Blood oxygen saturation measuring and calculating method and system based on Gr-WSe2-Pt flexible photoelectric sensor

Abstract

The invention discloses an oxyhemoglobin saturation measuring and calculating method and system based on a Gr-WSe2-Pt flexible photoelectric sensor, relates to a medical equipment built-in technology, and provides the scheme for solving the problems in the prior art. The method is mainly characterized in that a flexible photoelectric sensor is used for collecting optical signals, then an FPGA development board is used for carrying out median updating operation on 27 groups of electric signals, and then the FPGA development board is used for extracting extreme values of 49974 median values which are updated in real time within 10 seconds. And finally, controlling the light sources with the two wavelengths to perform periodic output respectively by utilizing 2.5 billion clock cycles, and obtaining an oxyhemoglobin saturation value based on an oxyhemoglobin saturation calculation formula. The device has the advantages that the simple light source and the flexible patch type sensor are used, so that the detection part can be attached to the skin. Measurement errors caused by movement are reduced, and wearing discomfort can also be reduced. Meanwhile, a simple algorithm is adopted to calculate and process the PPG signal obtained through measurement, and the requirement for a processor is lowered on the premise that noise can be well suppressed.

Description

Technical Field

[0001] The present invention relates to a built-in algorithm and system for medical equipment, and in particular to a blood oxygen saturation measurement method and system based on a Gr-WSe2-Pt flexible photoelectric sensor. Background Art

[0002] At present, there are many non-invasive blood oxygen saturation measurement methods on the market through photoelectric sensors, which can be mainly divided into two categories, namely multi-spectral and hyperspectral types and time-sharing detection types. The former has the advantages of high detection accuracy and good real-time performance, but it has problems such as large size, complex structure, high cost, and poor adaptability to different skin types and skin colors. The latter has a simpler structure and low cost, but because it often requires time-sharing irradiation of light of different wavelengths during the measurement process, and is easily interfered by electromagnetic waves in the environment, the measurement accuracy is relatively low.

[0003] For example, the public documents CN 116807468A and CN 114711766A are typical multi-spectral and hyperspectral types. Although both methods obtain more data through spectroscopy and introduce many error factors in the data processing part, further improving the accuracy of measurement, the acquisition and imaging of spectral images require a relatively complex optical system, and the data to be processed later is also more complex, and there is still a significant disadvantage in terms of system volume.

[0004] The time-sharing detection method usually uses two different wavelengths of waves to illuminate the tissue to be tested at different time periods, and obtains the tissue's absorption of light by recording the intensity of the incident light and the reflected light. Since hemoglobin and oxyhemoglobin have different absorptions of light of different wavelengths, the blood oxygen saturation can be solved by the absorbance of two sets of light of different wavelengths. The main difficulty of the time-sharing detection type is how to reduce a series of noises and errors caused by the environment and measurement; and when selecting data points on the PPG waveform graph obtained by the two waveforms, how to ensure that the time of the selected points is consistent.

[0005] In recent years, there are many time-sharing detection methods based on photoplethysmography (PPG) signals:

[0006] For example, in the public document CN 118177797A, they used green light for tissue irradiation while choosing to use red light and near-infrared light as the time-sharing irradiation light sources. Since the penetration depth of the green PPG signal in the skin is low, the obtained signal is less polluted by noise, which has a good guiding significance for the baseline drift removal and peak detection of the red and near-infrared PPG signals. However, the corresponding cost is also very obvious. The addition of green calibration light will lengthen the entire sampling period, and put forward higher requirements on the functionality of the light source and the photoelectric sensor, and may also be accompanied by the addition of additional processing hardware. At the same time, how to ensure the low noise of the green PPG signal has also become a new problem.

[0007] Another example is the public document CN 113598761A, which uses a non-contact CCD sensor to sample the light intensity around the light source, thereby obtaining the tissue light intensity under different wavelengths of light. At the same time, the durability of the device is improved. For different tissues or people, only the distance and angle between the CCD sensor and the tissue need to be changed, without replacing system components. However, the problems of this method are also very obvious: first, an additional set of tissue absorbance images in a lightless state needs to be measured, which increases the workload; second, the data obtained by the CCD sensor is in the form of an image rather than a direct data point, so additional data processing is required, which poses a great challenge to the processor selection and processing time; third, the CCD does not contact the skin, but is very sensitive to the imaging distance, and the light source needs to be placed at the center of the image as much as possible, which inevitably requires a more precise and reliable fixing device, and the overall volume of the system will also increase accordingly; finally, when changing the measured tissue or population, it is necessary to readjust the distance between the CCD and the tissue and the imaging center point more accurately, and the operation learning cost is high, which is not suitable for the general public.

[0008] Another example is the public document CN 116725529A, which proposes a blood oxygen saturation calculation method based on FIR filtering and mean filtering. The maximum and minimum values ​​in the PPG waveform are selected as data points to reduce the time error, and a dynamically updated finger touch state threshold Thre is used to control the start and end of the measurement. Although this method is very simple and efficient in theory, the FIR filter calculation is large in actual implementation and requires more hardware resources. Although FPGA can be used for processing, it is difficult to achieve integration.

[0009] Finally, as disclosed in the public document CN 117442199A, they first used a single wavelength of light for measurement, and modified the radiation transfer equation based on the measurement data, so that the light source group outputs the corresponding multi-wavelength light based on the radiation transfer equation. At the same time, a pre-trained Retinex-LSTM hybrid model is stored in the processing unit to calculate the blood oxygen saturation. Although the addition of a pre-trained processing model can improve the accuracy of blood oxygen saturation analysis, this undoubtedly places high demands on the performance and storage space of the processing unit, and is not friendly to the portability of the measurement system. Summary of the invention

[0010] The purpose of the present invention is to provide a blood oxygen saturation measurement method and system based on a Gr-WSe2-Pt flexible photoelectric sensor to solve the problems existing in the above-mentioned prior art.

[0011] The blood oxygen saturation measurement method based on the Gr-WSe2-Pt flexible photoelectric sensor described in the present invention uses two independent light sources with wavelengths of 650nm and 810nm to periodically and alternately illuminate the fingertips to be measured, obtain the transmitted light signal of the fingertips to measure the blood oxygen saturation and display it.

[0012] The Gr-WSe2-Pt flexible photoelectric sensor is attached to the fingertip to collect the transmitted light signal. After filtering, amplifying and analog-to-digital conversion of the collected light signal, the FPGA development board is used to perform the following operations:

[0013] S1. The number of repetitions of the clock cycle of the 50MHz clock frequency is counted as a;

[0014] S2. Whenever a reaches 10000, a is cleared, and the light source switching and blood oxygen calculation enable count value b is counted once, and the input voltage value at this time is recorded; if b=27, steps S3 to S4 are executed once; if b>27, steps S5 to S6 are executed once; if b<27, this step is repeated;

[0015] S3. taking the 27 initially recorded voltage values ​​as an initial array;

[0016] S4. First, divide the 27 voltage values ​​into three large groups of 9 data each, and then divide the large groups into three small groups of 3 data each. Each group has a maximum value, a minimum value, and a median. Find the minimum value of the three data of the maximum value of each of the three groups, the maximum value of the three data of the minimum value of each of the three groups, and the median of the three data of the median to form a new group of three data. Each large group forms a new group with the same rule. Each new group has a maximum value, a minimum value, and a median. Find the minimum value of the three data of the maximum value of each of the three groups, the maximum value of the three data of the minimum value of each of the three groups, and the median of the three data of the median to get the final three-number group, and the median of this three-number group is the median of the 27 voltages.

[0017] S5. Every time a new voltage value is input, the earliest input voltage value V b-26 Shift out the array and set the voltage value V 0.2ms ago b Assign values ​​to the previous V in sequence b-1 , assign the new input voltage value to V b ; Perform step S4 again to obtain a new median; obtain the waveform of voltage value change through median filtering;

[0018] S6. Whenever b reaches 25027, let b = 27 and execute steps S7 to S9 once;

[0019] S7. Invert the light source control value F to change the light source output;

[0020] S8. Find the n maximum points of the waveform within the current 5.0s and take the average value as m avg ;

[0021] S9. Find the n-1 low voltage intervals of the current waveform within 5.0s, take 1000 continuous data for each interval and calculate the average value, record it as n avg ;

[0022] S10. If F = 0, then m avg Assign to m 650nm , n avg Assign to n 650nm ; If F = 1, then m avg Assign to m 810nm , n avg Assign to n 810nm ; m 650nm , n 650nm , m 810nm , n 810nm Substitute the blood oxygen saturation calculation formula to obtain the blood oxygen saturation value and output it to the display screen;

[0023] in,

[0024] m 650nm is the average maximum value of the PPG signal corresponding to the wavelength of 650nm;

[0025] n 650nm is the average minimum value of the PPG signal corresponding to the wavelength of 650nm;

[0026] m 810nm is the average maximum value of the PPG signal corresponding to the wavelength of 810nm;

[0027] n 810nm It is the average minimum value of the PPG signal corresponding to the wavelength of 810nm.

[0028] The blood oxygen saturation measurement system based on the Gr-WSe2-Pt flexible photoelectric sensor described in the present invention uses the method to measure blood oxygen saturation.

[0029] The blood oxygen saturation measurement method and system based on the Gr-WSe2-Pt flexible photoelectric sensor described in the present invention has the advantages that a simple light source and a flexible patch sensor are used so that the detection part can be attached to the skin. This not only reduces the measurement error caused by movement, but also reduces the discomfort of wearing. At the same time, a simple algorithm is used to calculate and process the measured PPG signal, which reduces the requirements for the processor under the premise of good noise suppression. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the process of the method described in the present invention.

[0031] Figure 2 It is a schematic diagram of the voltage curve of the method described in the present invention in the low voltage small amplitude oscillation area. DETAILED DESCRIPTION

[0032] The blood oxygen saturation measurement system based on the Gr-WSe2-Pt flexible photoelectric sensor described in the present invention includes an FPGA development board and a 650nm light source, an 810nm light source, a Gr-WSe2-Pt flexible photoelectric sensor, a filter amplifier, an ADC module, and a display screen connected to the FPGA development board signal. The high-frequency AC light source emits light through the fingertip to be measured, and the photoelectric sensor converts the transmitted light signal into an electrical signal. The electrical signal is demodulated and amplified by the filter amplifier, and then converted from an analog signal to a digital signal by the ADC module and handed to the FPGA development board. The built-in algorithm of the FPGA development board is used to control the two wavelengths of the light source to switch and work alternately with a cycle of 5s. At the same time, the blood oxygen saturation is calculated using the data of the first two switching cycles, and the obtained blood oxygen saturation data is transmitted to the display screen, and the display screen displays the blood oxygen saturation.

[0033] The use of simple light sources and flexible patch sensors allows the detection part to be attached to the skin, which can effectively reduce the impact of ambient light on the measured light intensity. It can further reduce the noise error caused by motion displacement and optimize wearing comfort.

[0034] When the wavelength is greater than 600nm, the molar absorption coefficients of reduced hemoglobin and oxygenated hemoglobin are greatly reduced, that is, the light waves in this band have better penetration, which can ensure that there are still better detection results under low light intensity. And if one of the two wavelengths used for detection is selected below 720 nanometers, and the other wavelength is greater than 730 nanometers, the crosstalk is low, the separation is high, and accurate concentration changes can be obtained. Therefore, the present invention uses two wavelengths of 650nm and 810nm LED light-emitting tubes as light sources to detect human blood oxygen saturation. The two light sources are controlled by an FPGA development board and work alternately with a cycle of 5.0s.

[0035] After the FPGA development board works in one of the 650nm wavelength light source or the 810nm wavelength light source, it first samples at a period of 0.2ms to filter out a large amount of repeated or approximate data to reduce the subsequent workload. Then the median filter method is used to filter out the instantaneous extreme abnormal data in the original waveform to obtain a smoother waveform data group. With a period of 5.0s, the switching of the two light sources is controlled, and the data within these 5s is processed to obtain a new m avg and n avg , after assigning the corresponding variables, it is calculated according to the blood oxygen saturation formula.

[0036] The formula is:

[0037]

[0038] The operation parameters are: Hb650nm =3750.12cm -1 M -1 , ε Hb810nm =717.08cm -1 M -1 ,

[0039] Specifically, the system uses the FPGA development board as the core and uses the following method to measure blood oxygen saturation.

[0040] like Figure 1 As shown, the blood oxygen saturation measurement method based on the Gr-WSe2-Pt flexible photoelectric sensor described in the present invention includes the following steps:

[0041] S1. Count the number of repetitions of the clock cycle of the 50 MHz clock frequency as a.

[0042] S2. Whenever a reaches 10000, that is, after 0.2ms, a is cleared, the light source switching and blood oxygen calculation enable count value b is counted once, and the input voltage value at this time is recorded; if b=27, steps S3 to S4 are executed once; if b>27, steps S5 to S6 are executed once; if b<27, this step is repeated.

[0043] S3. After repeating step S2 27 times, b=27 at this time, the first 27 voltage values ​​are stored as the initial array, that is, the data recorded in the first 5.4 ms.

[0044] S4. First, divide the 27 voltage values ​​into three large groups of 9 data in each group, and then divide each group into three small groups of 3 data in each group. Each group has a maximum value, a minimum value, and a median. Find the minimum value of the three data of the maximum value of each of the three groups, the maximum value of the three data of the minimum value, and the median of the three data of the median, to form a new group of three data. Each large group will form such a new group, and each new group has a maximum value, a minimum value, and a median. Find the minimum value of the three data of the maximum value of each of the three new groups, the maximum value of the three data of the minimum value, and the median of the three data of the median, and get the final three-number group, and the median of these three data is the median of the 27 voltages. The median filter filters out most of the instantaneous (within 0.2ms) extreme abnormal data and eliminates the interference of some erroneous data.

[0045] S5. After that, the enable count value b is calculated and counted once every 0.2ms. At this time, b>27. At this time, each time a new voltage value is input, the voltage value V that enters the array earliest is b-26 Move out of the array and assign Vb 0.2ms ago to V b-1 , V b-1 Assign to V b-2 , V b-2 Assign to V b-3 ..., assign the new input voltage value to V b , and then perform step iv again to get a new median. After median filtering, a waveform with relatively smooth voltage value changes is obtained.

[0046] S6. Whenever b reaches 25027, that is, after 5.0 seconds, let b=27 and execute steps S7 to S9 once.

[0047] S7. Invert the light source control value F to change the light source type. In this embodiment, if F=0, only the light source with a wavelength of 650nm works, and if F=1, only the light source with a wavelength of 810nm works.

[0048] S8. Find the n maximum points of the waveform within 5.0s and record them as m1, m2…m n , take the average value and record it as m avg .

[0049] S9. Find n-1 low voltage intervals of the waveform within 5.0s, take 1000 (0.2s) continuous data for each interval, and take the average value of 1000 (n-1) data as n avg The principle and beneficial effects of this step are as follows: The photovoltages caused by the two wavelengths cannot be measured simultaneously, so in the low voltage and small oscillation area, such as Figure 2 As shown in the yellow box, when taking the photovoltage at a single data point, the difference between the values ​​of the two wavelengths may be large. When measuring the transmittance of 650nm wavelength light, the voltage value is taken at a small oscillation high point, that is, the voltage V corresponding to point A in the figure A When measuring the transmittance of 810nm wavelength light, the voltage value is taken at the low point of a small oscillation, that is, point B in the figure corresponds to the voltage V B Therefore, 1000 data points within 200ms are taken in the low voltage small oscillation area, such as the 1000 data points within 200ms in the α and β boxes in the low voltage small oscillation area diagram, and the voltage average value V is taken for these data points. α 、V β . Comparison | V A -V B |with|V α -V β |, we can find that |V α -Vβ |<<|V A -V B |This error is greatly reduced.

[0050] S10. If F = 0, then m avg Assign to m 650nm , n avg Assign to n 650nm If F = 1, then m avg Assign to m 810nm , n avg Assign to n 810nm . 650nm , n 650nm , m 810nm , n 810nm Substitute the blood oxygen saturation calculation formula to obtain the blood oxygen saturation value and output it to the display screen.

[0051] For those skilled in the art, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all of these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. The blood oxygen saturation measurement method based on the Gr-WSe2-Pt flexible photoelectric sensor uses two independent light sources with wavelengths of 650nm and 810nm to periodically and alternately illuminate the fingertips to be measured, obtain the transmitted light signal of the fingertips to measure the blood oxygen saturation and display it It is characterized in that The Gr-WSe2-Pt flexible photoelectric sensor is attached to the fingertip to collect the transmitted light signal. After filtering, amplifying and analog-to-digital conversion of the collected light signal, the FPGA development board is used to perform the following operations: S1. The number of repetitions of the clock cycle of the 50MHz clock frequency is counted as a; S2. Whenever a reaches 10000, a is cleared, and the light source switching and blood oxygen calculation enable count value b is counted once, and the input voltage value at this time is recorded; if b=27, steps S3 to S4 are executed once; if b>27, steps S5 to S6 are executed once; if b<27, this step is repeated; S3. taking the 27 initially recorded voltage values ​​as an initial array; S4. First, divide the 27 voltage values ​​into three large groups of 9 data each, and then divide the large groups into three small groups of 3 data each. Each group has a maximum value, a minimum value, and a median. Find the minimum value of the three data of the maximum value of each of the three groups, the maximum value of the three data of the minimum value of each of the three groups, and the median of the three data of the median to form a new group of three data. Each large group forms a new group with the same rule. Each new group has a maximum value, a minimum value, and a median. Find the minimum value of the three data of the maximum value of each of the three groups, the maximum value of the three data of the minimum value of each of the three groups, and the median of the three data of the median to get the final three-number group, and the median of this three-number group is the median of the 27 voltages. S5. Every time a new voltage value is input, the earliest input voltage value V b-26 Shift out the array and set the voltage value V 0.2ms ago b Assign values ​​to the previous V in sequence b-1 , assign the new input voltage value to V b ; Perform step S4 again to obtain a new median; obtain the waveform of voltage value change through median filtering; S6. Whenever b reaches 25027, let b = 27 and execute steps S7 to S9 once; S7. Invert the light source control value F to change the light source output; S8. Find the n maximum points of the waveform within the current 5.0s and take the average value as m avg ; S9. Find the n-1 low voltage intervals of the current waveform within 5.0s, take 1000 continuous data for each interval and calculate the average value, record it as n avg ; S10. If F = 0, then m avg Assign to m 650nm , n avg Assign to n 650nm ; If F = 1, then m avg Assign to m 810nm , n avg Assign to n 810nm ; m 650nm , n 650nm , m 810nm , n 810nm Substitute the blood oxygen saturation calculation formula to obtain the blood oxygen saturation value and output it to the display screen; in, m 650nm is the average maximum value of the PPG signal corresponding to the wavelength of 650nm; n 650nm is the average minimum value of the PPG signal corresponding to the wavelength of 650nm; m 810nm is the average maximum value of the PPG signal corresponding to the wavelength of 810nm; n 810nm It is the average minimum value of the PPG signal corresponding to the wavelength of 810nm.

2. The blood oxygen saturation measurement method based on the Gr-WSe2-Pt flexible photoelectric sensor according to claim 1 is characterized in that: The blood oxygen saturation calculation formula is: The operation parameters are: Hb650nm =3750.12cm -1 M -1 , ε Hb810nm =717.08cm -1 M -1 , 3. A blood oxygen saturation measurement system based on Gr-WSe2-Pt flexible photoelectric sensor, characterized in that: Blood oxygen saturation is calculated using the method described in any one of claims 1-2.

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