A multi-frequency synchronous bioelectrical impedance real-time acquisition method

Abstract

The present invention discloses a multi-frequency synchronous bioelectrical impedance real-time acquisition method, comprising the following steps: connecting an excitation electrode pair and a sampling electrode pair to the biological body to be measured, and connecting a reference resistor R in series to the excitation electrode pair. REF ; To the reference resistor R REF Access multi-frequency synchronous signal excitation source V IN , and respectively collect the reference resistance R REF The voltage V REF and the voltage V on the biological body to be tested X ; According to the reference resistance R REF , voltage V REF and voltage V X Calculate the bioelectrical impedance of the organism under test. This method uses a square wave multi-frequency synchronous signal to measure bioelectrical impedance. This signal has a rich spectrum and high real-time performance. Its generation structure is simple and controllable, and its real-time performance is strong. It can effectively meet the two requirements of high-precision biological measurement: multi-frequency points and real-time performance. It solves the measurement error caused by the change of bioelectrical impedance with frequency. By selecting frequency points, several more representative special frequency points can be selected to improve measurement efficiency and accuracy.

Description

Technical Field

[0001] The present invention belongs to the field of biomedical technology, and in particular relates to a method for real-time acquisition of multi-frequency synchronous bioelectrical impedance. Background Art

[0002] Bioelectrical impedance technology is a noninvasive measurement technique that uses the electrical characteristics of biological tissues and organs to extract physiological information. It uses electrodes placed on the body surface to input a weak test current into the organism. The voltage changes at appropriate locations are then measured to determine the impedance transformation of the relevant tissue or organ, thereby obtaining physiological and pathological information. Due to its non-invasive, safe, and affordable nature, this technique is widely used in modern medicine, primarily in areas such as reactance flow mapping, body impedance imaging, and body composition measurement.

[0003] Bioelectrical impedance measurement technology has evolved from DC to AC, from pure resistance to complex impedance, and from single-frequency to multi-frequency measurement techniques. However, the current mainstream multi-frequency bioelectrical impedance measurement method still uses a time-sharing single-frequency method, which sequentially scans the body's impedance from low to high frequencies. This is time-consuming and, because the body's physiological state fluctuates constantly due to heartbeats and blood flow, this method cannot accurately reflect the bioimpedance spectrum of the body at any given moment. Bioimpedance measurement using multiple single-frequency signals for time-sharing scanning introduces new bioimpedance detection errors. This error primarily arises from changes in bioimpedance caused by changes in body fluid composition during the body's metabolic cycle. For example, the cardiac cycle refers to the cycle in which blood completes the process of replenishing nutrients to tissues and removing metabolic waste during a heartbeat. During a cardiac cycle, the composition of the blood changes, and the impedance also fluctuates periodically.

[0004] Patent document 1 of CN103705236A discloses a method for rapid synchronous measurement of bioelectrical impedance spectrum. This method uses FPGA to implement a multi-frequency synchronous excitation signal source based on the Walsh function and a corresponding bioelectrical impedance acquisition method. However, due to some shortcomings of the Walsh function signal compared with the traditional sinusoidal signal, its autocorrelation is not ideal and the sidelobe value of the spectrum is large. On the one hand, this will produce false synchronization. On the other hand, the frequency accuracy of the excitation source obtained by this method is limited. Therefore, the number of DFT points must be increased during impedance extraction, and a correction algorithm must be added to solve the error caused by the DFT fence effect. This will greatly increase the amount of computation and complexity of the system.

[0005] Patent document 2 of CN104146709B discloses a method for rapidly acquiring multi-frequency bioelectrical impedance. This method utilizes FPGA programming to implement a multi-frequency synchronous excitation signal source based on a frequency synthesizer and a corresponding bioelectrical impedance acquisition method. However, on the one hand, this solution generates different frequency components based on the FPGA, and then synthesizes the multi-frequency current signal through an adder. The design scheme is complex and errors are prone to occur during synthesis. Moreover, the frequency components are implemented by the FPGA through a table lookup, making it difficult to change the preset frequency. On the other hand, this method utilizes several specific frequencies to "draw points into lines", sampling fewer frequency points, and ignoring the changes in human body impedance and the influence of actual parasitic parameters in the actual environment, resulting in difficulty in handling these errors in the subsequent calculation results.

[0006] Using an FPGA to generate different frequency components, which are then modulated by an adder into the multi-frequency current signal, is a complex design and prone to errors during modulation. Frequency components are generated by the FPGA through a table lookup, making it difficult to change the preset frequency. Furthermore, the currently used excitation signal does not conform to the characteristics of biological impedance, resulting in large errors in measuring biological impedance. Summary of the Invention

[0007] To address the above technical issues, this application proposes a method for detecting biological impedance based on multi-frequency synchronous signals. This method uses multi-frequency synchronous signals generated based on square waves to perform real-time, high-precision detection of biological impedance, making the detection process more consistent with the characteristics of biological impedance and solving the problem of insufficient detection accuracy. The specific technical solution is as follows:

[0008] A multi-frequency synchronous bioelectrical impedance real-time acquisition method comprises the following steps:

[0009] Connect the excitation electrode pair and the sampling electrode pair to the biological body to be tested, and connect the reference resistor R in series to the excitation electrode pair. REF ;

[0010] To the reference resistor R REF Access multi-frequency synchronous signal excitation source V IN , and respectively collect the reference resistance R REF The voltage V REF and the voltage V on the biological body to be tested X ;

[0011] According to the reference resistance R REF , voltage V REF and voltage V X Calculate the bioelectrical impedance value of the organism to be tested.

[0012] Furthermore, the multi-frequency synchronous signal excitation source V IN The generation method is:

[0013] Generate an initial square wave signal from the PWM source;

[0014] The initial square wave signal is modulated to reduce the rise time, increase the equivalent bandwidth, and obtain a second square wave signal;

[0015] The second square wave signal is subjected to high-pass filtering to increase the proportion of high-frequency components in the signal, and a third signal is obtained;

[0016] The third signal is subjected to amplitude-frequency modulation to enhance the signal amplitude and improve the signal waveform, and a multi-frequency synchronous signal excitation source V IN .

[0017] Further, the method for calculating the bioelectrical impedance value of the biological body is:

[0018] The sampling frequency fs of the voltage V REF and the voltage V X is selected as the measured frequency component f0;

[0019] The number of points N of Fourier transform is determined, satisfying fs / N = f0 / M, M is a natural number;

[0020] The amplitude V REF of the corresponding frequency point is calculated based on the Fourier transform frequency selection formula; f0_REF The amplitude V X of the corresponding frequency point is calculated based on the Fourier transform frequency selection formula; f0_X

[0021] The amplitude |Z X | and the phase angle θ of the biological impedance Z X are calculated based on the amplitude V f0_REF and the amplitude V f0_X .

[0022] Further, the method for calculating the amplitude |Z X | and the phase angle θ of the biological impedance Z X based on the amplitude V f0_REF and the amplitude V f0_X is:

[0023] Let the amplitude of V f0_REF be A;

[0024] V f0_REF is multiplied by V f0_X , and then a direct current component V S1 is obtained by filtering through a low-pass filter;

[0025] V f0_REF is phase-shifted by 90°, multiplied by V f0_X , and then a direct current component V S2 is obtained by filtering through a low-pass filter;

[0026] The amplitude |Z X of the biological impedance Z X is calculated based on the following formula respectively.| and phase angle θ;

[0027]

[0028] On the other hand, the present application also provides a multi-frequency synchronous bioelectrical impedance real-time acquisition system, which is applied to the above-mentioned multi-frequency synchronous bioelectrical impedance real-time acquisition method. The acquisition system includes:

[0029] Host computer;

[0030] An excitation square wave generator, the excitation square wave generator being electrically connected to a host computer;

[0031] Reference resistor R REF , the reference resistor R REF electrically connected to the excitation square wave generator;

[0032] AD reference signal sampler, the input end of the AD reference signal sampler is connected to the reference resistor R REF Electrical connection: the output end is electrically connected to the host computer;

[0033] An AD impedance signal sampler, the AD impedance signal sampler being electrically connected to a host computer;

[0034] The AD impedance signal sampler is connected to the sampling electrode pair, and the excitation square wave generator is connected to the reference resistor R REF Connect the excitation electrodes separately.

[0035] Furthermore, the excitation square wave generator includes:

[0036] MCU, generates the initial square wave signal;

[0037] a high-speed analog switch electrically connected to the MCU, modulating the initial square wave signal to reduce rise time, increase equivalent bandwidth, and output a second square wave signal;

[0038] an RC high-pass filter electrically connected to the high-speed analog switch to perform high-pass filtering to increase the proportion of high-frequency components in the signal and output a third signal;

[0039] Active differential amplifier circuit, the active differential amplifier circuit is electrically connected to the RC high-pass filter, enhances the signal amplitude and improves the signal waveform, and outputs a multi-frequency synchronous signal excitation source V IN .

[0040] The beneficial effects of the present invention are:

[0041] (1) The biological impedance is measured by a square wave multi-frequency synchronous signal. This signal has the characteristics of rich spectrum and high real-time performance. The generation structure is simple and controllable, and the measurement is real-time. It can better meet the two major requirements of multi-frequency points and real-time performance for high-precision biological measurement, and solve the measurement error problem caused by the change of biological impedance with frequency.

[0042] (2) Based on the rich spectrum characteristics of multi-frequency synchronous signals, multiple frequency points from low frequency to high frequency in the spectrum are selected for impedance calculation. On the one hand, the number of selected frequency points is much higher than that achievable by existing technologies, and the measurement is more accurate; on the other hand, by selecting frequency points, several more representative special frequency points can be selected to improve measurement efficiency and measurement accuracy;

[0043] (3) The square wave multi-frequency synchronous signal used in the measurement is a multi-frequency synchronous signal excitation source generated by further bandwidth modulation, low-frequency filtering, amplitude-frequency modulation and signal waveform improvement based on the square wave waveform;

[0044] (4) Based on the square wave multi-frequency synchronous signal to measure the biological impedance, the voltage signal can be collected with high precision and high speed, and the two core parameters of the bioelectrical impedance, amplitude and phase angle, can be further calculated based on the capacitive load characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Shown is a flow chart of a multi-frequency synchronous bioelectrical impedance real-time acquisition method;

[0046] Figure 2 Shown is the multi-frequency synchronous signal excitation source V IN Schematic diagram of the equivalent generation system;

[0047] Figure 3 Shown is the multi-frequency synchronous signal excitation source V IN A schematic flow chart of a modulation method;

[0048] Figure 4 Shown is the multi-frequency synchronous signal excitation source V IN Modulation circuit topology diagram;

[0049] Figure 5 The figure shows the final output of the multi-frequency synchronous signal excitation source V after modulation. IN spectrum;

[0050] Figure 6 Shown is a schematic diagram of the hardware framework for achieving real-time acquisition of bioelectrical impedance;

[0051] Figure 7 Shown is a schematic diagram of an IQ demodulation system. DETAILED DESCRIPTION

[0052] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the present application will be described clearly and completely below with reference to the embodiments.

[0053] Referring to Figure 1 , a flowchart of a multi-frequency synchronous bioelectrical impedance real-time acquisition method in the present application is shown, and the method is as follows:

[0054] An electrode is connected to the biological body to be measured, and a reference resistor R REF is connected in series on the detection circuit.

[0055] A multi-frequency synchronous signal excitation source V REF is connected to the reference resistor R IN , and the voltage V REF across the reference resistor R REF and the voltage V X across the biological body to be measured are collected respectively.

[0056] The bioelectrical impedance value of the biological body to be measured is calculated according to the reference resistor R REF , the collected voltage V REF across the reference resistor R REF and the voltage V X across the biological body to be measured.

[0057] As a basic condition in the above method, a multi-frequency synchronous signal excitation source V REF is connected to the reference resistor R IN . Figure 2 An equivalent generation system of the multi-frequency synchronous signal excitation source V IN that can be implemented in the present application is shown.

[0058] The generation system of the multi-frequency synchronous signal excitation source V IN includes:

[0059] A PWM source for generating a PWM square wave;

[0060] A high-speed analog switch for analog switch modulation of the PWM square wave to form a square wave signal with high effective bandwidth;

[0061] A high-pass filter module for filtering low-frequency signals;

[0062] An amplitude-frequency modulation module for modulating the amplitude of the signal, so that the square wave signal with high effective bandwidth is modulated into the multi-frequency synchronous signal excitation source V IN by the high-pass filter module and the amplitude-frequency modulation module.

[0063] An executable manner matched to the above system, Figure 3 a multi-frequency synchronous signal excitation source VIN a flowchart of a modulation method of a multi-frequency synchronous signal excitation source V

[0064] generating a square wave signal with narrow equivalent bandwidth from a PWM source;

[0065] generating a square wave signal with high equivalent bandwidth and low rise time from the square wave modulation with narrow equivalent bandwidth;

[0066] increasing the proportion of high-frequency components in the signal by high-pass filtering the square wave with wide equivalent bandwidth;

[0067] enhancing the signal amplitude and improving the signal waveform by amplitude-frequency modulation processing, and finally obtaining a multi-frequency synchronous signal excitation source V IN .

[0068] As an exemplary description, the modulation circuit topology of a multi-frequency synchronous signal excitation source V IN is shown in Figure 4 , which includes a PC host computer for user impedance measurement parameter control and data calculation, which is in communication connection with a control chip (MCU, model GD32F470) that generates and outputs a PWM square wave. The control chip is connected to and controls a high-speed analog switch (model SGM7222YMS10 / TR), which forms a square wave signal with high equivalent bandwidth after analog switch modulation of the PWM square wave. An RC high-pass filter connected to the high-speed analog switch filters low-frequency signals to generate a multi-frequency synchronous waveform, which is then processed by an active differential amplification circuit to obtain a multi-frequency synchronous excitation signal. The multi-frequency synchronous excitation signal is applied to the biological body to be tested through a sampling resistor (FC series) and a square wave electrode pair. At the same time, after the excitation signal is sampled by an active differential amplification circuit connected to the sampling resistor (FC series), it is sampled and converted into a digital signal by a 16-bit AD sampling chip (model AD9269) after an RC high-frequency impedance matching circuit, and transmitted to the control chip. On the other hand, a sampling electrode pair is applied to the biological body to be tested, and the biological complex impedance signal is collected and processed by an active differential amplification circuit, and then sampled and converted into a digital signal by a 16-bit AD sampling chip (model AD9269) after an RC high-frequency impedance matching circuit, and transmitted to the control chip.

[0069] The frequency spectrum of the multi-frequency synchronous signal excitation source V IN output by the above method is shown in Figure 5 , and the multi-frequency synchronous signal excitation source V INThe spectrum is very rich, with the highest bandwidth up to 15MHz. All frequency points in the spectrum can be used as measurable frequency points. The rich measurable frequency points can establish a complete spectrum diagram of the biological impedance ZX from low frequency to high frequency, thereby providing a complete impedance characteristic of the biological impedance.

[0070] As a more complete and specific record, Figure 6 The schematic diagram of the hardware framework for achieving real-time acquisition of bioelectrical impedance is shown, including:

[0071] The host computer is at least connected to the biological impedance detection input part and the biological impedance detection output part.

[0072] Among them, the biological impedance detection input part includes an excitation square wave generator, a reference resistor R REF , electrode pairs and AD sampling signal modules

[0073] The biological impedance detection output part includes an AD sampling impedance signal module and an electrode pair.

[0074] It can be understood that the host computer is a general term that can realize parameter control, parameter acquisition, and parameter calculation functions. The biological impedance detection input part and the biological impedance detection output part connected to it are essentially integrated with the host computer in a shell, and only the electrode pairs are exposed for contact with the tested organism.

[0075] The host computer generates a PWM square wave signal as a PWM source, which is modulated into a square wave signal with a low rise time and a high equivalent bandwidth by a high-speed analog switch. The square wave signal increases the proportion of high-frequency components in the signal through a high-pass filter circuit, and then enhances the signal amplitude and improves the signal waveform through an amplitude-frequency modulation circuit, and modulates it into a multi-frequency synchronous modulation signal excitation source V based on a square wave. IN .

[0076] Combine Figure 1 , and method description, based on the reference resistance R REF and the reference resistance R REF The voltage V REF and the voltage V on the biological body to be tested X The bioelectrical impedance value of the organism to be tested is calculated by using an analog-to-digital conversion chip to convert the reference resistance R REF The voltage signal V REF and the measured biological impedance Z X The voltage V X Converted into digital signals and uploaded to the host computer, the host computer uses the DFT algorithm to solve the voltage signal parameters of the two to obtain the biological complex impedance Z to be measured X After collecting the voltage signal with high precision and high speed, the two core parameters of bioelectrical impedance, amplitude and phase angle, are calculated based on the capacitive load characteristics. The specific method is as follows:

[0077] Select the reference resistor R REF The voltage V REF and the measured biological electrical impedance Z X The voltage V X The sampling frequency fs, select a frequency component f0, and select the number of points N for digital Fourier transform DFT. The sampling frequency fs and the number of points N for digital Fourier transform DFT must satisfy the formula fs / N=f0 / M, where M is a natural number, so that the reference resistor R REF The voltage V REF , the electrical impedance Z of the biological body to be measured X The voltage V X The frequency components a*f0, b*f0, and c*f0 (a, b, and c are natural numbers) fall exactly at the points M*a+1, M*b+1, and M*c+1 after the digital Fourier transform (DFT).

[0078] Calculate the DFT components of the selected DFT point number N to obtain the selected reference resistance R REF The voltage V REF , the electrical impedance Z of the biological body to be measured X The amplitude and phase of the frequency components a*f0, b*f0, and c*f0 in the voltage Vx on the body are used to obtain the electrical impedance Z of the biological body to be measured. X Amplitude and phase at frequencies a*f0, b*f0, and c*f0;

[0079] Select new frequency components f1, f2…fi(i <n),重复计算流程n次,从而得到生物体阻抗Z X A series of impedance characteristic parameters from low frequency to high frequency;

[0080] Based on this series of impedance characteristic parameters and the biological impedance model, the biological impedance Z is calculated. X The real and imaginary parts of .

[0081] As a more specific calculation example, select a frequency point f0 as the measurement frequency and calculate V based on the DFT frequency selection formula expressed in the following formula: REF The amplitude V of the corresponding frequency point f0_REF The amplitude V of the frequency point corresponding to VX f0_X .

[0082]

[0083] e(-jω)=cosω-jsinω

[0084] After calculating the amplitude corresponding to the frequency, V is demodulated based on the IQ demodulation principle. f0_X Demodulate. Assume Vf0_REF The amplitude is A, V f0_REF With V f0_X After multiplication, the DC component is filtered through a low-pass filter to obtain a DC component that is proportional to the phase difference between the input signal and the reference signal. Figure 7 The diagram shows the IQ demodulation system. The impedance Z of the biological body to be measured can be calculated through IQ demodulation. X Amplitude of |Z X | and phase angle θ.

[0085] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same.

Claims

1. A multi-frequency synchronous bioelectrical impedance real-time acquisition method, characterized in that: The following steps are involved: Connect the excitation electrode pair and the sampling electrode pair to the biological body to be tested, and connect the reference resistor R in series to the excitation electrode pair. REF ; To the reference resistor R REF Access multi-frequency synchronous signal excitation source V IN , and respectively collect the reference resistance R REF The voltage V REF and the voltage V on the biological body to be tested X ; According to the reference resistance R REF , voltage V REF and voltage V X Calculate the bioelectrical impedance value of the organism to be tested; The multi-frequency synchronous signal excitation source V IN The generation method is: Generate an initial square wave signal from the PWM source; Modulate the initial square wave signal to reduce the rise time and increase the equivalent bandwidth to obtain a second square wave signal; Performing high-pass filtering on the second square wave signal to increase the proportion of high-frequency components in the signal to obtain a third signal; The third signal is processed by amplitude-frequency modulation to enhance the signal amplitude and improve the signal waveform, and a multi-frequency synchronous signal excitation source V is obtained. IN .

2. A multi-frequency synchronous bioelectrical impedance real-time acquisition method according to claim 1, characterized in that: The method for calculating the bioelectrical impedance value of the organism to be tested is: At voltage V REF and voltage V X The frequency component f0 to be measured is selected from the sampling frequency fs; Determine the number of Fourier transform points N, satisfying fs / N=f0 / M, where M is a natural number; Calculate V based on Fourier transform frequency selection formula REF The amplitude V of the corresponding frequency point f0_REF and V X The amplitude V of the corresponding frequency point f0_X ; Based on V f0_REF and amplitude V f0_X Calculate the biological impedance Z X Amplitude of |Z X | and phase angle θ.

3. The method for real-time acquisition of multi-frequency synchronous bioelectrical impedance according to claim 2, characterized in that: Based on V f0_REF and amplitude V f0_X Calculate the biological impedance Z X Amplitude of |Z X | and the phase angle θ are: Let V f0_REF The amplitude is A; V f0_REF With V f0_X After multiplication, the DC component V is obtained by filtering through a low-pass filter. S1 ; V f0_REF After 90° phase shift, V f0_X After multiplication, the DC component V is obtained by filtering through a low-pass filter. S2 ; The biological impedance Z is calculated based on the following formula X Amplitude of |Z X | and phase angle θ; 。 4. A multi-frequency synchronous bioelectrical impedance real-time acquisition method according to any one of claims 1 to 3, characterized in that: The multi-frequency synchronous bioelectrical impedance real-time acquisition method is applied to an acquisition system, and the acquisition system includes: Host computer; An excitation square wave generator, the excitation square wave generator being electrically connected to a host computer; Reference resistor R REF , the reference resistor R REF electrically connected to the excitation square wave generator; AD reference signal sampler, the input end of the AD reference signal sampler is connected to the reference resistor R REF Electrical connection: the output end is electrically connected to the host computer; An AD impedance signal sampler, the AD impedance signal sampler being electrically connected to a host computer; The AD impedance signal sampler is connected to the sampling electrode pair, and the excitation square wave generator is connected to the reference resistor R REF Connect the excitation electrodes separately.

5. The method for real-time acquisition of multi-frequency synchronous bioelectrical impedance according to claim 4, characterized in that: The excitation square wave generator comprises: MCU, generates the initial square wave signal; a high-speed analog switch electrically connected to the MCU, modulating the initial square wave signal to reduce rise time, increase equivalent bandwidth, and output a second square wave signal; an RC high-pass filter electrically connected to the high-speed analog switch to perform high-pass filtering to increase the proportion of high-frequency components in the signal and output a third signal; Active differential amplifier circuit, the active differential amplifier circuit is electrically connected to the RC high-pass filter, enhances the signal amplitude and improves the signal waveform, and outputs a multi-frequency synchronous signal excitation source V IN .

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