Noninvasive blood oxygen detection and method

Abstract

The invention belongs to the technical field of blood oxygen detection, and particularly relates to a non-invasive blood oxygen detection method. The main machine shell is arranged on the upper portion of the blood oxygen machine, a blood oxygen sensor is arranged below the blood oxygen machine and electrically connected with the main machine shell, the main machine shell comprises a single chip microcomputer, an analog front end driving module, a display module, a circuit module, a signal receiving module, a digital signal processing module and a storage module, and meanwhile a lithium battery is arranged in the main machine shell. A power supply is provided for the oximeter; the blood oxygen sensor is directly connected with the signal receiving module to form a blood oxygen signal receiving module, and the blood oxygen signal receiving module is connected with the digital signal processing module to convert a voltage signal into a digital signal; according to the invention, the problem that detection signal pulse wave output signals are interfered by serious noise such as environmental noise and hardware circuits is solved; the problems of signal loss and signal superposition caused by a traditional filtering method are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of blood oxygen detection, and in particular to a non-invasive blood oxygen detection method. Background Art

[0002] Blood oxygen saturation (SpO2) is the most important indicator in blood oxygen detection. It indicates the percentage of oxygenated hemoglobin (HbO2) in the blood that is bound by oxygen to the total hemoglobin (Hb) capacity that can be bound. The blood oxygen saturation of normal human arterial blood is generally between 95% and 98%, and that of venous blood is about 75%;

[0003] Blood oxygen saturation is an important physiological parameter that reflects respiratory and circulatory functions. If the blood oxygen saturation is lower than the normal range, it may indicate that the body is hypoxic, such as lung disease (pneumonia, chronic obstructive pulmonary disease, etc.), cardiovascular disease (heart failure, etc.) or altitude sickness;

[0004] However, there are still some problems with the existing blood oxygen detection. For example, it is not accurate enough and is subject to a lot of interference during detection, such as environmental interference, hardware circuit noise interference, etc. In addition, traditional filtering methods are prone to signal loss and signal superposition problems, causing signal reception distortion, which will have an adverse effect on the detection results. Based on the above reasons, I proposed a non-invasive blood oxygen detection and method. Summary of the invention

[0005] The purpose of the present invention is to provide a non-invasive blood oxygen detection method to solve the problems raised in the above background technology.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a non-invasive blood oxygen detection and method, including a blood oxygen meter and a main housing;

[0007] The main housing is arranged on the upper part of the blood oxygen meter, a blood oxygen sensor is arranged below the blood oxygen meter, and the blood oxygen sensor is electrically connected to the main housing, the main housing includes a single chip microcomputer, an analog front-end drive module, a display module, a circuit module, a signal receiving module, a digital signal processing module, and a storage module, and a lithium battery is arranged in the main housing to provide power for the blood oxygen meter;

[0008] The blood oxygen sensor is directly connected to the signal receiving module to form a blood oxygen signal receiving module, and the blood oxygen signal receiving module is connected to the digital signal processing module to convert the voltage signal into a digital signal; the components in the main housing are connected through a data transmission line, and a shielding layer is provided outside the data transmission line;

[0009] The signals collected by the blood oximeter include electrocardiogram signals, photoelectric volume pulse wave signals and skin temperature signals. The detection method of the blood oximeter is:

[0010] Preprocess the collected physiological signals to remove noise and interference;

[0011] Extract characteristic parameters of ECG signal and photoplethysmogram signal, including heart rate, pulse wave amplitude, and pulse wave conduction time;

[0012] According to the extracted characteristic parameters, the blood oxygen saturation is calculated using the PPG measurement method;

[0013] The blood oxygen detection is optimized and the calculated blood oxygen saturation is corrected in combination with the skin temperature signal to improve the accuracy of the detection.

[0014] Preferably, the analog front-end driver module uses five connection ports including power interface VIN (3.3V / 5V), ground port GND, clock interface SCL, data interface SDA, and interrupt interface INT, wherein the clock interface SCL is connected to the microcontroller port PB6, the data interface SDA is connected to the port PB7, and the interrupt interface INT is connected to the port PC8.

[0015] Preferably, the analog front-end driver module includes an integrated blood oxygen signal collector and an I2C communication module, and the integrated blood oxygen signal collector adopts a miniature 5.6mm x 3.3mm x 1.55mm 14-pin light collection module; the analog front-end driver module includes a subsystem, and the subsystem includes ambient light elimination and a proprietary discrete time filter.

[0016] Preferably, the blood oxygen detection method is optimized, and the steps are as follows:

[0017] S1, collect at least three different wavelengths of light, illuminate the fingers (at least three groups of different fingers) and earlobes under test, and simultaneously collect the transmitted or reflected light signals; different wavelengths of light have different absorption characteristics for oxygenated hemoglobin and reduced hemoglobin, and multi-wavelength light signal collection can provide richer information;

[0018] S2, performing adaptive filtering on the collected optical signal; the adaptive filtering algorithm automatically adjusts the filter parameters according to the real-time characteristics of the signal.

[0019] S3, before the test, measure some basic physiological characteristics of the subject, such as skin color, tissue thickness and blood composition; according to these individual physiological characteristics, establish a personalized light absorption correction model, and optimize the test data based on the light absorption correction model.

[0020] Preferably, according to step S2, by analyzing the frequency and amplitude variation characteristics of the optical signal, high-frequency noise components related to the motion are identified and then filtered out.

[0021] Preferably, according to step S3, for individuals with darker skin, when calculating the blood oxygen saturation, the light absorption coefficient is adjusted accordingly to compensate for the effect of melanin on light absorption.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention solves the problem that the detection signal pulse wave output signal is seriously interfered by environmental noise, hardware circuit and other noises; the hardware circuit design method using HTF52352 as the core processor chip combined with the blood oxygen signal acquisition analog front end MAX30102 reduces the complexity of circuit design; when designing the hardware circuit, compared with the traditional circuit, the blood oxygen input signal input adopts a differential transmission design and adds shielding protection, which can effectively avoid electromagnetic interference and improve the stability of the signal;

[0024] The problems of signal loss and signal superposition caused by traditional filtering methods are solved, and the signal preprocessing method and signal feature point detection algorithm are studied and improved; based on the collected original pulse wave signal, in order to address the problems of signal data loss and distortion that may occur in the filtering process, a combination of wavelet transform and FFT is proposed to preprocess the waveform, and then the signal is reconstructed, which removes the power frequency interference, baseline drift and other noise in the original signal waveform to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the overall structure diagram of the blood oxygen signal acquisition module;

[0026] Figure 2 This is a schematic diagram of the single chip microcomputer circuit of the present invention;

[0027] Figure 3 It is a schematic diagram of the appearance of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0030] Example:

[0031] See also Figure 1-3 , the present invention provides a non-invasive blood oxygen detection and method technical solution: comprising a blood oxygen meter 1 and a main housing 2;

[0032] The main housing 2 is arranged on the upper part of the blood oxygen meter 1, and a blood oxygen sensor is arranged below the blood oxygen meter 1, and the blood oxygen sensor is electrically connected to the main housing 2. The main housing 2 includes a single-chip microcomputer, an analog front-end drive module, a display module, a circuit module, a signal receiving module, a digital signal processing module, and a storage module. At the same time, a lithium battery is arranged in the main housing 2 to provide power for the blood oxygen meter 1;

[0033] The blood oxygen sensor is directly connected to the signal receiving module to form a blood oxygen signal receiving module, and the blood oxygen signal receiving module is connected to the digital signal processing module to convert the voltage signal into a digital signal;

[0034] The components in the main housing 2 are connected via data transmission lines, and a shielding layer is provided outside the data transmission line;

[0035] The analog front-end driver module includes an integrated blood oxygen signal collector and an I2C communication module. The integrated blood oxygen signal collector uses a miniature 5.6mm x 3.3mm x 1.55mm 14-pin light collection module. The analog front-end driver module includes a subsystem, which includes ambient light elimination and a proprietary discrete time filter.

[0036] The analog front-end driver module uses five connection ports including power interface VIN (3.3V / 5V), ground port GND, clock interface SCL, data interface SDA, and interrupt interface INT. The clock interface SCL is connected to the microcontroller port PB6, the data interface SDA is connected to the port PB7, and the interrupt interface INT is connected to the port PC8.

[0037] The collected signals of the blood oxygen machine 1 include electrocardiogram signals, photoelectric volume pulse wave signals and skin temperature signals;

[0038] The blood oxygen detection method is:

[0039] Preprocess the collected physiological signals to remove noise and interference;

[0040] Extract characteristic parameters of ECG signal and photoplethysmogram signal, including heart rate, pulse wave amplitude, and pulse wave conduction time;

[0041] According to the extracted characteristic parameters, the blood oxygen saturation is calculated using the PPG measurement method;

[0042] Combine skin temperature signals to correct the calculated blood oxygen saturation and improve detection accuracy;

[0043] The MCU used in this solution is the HT32F52352 MCU, which has the advantages of good anti-electromagnetic interference performance, excellent light shielding performance, and high accuracy. This series of MCUs includes the Arm Cortex-M0+ processor, bus structure and memory system; -M0+ processor is a processor with low gate count and high performance, suitable for single-chip microcomputers and deeply embedded applications that require area optimization and low-power processors; the processor is based on the ARMv6-M architecture and supports Thumb* instruction set, single-cycle I / O port, hardware multiplier and low-latency interrupt response time; the integrated and advanced features make the Corex-M0+ processor suitable for market products that require high-performance and low-power single-chip microcomputers; in the process of collecting pulse wave data and processing, the I2C data read and write operations between the main chip and the analog front end MAX30102 are mainly completed by the microcontroller MCU (Micro controlunit), and the single-chip microcomputer circuit is shown in the attached Figure 2 As shown;

[0044] At the same time, the SpO2 subsystem in the MAX30102 microcontroller includes ambient light cancellation (ALC), continuous-time Σ-Δ ADC, and a proprietary discrete-time filter; ALC has an internal track / hold circuit to eliminate ambient light and increase the effective dynamic range; SpO2 ADC has a programmable full-scale range of 2μA to 16μA; ALC can eliminate up to 200μA of ambient current; the internal ADC is a continuous-time oversampling Σ-Δ converter with 18-bit resolution; the ADC sampling rate is 10.24MHz; the ADC output data rate can be programmed from 50sps (samples per second) to 3200sps. The overall structure of the blood oxygen signal acquisition module is shown in the attached figure. Figure 1 As shown;

[0045] PPG measurement principle:

[0046] A typical PPG system is mainly composed of a light-emitting diode (LED), a photodiode (PD), and an analog front end (AFE). First, the LED emits incident light to the skin, and its transmitted light is received by the PD and converted into a current signal, which is then converted into a digital quantity by the AFE. According to the Beer-Lambert law, different substances in blood vessels have different absorption rates for light, and as the heart beats, the volume and dissolved substances in the blood vessels also change periodically. Therefore, we can use optical methods to conduct quantitative research based on the Beer-Lambert law, and further extract vital signs such as heart rate, blood oxygen, and respiration through the PPG waveform.

[0047] The Beer-Lambert law describes how the attenuation of light depends on the properties of the material it passes through:

[0048] I=I0e -ε(λ)Cd

[0049]

[0050] Where A is the attenuation, λo is the incident light intensity, I is the transmitted (received) light intensity, ∈(λ) is the molar extinction coefficient of the substance, C is the substance concentration, and d is the optical path length;

[0051] Blood oxygen saturation measurement principle:

[0052] Use the Beer-Lambert law and optical methods to calculate blood oxygen. Here we define the R value as the quotient of the perfusion index (PI = AC / DC) of the red light PPG signal and the infrared PPG signal. Then blood oxygen can be expressed as a quadratic function of blood oxygen, where the coefficients a, b, and c of the quadratic function are related to the optical structure of the system. We can calibrate the calculated R value by fitting it with the blood oxygen output of the standard device used as a reference.

[0053] Definition:

[0054]

[0055] Calculation formula:

[0056]

[0057] in,

[0058]

[0059] (The calibration coefficients a, b, c are related to the structure of the coefficient optics and can be obtained by fitting); Discrete Fourier transform principle:

[0060] Lemma 1 (elimination lemma):

[0061]

[0062] Lemma 2 (half lemma):

[0063]

[0064] exist The values ​​y0, y1, ..., y n-1

[0065]

[0066] Fast Fourier Transform

[0067] First, for this n-1 polynomial, its coefficient vector is a

[0068]

[0069] We divide it into two vectors: even and odd.

[0070] even:

[0071]

[0072] odd number:

[0073]

[0074] The two polynomials they correspond to are A [0] (x) and A [1] (x), now substitute x into

[0075] A(x)=a0+a1x+a2x 2 +…+a n-1 x n-1

[0076] A [0] (x) = a0 + a2x + a4x 2 +…+a n-2 x n / 2-1

[0077] A [1] (x) = a1 + a3x + a5x 2 +...+a n-1 x n / 2-1

[0078] First replace the independent variable x in the last two expressions with x 2

[0079] A [0] (x 2 )=a0+a2x2 +a4x 4 +...+a n-2 x n-2

[0080] A [1] (x 2 )=a1+a3x 2 +a5x 4 +...+a n-1 x n-2

[0081] We are in A [1] (x2) is multiplied by x.

[0082] xA [1] (x3)=a1x+a3x 3 +a5x 5 +…+a n-1 x n-1

[0083] Finally we can find

[0084] A(x)=A [0] (x 2 )+xA [1] (x 2 )

[0085] Now we transform the original problem of finding the value of A(x) at each root of unity into finding two polynomials with a power bound of n / 2. [0] (x) and A [1] The values ​​of (x) on each unit root square are combined. We substitute two specific unit roots and obtain, according to Lemma 1 and Lemma 2,

[0086]

[0087] according to:

[0088]

[0089] Simplifying,

[0090]

[0091] A [0] (x) and A [1] (x) are all polynomials with a degree bound of n / 2, and the problem is transformed into a polynomial A with a degree bound of n / 2. [0] and A [1] At each n / 2th root of unity, we reduce the original problem by half.

[0092] We solve these two sub-problems recursively, and then quickly merge the results using the halving lemma. Based on this idea, we can run the recursive formula in time T(n).

[0093]

[0094] The total time is equal to twice the subproblem time plus O(n) merging time. According to the main theorem and the recursion tree, the time complexity can be obtained to be O(nlogn);

[0095] The following is a pseudo-code implementation of the FFT algorithm:

[0096]

[0097] a k =ak [0] +t

[0098] Butterfly Transformation:

[0099] if lim == 1 return

[0100] a [0] =(a0, a2, ..., a n-2 )

[0101] a [1] =(a1, a3, ..., a n-1 )

[0102] FFT(a [0] ,lim>>1)

[0103] FFT(a [1] ,lim>>1)

[0104]

[0105] ω=1

[0106] for k=0..n / 2-1

[0107] a k =ak [0] +t

[0108]

[0109] ω=ωω n

[0110] Wavelet transform principle:

[0111] Wavelet is a wave that exists in a smaller area. Let ψ(t) be a square integrable function, that is, ψ(t)∈R if its Fourier transform ψ(ω) satisfies the condition

[0112]

[0113] ψ(t) is called a basic wavelet, also known as a wavelet mother function. The wavelet mother function ψ(t) is scaled and translated, assuming that the scaling factor (scale factor) is a, the translation factor is τ, and the function after scaling and translation is ψ a，τ (t), take the real parameter pair ψ a，τ (t), take the real parameter pair (a, τ), and get the wavelet function:

[0114]

[0115] ψ a，τ (t) The wavelet basis function with parameters a and τ, because the values ​​of parameters a and τ change continuously. Therefore, it is also called continuous wavelet basis transform. 2 Any function f(t) of (R) is expanded in the wavelet basis and is called the continuous wavelet transform of the function f(t). The transformation formula is:

[0116]

[0117] WT f (a, τ) is the wavelet transform coefficient. When the permissible conditions of the wavelet used are met, its inverse transform exists. There are:

[0118]

[0119] Discrete wavelet transform. Especially when using computers to perform specific operations on signal data, discretization of continuous wavelets is a necessary step. The specific discretization method consists of the following two steps. First, the discretization of the scale factor a. The discretization method usually uses binary discretization, that is, a m =2 m . Where m is an integer. Secondly, the translation factor τ is discretized. Usually, discrete values ​​with equal intervals are selected. The discretization method follows a m The integer multiple of the translation factor τ is taken as T s , satisfying τ k =ka m T s

[0120] The wavelet function is expressed as:

[0121]

[0122] Wavelet transform is expressed as:

[0123]

[0124] From the above, we can see that the continuous wavelet transform and the discrete wavelet transform are unified in form. In the specific computer operation process, the signal is mainly expressed in the form of discrete signal, so the discrete wavelet transform is selected as the main method for signal processing.

[0125] To optimize blood oxygen detection in order to improve the accuracy of detection, the steps are as follows:

[0126] S1, use at least three different wavelengths of light to illuminate the finger and earlobe of the measured part, and simultaneously collect the light signals transmitted or reflected back; different wavelengths of light have different absorption characteristics for oxygenated hemoglobin and reduced hemoglobin, and multi-wavelength light signal collection can provide richer information;

[0127] S2, performing adaptive filtering on the collected optical signal; the adaptive filtering algorithm automatically adjusts the filter parameters according to the real-time characteristics of the signal; specifically, by analyzing the frequency and amplitude variation characteristics of the optical signal, the high-frequency noise components related to the motion are identified and then filtered out;

[0128] S3, before testing, measure some basic physiological characteristics of the subject, such as skin color, tissue thickness and blood composition; according to these individual physiological characteristics, establish a personalized light absorption correction model, and optimize the test data based on the light absorption correction model;

[0129] For individuals with darker skin, the light absorption coefficient is adjusted accordingly when calculating blood oxygen saturation to compensate for the effect of melanin on light absorption.

[0130] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention; therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description. Therefore, it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention, and any figure marks in the claims should not be regarded as limiting the claims involved.

[0131] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A non-invasive blood oxygen detection method, comprising a blood oxygen meter (1) and a main housing (2), characterized in that: The main housing (2) is arranged on the upper part of the blood oximeter (1), a blood oxygen sensor is arranged below the blood oximeter (1), and the blood oxygen sensor is electrically connected to the main housing (2), the main housing (2) comprises a single chip microcomputer, an analog front-end drive module, a display module, a circuit module, a signal receiving module, a digital signal processing module, and a storage module, and a lithium battery is arranged in the main housing (2) to provide power for the blood oximeter (1); The blood oxygen sensor is directly connected to the signal receiving module to form a blood oxygen signal receiving module, and the blood oxygen signal receiving module is connected to the digital signal processing module to convert the voltage signal into a digital signal; the components in the main housing (2) are connected via a data transmission line, and a shielding layer is provided outside the data transmission line; The signals collected by the blood oximeter (1) include electrocardiogram signals, photoplethysmogram signals and skin temperature signals. The detection method of the blood oximeter (1) is: Preprocess the collected physiological signals to remove noise and interference; Extract characteristic parameters of ECG signal and photoplethysmogram signal, including heart rate, pulse wave amplitude, and pulse wave conduction time; According to the extracted characteristic parameters, the blood oxygen saturation is calculated using the PPG measurement method; The blood oxygen detection is optimized and the calculated blood oxygen saturation is corrected in combination with the skin temperature signal to improve the accuracy of the detection.

2. The non-invasive blood oxygen detection and method according to claim 1, characterized in that: The analog front-end driver module uses five connection ports including power interface VIN (3.3V / 5V), ground port GND, clock interface SCL, data interface SDA, and interrupt interface INT. The clock interface SCL is connected to the microcontroller port PB6, the data interface SDA is connected to the port PB7, and the interrupt interface INT is connected to the port PC8.

3. The non-invasive blood oxygen detection and method according to claim 1, characterized in that: The analog front-end driver module includes an integrated blood oxygen signal collector and an I2C communication module. The integrated blood oxygen signal collector adopts a miniature 5.6mmx 3.3mm x 1.55mm 14-pin light collection module; the analog front-end driver module includes a subsystem, which includes ambient light elimination and a proprietary discrete time filter.

4. The non-invasive blood oxygen detection and method according to claim 1, characterized in that: To optimize the blood oxygen detection method, the steps are as follows: S1, collect at least three different wavelengths of light, illuminate the fingers (at least three groups of different fingers) and earlobes under test, and simultaneously collect the transmitted or reflected light signals; different wavelengths of light have different absorption characteristics for oxygenated hemoglobin and reduced hemoglobin, and multi-wavelength light signal collection can provide richer information; S2, performing adaptive filtering on the collected optical signal; Adaptive filtering algorithms automatically adjust the filter parameters according to the real-time characteristics of the signal. S3, before the test, measure some basic physiological characteristics of the subject, such as skin color, tissue thickness and blood composition; according to these individual physiological characteristics, establish a personalized light absorption correction model, and optimize the test data based on the light absorption correction model.

5. The non-invasive blood oxygen detection and method according to claim 4, characterized in that: According to step S2, by analyzing the frequency and amplitude variation characteristics of the optical signal, the high-frequency noise components related to the motion are identified and then filtered out.

6. The non-invasive blood oxygen detection and method according to claim 4, characterized in that: According to step S3, for individuals with darker skin, when calculating the blood oxygen saturation, the light absorption coefficient is adjusted accordingly to compensate for the effect of melanin on light absorption.

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