CN115500800A - Wearable physiological parameter detection system - Google Patents
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- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/0205—Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
- A61B5/02055—Simultaneously evaluating both cardiovascular condition and temperature
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- A—HUMAN NECESSITIES
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- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
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- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
- A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
- A61B5/6802—Sensor mounted on worn items
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
- A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
- A61B5/6843—Monitoring or controlling sensor contact pressure
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7203—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal
- A61B5/7207—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal of noise induced by motion artifacts
- A61B5/721—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal of noise induced by motion artifacts using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
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- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7225—Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7235—Details of waveform analysis
- A61B5/725—Details of waveform analysis using specific filters therefor, e.g. Kalman or adaptive filters
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7235—Details of waveform analysis
- A61B5/7253—Details of waveform analysis characterised by using transforms
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K13/00—Thermometers specially adapted for specific purposes
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- A—HUMAN NECESSITIES
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- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
- A61B2562/02—Details of sensors specially adapted for in-vivo measurements
- A61B2562/0247—Pressure sensors
Abstract
The invention discloses a wearable physiological parameter detection system. The light-emitting module comprises: the LED comprises two or more than two LEDs, emits light with the wavelength of 400nm-1200nm, and sequentially emits light with different wavelengths according to a set time sequence to irradiate the surface of the skin of a human body; photoelectric sensing module: receiving light reflected or transmitted by skin, converting the light signal into a current signal, and generating a PPG signal; a signal conditioning module: amplifying the current signal and converting the current signal into a voltage signal, removing high-frequency noise by using 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. The invention utilizes the IMU to measure the posture of the tested part, utilizes the posture change information to eliminate the influence of motion on PPG signals, and combines the characteristics of the wearable physiological parameter detection system to improve the precision and the reliability of the physiological parameter measurement.
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 concern of human beings on the health condition of the human beings, physiological monitoring systems are becoming more and more perfect. 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 basis for measuring health conditions of a blood circulation system, a respiratory system and the like, and has wide application prospect in the aspects of home health care, remote medical treatment, clinical medicine and the like.
The technical development of medical detection instruments tends to be portable and networked, and the traditional physiological parameter detection instrument has the problems of single function, large volume and incapability of meeting the increasing long-term real-time detection requirement. With the increasing integration and intelligence degree of the sensor technology, under the condition of keeping low cost, the integration of various sensors into a whole is possible to be applied to medical detection. The existing wearable physiological parameter detection system is easily influenced 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 precision is reduced.
In order to overcome the defects of the conventional detection system, the wearable physiological parameter detection system is developed, so that the physiological parameter detection precision can be obviously improved, and the wearable physiological parameter detection system has important practical value.
Disclosure of Invention
The invention aims to provide a wearable physiological parameter detection system, which can improve the test precision of the wearable physiological parameter detection system under the condition of external interference based on the system design of multiple sensors and a physiological parameter measurement method, and solves the problem that the measurement precision of the conventional 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: the LED comprises two or more than two LEDs, emits light with the wavelength of 400nm-1200nm, and sequentially emits light with different wavelengths according to a set time sequence to irradiate the surface of the skin of a human body;
the photoelectric sensing module: receiving light reflected or transmitted by skin, converting the light signal into a current signal, and generating a PPG signal;
a signal conditioning module: amplifying the current signal and converting the current signal into a voltage signal, removing high-frequency noise by using 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 of the physiological parameter detection system and the skin surface to generate a pressure signal;
an IMU: the device comprises a three-axis accelerometer, a three-axis gyroscope and a three-axis magnetometer, and is used for measuring the motion state of a physiological parameter detection part;
a temperature sensor: measuring body temperature;
the Bluetooth communication module: transmitting the measurement data to an upper computer;
a main controller: the device comprises a light emitting module, a photoelectric sensing module, a signal conditioning module, a pressure sensor, an IMU (inertial measurement Unit) and a temperature sensor, wherein working parameters of the light emitting module, the photoelectric sensing module, the signal conditioning module, the pressure sensor, an accelerometer, a gyroscope, magnetometer data of the IMU and a body temperature value of the temperature sensor are automatically set, and physiological parameters including heart rate, respiratory rate, blood pressure, blood oxygen saturation and body temperature are calculated.
Furthermore, the cut-off frequency range of the low-pass filter is 5Hz-100Hz, and the analog/digital signal conversion frequency is 20Hz-600Hz.
The light-emitting module and the photoelectric sensing module are in two geometric layouts, one of the photoelectric sensing module is located in the middle of the geometric layout and receives reflected or transmitted light of the skin, the number of the light-emitting modules is 4, the light-emitting modules are distributed around the photoelectric sensing module and emit light and extinguish the light according to a set time sequence, the frequency range of the light-on and extinguish is 20Hz-600Hz, the structure is shown in figure 2, and the photoelectric sensing module is located in the middle of the geometric layout and receives the reflected or transmitted light of the skin. The 4 light-emitting modules are arranged around the photoelectric sensing module, and emit light and extinguish according to a set time sequence, and the change frequency range of the light and the extinguish is 20Hz-600Hz. The distance between the light-emitting module and the photoelectric sensing module is different due to different selected test parts, and after the test parts are selected, the optimal distance is determined according to the signal waveform of the photoelectric sensing module; another kind of photoelectric sensing module be 4, light-emitting module be 5, 5 light-emitting module distribute around 4 photoelectric sensing modules, 4 photoelectric sensing modules make full use of the area of test position, gather 4 groups of parallel PPG signals simultaneously, reject the PPG signal that wherein receives external factor interference, it is shown in figure 3 to calculate the physiological parameter structure, there are 4 photoelectric sensing modules, 5 light-emitting modules distribute around photoelectric sensing module in addition, this design is applicable to the great condition of test position area, 4 groups of parallel PPG signals of 4 photoelectric sensing modules make full use of the area of test position, gather 4 groups of parallel PPG signals simultaneously, reject the PPG signal that wherein receives external factor interference, select more ideal PPG signal calculation physiological parameter, the precision and the reliability of physiological parameter measurement have then been improved. The weak current generated by the photoelectric sensing module is changed into a voltage signal with an increased amplitude value through the 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 the acquisition of the PPG digital signal; the PPG digital signal is transmitted over a serial bus to the main controller 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 light emitting time sequence of the light emitting module, and adjusting light emitting power to enable the amplitude of the PPG signal to be in an ideal interval;
(2) Setting a sampling time sequence of a signal conditioning module, and adjusting the amplification factor of a current/voltage amplifier and the cut-off frequency of a low-pass filter, so that PPG signals generated by light rays with different wavelengths can be sampled at a correct moment, and an ideal PPG signal is obtained to facilitate physiological parameter calculation;
(3) Acquiring a pressure sensor signal, judging whether the wearable physiological parameter detection system is in close contact with a tested part, automatically identifying the 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 an IMU (inertial measurement Unit), and estimating the real-time attitude of a tested part by a sensor fusion algorithm; to estimate the motion of the test site, the following mathematical model is first constructed:
in the formula (1), the reaction mixture is,
is the attitude quaternion of the tested part, and a is the acceleration data g 0 Is the acceleration of gravity, m is the magnetic field intensity data, m 0 For geomagnetic field reference, R (q) is a test part attitude matrix, and the following equation is satisfied:
by using the mathematical model of the formula (2) and combining a Bayesian optimal estimation algorithm, the posture change of the tested part can be estimated in real time; the PPG signal fluctuation is caused by the obvious posture change of the tested part, and the testing precision of the physiological parameters is indirectly influenced; according to the posture change estimated value obtained by calculation, the influence of the movement of the tested part on the PPG signal is eliminated, the signal waveform influenced by the movement is recovered to be an ideal signal waveform, the heart rate, the respiratory frequency, the blood pressure and the blood oxygen saturation are calculated on the basis, and then the physiological parameter testing precision is ensured.
The main controller realizes the measurement and calculation process including heart rate, respiratory rate, blood pressure, oxyhemoglobin saturation and body temperature, wherein the respiratory rate detection is that the respiratory rate is calculated by utilizing PPG signals, and the steps are as follows:
signal preprocessing: removing low-frequency components of the PPG signal by using a digital high-pass filter, cutting the high-pass filter to a frequency range of 0Hz-0.3Hz, and then removing a part of the PPG signal with the frequency higher than 40Hz by using a digital low-pass filter;
signal identification: identifying the effective part of the PPG signal, and removing the influences of jitter of a test part, ambient light interference and PPG signal saturation;
feature extraction: extracting the local maximum value and the local minimum value of the PPG signal, and calculating the typical characteristics of the PPG signal, including the signal amplitude, the period and the waveform width corresponding to different amplitudes in one period;
and (3) calculating the breathing frequency: and transforming the extracted PPG signal characteristics to a frequency domain, analyzing the peak value of the spectral energy, and determining the frequency corresponding to the peak value as the respiratory frequency.
The blood pressure detection is to analyze the pulse wave velocity by utilizing a PPG signal to calculate the blood pressure, and the steps are as follows:
signal preprocessing: removing low-frequency components of the PPG signal by using a digital high-pass filter, cutting the high-pass filter to a frequency range of 0Hz-0.3Hz, and then removing a part of the PPG signal with the frequency higher than 40Hz by using a digital low-pass filter;
signal quality analysis: the influence of jitter, ambient light interference and PPG signal saturation of a tested part is removed by combining the pressure sensor and IMU data, the waveform quality of each period of a PPG signal is analyzed, and a more ideal PPG signal waveform is selected for blood pressure measurement;
feature extraction: extracting two peak value time intervals of the PPG signal in one period to obtain the propagation time of the reflected pulse wave; the blood pressure was calculated using the following formula:
wherein RPTT is the reflection pulse wave propagation time, SBP is the systolic pressure, DBP is the diastolic pressure, K is a 、K b And K c The parameters to be calibrated are obtained;
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 parameter K by using acquired data and a nonlinear optimization method a 、K b And K c ；
And (3) real-time measurement: real-time systolic pressure and diastolic pressure can be calculated by using the measured propagation time of the reflected pulse wave and combining with calibrated optimal parameters.
The invention has the advantages that:
(1) The wearable blood oxygen saturation measuring instrument adopts a wearable design, can measure the heart rate, the respiratory rate, the blood pressure, the blood oxygen saturation and the body temperature in real time for a long time, improves the precision and the reliability of the measurement of physiological parameters, and provides effective data reference for the diagnosis and treatment of chronic diseases.
(2) The invention provides two geometric layouts of a light-emitting module and a photoelectric sensing module, which are suitable for different testing parts. The multi-path parallel PPG signals are collected, and the undisturbed PPG signals are selected to calculate physiological parameters, so that the measurement precision is improved.
(3) 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) The invention utilizes IMU to measure the gesture of the tested part and utilizes the gesture change information to eliminate the influence of motion on PPG signals.
(5) The invention provides a stable and reliable method for measuring the respiratory frequency and the blood pressure by combining the characteristics of a wearable physiological parameter detection system.
Drawings
FIG. 1 is a block diagram of a wearable physiological parameter sensing system;
FIG. 2 is a first geometric layout of the light emitting module and the photo sensor module;
fig. 3 is a second geometric layout of the light emitting module and the photo-electric sensing module.
Detailed Description
The present invention will be described in further detail with reference to the accompanying 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, can be applied to different testing parts such as fingers, wrists and the like by setting proper sensors and algorithm parameters, and the system composition is shown in figure 1 and comprises a light-emitting module, a photoelectric sensing module, a signal conditioning module, a pressure sensor, an IMU (inertial measurement Unit), a temperature sensor, a Bluetooth communication module and a main controller. 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 finished in the main controller, and the upper computer software provides a good human-computer 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 capable of emitting light in different spectral ranges with wavelengths from 400nm to 1200nm. The light emitting module sequentially emits light rays with different wavelengths to irradiate the surface of the skin of the human body according to a set time sequence;
photoelectric sensing module: receiving light reflected or transmitted by skin, converting the light signal into a current signal, and generating a PPG signal;
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 range of the low-pass filter is 5Hz-100Hz, and the analog/digital signal conversion frequency is 20Hz-600Hz;
a pressure sensor: measuring the contact pressure of the physiological parameter detection system and the skin surface;
an IMU: the device comprises a three-axis accelerometer, a three-axis gyroscope and a three-axis magnetometer, and is used for measuring the motion state of a physiological parameter detection part;
a temperature sensor: measuring body temperature;
the Bluetooth communication module: transmitting the measured data to an upper computer;
a main controller: the automatic setting light module, photoelectric sensing module, signal conditioning module, pressure sensor, IMU and temperature sensor's working parameter, the pressure signal of the PPG signal of receiving signal conditioning module, pressure sensor, IMU's accelerometer, gyroscope and magnetometer data and temperature sensor's body temperature numerical value for calculate each item physiological parameter, including rhythm of the heart, respiratory rate, blood pressure, oxyhemoglobin saturation and body temperature.
The geometric layout of the light-emitting modules and the photoelectric sensing modules is shown in fig. 2, the photoelectric sensing modules are positioned in the middle of the geometric layout and receive reflected or transmitted light of skin, 4 light-emitting modules are arranged around the photoelectric sensing modules and emit light and extinguish according to a set time sequence, the range of the on-off change frequency is 20Hz-600Hz, the distance between the light-emitting modules and the photoelectric sensing modules is different due to different selected test parts, and after the test parts are selected, the optimal distance is determined according to the signal waveform of the photoelectric sensing modules.
The weak current generated by the photoelectric sensing module is changed into a voltage signal with an increased amplitude value through the 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. And the analog/digital converter samples the voltage signal to complete acquisition of the PPG digital signal. The PPG digital signal is transmitted over a serial bus to the main controller for calculating heart rate, respiratory rate, blood pressure and blood oxygen saturation.
The main functions of the invention are realized by the main controller, which specifically comprises:
1. and setting a light emitting time sequence of the light emitting module, and adjusting light emitting power to enable the amplitude of the PPG signal to be in an ideal interval.
2. And a sampling time sequence of the signal conditioning module is set, and the amplification factor of the current/voltage amplifier and the cut-off frequency of the low-pass filter are adjusted, so that PPG signals generated by light rays with different wavelengths can be sampled at a correct moment, and an ideal PPG signal is obtained, and the physiological parameters can be calculated conveniently.
3. The method comprises the steps of obtaining a pressure sensor signal, judging whether a wearable physiological parameter detection system is in close contact with a tested part or not, automatically identifying the 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 a 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 attitude of the tested part by a sensor fusion algorithm. To estimate the motion of the test site, the following mathematical model is first constructed:
in the formula (1), the reaction mixture is,
is the attitude quaternion of the tested part, and a is the acceleration data g 0 Is the acceleration of gravity, m is the magnetic field intensity data, m 0 For geomagnetic field reference, R (q) is a test part attitude matrix, and the following equation is satisfied:
according to the method, the influence of the motion of the tested part on the PPG signal is eliminated according to the estimated value of the posture change obtained by calculation, the signal waveform influenced by the motion is recovered to be an ideal signal waveform, and the heart rate, the respiratory frequency, the blood pressure and the blood oxygen saturation are calculated on the basis, so that the physiological parameter testing precision is ensured.
6. The invention can detect various 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 were 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 shaking of a tested part, pressure change of a physiological parameter detection system in contact with the skin, ambient light interference, individual skin difference and the like, and a stable and reliable heart rate calculation method is very necessary to design. The invention provides a filtering method combining frequency domain information and time domain information, which utilizes the frequency domain information to effectively filter interference signals in a non-heart-rate frequency range, utilizes the time domain information to remove sudden change influences such as shaking of a tested part and the like, recovers a PPG signal waveform interfered by external factors into a more ideal PPG signal waveform, and ensures the heart rate measurement precision of a wearable physiological parameter detection system.
(2) Respiratory rate detection
The invention utilizes PPG signal to calculate respiratory frequency, and provides a PPG signal feature extraction and respiratory frequency measurement algorithm, which comprises the following steps:
firstly, preprocessing a PPG signal, removing a low-frequency component of the PPG signal by using a digital high-pass filter, cutting the frequency range of the high-pass filter to be 0Hz-0.3Hz, and then removing a part of the PPG signal with the frequency higher than 40Hz by using a digital low-pass filter;
identifying the effective part of the PPG signal, and removing the influences of jitter of a test part, ambient light interference and PPG signal saturation;
extracting the local maximum value and the local minimum value of the PPG signal, calculating the 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 to a frequency domain, analyzing the peak value of spectral energy, and determining the frequency corresponding to the peak value as the 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 the method specifically comprises the following steps:
and extracting the local maximum value and the local minimum value of the PPG signal by adopting a PPG signal processing method similar to the respiratory frequency detection.
And calculating the direct current component and the alternating current component of the PPG signal according to the local maximum value and the local minimum value of the PPG signal.
The blood oxygen saturation was calculated using the following formula:
in formula (5), SPO 2 To the degree of blood oxygen saturation, AC red And DC red Generating alternating and direct current components, AC, of PPG signals for red light red And DC red The alternating current component and the direct current component of the PPG signal are generated for infrared light, and the parameters a, b and c are parameters needing to be calibrated.
(4) Blood pressure detection
The invention uses PPG signal to analyze Pulse Wave Velocity (PWV) to calculate blood pressure. PWV is a function of blood density and volume and is expressed as follows:
in formula (6), p is blood density, v is blood volume, SBP is systolic pressure, DBP is diastolic pressure,
is the blood volume change. Formula (8) can be expressed as
In formula (7), RPTT is the reflected pulse wave propagation time, K a Are parameters which need to be calibrated. RPTT is the time interval of the pulse wave which is generated after the pulse wave is transmitted through the aorta and reaches the four limbs, and is obtained by measuring the time interval of two peak values of PPG signals in one period.
On the other hand, the mean blood pressure MBP can be expressed as
In the formula (8), K b And K c Are parameters that need to be calibrated.
The following can be obtained by using the formulae (3) and (4):
therefore, the parameter K is calibrated by extracting RPTT from PPG signal a 、K b And K c And calculating 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 provided, and another 5 light emitting modules are distributed around the photoelectric sensing modules. This design is applicable to the great condition of test site area, and 4 photoelectric sensing module make full use of test site's area gathers 4 groups of parallel PPG signals simultaneously, rejects the PPG signal that wherein receives the external factor interference, selects more ideal PPG signal to calculate physiological parameter, has improved physiological parameter measuring's precision and reliability then.
The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only preferred examples of the present invention, and do not limit the scope of the present invention. Any person skilled in the art can make any equivalent substitution or modification of the technical solution and technical content of the present invention without departing from the scope of the technical solution of the present invention, and the technical solution and the technical content of the present invention still belong to the protection scope of the present invention.
Claims (7)
1. A wearable physiological parameter sensing system, comprising:
a light emitting module: the LED comprises two or more than two LEDs, emits light with the wavelength of 400nm-1200nm, and sequentially emits light with different wavelengths according to a set time sequence to irradiate the surface of the skin of a human body;
the photoelectric sensing module: receiving light reflected or transmitted by skin, converting the light signal into a current signal, and generating a PPG signal;
a signal conditioning module: amplifying and converting the current signal into a voltage signal, removing high-frequency noise by using 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 of the physiological parameter detection system and the surface of the skin to generate a pressure signal;
an IMU: the device comprises a three-axis accelerometer, a three-axis gyroscope and a three-axis magnetometer, and is used for measuring the motion state of a physiological parameter detection part;
a temperature sensor: measuring body temperature;
the Bluetooth communication module: transmitting the measurement data to an upper computer;
the main controller: the working parameters of the light-emitting module, the photoelectric sensing module, the signal conditioning module, the pressure sensor, the IMU and the temperature sensor are automatically set, the PPG signal of the signal conditioning module, the pressure signal of the pressure sensor, the accelerometer, the gyroscope and the magnetometer data of the IMU and the body temperature value of the temperature sensor are received, and the physiological parameters including the heart rate, the respiratory frequency, the blood pressure, the blood oxygen saturation and the body temperature are calculated.
2. A wearable physiological parameter sensing system according to claim 1, wherein: the cut-off frequency range of the low-pass filter is 5Hz-100Hz, and the analog/digital signal conversion frequency is 20Hz-600Hz.
3. A wearable physiological parameter sensing system according to claim 1, wherein: the geometric layout of the light-emitting modules and the photoelectric sensing modules is that the photoelectric sensing modules are positioned in the middle of the geometric layout and used for receiving reflected or transmitted light of skin, the number of the light-emitting modules is 4, the light-emitting modules are distributed around the photoelectric sensing modules and used for emitting light and extinguishing light according to a set time sequence, and the light-on and light-off change frequency range is 20Hz-600Hz.
4. A wearable physiological parameter sensing system according to claim 1, wherein: the geometric layout of light emitting module and photoelectric sensing module do, photoelectric sensing module be 4, light emitting module be 5, 5 light emitting module distribute around 4 photoelectric sensing modules, 4 photoelectric sensing module make full use of test site's area gathers 4 groups of parallel PPG signals simultaneously, rejects the PPG signal that receives external factor interference wherein, calculates physiological parameter.
5. A wearable physiological parameter sensing system according to claim 1, wherein: the main controller is used for measuring physiological parameters and specifically comprises:
(1) Setting a light emitting time sequence of the light emitting module, and adjusting light emitting power to enable the amplitude of the PPG signal to be 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 a correct moment, and an ideal PPG signal is obtained to facilitate physiological parameter calculation;
(3) Acquiring a pressure sensor signal, judging whether the wearable physiological parameter detection system is in close contact with a tested part, automatically identifying the 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 an IMU (inertial measurement Unit), and estimating the real-time attitude of a tested part by a sensor fusion algorithm; to estimate the motion of the test site, the following mathematical model is first constructed:
wherein in formula (1)
Is the attitude quaternion of the tested part, a is the acceleration data, g 0 Is the acceleration of gravity, m is the magnetic field intensity data, m 0 For geomagnetic field reference, R (q) is a test part attitude matrix, and the following equation is satisfied:
by using the mathematical model of the formula (2) and combining a Bayes optimal estimation algorithm, the posture change of the tested part can be calculated in real time; the PPG signal fluctuation is caused by the obvious posture change of the tested part, and the testing precision of the physiological parameters is indirectly influenced; according to the posture change estimated value obtained by calculation, the influence of the movement of the tested part on the PPG signal is eliminated, the signal waveform influenced by the movement is recovered to be an ideal signal waveform, the heart rate, the respiratory rate, the blood pressure and the blood oxygen saturation are calculated on the basis, and then the physiological parameter testing precision is ensured.
6. A wearable physiological parameter sensing system according to claim 1, wherein: the main controller realizes the measurement and calculation process including heart rate, respiratory rate, blood pressure, oxyhemoglobin saturation and body temperature, wherein the respiratory rate detection is that the respiratory rate is calculated by utilizing PPG signals, and the steps are as follows:
signal preprocessing: removing low-frequency components of the PPG signal by using a digital high-pass filter, cutting the high-pass filter to a frequency range of 0Hz-0.3Hz, and then removing a part of the PPG signal with the frequency higher than 40Hz by using a digital low-pass filter;
signal identification: identifying the effective part of the PPG signal, and removing the influences of jitter of a test part, ambient light interference and PPG signal saturation;
feature extraction: extracting a local maximum value and a local minimum value of the PPG signal, and calculating typical characteristics of the PPG signal, including signal amplitude, period and waveform width corresponding to different amplitudes in one period;
and (3) calculating the breathing frequency: and transforming the extracted PPG signal characteristics to a frequency domain, analyzing the peak value of the spectral energy, and determining the frequency corresponding to the peak value as the respiratory frequency.
7. The wearable physiological parameter sensing system of claim 6, wherein: the blood pressure detection is to analyze the pulse wave velocity by utilizing a PPG signal to calculate the blood pressure, and the steps are as follows:
signal preprocessing: removing low-frequency components of the PPG signal by using a digital high-pass filter, cutting the high-pass filter to a frequency range of 0Hz-0.3Hz, and then removing a part of the PPG signal with the frequency higher than 40Hz by using a digital low-pass filter;
signal quality analysis: the influence of jitter, ambient light interference and PPG signal saturation of a tested part is removed by combining the pressure sensor and IMU data, the waveform quality of each period of a PPG signal is analyzed, and a more ideal PPG signal waveform is selected for blood pressure measurement;
feature extraction: extracting two peak value time intervals of the PPG signal in one period to obtain the transmission time of the reflected pulse wave; the blood pressure was calculated using the following formula:
wherein RPTT is the reflection pulse wave propagation time, SBP is the systolic pressure, DBP is the diastolic pressure, K is a 、K b And K c The parameters to be calibrated are obtained;
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; method of using acquired data and non-linear optimizationCalculating to obtain an optimal parameter K a 、K b And K c ；
And (3) real-time measurement: real-time systolic pressure and diastolic pressure can be calculated by using the measured propagation time of the reflected pulse wave and combining with calibrated optimal parameters.
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