CN106037706A - Wearable device capable of monitoring heart rate based on photoplethysmography and monitoring method - Google Patents

Abstract

The present invention discloses a wearable device capable of monitoring heart rate based on photoplethysmography and a monitoring method. The present invention is based on the photoplethysmography for real-time monitoring of the heart rate of the old person. A heart rate measuring module uses a heart rate sensor and the heart rate sensor is embedded in a wearable watch. A master chip is C8051F340, and is used for controlling the work of the sensor and processing signals and computing. In order to make the measured value more accurate, each wearable device is provided with two heart rate sensors which respectively measure heart rates at the ulnar artery and the radial artery. In the measuring process, the intentional or unintentional movement of the old person can produce motion artifacts, and computing results are affected, so an output PPG signal after amplification and analog-digital conversion input to the master chip firstly needs to be processed (remove motion artifacts), and then heart rate calculation is carried out. The invention utilizes a compression sensing algorithm to denoise the PPG signal. Since the signal and noise are unknown, a gradient projection algorithm is used to recover the signal, and finally the PPG signal is reconstructed.

Description

A heart rate monitoring wearable device and monitoring method based on photoplethysmography

technical field

The present invention relates to the technical field of wearable electronic devices, in particular to a wearable device and a monitoring method for heart rate monitoring based on photoelectric volumetric method.

Background technique

With the development of society, there are more and more empty-nest elderly people, and many elderly people are found dead at home for many days. Although many communities have enabled alarm tools such as "pagers", these devices require the initiative of the elderly living alone, which is not conducive to emergency treatment. Heart rate refers to the number of times the heart beats per minute, which can reflect the working state of the heart and is an important physiological indicator of the human body. Therefore, it is very meaningful to implement real-time monitoring and alarming of heart rate for empty-nest elderly.

According to whether it is in contact with the subject's body, heart rate measurement methods can be divided into contact and non-contact methods. The photoplethysmography (PPG for short) used in this design is a contact heart rate measurement method. This method is based on the principle that the amount of light absorbed by arterial blood changes with the pulse of the artery. A non-invasive method of detection of blood volume changes. The sensor based on this method generally consists of a light source and a photoelectric transducer. The light source generally selects a light-emitting diode with a certain wavelength (500-700nm) that absorbs oxygen and hemoglobin in human arterial blood better. The photoelectric transducer is used to absorb the light reflected by the skin, also called photodetector. When the light beam passes through the peripheral blood vessels of the human body, the light transmittance is different due to the change of the blood volume. At the same time, the photoelectric converter receives the light reflected by the human body and converts it into a current signal, and the change amplitude of the current signal is proportional to the pulse amplitude. Proportional. Since the pulse changes periodically with the beating of the heart, the change period of the electrical signal output by the photoelectric transducer is the heart rate. Because it is based on the photoelectric volume method, the signal output by the photoelectric converter is also called the PPG signal.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art and provide a heart rate monitoring wearable device and monitoring method based on the photoplethymetric method. sensor, and embed the heart rate sensor in the wearable watch. The main control chip is C8051F340, which is used to control the work of the sensor as well as signal processing and calculation. In order to make the measurement more accurate, there are two heart rate sensors on each wearable device, which measure the heart rate at the ulnar artery and the radial artery respectively.

During the measurement process, due to the intentional or unintentional movement of the elderly, motion artifacts will be generated, which will affect the calculation results. Therefore, the output photoelectric volume (PPG) signal needs to be processed first after being amplified and input to the main control chip through analog-to-digital conversion (remove motion Artifacts) and then calculate the heart rate. The invention utilizes a compressed sensing algorithm to filter the noise of the photoelectric volume (PPG) signal. Since both the signal and the noise are unknown, the gradient projection algorithm is used to restore the signal, and finally the photoelectric volume (PPG) signal is reconstructed.

The purpose of the present invention is achieved through the following technical solutions:

A wearable device for heart rate monitoring based on photoplethysmography, including a main control chip, a first heart rate sensor, a second heart rate sensor, a communication module and a display module, wherein:

The main control chip is provided with a control module, a signal processing module, an early warning module and an output module,

The control module controls the first heart rate sensor and the second heart rate sensor to collect the user's heart rate value and output a PPG signal, and the first heart rate sensor and the second heart rate sensor are used to detect the heart rate at the user's ulnar artery and radial artery respectively value;

The signal processing module is used to filter the PPG signal and calculate the actual heart rate;

The early warning module is used to judge whether the user's heart rate value is zero according to the actual heart rate, and convert the judgment result into a corresponding control signal;

The output module is used to output the control signal;

The communication module is provided with a GPS module;

The display module is used for displaying the heart rate value.

The main control chip adopts C8051F340, and the communication module adopts SIM908.

A monitoring method for a heart rate monitoring wearable device based on photoplethysmography, comprising:

The main control chip controls the first heart rate sensor to collect the user's first heart rate value in real time;

The first heart rate sensor amplifies and converts the first heart rate value and then inputs the PPG signal to the main control chip, and performs signal processing on the PPG signal to obtain the first actual heart rate value:

If the first actual heart rate value is not zero, the first actual heart rate value is displayed through the display module;

If the first actual heart rate value is zero, the main control chip controls the second heart rate sensor to collect the second heart rate value of the user;

The second heart rate sensor amplifies and converts the second heart rate value and then inputs the PPG signal to the main control chip, and performs signal processing on the second heart rate value to obtain a second actual heart rate value:

If the second actual heart rate value is not zero, notify the user and the user's family members to replace the first heart rate sensor through the communication module;

If the second actual heart rate value is also zero, the user's family members are contacted through the communication module.

The signal processing method includes using a compressed sensing algorithm and a gradient projection algorithm to filter and restore the PPG signal, and finally reconstruct the PPG signal.

Compared with the prior art, the beneficial effects brought by the technical solution of the present invention are:

1. The communication module of the present invention is equipped with a GPS module, which can upload user location information in real time to ensure that the user can be found in time, safe and reliable.

2. The main control chip of the present invention is equipped with a signal processing module, which can denoise and reconstruct the measured PPG signal, with high efficiency and ensures accurate and reliable monitoring data.

3. In order to make the monitoring value more accurate and reliable, there are two heart rate sensors on each wearable device, which measure the heart rate at the ulnar artery and the radial artery respectively.

Description of drawings

Fig. 1 is a schematic flow chart of the monitoring method of the present invention.

Fig. 2 is a schematic diagram of the processing flow in the signal processing module.

Fig. 3 is a schematic diagram of signal processing when the wrist is shaken vertically.

Fig. 4 is a schematic diagram of signal processing when the wrist is shaken horizontally.

Fig. 5 is a schematic diagram of signal processing when the wrist is bent.

detailed description

Below in conjunction with accompanying drawing, the present invention will be further described:

A wearable device for heart rate monitoring based on photoplethysmography, including a main control chip, a first heart rate sensor, a second heart rate sensor, a communication module and a display module, wherein:

The main control chip is provided with a control module, a signal processing module, an early warning module and an output module,

The control module controls the first heart rate sensor and the second heart rate sensor to collect the user's heart rate value and output a PPG signal. The first heart rate sensor and the second heart rate sensor are embedded on the watch chain of the wearable watch, and are used to detect the user's size respectively. The heart rate at the arterial artery and the radial artery. The pulse beats at these two places are relatively obvious and easy to measure. Both heart rate sensors are attached to the skin surface, but not too tight; under normal circumstances, only the first heart rate sensor at the ulnar artery in working condition.

The signal processing module is used to filter the PPG signal and obtain the actual heart rate;

The early warning module is used to judge whether the user's heart rate value is zero according to the actual heart rate, and convert the judgment result into a corresponding control signal;

The output module is used to output the control signal;

The communication module is provided with a GPS module;

The display module is used for displaying the heart rate value.

In this embodiment, the communication module is SIM908. SIM908 is a four-frequency GSM/GPRS module integrating GPS navigation technology. It has a compact module size and integrates GPRS and GPS in an SMT package. Its industrial-grade standard interface and GPS function are available in The places covered by GSM and GPS signals can realize seamless tracking anytime and anywhere, and can be purchased at Shenzhen Fuweida Co., Ltd.

In this embodiment, the main control circuit uses C8051F340 as the main chip to control the working state of the two heart rate sensors. Normally, only the first heart rate sensor (Pulse Sensor1) is in the working state of the two sensors, while the second heart rate sensor (Pulse Sensor2) is in the working state. In the closed state, its switch is controlled by the main control chip. Under normal working conditions, the photoelectric volume (PPG) signal detected by the first heart rate sensor (Pulse Sensor1) is first amplified and subjected to analog-to-digital conversion, and the converted digital signal is input to the main control chip for related processing and heart rate calculation. When the single-chip microcomputer detects that the photoelectric volume (PPG) signal output by the first heart rate sensor (Pulse Sensor1) has a heart rate of zero, it controls and starts the second heart rate sensor (Pulse Sensor2) to enter the working state to specifically determine whether the sensor is faulty or the heartbeat of the elderly Sudden arrest. If the calculation result of the second heart rate sensor (Pulse Sensor2) is not zero and is a normal value, it indicates that the sensor has failed, and a message is sent through the communication module (SIM908) to notify the child to replace the sensor; if the second heart rate sensor (PulseSensor2) If the calculated value is also zero, it may be that the old man has stopped his heartbeat. At this time, the communication module (SIM908) can be used to contact the elderly, children and doctors, and send a distress signal, and the GPS module embedded in the communication module (SIM908) can realize accurate positioning, and the positioning information is also available. It can be sent through the communication module (SIM908). In this way, an active call for help can be implemented without the operation of the elderly. The main work flow chart is shown in Figure 1:

For the convenience of description and concise display, the first heart rate sensor involved in Figure 1 and below is replaced by Pulse Sensor1, the second heart rate sensor is replaced by Pulse Sensor2, and the main control chip is replaced by F340.

During the test, control the two sensors to work at the same time, and observe their working status. Then test when Pulse Sensor1 works normally, and when Pulse Sensor1 measures the heart rate to zero. At this time, when Pulse Sensor2 is not zero, it may be because the sensor Pulse Sensor1 is damaged. Send a message through SIM908 to contact others to replace the sensor. This is command 2; if Pulse Sensor2 is also zero, there may be an emergency such as cardiac arrest, and at this time, a distress signal is sent through SIM908, which is command 1. The normal test of the two heart rate sensors is divided into motion and immobility to test the feasibility and effectiveness of the algorithm in the design.

During the experiment through the wearable device, the PPG signal is sampled and saved every 1 minute to calculate the heart rate. After testing, both heart rate sensors can obtain relatively stable and accurate PPG signals when the subject remains quiet. When testing, first set the Pulse Sensor1 to the working state, output a stable PPG signal, and measure the accurate heart rate. Finally, keep the sensor away from the tester's skin and let its output be zero. When the single-chip microcomputer detects that the heart rate is zero, Pulse Sensor2 will automatically turn on to obtain the PPG signal. When the Pulse Sensor2 is in normal working condition, the measured PPG signal is more accurate, and the calculated heart rate is in the normal range, the MCU will send an instruction to the SIM908, and the SIM908 will send the replacement sensor information to the pre-set number after receiving the instruction. Keep the Pulse Sensor2 away from the skin of the subject to make the output zero. At this time, the MCU will send different commands to the SIM908, and the SIM908 will also send a distress signal and send the location information transmitted by GPRS. The location information is accurate after testing.

In the process of PPG signal measurement, due to the intentional or unintentional movement of the elderly, motion artifacts will be generated, which will affect the final calculation results. In order to filter out noise, the digital PPG signal input to the single master chip first passes through a Butterworth filter. Then use compressive sensing algorithm to remove noise. The compressive sensing algorithm mainly includes three aspects: the sparse representation of the signal, the design of the observation matrix and the fast recovery algorithm. As shown in Figure 2, the sparse representation uses the Haar wavelet transform in this design to construct a wavelet base to sparse the measurement signal, and the observation matrix uses a Gaussian random matrix. Since the PPG signal and noise are both unknown, we reduce the problem of finding a sparse solution to a band-limited quadratic programming problem, and use the gradient projection algorithm to restore the signal and remove the noise. The reconstructed signal is a noiseless and accurate PPG signal, which is used to calculate the heart rate and display the calculated value on the liquid crystal display, that is, the display module.

When the tester performs intense exercise, motion artifacts will be generated, which will affect the calculation of heart rate. Therefore, when the PPG signal is input to the main control chip to calculate the heart rate, it is necessary to filter the noise first, use the compressed sensing algorithm to sparse the signal and restore and reconstruct it, and use the gradient projection algorithm to restore the signal, and filter out the noise while restoring, in order to verify the effectiveness of the algorithm To compare it with the Orthogonal Matching Pursuit (OMP), the experiment measures the motion artifacts produced by three kinds of motion: vertical shaking of the wrist, horizontal shaking of the wrist and bending of the wrist. The PPG signal with three kinds of noise is processed by two methods of gradient projection algorithm (GPSR) and orthogonal matching pursuit algorithm (OMP). The results are shown in Figure 3, Figure 4 and Figure 5:

In Fig. 3, (a) is the noise generated by vertical motion, (b) and (d) are the sparse recovery graphics using two methods, and (c) and (e) are the reconstructed PPG signal diagrams of the two methods;

In Fig. 4, (a) is noise generated by horizontal movement, (b) and (d) are sparse recovery graphics using two methods, and (c) and (e) are reconstructed PPG signal diagrams of two methods;

In Figure 5, (a) is the noise generated by the bending motion, (b) and (d) are the sparse recovery graphs using the two methods, and (c) and (e) are the reconstructed PPG signal diagrams of the two methods

It can be seen from the three figures that the signal recovered and reconstructed by the gradient projection algorithm (GPSR) is closer to the normal heart rate signal waveform. Compared with the heart rate of the calculated reconstructed PPG signal and the heart rate of the original signal directly input into the microcontroller, the heart rate of the reconstructed signal is closer to the heart rate of the tester. Calculate the heart rate of the PPG signal reconstructed by the two methods, and compare it with the tester's normal heart rate. Five healthy testers, aged between 20 and 45 years old, are used in the experiment. The results are shown in Table 1. The normal value refers to the heart rate of the tester under normal conditions. It can be seen from Table 1 that GPSR is more efficient in signal reconstruction and noise removal.

Table 1

The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solution of the present invention, and the above specific embodiments are only illustrative and not restrictive. Without departing from the gist of the present invention and the scope of protection of the claims, those skilled in the art can also make many specific changes under the inspiration of the present invention, and these all belong to the protection scope of the present invention.

Claims (4)

1. A wearable device for heart rate monitoring based on photoplethysmography, characterized in that it includes a main control chip, a first heart rate sensor, a second heart rate sensor, a communication module and a display module, wherein: The main control chip is provided with a control module, a signal processing module, an early warning module and an output module; The control module controls the first heart rate sensor and the second heart rate sensor to collect the user's heart rate value and output a PPG signal, and the first heart rate sensor and the second heart rate sensor are used to detect the heart rate at the user's ulnar artery and radial artery respectively value; The signal processing module is used to filter the PPG signal and calculate the actual heart rate; The early warning module is used to judge whether the user's heart rate value is zero according to the actual heart rate, and convert the judgment result into a corresponding control signal; The output module is used to output the control signal; The communication module is provided with a GPS module; The display module is used for displaying the heart rate value. 2. A wearable device for heart rate monitoring based on photoplethysmography according to claim 1, wherein the main control chip adopts C8051F340, and the communication module adopts SIM908. 3. A kind of monitoring method based on the heart rate monitoring wearable device of photoplethysmography according to claim 1, is characterized in that, comprises: The main control chip controls the first heart rate sensor to collect the user's first heart rate value in real time; The first heart rate sensor amplifies and converts the first heart rate value and then inputs the PPG signal to the main control chip, and performs signal processing on the PPG signal to obtain the first actual heart rate value: If the first actual heart rate value is not zero, the first actual heart rate value is displayed through the display module; If the first actual heart rate value is zero, the main control chip controls the second heart rate sensor to collect the second heart rate value of the user; The second heart rate sensor amplifies and converts the second heart rate value and then inputs the PPG signal to the main control chip, and performs signal processing on the second heart rate value to obtain a second actual heart rate value: If the second actual heart rate value is not zero, notify the user and the user's family members to replace the first heart rate sensor through the communication module; If the second actual heart rate value is also zero, the user's family members are contacted through the communication module. 4. according to the described a kind of monitoring method of the heart rate monitoring wearable device based on photoplethysmography according to claim 3, it is characterized in that, described signal processing mode comprises utilizing compressive sensing algorithm and gradient projection algorithm to carry out noise filtering and Restoring, and finally reconstructing the PPG signal.