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CN116919373B - Non-anesthetized animal heart rate monitoring system and method based on dual-channel PPG - Google Patents

Non-anesthetized animal heart rate monitoring system and method based on dual-channel PPG Download PDF

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CN116919373B
CN116919373B CN202311192094.2A CN202311192094A CN116919373B CN 116919373 B CN116919373 B CN 116919373B CN 202311192094 A CN202311192094 A CN 202311192094A CN 116919373 B CN116919373 B CN 116919373B
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CN116919373A (en
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张晶晶
高童
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China University of Geosciences
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    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/024—Measuring pulse rate or heart rate
    • A61B5/02416—Measuring pulse rate or heart rate using photoplethysmograph signals, e.g. generated by infrared radiation
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/024—Measuring pulse rate or heart rate
    • A61B5/02416—Measuring pulse rate or heart rate using photoplethysmograph signals, e.g. generated by infrared radiation
    • A61B5/02427—Details of sensor
    • A—HUMAN NECESSITIES
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    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/024—Measuring pulse rate or heart rate
    • A61B5/02416—Measuring pulse rate or heart rate using photoplethysmograph signals, e.g. generated by infrared radiation
    • A61B5/02427—Details of sensor
    • A61B5/02433—Details of sensor for infrared radiation
    • A—HUMAN NECESSITIES
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    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/024—Measuring pulse rate or heart rate
    • A61B5/02438—Measuring pulse rate or heart rate with portable devices, e.g. worn by the patient
    • A—HUMAN NECESSITIES
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    • A—HUMAN NECESSITIES
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    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
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    • A61B5/7225—Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2503/00—Evaluating a particular growth phase or type of persons or animals
    • A61B2503/40—Animals

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Abstract

The invention provides a non-anesthetized animal heart rate monitoring system and method based on a dual-channel PPG, comprising a controller, wherein the controller controls PPG sensors and a triaxial gyroscope module at the left side and the right side to synchronously sample, and the sampling frequency of the PPG sensors is more than 200 Hz; the upper computer sequentially executes the following processes: the method comprises the steps of preprocessing a dual-channel PPG signal to improve the quality of the PPG signal, adaptively filtering the dual-channel PPG signal in combination with an acceleration signal to eliminate motion artifacts and noise interference, interpolating the dual-channel PPG signal to complement missing data, aligning the dual-channel PPG signal to eliminate time delay or phase difference, fusing the dual-channel PPG signal to obtain a more reliable PPG signal, and calculating a heart rate estimated value according to the frequency corresponding to the maximum amplitude of the fused PPG signal. The invention can monitor the static and dynamic heart rate of non-anesthetized animals and can improve the accuracy and stability of animal heart rate monitoring.

Description

Non-anesthetized animal heart rate monitoring system and method based on dual-channel PPG
Technical Field
The invention belongs to the technical field of measurement, and particularly relates to a non-anesthetized animal heart rate monitoring system and method based on a dual-channel PPG.
Background
Heart rate is an important indicator reflecting biological physiological state and health condition, and for animals, the monitoring and analysis of heart rate can be used for researching aspects of animal behavior, emotion, stress, diseases and the like. At present, the common animal heart rate monitoring methods mainly comprise the following steps:
electrocardiography (ECG) method: the heart rate of the animal is calculated by attaching an electrode plate on the body surface of the animal, collecting electrocardiosignals of the animal, and then carrying out peak detection or wavelet transformation and other methods. The method has higher accuracy and stability, but has the defects that the electrode plates are easy to fall off or interfere, the tested animal needs to be fixed by using a restraint device after anesthesia, and the free movement heart rate of the animal cannot be measured.
Camera (Camera) method: the animal heart rate is calculated by aligning the face or body part of the animal, collecting the video signal of the animal, and then by image processing or machine learning. The method has the advantages of no wound and no equipment wearing, but has the defects that the camera needs to keep a fixed distance and angle, video signals are easy to be interfered by illumination, shielding, movement and the like, and the calculation process needs higher calculation capacity and storage space and the like.
Although each of the above methods has advantages, it has a common problem that it cannot accommodate free movement of animals under non-anesthetized conditions. Since animals exhibit a variety of different behaviors and emotions under non-anesthetized conditions, such as running, jumping, fighting, sleeping, panic, excitement, etc., these behaviors and emotions can cause significant changes in the animal's heart rate. Importantly, the anesthesia operation can not accurately control the anesthesia dosage, and the animal experimental result is difficult to unify and quantitatively interfere. Therefore, non-anesthesia systems for tracking animal heart rate signals are of great interest. Monitoring the heart rate of an animal under non-anesthetized conditions requires treatment in several ways:
signal quality: the heart rate signal becomes blurred or loses some of its information due to a significant amount of motion artifact and noise interference that the animal may produce during its activity. Therefore, a method capable of suppressing motion artifact and noise interference and improving signal quality is required.
Signal stability: the amplitude and phase of the heart rate signal change due to the different postures and position changes of the animal during the activity. Therefore, a method capable of adapting to the posture and position change and maintaining the stability of the signal is required.
Signal reliability: the frequency and rhythm of the heart rate signal change due to different physiological states that the animal may have during its activity. Therefore, a method capable of reflecting the state of the animal to be tested and improving the signal reliability is required.
Range of heart rate: the frequency used by a PPG (photoplethysmogram) sensor refers to the number of data points of the PPG signal acquired per second by the PPG sensor, reflecting the resolution and accuracy of the PPG signal. The higher the frequency used by the PPG sensor, the better the quality of the PPG signal, the higher the accuracy and stability of the heart rate estimation, and the heart rate of animals is much higher than that of humans, thus requiring hardware designs that use higher PPG sampling rates.
In summary, the current animal heart rate monitoring method cannot meet the requirement of free animal activity under non-anesthetic state, so it is necessary to develop a new animal heart rate monitoring method and system to solve the above-mentioned problems.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a non-anesthetized animal heart rate monitoring system based on a dual-channel PPG, which comprises: two PPG sensors are used for respectively acquiring two-channel PPG signals of the skin surfaces at the left side and the right side of the animal; the triaxial gyroscope module is used for collecting acceleration signals of animals; the controller is used for controlling the PPG sensors on the left side and the right side and the triaxial gyroscope module to synchronously sample to obtain a digital dual-channel PPG signal and an acceleration signal, and the sampling frequency of the PPG sensors is above 200 Hz; the upper computer sequentially executes the following signal processing steps according to the two-channel PPG signal and the acceleration signal uploaded by the controller: the method comprises the steps of preprocessing a dual-channel PPG signal to improve the quality of the PPG signal, adaptively filtering the dual-channel PPG signal in combination with an acceleration signal to eliminate motion artifacts and noise interference, interpolating the dual-channel PPG signal to complement missing data or equalize the lengths of the dual-channel PPG signal, aligning the dual-channel PPG signal to eliminate time delay or phase difference, fusing the dual-channel PPG signal to obtain a more reliable PPG signal, and calculating a heart rate estimated value according to the frequency corresponding to the maximum amplitude of the fused PPG signal.
Further, the preprocessing comprises the steps of removing direct current components, removing baseline drift and removing high-frequency noise, and the preprocessing formula is as follows:
wherein,and->PPG signals on the left and right sides after pretreatment, respectively>And->Original PPG signals on the left and right sides, respectively, < >>Representation->Direct current component of>Representation->Is used for the direct current component of the (c),representation->Baseline drift of ∈10->Representation->Baseline drift of ∈10->Representation->High frequency noise of->Representation->Is a high frequency noise of (a).
Further, the adaptive filtering is to use an adaptive filter, and calculate parameters of the filter according to the phase difference and the amplitude ratio between the acceleration signal and the PPG signal so as to achieve the optimal filtering effect; the filtering formula is:
wherein,and->The filtered left and right PPG signals, respectively, ">Representing convolution, h θ (t, a (t)) represents the impulse response function of the adaptive filter, θ represents the parameters of the filter,/->Representing the acceleration signal;
where δ (t) represents a unit impulse function, δ' (t) represents a derivative of the unit impulse function, g (θ, a (t)) and f (θ, a (t)) represent gain and phase factors of the filter, respectively, are functions concerning θ and a (t).
Further, the adaptive filtering device for carrying out the adaptive filtering on the dual-channel PPG signal by combining the acceleration signal The method comprises the following steps: the nonlinear least square method is used for estimating the two-channel PPG signal and the acceleration signal to obtain the amplitude B of each channel PPG signal, the amplitude A of the acceleration signal and the phase difference between the acceleration signal and each channel PPG signalThe method comprises the steps of carrying out a first treatment on the surface of the Let->、Thereby obtaining the impulse response function h of the adaptive filter of the PPG signal of each channel θ (t, a (t)); and filtering the PPG signal of each channel according to the filtering formula.
Further, the interpolation formula is:
wherein,and->Respectively, the PPG signals of the left side and the right side after interpolation, I [. Cndot.]Representing an interpolation function;
the formula of the alignment is:
wherein,and->Respectively aligned PPG signals, +.>Representing the time delay.
The fusion is obtained by adopting the PPG signals on the left side and the right side through weighted average, and the calculation formula of the heart rate estimated value is as follows:
wherein,for heart rate estimation, Δt is the interpolated sampling interval, α is the fused weighted average coefficient, +.>And->Frequency domain representations of the PPG signal on the left and right sides, respectively, namely:
wherein F [. Cndot ] represents the Fourier transform.
A non-anesthetized animal heart rate monitoring method based on a dual-channel PPG comprises the following steps: the controller controls two PPG sensors and a triaxial gyroscope module on the skin surfaces on the left side and the right side of the animal to synchronously sample, and digital two-channel PPG signals and acceleration signals corresponding to the animal are obtained and uploaded to the upper computer, wherein the sampling frequency of the PPG sensors is more than 200 Hz; the upper computer sequentially executes the following signal processing steps according to the two-channel PPG signal and the acceleration signal uploaded by the controller: the method comprises the steps of preprocessing a dual-channel PPG signal to improve the quality of the PPG signal, adaptively filtering the dual-channel PPG signal in combination with an acceleration signal to eliminate motion artifacts and noise interference, interpolating the dual-channel PPG signal to complement missing data or equalize the lengths of the dual-channel PPG signal, aligning the dual-channel PPG signal to eliminate time delay or phase difference, fusing the dual-channel PPG signal to obtain a more reliable PPG signal, and calculating a heart rate estimated value according to the frequency corresponding to the maximum amplitude of the fused PPG signal.
Further, the preprocessing comprises the steps of removing direct current components, removing baseline drift and removing high-frequency noise, and the preprocessing formula is as follows:
wherein,and->PPG signals on the left and right sides after pretreatment, respectively>And->Original PPG signals on the left and right sides, respectively, < >>Representation->Direct current component of>Representation->Is used for the direct current component of the (c),representation->Baseline drift of ∈10->Representation->Baseline drift of ∈10->Representation->High frequency noise of->Representation->Is a high frequency noise of (a).
Further, the adaptive filtering is to use an adaptive filter, and calculate parameters of the filter according to the phase difference and the amplitude ratio between the acceleration signal and the PPG signal so as to achieve the optimal filtering effect; the filtering formula is:
wherein,and->The filtered left and right PPG signals, respectively, ">Representing convolution, h θ (t, a (t)) represents the impulse response function of the adaptive filter, θ represents the parameters of the filter,/->Representing the acceleration signal;
where δ (t) represents a unit impulse function, δ' (t) represents a derivative of the unit impulse function, g (θ, a (t)) and f (θ, a (t)) represent gain and phase factors of the filter, respectively, are functions concerning θ and a (t).
Further, the specific steps of adaptively filtering the dual-channel PPG signal by combining the acceleration signal are as follows: the nonlinear least square method is used for estimating the two-channel PPG signal and the acceleration signal to obtain the amplitude B of each channel PPG signal, the amplitude A of the acceleration signal and the phase difference between the acceleration signal and each channel PPG signal The method comprises the steps of carrying out a first treatment on the surface of the Let->、Thereby obtaining the impulse response function h of the adaptive filter of the PPG signal of each channel θ (t, a (t)); and filtering the PPG signal of each channel according to the filtering formula.
Further, the interpolation formula is:
wherein,and->Respectively, the PPG signals of the left side and the right side after interpolation, I [. Cndot.]Representing an interpolation function;
the formula of the alignment is:
wherein,and->Respectively aligned PPG signals, +.>Representing the time delay.
The fusion is obtained by adopting the PPG signals on the left side and the right side through weighted average, and the calculation formula of the heart rate estimated value is as follows:
wherein,for heart rate estimation, Δt is the interpolated sampling interval, α is the fused weighted average coefficient, +.>And->Frequency domain representations of the PPG signal on the left and right sides, respectively, namely:
wherein F [. Cndot ] represents the Fourier transform.
The technical scheme adopted by the invention has the beneficial effects that: the invention fully considers the difference of animal heart rate and human heart rate in frequency, rhythm, variability and the like, particularly the sampling frequency of the PPG sensor is more than 200Hz, the highest monitoring heart rate can be improved to 6000 times/min, thereby expanding the monitoring variety of the animal, improving the accuracy and stability of heart rate monitoring, and simultaneously, the PPG signal is preprocessed, adaptively filtered, interpolated, aligned, fused and the like by utilizing the information of the dual-channel PPG signal and the acceleration signal to obtain a clearer, stable and reliable PPG signal, and then the PPG signal is converted into a frequency domain through Fourier transformation, so that the frequency corresponding to the maximum amplitude of the PPG signal is found as a heart rate estimated value, thereby effectively inhibiting motion artifact and noise interference, and improving the accuracy and stability of animal heart rate monitoring.
Drawings
FIG. 1 is a circuit block diagram of a non-anesthetized animal heart rate monitoring device based on dual channel PPG of the present invention;
fig. 2 is a flow chart of a non-anesthetized animal heart rate monitoring method based on dual-channel PPG according to the present invention.
Detailed Description
For a clearer understanding of the objects, technical solutions and effects of the present invention, embodiments of the present invention will be further described with reference to the accompanying drawings.
The embodiment of the invention provides a non-anesthetized animal heart rate monitoring system based on a dual-channel PPG, which comprises two parts, namely hardware and software. The hardware includes: two PPG sensors are used for respectively acquiring two-channel PPG signals of the skin surfaces at the left side and the right side of the animal; the triaxial gyroscope module is used for collecting acceleration signals of animals; the controller is used for controlling the PPG sensors on the left side and the right side and the triaxial gyroscope module to synchronously sample, obtaining a digital dual-channel PPG signal and an acceleration signal and uploading the digital dual-channel PPG signal and the acceleration signal to the upper computer; and the upper computer executes a signal processing step according to the dual-channel PPG signal and the acceleration signal uploaded by the controller.
In a preferred embodiment, the hardware part uses a dual-channel max30105, a tri-axial gyroscope and an esp32 pico d4 to form a small, portable and low-power wearable device, the wearable device can be fixed on the neck or chest of an animal, photo-volume pulse wave (PPG) signals of skin surfaces on the left side and the right side of the animal are respectively acquired through two max30105 modules, meanwhile Acceleration (ACC) signals of the animal are acquired through the tri-axial gyroscope modules, and then the signals are processed and transmitted through the esp32 pico d4 chip. Specifically:
Dual-channel max30105 module: max30105 is a photosensor module integrating infrared, green and red light sources and photodetectors, and can be used to collect PPG signals. The invention uses two max30105 modules which are respectively placed on the skin surfaces at the left side and the right side of an animal, irradiates the skin through a red light source, and receives the reflected light intensity change through a photoelectric detector, thereby obtaining PPG signals at the left side and the right side. The purpose of this is to increase the diversity and redundancy of the signal to cope with the effects of different skin colors, hair density, blood vessel position etc. on the PPG signal.
Triaxial gyroscope module: a tri-axis gyroscope is a sensor module that can measure rotational angular velocity of an object in space about three axes and can be used to collect ACC signals. The invention uses a triaxial gyroscope module which is placed in a central position parallel to the double-channel max30105 module, and obtains ACC signals by measuring rotation angular velocities of animals in three directions of x, y and z. The purpose of this is to obtain information on the animal's motion state and motion intensity, so that the PPG signal is correspondingly pre-processed and filtered to eliminate motion artefacts and noise disturbances.
esp32 pico d4 chip: esp32 pico d4 is a micro controller chip integrated with Wi-Fi, bluetooth, dual-core processor, memory and peripherals, which can be used to process and transmit signals. The invention uses an esp32 pico d4 chip as a core controller of a hardware part, and realizes the following functions by being connected with a double-channel max30105 module and a triaxial gyroscope module:
and (3) signal sampling: and synchronously sampling the PPG signal and the ACC signal on the left side and the right side by setting proper sampling frequency and sampling bit number to obtain digitized signal data.
And (3) signal transmission: and the Wi-Fi or Bluetooth module is used for sending the acquired original PPG and acceleration value to the upper computer, so that the heart rate calculation data is acquired.
The two signals of the dual-channel PPG and the triaxial gyroscope acceleration are the cores of a non-anesthetized animal heart rate monitoring method and system based on the dual-channel PPG signals, and can effectively filter the motion interference of animals and the interference of ambient light, and improve the accuracy and stability of heart rate monitoring.
The upper computer executes a signal processing step according to the two-channel PPG signal and the acceleration signal uploaded by the controller, and the signal processing comprises the following steps: the algorithm provided by the software part is used for preprocessing, filtering, interpolating, aligning, fusing and the like on the signal data obtained by sampling, so that a clearer, stable and reliable PPG signal is obtained, and the heart rate value of the animal is calculated.
Binary channels PPG signal: the PPG signal is an electro-optical signal reflecting the change in blood flow in the blood vessel, which can be used to monitor heart rate. Two max30105 modules are used for respectively acquiring PPG signals on the left side and the right side of an animal so as to increase the diversity and redundancy of the signals. The purpose of this is to cope with the influence of different skin colors, hair densities, blood vessel positions and other factors on the PPG signal, and the interference of the motion state, posture change, position change and other factors on the PPG signal. By using the dual-channel PPG signal, the heartbeat condition of the animal can be observed from two different angles, thereby improving the reliability of heart rate monitoring.
Triaxial gyroscope acceleration signal: the acceleration signal is a signal reflecting the rotational angular velocity of an object in space about three axes, and can be used to obtain information on the state of motion and the intensity of motion of an animal. A tri-axial gyroscope module is used to collect the acceleration signals of the animal to assist in PPG signal processing and analysis. The purpose of this is to improve the quality and stability of the PPG signal in order to eliminate motion artefacts and noise interference. By using the acceleration signal, different preprocessing and filtering operations can be performed on the PPG signal according to the motion state and the motion intensity of the animal so as to adapt to different motion environments, thereby improving the accuracy of heart rate monitoring.
The system consists of an ESP32 PICO D4 data processing module, a double-channel PPG sensor and a triaxial gyroscope. The data processing module is responsible for collecting sensor data of animals and sending the sensor data to the upper computer after processing the sensor data. Consists of a main chip ESP32-PICO-D4, an LDO power supply circuit, a reset circuit, a radio frequency antenna circuit and the like. The ESP32-PICO-D4 is a system in package module integrated with a dual-core processor chip, a radio frequency front end and packaged in a miniature flat package. And a 32-bit multiplier and floating point operation support are built in. The heart rate measuring device also comprises a 416KB memory which is used for storing programs, data and a cache, and has the following characteristics of being beneficial to heart rate measurement: ESP32-PICO-D4 supports Wi-Fi (802.11 b/g/n) and Bluetooth (v 4.2 and v 5.0) wireless communication standards, and can wirelessly transmit data back to an upper computer in real time. ESP32-PICO-D4 integrates a radio frequency front end including a power amplifier, transceiver and low noise amplifier to provide high performance radio frequency transceiver capability. ESP32-PICO-D4 supports multiple low power consumption modes, and can effectively prolong the service life of a battery in different application scenes. ESP32-PICO-D4 is provided in a flat package, has a very small shape, occupies a small amount of PCB space, is convenient to be embedded into various compact device designs, and the PCB main body designed by the invention has the size of only 2.6cm multiplied by 1.8cm, so that the PCB main body is convenient to be worn on the limited back space of animals. The power supply part adopts an LDO scheme of RT9013, and the power supply output ripple is small, so that the circuit stability can be effectively improved. The design principle block diagrams of the main chip ESP32-PICO-D4, the LDO power supply circuit, the reset circuit, the radio frequency antenna circuit and the like are shown in figure 1.
The sensor module is responsible for collecting pulse wave data of animals and acceleration signals of the animals and transmitting the pulse wave data and the acceleration signals to the data processing module through the IIC communication protocol. The PPG module is composed of two MAX30102 arranged in parallel, the triaxial gyroscope is composed of an MPU6050 chip, and a 1.8V LDO power supply is configured to independently supply power to the PPG sensor. The circuit design of the system consists of a top layer, a bottom layer, a signal layer and a power GND four-layer PCB, wherein a main chip, a triaxial gyroscope, a radio frequency antenna circuit and a reset circuit are arranged on the top layer, and two PPG sensors and a 1.8V LDO power supply are arranged on the bottom layer at a parallel interval of 1.5 cm.
In the embodiment of the invention, the sampling frequency of the PPG sensor is more than 200 Hz.
According to the nyquist sampling theorem: fs is more than or equal to 2fm; where fs denotes the PPG sensor usage frequency and fm denotes the highest frequency component of the heart rate. A continuous signal is to be completely recovered, and its sampling frequency must be greater than or equal to twice the highest frequency component of the continuous signal. Thus, to ensure that the PPG signal can be fully recovered, it is necessary to know what the highest frequency component of the PPG signal is. There is a large difference in heart rate between different species of animals or humans, for example, mice have an average heart rate of 600 beats/min (10 Hz), rats have an average heart rate of 350 beats/min (5.83 Hz), and humans have an average heart rate of 72 beats/min (1.2 Hz). These differences are mainly related to factors such as weight, metabolic rate of animals or humans. Therefore, in order to adapt to the heart rate of different animals, the frequency of the PPG sensor needs to be raised to a level which can cover all possible heart rate ranges, and the invention can collect 6000 times/min heart rate at the highest time when the frequency of the PPG sensor is raised to 200 Hz.
The advantage of being lifted to 200 Hz: the existing PPG sensor adopts a frequency which at least needs to reach 25Hz or 50Hz to ensure the reliability and effectiveness of heart rate estimation. However, these studies are based on static or low intensity movements, and if the animal under test is in a higher intensity movement or complex environment, the PPG signal is subject to greater movement artefacts and noise interference, resulting in increased errors in heart rate estimation. Therefore, to accommodate different motion states and environmental conditions, the PPG sensor adoption frequency needs to be raised to 200Hz. The use of a frequency boost to 200Hz for PPG sensors has several advantages:
increasing the amount of signal information: increasing the frequency of the PPG sensor to 200Hz means that more PPG signal data points can be acquired per second, thereby increasing the amount of signal information. This may allow the PPG signal to more fully and carefully reflect changes in the flow of blood in the blood vessel, thereby improving the accuracy of the heart rate estimation.
Enhancing signal anti-interference capability: raising the PPG sensor frequency to 200Hz means that the time interval occupied by each PPG signal data point is shorter, thus enhancing the signal immunity. In this way, the PPG signal can be more easily distinguished from the actual heartbeat waveform and waveform changes caused by motion artifacts or noise interference, thereby improving the stability of heart rate estimation.
Increase signal processing flexibility: increasing the frequency of the PPG sensor to 200Hz means that the frequency range corresponding to each PPG signal data point is wider, thereby increasing signal processing flexibility. Therefore, the PPG signal is more suitable for preprocessing, filtering, interpolation, alignment, fusion and other operations by using different signal processing methods and machine learning models, so that the reliability of heart rate estimation is improved.
Software part: the upper computer sequentially executes the following signal processing steps according to the two-channel PPG signal and the acceleration signal uploaded by the controller: the method comprises the steps of preprocessing a dual-channel PPG signal to improve the quality of the PPG signal, adaptively filtering the dual-channel PPG signal in combination with an acceleration signal to eliminate motion artifacts and noise interference, interpolating the dual-channel PPG signal to complement missing data or equalize the lengths of the dual-channel PPG signal, aligning the dual-channel PPG signal to eliminate time delay or phase difference, fusing the dual-channel PPG signal to obtain a more reliable PPG signal, and calculating a heart rate estimated value according to the frequency corresponding to the maximum amplitude of the fused PPG signal.
The invention combines the PPG signal of the dual-channel PPG sensor with the acceleration signal of the gyroscope, and strengthens the usability and signal-to-noise ratio of the signals. Specifically:
Pretreatment: according to the characteristics of the acceleration ACC signals, the motion state and the motion intensity of the animal are judged, and then different preprocessing operations, such as DC component removal, baseline drift removal, high-frequency noise removal and the like, are performed on the PPG signals on the left side and the right side according to different motion states and motion intensities so as to improve the quality of the PPG signals.
Specifically, the preprocessing formula is as follows:
wherein,and->PPG signals on the left and right sides after pretreatment, respectively>And->Original PPG signals on the left and right sides, respectively, < >>Representation->Direct current component of>Representation->Is used for the direct current component of the (c),representation->Baseline drift of ∈10->Representation->Baseline drift of ∈10->Representation->High frequency noise of->Representation->Is a high frequency noise of (a).
The principle of the formula is that the motion state and the motion strength of an animal are judged according to acceleration signals, and then different preprocessing operations are carried out on PPG signals on the left side and the right side, such as DC component removal, baseline drift removal, high-frequency noise removal and the like, so that the quality of the PPG signals is improved. The direct current component refers to a constant part of the PPG signal that is independent of the heartbeat and affects the amplitude of the PPG signal; baseline drift refers to the time-varying portion of the PPG signal that affects the shape of the PPG signal; high frequency noise refers to high frequency interference in the PPG signal introduced by ambient light or electronics, etc., which can affect the clarity of the PPG signal. By removing these interfering factors, a clearer, more stable, and more reliable PPG signal may be obtained.
And (3) filtering: according to the correlation between the ACC signal and the PPG signal, an adaptive filter is designed, and filtering operation is carried out on the PPG signals on the left side and the right side so as to eliminate motion artifact and noise interference. The filter can automatically adjust parameters of the filter according to the phase difference and amplitude ratio between the ACC signal and the PPG signal so as to achieve the optimal filtering effect.
Specifically, the filtering formula is:
wherein,and->The filtered left and right PPG signals, respectively, ">Representing convolution, h θ (t, a (t)) represents the impulse response function of the adaptive filter, θ represents the parameters of the filter,/->Representing the acceleration signal;
where δ (t) represents a unit impulse function, δ' (t) represents a derivative of the unit impulse function, g (θ, a (t)) and f (θ, a (t)) represent gain and phase factors of the filter, respectively, are functions concerning θ and a (t).
The principle of the formula is to design an adaptive filter according to the correlation between the acceleration signal and the PPG signal, and filter the PPG signals on the left side and the right side so as to eliminate motion artifact and noise interference. Motion artifact refers to changes in the PPG signal due to physical movement or vascular movement of an animal during activity, etc., which affects the frequency and rhythm of the PPG signal; noise interference refers to random or periodic interference introduced by the external environment or electronic equipment, etc. to which the animal is subjected during the course of activity, which affects the amplitude and phase of the PPG signal. By using the adaptive filter, parameters of the filter are automatically adjusted according to the phase difference and amplitude ratio between the acceleration signal and the PPG signal, so as to achieve the optimal filtering effect.
In a preferred embodiment, the specific steps of adaptively filtering the dual-channel PPG signal in combination with the acceleration signal are as follows: the nonlinear least square method is used for estimating the two-channel PPG signal and the acceleration signal to obtain the amplitude B of each channel PPG signal, the amplitude A of the acceleration signal and the phase difference between the acceleration signal and each channel PPG signalThe method comprises the steps of carrying out a first treatment on the surface of the Order the、/>Thereby obtaining the impulse response function h of the adaptive filter of the PPG signal of each channel θ (t, a (t)); and filtering the PPG signal of each channel according to the filtering formula.
h θ (t, a (t)) represents the impulse response of the adaptive filter as a function of time t and the acceleration signal a (t), the invention being based on the amplitude ratio and the phase difference between the acceleration signal and the PPG signal. θ represents a parameter of the filter, an adaptively updated variable, which reflects the characteristics of the filter. Generally, h θ (t, a (t)) may be expressed in the form:
where δ (t) represents a unit impulse function, δ' (t) represents a derivative of the unit impulse function, g (θ, a (t)) and f (θ, a (t)) represent gain and phase factors of the filter, respectively, are functions concerning θ and a (t).
When the input signal is a unit impulse function, the output signal is composed of two parts: a part is a part synchronized with the input signal, the amplitude of which is determined by a gain factor g (θ, a (t)); the other part is a part having a phase difference of pi/2 from the input signal, and its amplitude is determined by a phase factor f (θ, a (t)). This allows the filter to have different gain and phase characteristics for different frequency components, thereby achieving filtering of the input signal.
It is assumed that there is a non-linear relationship between the acceleration signal a (t) and the PPG signal x (t), namely:
wherein ω represents the heart rate frequency,the phase difference, a, B, is an unknown constant, C represents the dc component of the acceleration signal a (t), and D represents the dc component of the PPG signal x (t). Non-linear least squares method can be used to estimate ω,/and>a, B, C, D, then they are taken as filter parameters θ= [ ω, ]>,A,B,C,D]T. We can then define the gain factor and the phase factor as:
this may allow the filter to have a lower gain and a larger phase difference for frequency components having the same frequency but different phases and magnitudes between the acceleration signal and the PPG signal, thereby eliminating motion artifacts and noise interference.
Interpolation: the two PPG signals may have unequal lengths or a gap due to the fact that there may be inconsistent sampling or missing data in the PPG signals on the left and right sides. Therefore, interpolation operations are required for the PPG signals on the left and right sides to complement the missing data or to equalize the two PPG signals in length.
Specifically, the interpolation formula is:
wherein,and->Respectively, the PPG signals of the left side and the right side after interpolation, I [. Cndot.]Representing the interpolation function.
The principle of the formula is that the two PPG signals are unequal in length or have a gap due to the fact that the PPG signals on the left side and the right side may have problems of inconsistent sampling or missing data. Therefore, interpolation operations are required for the PPG signals on the left and right sides to complement the missing data or to equalize the two PPG signals in length. Interpolation operation the unknown data point is calculated from the known data point by using a cubic spline interpolation method, thereby obtaining a more complete and uniform PPG signal.
Alignment: because of the problems of time delay or phase difference of the PPG signals on the left and right sides, the two PPG signals are not synchronous or consistent. Therefore, an alignment operation is required for the PPG signals on the left and right sides to eliminate the time delay or phase difference. The alignment operation may find the best matching position between the two PPG signals by using cross-correlation or dynamic time warping, etc., and translate or rotate the two PPG signals to be synchronized or coincident.
Specifically, the alignment formula is:
wherein,and->Respectively aligned PPG signals, +.>Representing the time delay.
The principle of the formula is that the two PPG signals are not synchronous or consistent due to the fact that there may be a time delay or a phase difference between the PPG signals on the left and right sides. Therefore, an alignment operation is required for the PPG signals on the left and right sides to eliminate the time delay or phase difference. The alignment operation may find the best matching position between the two PPG signals by using cross-correlation or dynamic time warping, etc., and translate or rotate the two PPG signals to be synchronized or coincident. The cross-correlation method is to find the time delay corresponding to its maximum value by calculating the cross-correlation function between two PPG signals and translate one of the PPG signals into alignment with the other PPG signal.
Fusion: the reliability of the two PPG signals is different due to the fact that PPG signals on the left and right sides may have different degrees of interference or distortion. Therefore, a fusion operation is required for the PPG signals on the left and right sides to obtain a more reliable PPG signal. The fusion operation can give different weights to the two PPG signals according to the signal-to-noise ratio or the signal-to-noise ratio of the two PPG signals by using methods such as weighted average or maximum likelihood, and the two PPG signals are weighted and summed or likelihood is maximized to obtain a clearer, stable and reliable PPG signal.
Heart rate estimation formula: the fusion is obtained by adopting the PPG signals on the left side and the right side through weighted average, and the calculation formula of the heart rate estimated value is as follows:
wherein,for heart rate estimation, Δt is the interpolated sampling interval, α is the fused weighted average coefficient, +.>And->Frequency domain representations of the PPG signal on the left and right sides, respectively, namely:
wherein F [. Cndot ] represents the Fourier transform.
The invention fully considers the difference of animal heart rate and human heart rate in frequency, rhythm, variability and the like, particularly the sampling frequency of the PPG sensor is more than 200Hz, the highest monitoring heart rate can be improved to 6000 times/min, thereby expanding the monitoring variety of the animal, improving the accuracy and stability of heart rate monitoring, and simultaneously, the PPG signal is preprocessed, adaptively filtered, interpolated, aligned, fused and the like by utilizing the information of the dual-channel PPG signal and the acceleration signal to obtain a clearer, stable and reliable PPG signal, and then the PPG signal is converted into a frequency domain through Fourier transformation, so that the frequency corresponding to the maximum amplitude of the PPG signal is found as a heart rate estimated value, thereby effectively inhibiting motion artifact and noise interference, and improving the accuracy and stability of animal heart rate monitoring.
The embodiment of the invention also provides a non-anesthetized animal heart rate monitoring method based on the dual-channel PPG, which comprises the following steps: the controller controls two PPG sensors and a triaxial gyroscope module on the skin surfaces on the left side and the right side of the animal to synchronously sample, and digital two-channel PPG signals and acceleration signals corresponding to the animal are obtained and uploaded to the upper computer, wherein the sampling frequency of the PPG sensors is more than 200 Hz; the upper computer sequentially executes the following signal processing steps according to the two-channel PPG signal and the acceleration signal uploaded by the controller: the method comprises the steps of preprocessing a dual-channel PPG signal to improve the quality of the PPG signal, adaptively filtering the dual-channel PPG signal in combination with an acceleration signal to eliminate motion artifacts and noise interference, interpolating the dual-channel PPG signal to complement missing data or equalize the lengths of the dual-channel PPG signal, aligning the dual-channel PPG signal to eliminate time delay or phase difference, fusing the dual-channel PPG signal to obtain a more reliable PPG signal, and calculating a heart rate estimated value according to the frequency corresponding to the maximum amplitude of the fused PPG signal.
Specifically, the preprocessing comprises the steps of removing direct current components, removing baseline drift and removing high-frequency noise, and the preprocessing formula is as follows:
Wherein,and->PPG signals on the left and right sides after pretreatment, respectively>And->Original PPG signals on the left and right sides, respectively, < >>Representation->Direct current component of>Representation->Is used for the direct current component of the (c),representation->Baseline drift of ∈10->Representation->Baseline drift of ∈10->Representation->High frequency noise of->Representation->Is a high frequency noise of (a).
The principle of the formula is that the motion state and the motion strength of an animal are judged according to acceleration signals, and then different preprocessing operations are carried out on PPG signals on the left side and the right side, such as DC component removal, baseline drift removal, high-frequency noise removal and the like, so that the quality of the PPG signals is improved. The direct current component refers to a constant part of the PPG signal that is independent of the heartbeat and affects the amplitude of the PPG signal; baseline drift refers to the time-varying portion of the PPG signal that affects the shape of the PPG signal; high frequency noise refers to high frequency interference in the PPG signal introduced by ambient light or electronics, etc., which can affect the clarity of the PPG signal. By removing these interfering factors, a clearer, more stable, and more reliable PPG signal may be obtained.
Specifically, the filtering formula is:
wherein,and->The filtered left and right PPG signals, respectively, " >Representing convolution, h θ (t, a (t)) represents the impulse response function of the adaptive filter, θ represents the parameters of the filter,/->Representing the acceleration signal;
where δ (t) represents a unit impulse function, δ' (t) represents a derivative of the unit impulse function, g (θ, a (t)) and f (θ, a (t)) represent gain and phase factors of the filter, respectively, are functions concerning θ and a (t).
The principle of the formula is to design an adaptive filter according to the correlation between the acceleration signal and the PPG signal, and filter the PPG signals on the left side and the right side so as to eliminate motion artifact and noise interference. Motion artifact refers to changes in the PPG signal due to physical movement or vascular movement of an animal during activity, etc., which affects the frequency and rhythm of the PPG signal; noise interference refers to random or periodic interference introduced by the external environment or electronic equipment, etc. to which the animal is subjected during the course of activity, which affects the amplitude and phase of the PPG signal. By using the adaptive filter, parameters of the filter are automatically adjusted according to the phase difference and amplitude ratio between the acceleration signal and the PPG signal, so as to achieve the optimal filtering effect.
In a preferred embodiment, the specific steps of adaptively filtering the dual-channel PPG signal in combination with the acceleration signal are as follows: the nonlinear least square method is used for estimating the two-channel PPG signal and the acceleration signal to obtain the amplitude B of each channel PPG signal, the amplitude A of the acceleration signal and the phase difference between the acceleration signal and each channel PPG signal The method comprises the steps of carrying out a first treatment on the surface of the Order the、/>Thereby obtaining the impulse response function h of the adaptive filter of the PPG signal of each channel θ (t, a (t)); and filtering the PPG signal of each channel according to the filtering formula.
h θ (t, a (t)) represents the impulse response of the adaptive filter as a function of time t and the acceleration signal a (t), the invention being based on the amplitude ratio and the phase difference between the acceleration signal and the PPG signal. θ represents a parameter of the filter, an adaptively updated variable, which reflects the characteristics of the filter. Generally, h θ (t, a (t)) may be expressed in the form:
where δ (t) represents a unit impulse function, δ' (t) represents a derivative of the unit impulse function, g (θ, a (t)) and f (θ, a (t)) represent gain and phase factors of the filter, respectively, are functions concerning θ and a (t).
When the input signal is a unit impulse function, the output signal is composed of two parts: a part is a part synchronized with the input signal, the amplitude of which is determined by a gain factor g (θ, a (t)); the other part is a part having a phase difference of pi/2 from the input signal, and its amplitude is determined by a phase factor f (θ, a (t)). This allows the filter to have different gain and phase characteristics for different frequency components, thereby achieving filtering of the input signal.
It is assumed that there is a non-linear relationship between the acceleration signal a (t) and the PPG signal x (t), namely:
wherein ω represents the heart rate frequency,the phase difference, a, B, is an unknown constant, C represents the dc component of the acceleration signal a (t), and D represents the dc component of the PPG signal x (t). Non-linear least squares method can be used to estimate ω,/and>a, B, C, D, then they are taken as filter parameters θ= [ ω, ]>,A,B,C,D]T. We can then define the gain factor and the phase factor as:
this may allow the filter to have a lower gain and a larger phase difference for frequency components having the same frequency but different phases and magnitudes between the acceleration signal and the PPG signal, thereby eliminating motion artifacts and noise interference.
Specifically, the interpolation formula is:
wherein,and->Respectively, the PPG signals of the left side and the right side after interpolation, I [. Cndot.]Representing the interpolation function.
The principle of the formula is that the two PPG signals are unequal in length or have a gap due to the fact that the PPG signals on the left side and the right side may have problems of inconsistent sampling or missing data. Therefore, interpolation operations are required for the PPG signals on the left and right sides to complement the missing data or to equalize the two PPG signals in length. Interpolation operation the unknown data point is calculated from the known data point by using a cubic spline interpolation method, thereby obtaining a more complete and uniform PPG signal.
Specifically, the alignment formula is:
wherein,and->Respectively aligned PPG signals, +.>Representing the time delay.
The principle of the formula is that the two PPG signals are not synchronous or consistent due to the fact that there may be a time delay or a phase difference between the PPG signals on the left and right sides. Therefore, an alignment operation is required for the PPG signals on the left and right sides to eliminate the time delay or phase difference. The alignment operation may find the best matching position between the two PPG signals by using cross-correlation or dynamic time warping, etc., and translate or rotate the two PPG signals to be synchronized or coincident. The cross-correlation method is to find the time delay corresponding to its maximum value by calculating the cross-correlation function between two PPG signals and translate one of the PPG signals into alignment with the other PPG signal.
Specifically, the heart rate estimation formula: the fusion is obtained by adopting the PPG signals on the left side and the right side through weighted average, and the calculation formula of the heart rate estimated value is as follows:
wherein,for heart rate estimation, Δt is the interpolated sampling interval, α is the fused weighted average coefficient, +.>And->Frequency domain representation of PPG signals on the left and right sides, respectivelyThe method comprises the following steps:
Wherein F [. Cndot ] represents the Fourier transform.
In a preferred embodiment, the controller uploads the acquired original PPG and acceleration data to an upper computer terminal with stronger computing capability for computing by using a Wi-Fi or Bluetooth module, so as to realize wireless heart rate monitoring.
The specific monitoring process is as follows: 1) Removing the epidermal hair with the length of 2-3 cm and the width of 1.5-2 cm below the rear neck of the tested animal by using a shaver; 2) Adjusting the pose of the heart rate acquisition module, wherein two parallel PPG modules below the heart rate acquisition module are positioned at dehairing positions; 3) The auxiliary wearing binding belt is used, penetrates through the left fixing hole and the right fixing hole of the heart rate acquisition device and is firmly bound on the back of the tested animal; 4) After being decoded by the main control chip, the PPG and triaxial acceleration sensor data are transmitted to a computer upper computer through a Bluetooth SPP protocol; 5) And (5) unlocking the fixing straps, and taking down the heart rate acquisition module.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims (4)

1. A non-anesthetized animal heart rate monitoring system based on dual channel PPG, comprising: two PPG sensors are used for respectively acquiring two-channel PPG signals of the skin surfaces at the left side and the right side of the animal; the triaxial gyroscope module is used for collecting acceleration signals of animals; the controller is used for controlling the PPG sensors on the left side and the right side and the triaxial gyroscope module to synchronously sample to obtain a digital dual-channel PPG signal and an acceleration signal, the sampling frequency of the PPG sensor is above 200Hz, and the controller uploads the acquired dual-channel PPG signal and acceleration signal to the upper computer by using a Wi-Fi or Bluetooth module; the upper computer sequentially executes the following signal processing steps according to the two-channel PPG signal and the acceleration signal uploaded by the controller: preprocessing the two-channel PPG signals to improve the quality of the PPG signals, carrying out self-adaptive filtering on the two-channel PPG signals in combination with the acceleration signals to eliminate motion artifacts and noise interference, interpolating the two-channel PPG signals to complement missing data or equalize the lengths of the two-channel PPG signals, aligning the two-channel PPG signals to eliminate time delay or phase difference, fusing the two-channel PPG signals to obtain more reliable PPG signals, and calculating to obtain a heart rate estimated value according to the frequency corresponding to the maximum amplitude of the fused PPG signals; wherein,
The specific steps of carrying out self-adaptive filtering on the dual-channel PPG signal by combining the acceleration signal are as follows: the nonlinear least square method is used for estimating the two-channel PPG signal and the acceleration signal to obtain the amplitude B of each channel PPG signal, the amplitude A of the acceleration signal and the phase difference between the acceleration signal and each channel PPG signalThe method comprises the steps of carrying out a first treatment on the surface of the Let->、Thereby obtaining the impulse response function h of the adaptive filter of the PPG signal of each channel θ (t, a (t)); filtering the PPG signal of each channel according to a filtering formula, wherein the filtering formula is as follows:
wherein the method comprises the steps of，And->The filtered left and right PPG signals, respectively, ">And->PPG signals on the left and right sides after pretreatment, respectively>Representing convolution, h θ (t, a (t)) represents the impulse response function of the adaptive filter, θ represents the parameters of the filter,/->Representing the acceleration signal;
wherein δ (t) represents a unit impulse function, δ' (t) represents a derivative of the unit impulse function, g (θ, a (t)) and f (θ, a (t)) represent gain and phase factors of the filter, respectively, are functions concerning θ and a (t);
the interpolation formula is as follows:
wherein,and->Respectively, the PPG signals of the left side and the right side after interpolation, I [. Cndot.]Representing an interpolation function;
the formula of the alignment is:
Wherein,and->Respectively aligned PPG signals, +.>Representing a time delay;
the fusion is obtained by adopting the PPG signals on the left side and the right side through weighted average, and the calculation formula of the heart rate estimated value is as follows:
wherein,for heart rate estimation, Δt is the interpolated sampling interval, α is the fused weighted average coefficient, +.>Andfrequency domain representations of the PPG signal on the left and right sides, respectively, namely:
wherein F [. Cndot ] represents the Fourier transform.
2. The non-anesthetized dual channel PPG-based animal heart rate monitoring system of claim 1, wherein the preprocessing comprises removing direct current components, removing baseline wander, and removing high frequency noise, the preprocessing formula being as follows:
wherein,and->Original PPG signals on the left and right sides, respectively, < >>Representation->Direct current component of>Representation->Direct current component of>Representation->Baseline drift of ∈10->Representation->Baseline drift of ∈10->Representation->High frequency noise of->Representation->Is a high frequency noise of (a).
3. The non-anesthetized animal heart rate monitoring method based on the dual-channel PPG is characterized by comprising the following steps of: the controller controls two PPG sensors and a triaxial gyroscope module on the skin surfaces on the left side and the right side of an animal to synchronously sample, digital two-channel PPG signals and acceleration signals corresponding to the animal are obtained and uploaded to the upper computer, the sampling frequency of the PPG sensors is more than 200Hz, and the controller uploads the acquired two-channel PPG signals and acceleration signals to the upper computer by using a Wi-Fi or Bluetooth module; the upper computer sequentially executes the following signal processing steps according to the two-channel PPG signal and the acceleration signal uploaded by the controller: preprocessing the two-channel PPG signals to improve the quality of the PPG signals, carrying out self-adaptive filtering on the two-channel PPG signals in combination with the acceleration signals to eliminate motion artifacts and noise interference, interpolating the two-channel PPG signals to complement missing data or equalize the lengths of the two-channel PPG signals, aligning the two-channel PPG signals to eliminate time delay or phase difference, fusing the two-channel PPG signals to obtain more reliable PPG signals, and calculating to obtain a heart rate estimated value according to the frequency corresponding to the maximum amplitude of the fused PPG signals; wherein,
The specific steps of carrying out self-adaptive filtering on the dual-channel PPG signal by combining the acceleration signal are as follows: the nonlinear least square method is used for estimating the two-channel PPG signal and the acceleration signal to obtain the amplitude B of each channel PPG signal, the amplitude A of the acceleration signal and the phase difference between the acceleration signal and each channel PPG signalThe method comprises the steps of carrying out a first treatment on the surface of the Let->、Thereby obtaining the impulse response function h of the adaptive filter of the PPG signal of each channel θ (t, a (t)); filtering the PPG signal of each channel according to a filtering formula, wherein the filtering formula is as follows:
wherein,and->Respectively the left side and the right side after filteringIs>And->PPG signals on the left and right sides after pretreatment, respectively>Representing convolution, h θ (t, a (t)) represents the impulse response function of the adaptive filter, θ represents the parameters of the filter,/->Representing the acceleration signal;
wherein δ (t) represents a unit impulse function, δ' (t) represents a derivative of the unit impulse function, g (θ, a (t)) and f (θ, a (t)) represent gain and phase factors of the filter, respectively, are functions concerning θ and a (t);
the interpolation formula is as follows:
wherein,and->Respectively, the PPG signals of the left side and the right side after interpolation, I [. Cndot.]Representing an interpolation function;
the formula of the alignment is:
Wherein,and->Respectively aligned PPG signals, +.>Representing a time delay;
the fusion is obtained by adopting the PPG signals on the left side and the right side through weighted average, and the calculation formula of the heart rate estimated value is as follows:
wherein,for heart rate estimation, Δt is the interpolated sampling interval, α is the fused weighted average coefficient, +.>Andfrequency domain representations of the PPG signal on the left and right sides, respectively, namely:
wherein F [. Cndot ] represents the Fourier transform.
4. A non-anesthetized animal heart rate monitoring method based on dual channel PPG as claimed in claim 3, wherein the preprocessing comprises removing direct current component, removing baseline drift and removing high frequency noise, the preprocessing formula is as follows:
wherein,and->Original PPG signals on the left and right sides, respectively, < >>Representation->Direct current component of>Representation->Direct current component of>Representation->Baseline drift of ∈10->Representation->Baseline drift of ∈10->Representation->High frequency noise of->Representation->Is a high frequency noise of (a).
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