengthening the physiological characteristic differences among the tested individuals. Description of the Drawings

[0038] Figure 1 It is a schematic structural diagram of the data acquisition and processing center used in the present invention.

[0039] Figure 2 It is a schematic diagram of the radial artery pulse wave signal.

[0040] Figure 3 It is a schematic diagram of the disappearance of the radial artery pulse wave signal.

[0041] Figure 4 It is the first detectable pulse wave characteristic signal.

[0042] Figure 5 It is a schematic diagram of the pulse wave signal within one cardiac cycle.

[0043] Figure 6 It is a schematic diagram of the first-order differential of the pulse wave signal.

[0044] Figure 7 It is a schematic diagram of the Nth previous pulse wave signal sampling point RealP of the detectable point P of the first pulse wave signal.

[0045] Figure 8 It is the pressure value corresponding to RealP on the pressure waveform.

[0046] Figure 9Basic information of subjects aged 20 - 29.

[0047] Figure 10 Measurement results of subjects aged 20 - 29.

[0048] Figure 11 Basic information of subjects aged 30 - 39.

[0049] Figure 12 Measurement results of subjects aged 30 - 39.

[0050] Figure 13 Basic information of subjects aged 40 - 49.

[0051] Figure 14 Measurement results of subjects aged 40 - 49.

[0052] Figure 15 Basic information of subjects aged 50 - 59.

[0053] Figure 16 Measurement results of subjects aged 50 - 59.

[0054] Figure 17 Basic information of subjects aged 60 - 29.

[0055] Figure 18 Measurement results of subjects aged 60 - 29.

[0056] Wherein:

[0057] Point a represents the disappearance point of the pulse wave signal;

[0058] Point b represents the first detectable characteristic signal point of the pulse wave;

[0059] Point c represents N sampling points corrected forward considering the pulse transit time;

[0060] Point d represents the corrected position considering the pulse transit time;

[0061] Point e represents the corresponding position of the pressure curve considering the pulse transit time;

[0062] Point f represents the first detectable pulse wave signal;

[0063] g represents the position considering the pulse transit time;

[0064] h represents the corresponding position on the pressure curve;

[0065] k represents the detected corresponding pressure value. Detailed implementation manners

[0066] The systolic blood pressure measuring device based on real-time pulse wave signals of the present invention comprises: a data acquisition and processing center and a measuring accessory. The data acquisition and processing center mainly consists of a main control MCU, a high-precision AD acquisition module, a pressure sensor, an air pump, a linear valve, and a display module; the measuring accessory includes: 1 cuff and 1 pulse wave sensor.

[0067] The cuff is used to apply pressure to the human blood vessels, the pulse sensor is used to collect human pulse signals, the pressure sensor is used to convert the real-time pressure in the cuff into an electrical signal, the air pump is used to inflate the airbag in the cuff, the linear valve is used to linearly deflate the cuff, the high-precision AD acquisition module is used to collect the electrical signals of the pressure sensor and the pulse wave sensor, and the main control MCU is used to control and detect the working states of each hardware component, including controlling the air pump to inflate, controlling the linear valve to deflate, and reading digital quantities from the high-precision AD acquisition module in real time. At the same time, it is also responsible for real-time processing of the data collected by the hardware system, obtaining the final SP according to the characteristics of the data, and dynamically determining the test process to complete the test process.

[0068] The method for measuring systolic blood pressure using the measuring device of the present invention is as follows:

[0069] (1) System initialization: After the system is powered on, the initialization program is called to complete the routine detection of the system hardware and the setting of the normal working state. After shaking hands with the host computer, it enters the main program and waits for commands;

[0070] (2) Information entry: Enter the gender, age, height, and weight information of the subject;

[0071] The subject is in a sitting state, lying flat and other standard postures and states for blood pressure measurement. During the whole test process, the subject should keep the body posture stable and breathe evenly to avoid the stimulation causing unstable heartbeat;

[0072] (3) Fix the cuff and the pulse wave sensor: Fasten the cuff flatly on the brachial artery of the subject's upper arm, and fix the pulse wave sensor on the radial artery of the subject;

[0073] (4) Acquisition of pulse wave characteristic signals:

[0074] (4-1) After the system starts measuring, the air pump is commanded to continuously inflate and pressurize the cuff. The airbag in the cuff gradually expands and gradually flattens the subject's blood vessels. When the blood vessels are completely clamped and the blood no longer flows from the upper arm artery to the radial artery, the pulse wave characteristic signal disappears at this time, as Figure 3 shown, and at this time the air pump stops inflating the cuff.

[0075] (4-2) Slowly deflate the airbag. As the air pressure in the cuff gradually decreases, the flow of a small amount of blood will generate a detectable pulse wave signal, thereby forming the first detectable pulse wave characteristic signal, as Figure 4As shown, collect and record the first pulse wave characteristic signal.

[0076] (5) Processing of the pulse wave characteristic signal:

[0077] Collect the pulse wave signal and perform smoothing processing to obtain a stable pulse wave signal.

[0078] (5-1) Starting from the first sampling point, use the moving average method to calculate the average of each sampling point together with the two adjacent sampling points on the left and right as the smoothed value of this point; at the same time, detect whether the sampling point is a mutation point, that is, calculate whether the difference between the values of two adjacent sampling points is greater than a given threshold. If it is greater than the set threshold, then this sampling point is a mutation point; use a cubic polynomial to perform fitting interpolation on the existing sampling points. Figure 5 It is a schematic diagram of the pulse wave signal within one heartbeat cycle.

[0079] (6) Calculate the heartbeat cycle: Obtain the first-order differential of the pulse wave signal. As Figure 6 shown, identify the wave peaks through the adaptive threshold method. This wave peak value is the starting point of one heartbeat cycle. Calculate the number of samplings between two wave peaks, which is the heartbeat cycle.

[0080] (7) During the process of gradually reducing the pressure of the cuff, find the first detectable point after the pulse wave signal recovers, specifically as follows: Obtain its first-order differential. As Figure 6 shown, judge one by one whether the differential value of the previous sampling point of each sampling point is less than 0 and the differential value of the next sampling point is greater than 0. If this condition is met, then judge whether the signal values of the next 8 consecutive sampling points show an upward trend. If this condition is met, within the heartbeat cycle obtained in (6), repeat the above judgment to see if there is another sampling point that meets the above conditions. If there is, then this point is the first detectable point of the pulse wave signal sought, denoted as P, as Figure 4 shown.

[0081] (8) According to the "Chinese Adult Human Body Dimensions" table, use the age and height of the subject to find the corresponding upper arm length and forearm length and sum them. The value is the pulse wave propagation distance S; use the pulse wave propagation speed calculation formula to find the pulse wave propagation speed C, substitute it into the pulse wave conduction time calculation formula to find the propagation time difference T from the brachial artery to the radial artery, use the sampling frequency (256HZ) to calculate the number of sampling points N corresponding to T, and find the sampling point of the pulse wave signal that is the Nth before the first detectable point P of the pulse wave signal, denoted as RealP, as Figure 7 shown.

[0082] Due to the propagation time difference of blood from the brachial artery to the radial artery, in order to accurately represent the SP at the brachial artery, the pulse wave transit time from the brachial artery to the radial artery is calculated, and the number of sampling points N corresponding to this period is calculated using the sampling frequency. The first detectable pulse wave characteristic signal is moved forward by N sampling points, and the corresponding pressure value in the airbag at this time is used as the SP.

[0083] Among them, the calculation formula for the pulse wave transit time PWTT from the brachial artery to the radial artery is:

[0084]

[0085] Among them, C is the pulse wave propagation velocity, and S is the pulse wave propagation distance.

[0086] The calculation formula for the pulse wave propagation velocity C is:

[0087]

[0088] Among them, h is the blood vessel wall thickness, D is the blood vessel inner diameter, E is the Young's elastic modulus of the blood vessel, ρ is the blood density, and K is the Moens constant. For the human aorta, the K value is 0.8.

[0089] (9) On the pressure waveform, find the pressure value corresponding to RealP, which is the SP, as Figure 8 shown.

Claims

1. A systolic blood pressure measuring device based on real-time pulse wave characteristic signals, characterized in that The device includes: a data acquisition and processing center and a measurement accessory. The data acquisition and processing center mainly consists of a main control MCU, a high-precision AD acquisition module, a pressure sensor, an air pump, a linear valve, and a display module. The measurement accessory includes: 1 cuff and 1 pulse wave sensor. The cuff is used to apply pressure to the human blood vessel, the pulse wave sensor is used to collect the human pulse signal, the pressure sensor is used to convert the real-time pressure in the cuff into an electrical signal, the air pump is used to inflate the airbag in the cuff, the linear valve is used to linearly deflate the cuff, the high-precision AD acquisition module is used to collect the electrical signals of the pressure sensor and the pulse wave sensor, and the main control MCU is used to control and detect the working states of each hardware component, including controlling the air pump to inflate, controlling the linear valve to deflate, reading the digital quantity from the high-precision AD acquisition module in real time, and also responsible for real-time processing of the data collected by the hardware system, obtaining the final SP according to the characteristics of the data, and dynamically determining the test process to complete the test process; The steps for the measurement device to measure the systolic blood pressure are as follows: (1) System initialization: After the system is powered on, call the initialization program to complete the routine detection of the system hardware and the setting of the normal working state. After completing the handshake with the host computer, transfer to the main program and wait for commands; (2) Information entry: Enter the gender, age, height, and weight information of the subject. The subject is in the standard body position and state for blood pressure measurement. During the whole test process, the subject should keep the body posture stable and breathe evenly to avoid the stimulation causing unstable heartbeat; (3) Fix the cuff and the pulse wave sensor: Smoothly bind the cuff to the brachial artery of the subject's upper arm, and fix the pulse wave sensor to the radial artery of the subject; (4) Collection of pulse wave characteristic signals: (4-1) After the system starts to measure, let the air pump continuously inflate and pressurize the cuff. The airbag in the cuff gradually expands and gradually flattens the subject's blood vessel. When the blood vessel is completely clamped and the blood no longer flows from the upper arm artery to the radial artery, the pulse wave characteristic signal disappears at this time, and the air pump stops inflating the cuff; (4-2) Slowly deflate the airbag. As the air pressure in the cuff gradually decreases, the flow of a small amount of blood will generate a detectable pulse wave characteristic signal, thus forming the first detectable pulse wave characteristic signal. Collect and record this first pulse wave characteristic signal; (5) Processing of pulse wave characteristic signals: Collect the pulse wave characteristic signals and perform smoothing processing to obtain stable pulse wave characteristic signals; (5-1) Starting from the first sampling point, use the moving average method to calculate the average of each sampling point and the two adjacent sampling points on the left and right as the smoothed value of this point. At the same time, detect whether the sampling point is a mutation point, that is, calculate whether the difference between the values of two adjacent sampling points is greater than a given threshold. If it is greater than the set threshold, then this sampling point is a mutation point. Use a cubic polynomial to perform fitting interpolation on the existing sampling points; (6) Calculate the heart rate cycle: Take the first derivative of the pulse wave characteristic signal, and identify the wave peak through the adaptive threshold method. This wave peak value is the starting point of a heart rate cycle. Calculate the number of sampling points between two wave peaks, which is the heart rate cycle; (7) During the process of gradually reducing the pressure of the cuff, find the first detectable point after the pulse wave characteristic signal recovers, specifically as follows: Take its first derivative, and judge one by one whether the derivative value of the previous sampling point of each sampling point is less than 0 and whether the derivative value of the next sampling point is greater than 0. If this condition is met, then judge whether the signal values of the next 8 consecutive sampling points show an upward trend. If this condition is met, within the heartbeat period obtained in step (6), repeat the above judgment to see if there is another sampling point that meets the above conditions. If there is, then this point is the detectable point of the first pulse wave characteristic signal, denoted as P; (8) According to the "Chinese Adult Human Body Dimensions" table, use the age and height of the subject to find the corresponding upper arm length and forearm length and sum them up, and the value is the pulse wave propagation distance S; use the pulse wave propagation speed calculation formula to calculate the pulse wave propagation speed C, substitute it into the pulse wave conduction time calculation formula to calculate the propagation time difference T from the brachial artery to the radial artery, use the sampling frequency of 256HZ to calculate the number of sampling points N corresponding to T, and find the (N)th previous pulse wave characteristic signal sampling point of the first detectable point P of the pulse wave characteristic signal, denoted as RealP; Since there is a propagation time difference for blood from the brachial artery to the radial artery, in order to accurately represent the SP at the brachial artery, the pulse wave conduction time from the brachial artery to the radial artery is calculated, the number of sampling points N corresponding to this period of time is calculated using the sampling frequency, and the first detectable pulse wave characteristic signal is moved forward by N sampling points, and the corresponding airbag pressure value at this time is used as SP; Among them, the calculation formula for the pulse wave conduction time PWTT from the brachial artery to the radial artery is: Among them, C is the pulse wave propagation speed, and S is the pulse wave propagation distance; The calculation formula for the pulse wave propagation speed C is: ； Among them, h is the blood vessel wall thickness, D is the blood vessel inner diameter, E is the Young's elastic modulus of the blood vessel, ρ is the blood density, K is the Moens constant, and for the human aorta, the K value is 0.8; (9) On the pressure waveform, find the pressure value corresponding to RealP, which is SP.

2. The systolic blood pressure measuring device according to claim 1, wherein in the information entry step, the subject is in a sitting or lying position.

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