CN115500800B - Wearable physiological parameter detection system - Google Patents
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Abstract
The invention discloses a wearable physiological parameter detection system. Comprises a light emitting module: comprises two or more light emitting diodes, emits light with the wavelength of 400nm-1200nm, and sequentially emits light with different wavelengths to irradiate the skin surface of a human body according to a set time sequence; photoelectric sensing module: receiving light reflected or transmitted through skin, converting the light signal into a current signal, and generating a PPG signal; and a signal conditioning module: amplifying and converting the current signal into a voltage signal, removing high-frequency noise by a low-pass filter, and converting the voltage signal into a digital signal through analog/digital conversion to form a digital PPG signal; a pressure sensor; an IMU; a temperature sensor; a Bluetooth communication module; and a main controller. According to the invention, the IMU is used for measuring the gesture of the test part, the gesture change information is used for eliminating the influence of motion on the PPG signal, and the accuracy and reliability of physiological parameter measurement are improved by combining the characteristics of the wearable physiological parameter detection system.
Description
Technical Field
The invention relates to a physiological parameter detection system, in particular to a wearable physiological parameter detection system.
Background
With the increasing attention of human beings to self health conditions, physiological monitoring systems are becoming more and more sophisticated. For chronic disease patients, long-term accurate physiological parameter detection can effectively reduce disease risk, and provide effective data reference for treatment. The traditional physiological parameter detection equipment comprises simple medical and health care appliances for measuring heart rate, respiratory rate, blood pressure, blood oxygen saturation, body temperature and the like, provides a basis for measuring health conditions of the blood circulation system, the respiratory system and the like, and has wide application prospects in the aspects of home health care, telemedicine, clinical medicine and the like.
The technical development of medical detection instruments tends to be portable and networked, and the traditional physiological parameter detection instruments have the problems of single function, large volume and incapability of meeting the increasingly long-term real-time detection demands. With the continuous improvement of the integration and intelligence degree of the sensor technology, the integration of various sensors into one body for medical detection is possible under the condition of keeping the cost low. The existing wearable physiological parameter detection system is easily affected by factors such as human body movement, the fastening degree of the detection system and a test part, individual skin difference, ambient light interference and the like, so that the measurement accuracy is reduced.
In order to solve the defects of the existing detection system, the invention develops a wearable physiological parameter detection system, which can obviously improve the physiological parameter detection precision and has important practical value.
Disclosure of Invention
The invention aims to provide a wearable physiological parameter detection system, which is based on a multi-sensor system design and a physiological parameter measurement method, can improve the test precision of the wearable physiological parameter detection system under the condition of external interference, and solves the problem that the measurement precision of the existing wearable physiological parameter detection system is easily influenced by external factors.
The invention is realized by the following technical scheme:
A wearable physiological parameter detection system, comprising:
A light emitting module: comprises two or more light emitting diodes, emits light with the wavelength of 400nm-1200nm, and sequentially emits light with different wavelengths to irradiate the skin surface of a human body according to a set time sequence;
photoelectric sensing module: receiving light reflected or transmitted through skin, converting the light signal into a current signal, and generating a PPG signal;
and a signal conditioning module: amplifying and converting the current signal into a voltage signal, removing high-frequency noise by a low-pass filter, and converting the voltage signal into a digital signal through analog/digital conversion to form a digital PPG signal;
a pressure sensor: measuring the contact pressure between the physiological parameter detection system and the skin surface to generate a pressure signal;
IMU: the device comprises a triaxial accelerometer, a triaxial gyroscope and a triaxial magnetometer, wherein the triaxial accelerometer is used for measuring the motion state of a physiological parameter detection part;
temperature sensor: measuring body temperature;
bluetooth communication module: transmitting the measurement data to an upper computer;
And (3) a main controller: automatically setting working parameters of a light emitting module, a photoelectric sensing module, a signal conditioning module, a pressure sensor, an IMU and a temperature sensor, receiving PPG signals of the signal conditioning module, pressure signals of the pressure sensor, accelerometer, gyroscope and magnetometer data of the IMU and body temperature values of the temperature sensor, and calculating physiological parameters including heart rate, respiratory rate, blood pressure, blood oxygen saturation and body temperature.
Further, the cut-off frequency of the low-pass filter ranges from 5Hz to 100Hz, and the analog/digital signal conversion frequency ranges from 20Hz to 600Hz.
The two types of the geometric layouts of the light-emitting module and the photoelectric sensing module are arranged in the middle of the geometric layout, the photoelectric sensing module is used for receiving the reflected or transmitted light rays of the skin, the 4 types of the light-emitting modules are distributed around the photoelectric sensing module, the light-emitting modules emit light and extinguish according to a set time sequence, the change frequency range of the light-on and the light-off is 20Hz-600Hz, the structure is shown in the figure 2, and the photoelectric sensing module is arranged in the middle of the geometric layout, and is used for receiving the reflected or transmitted light rays of the skin. The 4 light-emitting modules are arranged around the photoelectric sensing module and emit light and extinguish according to set time sequence, and the frequency range of the change of the on and off is 20Hz-600Hz. The distance between the light emitting module and the photoelectric sensing module is different according to the selected test part, and after the test part is selected, the optimal distance is determined according to the signal waveform of the photoelectric sensing module; the other photoelectric sensing modules are 4, the number of the light emitting modules is 5, the 5 light emitting modules are distributed around the 4 photoelectric sensing modules, the 4 photoelectric sensing modules fully utilize the area of a test part, meanwhile, collect 4 groups of parallel PPG signals, reject the PPG signals interfered by external factors, calculate physiological parameter structures as shown in figure 3, and have 4 photoelectric sensing modules, and the other 5 light emitting modules are distributed around the photoelectric sensing modules. The weak current generated by the photoelectric sensing module is changed into a voltage signal with increased amplitude through a current/voltage amplifier, and the signal amplification factor is adjustable; the low-pass filter can effectively filter high-frequency noise, and the cut-off frequency range is 5Hz-100Hz; the analog/digital converter samples the voltage signal to finish acquisition of PPG digital signals; the PPG digital signal is transmitted to the main controller via the serial bus for calculating heart rate, respiratory rate, blood pressure and blood oxygen saturation.
The main controller is used for measuring physiological parameters and specifically comprises:
(1) Setting a luminous time sequence of the luminous module, and adjusting luminous power to ensure that the amplitude of the PPG signal is in an ideal interval;
(2) Setting a sampling time sequence of the signal conditioning module, and adjusting the amplification factor of the current/voltage amplifier and the cut-off frequency of the low-pass filter, so that PPG signals generated by light rays with different wavelengths can be sampled at the right moment, and an ideal PPG signal is obtained, so that physiological parameters are convenient to calculate;
(3) Acquiring a pressure sensor signal, judging whether the wearable physiological parameter detection system is in close contact with a test part, automatically identifying shaking and falling conditions of the physiological parameter detection system, and improving the reliability of physiological parameter measurement;
(4) Acquiring acceleration data, angular velocity data and magnetic field data output by the IMU, and estimating the real-time posture of the test part through a sensor fusion algorithm; in order to estimate the motion of the test site, the following mathematical model is first established:
（1）
in the formula (1), the components are as follows, For the posture quaternion of the test part, a is acceleration data g 0, gravity acceleration, m is magnetic field intensity data, m 0 is geomagnetic field reference, R (q) is a posture matrix of the test part, and the following equation is satisfied:
（2）
The mathematical model of the formula (2) is utilized to be combined with a Bayesian optimal estimation algorithm, so that the posture change of the test part can be estimated in real time; obvious posture change of the test part can lead to PPG signal fluctuation, and the physiological parameter test precision is indirectly affected; and removing the influence of the motion of the tested part on the PPG signal according to the calculated attitude change estimated value, recovering the signal waveform influenced by the motion into an ideal signal waveform, calculating the heart rate, the respiratory rate, the blood pressure and the blood oxygen saturation on the basis, and further ensuring the physiological parameter testing precision.
The main controller realizes the measurement and calculation process of heart rate, respiratory rate, blood pressure, blood oxygen saturation and body temperature, wherein the respiratory rate is detected by using PPG signals, and the steps are as follows:
signal pretreatment: removing low-frequency components of the PPG signal by using a digital high-pass filter, cutting the frequency range of the high-pass filter to 0Hz-0.3Hz, and removing a part of the PPG signal with the frequency higher than 40Hz by using the digital low-pass filter;
And (3) signal identification: identifying an effective part of the PPG signal, and removing the influence of test part jitter, ambient light interference and PPG signal saturation;
Feature extraction: extracting local maximum and minimum values of the PPG signal, and calculating typical characteristics of the PPG signal, wherein the typical characteristics comprise signal amplitude, period and waveform width corresponding to different amplitudes in one period;
respiratory rate calculation: and transforming the extracted PPG signal characteristics into a frequency domain, analyzing the peak value of the spectrum energy, and obtaining the corresponding frequency as the respiratory frequency.
The blood pressure detection is to analyze pulse wave velocity by using PPG signals to calculate blood pressure, and the steps are as follows:
signal pretreatment: removing low-frequency components of the PPG signal by using a digital high-pass filter, cutting the frequency range of the high-pass filter to 0Hz-0.3Hz, and removing a part of the PPG signal with the frequency higher than 40Hz by using the digital low-pass filter;
Signal quality analysis: combining the pressure sensor and IMU data, removing the influence of jitter, ambient light interference and PPG signal saturation of the test part, analyzing the waveform quality of each period of the PPG signal, and selecting an ideal PPG signal waveform for blood pressure measurement;
feature extraction: extracting two peak time intervals of the PPG signal in a period to obtain the propagation time of the reflected pulse wave; the blood pressure is calculated using the following formula:
（3）
（4）
Wherein RPTT in the formula (3) and the formula (4) are reflected pulse wave propagation time, SBP is systolic pressure, DBP is diastolic pressure, and K a、Kb and K c are parameters to be calibrated;
Parameter calibration: the wearable physiological parameter detection system and the standard sphygmomanometer simultaneously measure the blood pressure of the same test object, and record the measured reflected pulse wave propagation time and the corresponding standard blood pressure; calculating to obtain optimal parameters K a、Kb and K c by using the acquired data and a nonlinear optimization method;
real-time measurement: and calculating the real-time systolic pressure and diastolic pressure by utilizing the measured propagation time of the reflected pulse wave and combining the calibrated optimal parameters.
The invention has the advantages that:
(1) The invention adopts a wearable design, can measure heart rate, respiratory rate, blood pressure, blood oxygen saturation and body temperature in real time for a long time, improves the accuracy and reliability of physiological parameter measurement, and provides effective data reference for chronic disease diagnosis and treatment.
(2) The invention provides geometric layouts of two light emitting modules and photoelectric sensing modules, which are suitable for different test positions. And multiple paths of parallel PPG signals are collected, undisturbed PPG signals in the signals are selected to calculate physiological parameters, and measurement accuracy is improved.
(3) According to the invention, the pressure sensor is added in the system design, so that the shaking and falling conditions of the physiological parameter detection system are automatically identified, and the reliability of physiological parameter measurement is improved.
(4) According to the invention, the IMU is used for measuring the gesture of the test part, and the gesture change information is used for eliminating the influence of the motion on the PPG signal.
(5) The invention provides a stable and reliable respiratory frequency and blood pressure measuring method by combining the characteristics of a wearable physiological parameter detecting system.
Drawings
FIG. 1 is a block diagram of a wearable physiological parameter detection system;
FIG. 2 is a first geometric layout of a light emitting module and a photo-sensing module;
fig. 3 is a second geometric layout of the light emitting module and the photo-sensing module.
Detailed Description
The invention is described in further detail below with reference to the drawings and examples.
Example 1
The invention relates to a design method of a wearable physiological parameter detection system, which can accurately measure heart rate, respiratory rate, blood pressure, blood oxygen saturation and body temperature. The invention is suitable for obtaining physiological parameters by a reflection type or transmission type measuring method, and can be applied to different testing positions such as fingers, wrists and the like by setting proper sensor and algorithm parameters, wherein the system comprises a light-emitting module, a photoelectric sensing module, a signal conditioning module, a pressure sensor, an IMU, a temperature sensor, a Bluetooth communication module and a main controller, and the system is shown in figure 1. In the invention, the signal conditioning module, the pressure sensor, the IMU, the temperature sensor and the Bluetooth communication module are connected with the main controller through a serial bus, and the physiological parameter detection system exchanges data with the upper computer through Bluetooth wireless communication. The calculation of heart rate, respiratory rate, blood pressure, blood oxygen saturation and body temperature is completed by the main controller, and the upper computer software provides a good man-machine interaction interface to display the measurement result. The system of the invention comprises the following components:
a light emitting module: comprises a plurality of light emitting diodes, can emit light rays with different spectral ranges and has the wavelength ranging from 400nm to 1200nm. The light-emitting module sequentially emits light rays with different wavelengths to irradiate the skin surface of a human body according to a set time sequence;
photoelectric sensing module: receiving light reflected or transmitted through skin, converting the light signal into a current signal, and generating a PPG signal;
and a signal conditioning module: the current signal is amplified and converted into a voltage signal, the low-pass filter removes high-frequency noise, and the voltage signal is converted into a digital signal through analog/digital conversion to form a digital PPG signal. The cut-off frequency of the low-pass filter ranges from 5Hz to 100Hz, and the conversion frequency of the analog/digital signal ranges from 20Hz to 600Hz;
a pressure sensor: measuring the contact pressure of the physiological parameter detection system with the skin surface;
IMU: the device comprises a triaxial accelerometer, a triaxial gyroscope and a triaxial magnetometer, wherein the triaxial accelerometer is used for measuring the motion state of a physiological parameter detection part;
temperature sensor: measuring body temperature;
bluetooth communication module: transmitting the measurement data to an upper computer;
And (3) a main controller: the system comprises a light emitting module, a photoelectric sensing module, a signal conditioning module, a pressure sensor, an IMU and a temperature sensor, wherein the working parameters of the light emitting module, the photoelectric sensing module, the signal conditioning module, the pressure sensor, the PPG signal of the signal conditioning module, the pressure signal of the pressure sensor, accelerometer, gyroscope and magnetometer data of the IMU and the body temperature value of the temperature sensor are automatically set, and the system is used for calculating various physiological parameters including heart rate, respiratory rate, blood pressure, blood oxygen saturation and body temperature.
The geometric layout of the light emitting module and the photoelectric sensing module is shown in fig. 2, the photoelectric sensing module is positioned in the middle of the geometric layout and receives the reflected or transmitted light of the skin, 4 light emitting modules are arranged around the photoelectric sensing module and emit light and extinguish according to a set time sequence, the change frequency range of the light and the extinguishment is 20Hz-600Hz, the distance between the light emitting module and the photoelectric sensing module is different according to the selected test position, and the optimal distance is determined according to the signal waveform of the photoelectric sensing module after the test position is selected.
Weak current generated by the photoelectric sensing module is changed into a voltage signal with increased amplitude through a current/voltage amplifier, and the signal amplification factor is adjustable. The low-pass filter can effectively filter high-frequency noise, and the cut-off frequency range is 5Hz-100Hz. The analog/digital converter samples the voltage signal to complete acquisition of the PPG digital signal. The PPG digital signal is transmitted to the main controller via the serial bus for calculating heart rate, respiratory rate, blood pressure and blood oxygen saturation.
The main functions of the invention are realized by the main controller, and the invention concretely comprises:
1. setting the luminous time sequence of the luminous module, and adjusting luminous power to ensure that the amplitude of the PPG signal is in an ideal interval.
2. The sampling time sequence of the signal conditioning module is set, and the amplification factor of the current/voltage amplifier and the cutoff frequency of the low-pass filter are adjusted, so that PPG signals generated by light rays with different wavelengths can be sampled at the right moment, and ideal PPG signals are obtained, so that physiological parameters are convenient to calculate.
3. And acquiring a signal of the pressure sensor, judging whether the wearable physiological parameter detection system is in close contact with the test part, automatically identifying shaking and falling conditions of the physiological parameter detection system, and improving the reliability of physiological parameter measurement.
4. And reading the data of the temperature sensor to obtain the body temperature measurement value.
5. And acquiring acceleration data, angular velocity data and magnetic field data output by the IMU, and estimating the real-time posture of the test part through a sensor fusion algorithm. In order to estimate the motion of the test site, the following mathematical model is first established:
()
in the formula (1), the components are as follows, For the posture quaternion of the test part, a is acceleration data g 0, gravity acceleration, m is magnetic field intensity data, m 0 is geomagnetic field reference, R (q) is a posture matrix of the test part, and the following equation is satisfied:
(2)
the invention eliminates the influence of the motion of the test part on the PPG signal according to the calculated estimated value of the posture change, restores the signal waveform influenced by the motion into an ideal signal waveform, calculates the heart rate, the respiratory rate, the blood pressure and the blood oxygen saturation on the basis, and then ensures the physiological parameter test precision.
6. The invention is capable of detecting a variety of physiological parameters including heart rate, respiratory rate, blood pressure, blood oxygen saturation and body temperature. All physiological parameter measurements and calculations are done at the master controller. Heart rate, respiratory rate, blood pressure and blood oxygen saturation are calculated using PPG signals.
(1) Heart rate detection
The PPG signal is a periodic signal that coincides with the heart beat frequency, so the heart rate can be obtained by measuring the period of the PPG signal. The PPG signal is easily affected by external factors, such as jitter of a test part, pressure change of a physiological parameter detection system in contact with skin, interference of ambient light, individual skin difference and the like, and it is necessary to design a stable and reliable heart rate calculation method. The filtering method combining the frequency domain information and the time domain information utilizes the frequency domain information to effectively filter the interference signals in the non-heart rate frequency range, utilizes the time domain information to remove the abrupt change influences such as shaking of the test part, and recovers the PPG signal waveform interfered by external factors into an ideal PPG signal waveform, thereby ensuring the heart rate measurement precision of the wearable physiological parameter detection system.
(2) Respiratory rate detection
The invention utilizes PPG signals to calculate respiratory rate, and provides a PPG signal characteristic extraction and respiratory rate measurement algorithm, which comprises the following steps:
Firstly, preprocessing a PPG signal, removing low-frequency components of the PPG signal by using a digital high-pass filter, cutting the low-frequency components of the PPG signal to a frequency range of 0Hz-0.3Hz by using the high-pass filter, and removing a part of the PPG signal with the frequency higher than 40Hz by using the digital low-pass filter;
Identifying an effective part of the PPG signal, and removing the influence of test part jitter, ambient light interference and PPG signal saturation;
Extracting local maximum and minimum values of the PPG signal, calculating typical characteristics of the PPG signal, including signal amplitude, period and waveform width corresponding to different amplitudes in one period, converting the extracted PPG signal characteristics into a frequency domain, analyzing peak values of spectrum energy, and obtaining the corresponding frequency as respiratory frequency.
(3) Blood oxygen saturation detection
The invention utilizes PPG signals generated by red light and infrared light to measure the blood oxygen saturation, and specifically comprises the following steps:
local maxima and minima of the PPG signal are extracted using PPG signal processing methods similar to respiratory rate detection.
The direct and alternating current components of the PPG signal are calculated from the local maxima and minima of the PPG signal.
The blood oxygen saturation was calculated using the following:
（5）
In formula (5), SPO 2 is blood oxygen saturation, AC red and DC red are AC components and DC components of the PPG signal generated by red light, AC red and DC red are AC components and DC components of the PPG signal generated by infrared light, and parameters a, b and c are parameters to be calibrated.
(4) Blood pressure detection
The present invention uses the PPG signal to analyze Pulse Wave Velocity (PWV) to calculate blood pressure. PWV is a function of blood density and volume, expressed as follows:
（6）
In the formula (6), p is the blood density, v is the blood volume, SBP is the systolic pressure, DBP is the diastolic pressure, Is a change in blood volume. Formula (8) may be expressed as
（7）
In the formula (7), RPTT is the propagation time of the reflected pulse wave, and K a is the parameter to be calibrated. RPTT is the time interval during which the pulse wave propagates through the aorta to reach the limb segment, and RPTT is obtained by measuring the two peak time intervals of the PPG signal in one cycle.
On the other hand, the mean blood pressure MBP can be expressed as
（8）
In the formula (8), K b and K c are parameters required to be calibrated.
Using formula (3) and formula (4):
（3）
（4）
therefore, through PPG signal extraction RPTT, calibration parameters K a、Kb and K c can be calculated to obtain the blood pressure.
Example 2
The geometric layout of the light emitting modules and the photoelectric sensing modules is shown in fig. 3, wherein 4 photoelectric sensing modules are arranged, and 5 light emitting modules are distributed around the photoelectric sensing modules. The design is suitable for the condition that the area of the test part is large, 4 photoelectric sensing modules fully utilize the area of the test part, collect 4 groups of parallel PPG signals at the same time, reject PPG signals interfered by external factors, select more ideal PPG signals to calculate physiological parameters, and further improve the accuracy and reliability of physiological parameter measurement.
The foregoing detailed description of the preferred embodiments has been presented for purposes of illustration and description, and it should be appreciated that the foregoing is merely exemplary of the invention and is not intended to limit the scope of the invention in any way. Any person skilled in the art will make any equivalent substitution or modification to the technical solution and the technical content proposed by the present invention without departing from the scope of the technical solution of the present invention, and all the changes belong to the content of the technical solution without departing from the scope of the present invention.
Claims (3)
1. A wearable physiological parameter detection system, comprising:
A light emitting module: comprises two or more light emitting diodes, emits light with the wavelength of 400nm-1200nm, and sequentially emits light with different wavelengths to irradiate the skin surface of a human body according to a set time sequence;
photoelectric sensing module: receiving light reflected or transmitted through skin, converting the light signal into a current signal, and generating a PPG signal;
and a signal conditioning module: amplifying and converting the current signal into a voltage signal, removing high-frequency noise by a low-pass filter, and converting the voltage signal into a digital signal through analog/digital conversion to form a digital PPG signal; the cut-off frequency of the low-pass filter ranges from 5Hz to 100Hz, and the conversion frequency of the analog/digital signal ranges from 20Hz to 600Hz;
a pressure sensor: measuring the contact pressure between the physiological parameter detection system and the skin surface to generate a pressure signal;
IMU: the device comprises a triaxial accelerometer, a triaxial gyroscope and a triaxial magnetometer, wherein the triaxial accelerometer is used for measuring the motion state of a physiological parameter detection part;
temperature sensor: measuring body temperature;
bluetooth communication module: transmitting the measurement data to an upper computer;
and (3) a main controller: automatically setting working parameters of a light emitting module, a photoelectric sensing module, a signal conditioning module, a pressure sensor, an IMU and a temperature sensor, receiving PPG signals of the signal conditioning module, pressure signals of the pressure sensor, accelerometer, gyroscope and magnetometer data of the IMU and body temperature values of the temperature sensor, and calculating physiological parameters including heart rate, respiratory rate, blood pressure, blood oxygen saturation and body temperature; the main controller is used for measuring physiological parameters and specifically comprises:
(1) Setting a luminous time sequence of the luminous module, and adjusting luminous power to ensure that the amplitude of the PPG signal is in an ideal interval;
(2) Setting a sampling time sequence of the signal conditioning module, and adjusting the amplification factor of the current/voltage amplifier and the cut-off frequency of the low-pass filter, so that PPG signals generated by light rays with different wavelengths can be sampled at the right moment, and an ideal PPG signal is obtained, so that physiological parameters are convenient to calculate;
(3) Acquiring a pressure sensor signal, judging whether the wearable physiological parameter detection system is in close contact with a test part, automatically identifying shaking and falling conditions of the physiological parameter detection system, and improving the reliability of physiological parameter measurement;
(4) Acquiring acceleration data, angular velocity data and magnetic field data output by the IMU, and estimating the real-time posture of the test part through a sensor fusion algorithm; in order to estimate the motion of the test site, the following mathematical model is first established:
（1）
Wherein in formula (1) For the posture quaternion of the test part, a is acceleration data, g 0 is gravitational acceleration, m is magnetic field strength data, m 0 is geomagnetic field reference, R (q) is a posture matrix of the test part, and the following equation is satisfied:
（2）
The mathematical model of the formula (2) is utilized to be combined with a Bayesian optimal estimation algorithm, so that the posture change of the test part can be calculated in real time; obvious posture change of the test part can lead to PPG signal fluctuation, and the physiological parameter test precision is indirectly affected; removing the influence of the motion of the tested part on the PPG signal according to the calculated attitude change estimated value, recovering the signal waveform influenced by the motion into an ideal signal waveform, calculating the heart rate, the respiratory rate, the blood pressure and the blood oxygen saturation on the basis, and further ensuring the physiological parameter testing precision;
The photoelectric sensing modules are positioned in the middle of the geometric layout, and are used for receiving reflected or transmitted light of skin, 4 photoelectric sensing modules are distributed around the photoelectric sensing modules, light is emitted and extinguished according to a set time sequence, the change frequency range of the light and the extinguishment is 20Hz-600Hz, 5 light emitting modules are distributed around the 4 photoelectric sensing modules, the 4 photoelectric sensing modules fully utilize the area of a test part, meanwhile, 4 groups of parallel PPG signals are collected, the PPG signals interfered by external factors are removed, and physiological parameters are calculated.
2. The wearable physiological parameter detection system of claim 1, wherein: the main controller realizes the measurement and calculation process of heart rate, respiratory rate, blood pressure, blood oxygen saturation and body temperature, wherein the respiratory rate is detected by using PPG signals, and the steps are as follows:
signal pretreatment: removing low-frequency components of the PPG signal by using a digital high-pass filter, cutting the frequency range of the high-pass filter to 0Hz-0.3Hz, and removing a part of the PPG signal with the frequency higher than 40Hz by using the digital low-pass filter;
And (3) signal identification: identifying an effective part of the PPG signal, and removing the influence of test part jitter, ambient light interference and PPG signal saturation;
Feature extraction: extracting local maximum and minimum values of the PPG signal, and calculating typical characteristics of the PPG signal, wherein the typical characteristics comprise signal amplitude, period and waveform width corresponding to different amplitudes in one period;
respiratory rate calculation: and transforming the extracted PPG signal characteristics into a frequency domain, analyzing the peak value of the spectrum energy, and obtaining the corresponding frequency as the respiratory frequency.
3. A wearable physiological parameter sensing system according to claim 2, wherein: the blood pressure detection is to analyze pulse wave velocity by using PPG signals to calculate blood pressure, and the steps are as follows:
signal pretreatment: removing low-frequency components of the PPG signal by using a digital high-pass filter, cutting the frequency range of the high-pass filter to 0Hz-0.3Hz, and removing a part of the PPG signal with the frequency higher than 40Hz by using the digital low-pass filter;
Signal quality analysis: combining the pressure sensor and IMU data, removing the influence of jitter, ambient light interference and PPG signal saturation of the test part, analyzing the waveform quality of each period of the PPG signal, and selecting an ideal PPG signal waveform for blood pressure measurement;
feature extraction: extracting two peak time intervals of the PPG signal in a period to obtain the propagation time of the reflected pulse wave; the blood pressure is calculated using the following formula:
（3）
（4）
wherein RPTT in the formula (3) and the formula (4) are reflected pulse wave propagation time, SBP is systolic pressure, DBP is diastolic pressure, and Ka, kb and Kc are parameters to be calibrated;
Parameter calibration: the wearable physiological parameter detection system and the standard sphygmomanometer simultaneously measure the blood pressure of the same test object, and record the measured reflected pulse wave propagation time and the corresponding standard blood pressure; calculating to obtain optimal parameters Ka, kb and Kc by using the acquired data and a nonlinear optimization method;
real-time measurement: and calculating the real-time systolic pressure and diastolic pressure by utilizing the measured propagation time of the reflected pulse wave and combining the calibrated optimal parameters.
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