A method for calculating low-perfusion blood oxygen parameters and a blood oxygen meter

Abstract

A method for calculating low-perfusion blood oxygenation parameters includes: acquiring PPG signals of red and infrared light from multiple cycles collected by a pulse oximeter under normal measurement conditions; performing low-pass filtering and peak-valley identification on the AC component waveform of the infrared light to obtain the amplitude of the AC component; if the amplitude of the AC component is less than a set threshold for at least three consecutive cycles, then entering a low-perfusion calculation mode; extracting at least two cycles of low-pass filtered PPG signals of infrared light and performing autocorrelation calculation to determine the average peak interval of the autocorrelation signal; using this average interval to window the smoothed and filtered original red and infrared PPG signals; and calculating the blood oxygen saturation value based on the windowed red and infrared PPG signals. This invention can achieve accurate calculation of blood oxygen and pulse rate values ​​with a perfusion index of 0.1%, optimizing the low-perfusion measurement level and real-time performance of the pulse oximeter.

Description

Technical Field

[0001] This invention relates to the field of bioinformatics detection, specifically to a method for calculating low perfusion oxygenation parameters and a pulse oximeter. Background Technology

[0002] Existing pulse oximeters, when encountering factors such as muscle tension or low temperature environments that reduce blood flow to the fingertips, leading to hypoperfusion (generally, the hypoperfusion index is less than 0.5%), will fail to measure blood oxygen saturation and pulse rate, or will produce erroneous values, affecting user experience.

[0003] Mindray's patent US8275434 uses signal integration to identify low perfusion signals, but its drawback is the potential for false detection of interference signals. CN103027690B proposes an autocorrelation modeling method to address the low perfusion problem, but its reliance on model accuracy and real-time performance is an issue, and errors may occur in special cases. CN113017623B uses big data statistical user information to set dynamic thresholds to determine the validity of pulse signals, but its drawback is the need for a large number of samples.

[0004] Therefore, how to overcome the shortcomings of the existing technology is the subject of this invention. Summary of the Invention

[0005] The purpose of this invention is to provide a method for calculating low perfusion blood oxygen parameters, which can improve the real-time performance of measurements in normal perfusion populations, improve the perfusion level of existing products, and increase the perfusion level by up to 0.1%.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for calculating low perfusion oxygenation parameters, the method comprising:

[0007] S1. Acquire PPG signals of red and infrared light from multiple cycles collected by the pulse oximeter under normal measurement conditions; wherein, the normal measurement conditions are non-current regulation conditions or non-gain regulation conditions;

[0008] S2. The PPG signals of the multiple cycles of red and infrared light are low-pass filtered;

[0009] S3. Extract the AC component waveform of the infrared light after low-pass filtering in step S2, identify peaks and valleys, and calculate the amplitude ir of the AC component of the infrared light in each period. maxmin ;

[0010] S4. Convert the ir values ​​of each period. maxmin Compared with a set threshold, if the ir value is low for at least three consecutive periods... maxminIf all values ​​are less than the threshold, then proceed to the low perfusion calculation mode in step S5; otherwise, proceed to the normal perfusion calculation mode in step S6.

[0011] S5. Low Infusion Calculation Mode:

[0012] S501. Extract and store the PPG signal of infrared light that has been low-pass filtered for at least two periods in step S2, and use the autocorrelation algorithm to perform waveform processing on the PPG signal of infrared light to obtain the autocorrelation signal.

[0013] S502. Identify the peaks and valleys of the autocorrelation signal and calculate the average interval number n of the peaks. ir ', and based on that n ir 'Identified a low perfusion pulse rate;'

[0014] S503. The PPG signals of red and infrared light acquired in step S1 are smoothed and filtered to obtain the n ir The PPG signals of red and infrared light after smoothing and filtering are windowed according to the window length, and then the blood oxygen saturation value is calculated based on the PPG signals of red and infrared light within the window.

[0015] S6. Normal perfusion calculation mode: Calculates blood oxygen saturation value and normal perfusion pulse rate based on PPG signals of red and infrared light after low-pass filtering.

[0016] In a further embodiment, the low-pass filtering method described in step S2 is as follows:

[0017] S201. A 0.1Hz second-order IIR low-pass filter is used to perform low-pass filtering on the PPG signals of the multiple periods of red light and infrared light respectively.

[0018] S202. Remove the DC component of the PPG signal from the red and infrared light, and then perform a second-order IIR low-pass filter with a cutoff frequency of 6Hz.

[0019] In a further embodiment, the threshold set in step S4 is 50.

[0020] In a further embodiment, the autocorrelation algorithm described in step S501 is as follows: delay the PPG signal of the infrared light by m, multiply the corresponding positions of the signals before and after the delay, sum them, and then calculate the average value to obtain the autocorrelation signal value R. xx (m), the autocorrelation formula is:

[0021]

[0022] Where x is the AC component of infrared light, m ​​is 0 to (a-1), and a is the number of PPG signal points of infrared light with at least two cycles and low-pass filtering.

[0023] In a further embodiment, the calculation method for the low perfusion pulse rate mentioned in step S502 is as follows:

[0024] Peak and valley identification is performed on the autocorrelation signal, and the number of peak points and valley points of the autocorrelation signal within at least two periods is calculated to obtain the average interval number n of the peak points. ir ';

[0025] Based on the n ir 'and the sampling frequency f of the PPG signal of the infrared light' c Calculate the low perfusion pulse rate PR', PR' = 60 / (n ir '*(1 / f c )).

[0026] In a further embodiment, the method for calculating the blood oxygen saturation value in step S503 includes:

[0027] The PPG signals of red and infrared light acquired in step S1 are smoothed and filtered to obtain the DC component of the smoothed and filtered red light. dc ', DC component of infrared light ir dc ';

[0028] With the n ir 'The PPG signals of red and infrared light after smoothing and filtering are windowed to a window length, and the amplitude of the AC component of red light in each period within the window is calculated.' maxmin 'Amplitude of the AC component of infrared light ir maxmin ';

[0029] Based on the red maxmin 'and the ir maxmin 'and the corresponding period of red' dc 'and the ir dc Calculate the blood oxygen saturation (R) value for two cycles, and then obtain the average value of R'. based on The blood oxygen saturation value is obtained by looking up a table / calculating; wherein, the formula for calculating the blood oxygen R' value is:

[0030]

[0031] In a further embodiment, the amplitude of the AC component is red. maxmin 'Ir' represents the difference between the maximum and minimum values ​​of the red light signal in each period within the window, and the amplitude of the AC component of the infrared light is ir. maxmin'This represents the difference between the maximum and minimum values ​​of the infrared light signal inside the window.

[0032] In a further scheme, the method for calculating the blood oxygen saturation value based on the PPG signals of red and infrared light after low-pass filtering in step S6 is as follows:

[0033] S601. Extract the DC component of the red light for each period from the PPG signal of the red light in multiple periods after low-pass filtering in step S2. dc DC component of infrared light ir dc And the waveform of the alternating current component of red light;

[0034] S602. Perform peak and valley identification on the AC component waveform of the red light, and calculate the amplitude of the AC component of the red light in each period. maxmin ;

[0035] S603. Based on the red of each period dc The ir dc The red maxmin and the ir maxmin Calculate the blood oxygen saturation (R) value for each cycle, and then obtain the average value of R. based on The blood oxygen saturation value is obtained by looking up a table / calculating; wherein, the formula for calculating the blood oxygen R value is:

[0036]

[0037] The method for calculating blood oxygen saturation values ​​based on the PPG signals of red and infrared light after low-pass filtering in step S6 is as follows:

[0038] Peak and valley identification is performed on the AC component waveform of the low-pass filtered infrared light. The number of peak points and valley points of the AC component waveform of the infrared light is calculated, and the average interval number n of the peak points is obtained. ir Based on this n ir The normal perfusion pulse rate PR was calculated as follows: PR = 60 / (n ir *(1 / f c )).

[0039] Secondly, the present invention provides a pulse oximeter, which includes a pulse oximeter acquisition terminal and a microcontroller. The pulse oximeter acquisition terminal is used to acquire PPG signals of red light and infrared light in multiple cycles, and the microcontroller is used to implement the above-mentioned method for calculating low perfusion oxygenation parameters.

[0040] In a further embodiment, the microcontroller includes a buffer program that uses an adjustment flag to distinguish between red and infrared PPG signals under current regulation or gain regulation states; it also includes a running program that uses a low-injection processing flag to distinguish between low-injection calculation mode and normal-injection calculation mode.

[0041] The working principle and advantages of this invention are as follows:

[0042] This invention utilizes the AC component waveform after DC removal and filtering to calculate the inflection point and find the peak value. The peak value is compared with a set threshold. If the peak value of three consecutive waveforms is less than the set threshold, a low perfusion calculation mode is entered. After entering the low perfusion mode, the periodicity of the PPG signal and the randomness of the noise signal are used to perform autocorrelation on the filtered signal to determine the average interval of the peak value of the autocorrelation signal. The low perfusion pulse rate value is obtained using the average interval. The smoothed original red and infrared PPG signals are then windowed using the average interval. Based on the amplitude of the AC component and the DC component after windowing, the blood oxygen value can be accurately calculated with a perfusion index of 0.1%, greatly improving the perfusion level and optimizing the performance of current pulse oximeters.

[0043] The method for calculating low perfusion oxygenation parameters provided by this invention can be directly applied to a microcontroller. If the peak value of three consecutive waveforms is less than a set threshold, the system enters the low perfusion calculation mode; otherwise, it enters the normal perfusion calculation mode. This can improve the real-time performance of measurements in normal perfusion populations. Attached Figure Description

[0044] Appendix Figure 1 The flowchart illustrates the application of the method for calculating low perfusion oxygen parameters in this invention to a microcontroller for calculating oxygen saturation.

[0045] Appendix Figure 2 The image shows the low-pass filtered waveform of the PPG signal under a 0.1% perfusion index according to an embodiment of the present invention.

[0046] Appendix Figure 3 The waveform of the PPG signal after autocorrelation processing at a 0.1% perfusion index is shown in this embodiment of the invention.

[0047] Appendix Figure 4 This is a peak-valley identification diagram of the PPG signal autocorrelation waveform under a 0.1% perfusion index according to an embodiment of the present invention. Detailed Implementation

[0048] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0049] Example: The present invention will be clearly described below with illustrations and detailed description. Any person skilled in the art who understands the examples of the present invention can make changes and modifications based on the technology taught in the present invention without departing from the spirit and scope of the present invention.

[0050] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of this work. Singular forms such as “a,” “this,” “this,” “the,” and “the” as used herein also include plural forms.

[0051] The terms “include,” “including,” and “have” used in this article are all open-ended, meaning they include but are not limited to.

[0052] Unless otherwise specified, the terms used herein generally have their ordinary meaning in the context of the art, the subject matter, and the specific context. Certain terms used to describe this case will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing this case.

[0053] See appendix Figure 1 As shown, this embodiment of the invention provides a method for calculating low perfusion oxygenation parameters, the method comprising:

[0054] S1. Acquire PPG signals of red and infrared light from multiple cycles collected by the pulse oximeter under normal measurement conditions; wherein, the normal measurement conditions are non-current regulation conditions or non-gain regulation conditions. The waveforms under these two conditions will undergo large vertical jumps, resulting in results of different magnitudes, which will affect subsequent parameter calculations, autocorrelation calculations, etc.

[0055] S2. A 0.1Hz second-order IIR low-pass filter is used to perform low-pass filtering on the PPG signals of the multiple periods of red light and infrared light respectively.

[0056] The DC component of the PPG signal of red and infrared light is removed, and then a second-order IIR low-pass filter with a cutoff frequency of 6Hz is applied to obtain the AC component waveform of infrared light in each cycle.

[0057] S3. Perform peak and valley identification on the AC component waveform of the infrared light, and calculate the amplitude ir of the AC component of the infrared light. maxmin =ir max -ir min ; among them, ir max and ir min These are the peak and valley points of the AC component waveform of infrared light, respectively.

[0058] S4. Convert the ir values ​​of each period. maxminCompared to the set threshold of 50, if the ir value is continuously below 50 for at least three consecutive periods... maxmin If all values ​​are less than the threshold, it indicates that the current signal amplitude is small, i.e., it is in a low-injection state. At this time, it enters the low-injection calculation mode in step S5; otherwise, it enters the normal injection calculation mode in step S6.

[0059] S5. Low Infusion Calculation Mode:

[0060] S501. Because the original signal is in a low-injection state, the signal-to-noise ratio is too low, and the effective signal is buried in noise. The amplitude of the signal after conventional injection calculation and filtering cannot be accurately calculated. Therefore, the waveform must be preprocessed first. The specific method is as follows:

[0061] After entering the low-perfusion calculation mode, extract and store at least two cycles of low-pass filtered infrared PPG signals, such as... Figure 2 The image shows a 0.1% perfusion, low-pass filtered, two-cycle (512-length) infrared light PPG signal.

[0062] The system sets up a buffer area for infrared light signals to store at least two cycles of low-pass filtered PPG signals of infrared light.

[0063] The PPG signal of infrared light is processed using an autocorrelation algorithm to obtain an autocorrelation signal, such as... Figure 3 As shown; specifically, the autocorrelation algorithm is:

[0064] The PPG signal of the infrared light is delayed by m. The corresponding positions of the signals before and after the delay are multiplied, summed, and then averaged to obtain the autocorrelation signal value R. xx (m), the autocorrelation formula is:

[0065]

[0066] Where x is the AC component of infrared light, m ​​is 0 to (a-1), and a is the number of PPG signal points of infrared light with at least two cycles and low-pass filtering.

[0067] S502. Perform peak and valley identification on the autocorrelation signal, calculate the number of peak points and valley points within the at least two periods, and obtain the average interval number n of peak points. ir ,,like Figure 4 As shown;

[0068] Based on the n ir 'and the sampling frequency f of the PPG signal of the infrared light' c Calculate the low perfusion pulse rate PR', PR' = 60 / (n ir'*(1 / f c ));

[0069] S503. Perform smoothing filtering on the PPG signals of red and infrared light acquired in step S1 without low-pass filtering to obtain the DC component of the smoothed red light. dc ', DC component of infrared light ir dc ';

[0070] With the average interval number n ir ', Determine the window length as n ir The PPG signals of red and infrared light after smoothing and filtering are windowed, and then the amplitude of the AC component of red light in each period within the window is calculated. maxmin 'Amplitude of the AC component of infrared light ir maxmin '; where the amplitude of the AC component is red maxmin 'Ir' represents the difference between the maximum and minimum values ​​of the red light signal in each period within the window, and the amplitude of the AC component of the infrared light is ir. maxmin 'This represents the difference between the maximum and minimum values ​​of the infrared light signal inside the window;

[0071] Based on the red maxmin 'and the ir maxmin 'and the corresponding period of red' dc 'and the ir dc 'Calculate the blood oxygen R value over two cycles'

[0072] Then calculate the average value of R' for the two periods. based on The blood oxygen saturation value was calculated by referring to the table / Meixin fitting formula.

[0073] S6. Normal Infusion Calculation Mode:

[0074] S601. Extract the DC component of the red light for each period from the PPG signal of the red light in multiple periods after low-pass filtering in step S2. dc DC component of infrared light ir dc And the waveform of the alternating current component of red light;

[0075] S602. Perform peak and valley identification on the AC component waveform of the red light, and calculate the amplitude of the AC component of the red light in each period. maxmin =red max -red min red max and red min These are the peak and valley points of the AC component waveform of red light, respectively.

[0076] S603. Based on the red of each period dc The ir dc The red maxmin and the ir maxmin Calculate the blood oxygen R value for each cycle. Then calculate the average value of the blood oxygen R value for each cycle. Based on the above The blood oxygen saturation value was calculated by referring to the table / Meixin fitting formula.

[0077] Peak and valley identification is performed on the AC component waveform of the low-pass filtered infrared light. The number of peak points and valley points of the AC component waveform of the infrared light is calculated, and the average interval number n of the peak points is obtained. ir Based on this n ir The normal perfusion pulse rate PR was calculated as follows: PR = 60 / (n ir *(1 / f c )).

[0078] This invention also provides a pulse oximeter, which includes a pulse oximeter acquisition terminal and a microcontroller. The pulse oximeter acquisition terminal is used to acquire PPG signals of red light and infrared light in multiple cycles, and the microcontroller is used to implement the calculation method for low perfusion pulse oximetry parameters described in the above embodiments.

[0079] The microcontroller includes a buffer program that uses an adjustment flag to distinguish between red and infrared PPG signals under current adjustment or gain adjustment states; it also includes a running program that uses a low-injection processing flag to distinguish between low-injection calculation mode and normal-injection calculation mode.

[0080] Specifically, when the pulse oximeter system performs pulse oximetry measurement, it may perform current adjustment or gain adjustment. Therefore, when the system performs current adjustment or gain adjustment, it sets an adjustment flag. When PPG signal acquisition is performed in step S1, if the adjustment flag is detected, the previously saved waveform will be cleared and saved again until at least three cycles of PPG signal are stored.

[0081] In the ir of each period maxmin After comparing with a set threshold, the system sets a low perfusion flag. When the ir rate reaches a certain threshold for at least three consecutive cycles... maxmin If all values ​​are less than the threshold, determine whether the low perfusion treatment flag is set. If it is set, clear the flag and enter the normal perfusion calculation mode. If it is not set, enter the low perfusion calculation mode.

[0082] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for calculating low perfusion oxygenation parameters, characterized in that, The method includes: S1. Acquire PPG signals of red and infrared light from multiple cycles collected by the pulse oximeter under normal measurement conditions; wherein, the normal measurement conditions are non-current regulation conditions or non-gain regulation conditions; S2. The PPG signals of the multiple cycles of red and infrared light are low-pass filtered; S3. Extract the AC component waveform of the infrared light after low-pass filtering in step S2, identify peaks and valleys, and calculate the amplitude ir of the AC component of the infrared light in each period. maxmin ; S4. Convert the ir values ​​of each period. maxmin Compared with a set threshold, if the ir value is low for at least three consecutive periods... maxmin If all values ​​are less than the threshold, then proceed to the low perfusion calculation mode in step S5; otherwise, proceed to the normal perfusion calculation mode in step S6. S5. Low Infusion Calculation Mode: S501. Extract and store the PPG signal of infrared light that has been low-pass filtered for at least two periods in step S2, and use the autocorrelation algorithm to perform waveform processing on the PPG signal of infrared light to obtain the autocorrelation signal. S502. Identify the peaks and valleys of the autocorrelation signal and calculate the average interval number n of the peaks. ir ', and based on that n ir 'Identified a low perfusion pulse rate;' S503. The PPG signals of red and infrared light acquired in step S1 are smoothed and filtered to obtain the n ir The PPG signals of red and infrared light after smoothing and filtering are windowed according to the window length, and then the blood oxygen saturation value is calculated based on the PPG signals of red and infrared light within the window. S6. Normal perfusion calculation mode: Calculates blood oxygen saturation value and normal perfusion pulse rate based on PPG signals of red and infrared light after low-pass filtering.

2. The method for calculating low perfusion oxygenation parameters according to claim 1, characterized in that: The low-pass filtering method described in step S2 is as follows: S201. A 0.1Hz second-order IIR low-pass filter is used to perform low-pass filtering on the PPG signals of the multiple periods of red light and infrared light respectively. S202. Remove the DC component of the PPG signal from the red and infrared light, and then perform a second-order IIR low-pass filter with a cutoff frequency of 6Hz.

3. The method for calculating low perfusion oxygenation parameters according to claim 1, characterized in that: The threshold set in step S4 is 50.

4. The method for calculating low perfusion oxygenation parameters according to claim 1, characterized in that: The autocorrelation algorithm described in step S501 is as follows: delay the PPG signal of the infrared light by m, multiply the corresponding positions of the signals before and after the delay, sum them, and then calculate the average value to obtain the autocorrelation signal value R. xx (m), the autocorrelation formula is: Where x is the AC component of infrared light, m ​​is 0 to (a-1), and a is the number of PPG signal points of infrared light with at least two cycles and low-pass filtering.

5. The method for calculating low perfusion oxygenation parameters according to claim 1, characterized in that: The method for calculating the low perfusion pulse rate mentioned in step S502 is as follows: Peak and valley identification is performed on the autocorrelation signal, and the number of peak points and valley points of the autocorrelation signal within at least two periods is calculated to obtain the average interval number n of the peak points. ir '; Based on the n ir 'and the sampling frequency f of the PPG signal of the infrared light' c Calculate the low perfusion pulse rate PR', PR' = 60 / (n ir '*(1 / f c )).

6. The method for calculating low perfusion oxygenation parameters according to claim 1, characterized in that: The method for calculating blood oxygen saturation value in step S503 includes: The PPG signals of red and infrared light acquired in step S1 are smoothed and filtered to obtain the DC component of the smoothed and filtered red light. dc ', DC component of infrared light ir dc '; With the n ir 'The PPG signals of red and infrared light after smoothing and filtering are windowed to a window length, and the amplitude of the AC component of red light in each period within the window is calculated.' maxmin 'Amplitude of the AC component of infrared light ir maxmin '; Based on the red maxmin 'and the ir maxmin 'and the corresponding period of red' dc 'and the ir dc Calculate the blood oxygen saturation (R) value for two cycles, and then obtain the average value of R'. based on The blood oxygen saturation value is obtained by looking up a table / calculating; wherein, the formula for calculating the blood oxygen R' value is:

7. The method for calculating low perfusion oxygenation parameters according to claim 6, characterized in that: The amplitude of the AC component red maxmin 'Ir' represents the difference between the maximum and minimum values ​​of the red light signal in each period within the window, and the amplitude of the AC component of the infrared light is ir. maxmin 'This represents the difference between the maximum and minimum values ​​of the infrared light signal inside the window.

8. A method for calculating low perfusion oxygenation parameters according to claim 1 or 2, characterized in that: The method for calculating blood oxygen saturation values ​​based on the PPG signals of red and infrared light after low-pass filtering in step S6 is as follows: S601. Extract the DC component of the red light for each period from the PPG signal of the red light in multiple periods after low-pass filtering in step S2. dc DC component of infrared light ir dc And the waveform of the alternating current component of red light; S602. Perform peak and valley identification on the AC component waveform of the red light, and calculate the amplitude of the AC component of the red light in each period. maxmin ; S603. Based on the red of each period dc The ir dc The red maxmin and the ir maxmin Calculate the blood oxygen saturation (R) value for each cycle, and then obtain the average value of R. based on The blood oxygen saturation value is obtained by looking up a table / calculating; wherein, the formula for calculating the blood oxygen R value is: The method for calculating blood oxygen saturation values ​​based on the PPG signals of red and infrared light after low-pass filtering in step S6 is as follows: Peak and valley identification is performed on the AC component waveform of the low-pass filtered infrared light. The number of peak points and valley points of the AC component waveform of the infrared light is calculated, and the average interval number n of the peak points is obtained. ir Based on this n ir The normal perfusion pulse rate PR was calculated as follows: PR = 60 / (n ir *(1 / f c )).

9. A pulse oximeter, characterized in that: The pulse oximeter includes a pulse oximeter acquisition terminal and a microcontroller. The pulse oximeter acquisition terminal is used to acquire PPG signals of red light and infrared light in multiple cycles. The microcontroller is used to implement the calculation method for low perfusion pulse oximetry parameters as described in any one of claims 1-8.

10. A pulse oximeter according to claim 9, characterized in that: The microcontroller includes a buffer program that uses an adjustment flag to distinguish between red and infrared PPG signals under current adjustment or gain adjustment states; it also includes a running program that uses a low-injection processing flag to distinguish between low-injection calculation mode and normal-injection calculation mode.

Images