Multi-frequency synchronous bioelectrical impedance real-time acquisition method

Abstract

The invention discloses a multi-frequency synchronous bioelectrical impedance real-time acquisition method, which comprises the following steps of: connecting an excitation electrode pair and a sampling electrode pair on a living body to be measured, and connecting a reference resistor RREF on the excitation electrode pair in series; accessing a multi-frequency synchronous signal excitation source VIN to the reference resistor RREF, and respectively acquiring the voltage VREF on the reference resistor RREF and the voltage VX on the living body to be measured; and according to the reference resistance RREF, the voltage VREF and the voltage VX, calculating the bioelectrical impedance value of the to-be-measured organism. A square wave-based multi-frequency synchronous signal is adopted to measure the impedance of an organism, the signal has the characteristics of rich frequency spectrum and high real-time performance, the generation structure is simple and controllable, the measurement real-time performance is high, and the two requirements of multi-frequency point and real-time performance of biological high-precision measurement can be well met; according to the method, the problem of measurement errors caused by the fact that the impedance of the living body changes along with the frequency change is solved, several more representative special frequency points can be selected by selecting the frequency points, the measurement efficiency is improved, and the measurement precision is improved.

Description

Technical Field

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

[0002] Bioimpedance technology is a non-invasive detection technology that uses the electrical characteristics of biological tissues and organs to extract biological physiological information. It uses electrodes placed on the body surface to input weak detection current into the organism, and then measures the voltage changes at appropriate parts to obtain the impedance transformation of related tissues or organs to obtain physiological and pathological information. This technology is widely used in modern medicine due to its advantages such as non-invasiveness, safety, and low price, mainly including: reactance blood flow diagram, human impedance imaging, and human body composition measurement.

[0003] Bioimpedance measurement technology has evolved from direct current to alternating current, from pure resistance to complex impedance, and from single frequency point to multi-frequency point measurement technology. However, the current mainstream multi-frequency bioimpedance measurement method still belongs to the time-sharing single-frequency measurement method, that is, scanning the impedance of the organism from low frequency to high frequency, which is time-consuming. In addition, since the physiological state of the organism is constantly affected by the heartbeat and blood flow, the time-sharing single-frequency measurement method cannot accurately reflect the biological impedance spectrum information of the organism at a certain moment. The biological impedance measurement method using multiple single-frequency signals for time-sharing scanning will introduce new biological impedance detection errors. This error mainly comes from the biological impedance changes caused by changes in body fluid composition during the biological circulation and metabolic cycle. For example, the cardiac cycle of an organism refers to a cycle in which the blood completes the nutritional supply of the biological tissue and takes away metabolic waste when the heart beats once. In a cardiac cycle, the composition of the blood changes, and the impedance also changes periodically.

[0004] Patent document 1 of CN103705236A discloses a method for rapid synchronous measurement of bioimpedance spectrum, which utilizes FPGA to realize a multi-frequency synchronous excitation signal source based on Walsh function and a corresponding bioimpedance acquisition method. However, compared with traditional sinusoidal signals, Walsh function signals have some disadvantages, such as unsatisfactory autocorrelation and large sidelobe values ​​of the spectrum. On the one hand, false synchronization will be generated, and 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, which 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 bioimpedance. The method uses FPGA programming to implement a multi-frequency synchronous excitation signal source based on a frequency synthesizer and a corresponding bioimpedance acquisition method. However, on the one hand, the scheme generates different frequency components based on 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 component is implemented by FPGA through table lookup, and it is difficult to change the preset frequency. On the other hand, the method uses several specific frequencies to "draw points into lines", and the sampling frequency points are relatively small, 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 later calculation results.

[0006] FPGA is used to generate different frequency components, and then the multi-frequency current signal is modulated by an adder. The design scheme is complex and errors are prone to occur during modulation. The frequency component is realized by FPGA through table lookup, and it is difficult to change the preset frequency. In addition, the excitation signal currently used does not conform to the impedance characteristics of the biological body, and there is a problem of large detection error in detecting the biological impedance. Summary of the invention

[0007] In view of the above technical problems, this application proposes a biological impedance detection method based on multi-frequency synchronous signals, which uses multi-frequency synchronous signals generated based on square waves to perform real-time high-precision detection of biological impedance, so that the detection process is more in line with the biological impedance characteristics and solves 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 to 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] An initial square wave signal is generated by the PWM source;

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

[0015] 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;

[0016] 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 .

[0017] Furthermore, the method for calculating the bioelectrical impedance value of the organism to be tested is:

[0018] At voltage V REF and voltage V X Select the measured frequency component f0 from the sampling frequency fs;

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

[0020] Calculate V based on Fourier transform frequency selection formula REF The amplitude V corresponding to the frequency point f0_REF and V X The amplitude V corresponding to the frequency point f0_X ;

[0021] Based on V f0_REF and amplitude V f0_X Calculate the bioimpedance Z X The magnitude of |Z X | and phase angle θ.

[0022] Furthermore, based on V f0_REF and amplitude V f0_X Calculate the bioimpedance Z X The amplitude of Z X | and the phase angle θ are:

[0023] Let V f0_REF The amplitude is A;

[0024] V f0_REF With V f0_X After multiplication, the DC component V is obtained by filtering through a low-pass filter. S1 ;

[0025] 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 ;

[0026] The bioimpedance Z is calculated based on the following formula: X The amplitude of Z X| 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, and the acquisition system includes:

[0029] Host computer;

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

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

[0032] An AD reference signal sampler, wherein the input end of the AD reference signal sampler is connected to a 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 is 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 respectively.

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

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

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

[0038] An RC high-pass filter, the RC high-pass filter is electrically connected to the high-speed analog switch, performs high-pass filtering, increases the proportion of high-frequency components in the signal, and outputs a third signal;

[0039] An active differential amplifier circuit is electrically connected to the RC high-pass filter to enhance the signal amplitude and improve the signal waveform, and output 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 using 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 real-time performance is strong. 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 after the square wave waveform is generated;

[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 bioimpedance amplitude and phase angle can be further calculated based on the capacitive load characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0047] Figure 3 The multi-frequency synchronous signal excitation source V IN A schematic diagram of a modulation method;

[0048] Figure 4 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 of

[0050] Figure 6 What is shown is a schematic diagram of a 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 purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0053] See also Figure 1 , shows a schematic flow chart of a multi-frequency synchronous bioelectrical impedance real-time acquisition method in the present application, the method is:

[0054] Use electrodes to connect the organism to be tested, and connect a reference resistor R in series in the detection circuit. REF ;

[0055] To the reference resistor R REF Access to 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 ;

[0056] According to the reference resistance R REF , the reference resistance R REF The voltage V REF And the voltage V on the biological body to be tested X Calculate the bioelectrical impedance value of the organism to be tested.

[0057] As a basic condition in the above method, it is necessary to provide a reference resistor R REF Access to multi-frequency synchronous signal excitation source V IN , Figure 2 The multi-frequency synchronous signal excitation source V that can be implemented in this application is shown. IN Schematic diagram of the equivalent generation system.

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

[0059] PWM source, which is used to generate a PWM square wave;

[0060] A high-speed analog switch, which performs analog switch modulation on the PWM square wave to form a square wave signal with a high equivalent bandwidth;

[0061] A high-pass filter module, which is used to filter low-frequency signals;

[0062] Amplitude-frequency modulation module, which is used to modulate the amplitude of the signal. Through the high-pass filter module and the amplitude-frequency modulation module, the square wave signal with high equivalent bandwidth is modulated into a multi-frequency synchronous signal excitation source V IN .

[0063] An executable method matching the above system, Figure 3 shows a multi-frequency synchronous signal excitation source VIN A flow chart of a modulation method is shown in FIG. 1 , wherein the modulation method is:

[0064] A square wave signal with narrow equivalent bandwidth is generated by the PWM source;

[0065] A square wave signal with low rise time and high equivalent bandwidth is generated by modulating a square wave with narrow equivalent bandwidth by a high-speed analog switch;

[0066] The square wave with equivalent wide bandwidth is processed by high-pass filtering to increase the proportion of high-frequency components in the signal;

[0067] Then the signal is processed by amplitude-frequency modulation to enhance the signal amplitude and improve the signal waveform, and finally a multi-frequency synchronous signal excitation source V is obtained. IN .

[0068] As an exemplary record, the multi-frequency synchronous signal excitation source V IN The modulation circuit topology is as follows Figure 4 As shown, the modulation circuit includes a PC host computer, which controls the parameters of user impedance measurement and calculates data. The PC host computer is connected to a control chip (MCU, model GD32F470), and the control chip generates and outputs a PWM square wave. The control chip is connected to and controls a high-speed analog switch (model SGM7222YMS10 / TR). The PWM square wave is modulated by analog switch through the high-speed analog switch to form a square wave signal with a high equivalent bandwidth. The RC high-pass filter electrically connected to the high-speed analog switch filters the low-frequency signal to generate a multi-frequency synchronous waveform, and then the multi-frequency synchronous excitation signal is obtained through the active differential amplifier circuit. The 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, the active differential amplifier circuit electrically connected to the sampling resistor (FC series) samples the excitation signal, and then passes through an RC high-frequency impedance matching circuit and a 16-bit AD sampling chip (model AD9269) to sample the analog signal and convert it into a digital signal for transmission to the control chip; on the other hand, the sampling electrode pair is applied to the biological body to be tested, collects the biological complex impedance signal, and performs signal conditioning through an active differential amplifier circuit, and then passes through an RC high-frequency impedance matching circuit and a 16-bit AD sampling chip (model AD9269) to sample the analog signal and convert it into a digital signal for transmission to the control chip.

[0069] The multi-frequency synchronous signal excitation source V is finally output after modulation by the above method. IN The spectrum of Figure 5 , the multi-frequency synchronous signal excitation source V INThe spectrum is very rich, with the highest bandwidth up to 15MHz. All the frequency points in the spectrum can be used as measurable frequency points. The measurable frequency points are rich, and a complete spectrum diagram of the biological impedance ZX from low frequency to high frequency can be established, 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 body impedance detection input part and the biological body 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] Combination 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 The digital signal is converted into a digital signal and uploaded to the host computer, where the voltage signal parameters of the two are solved using the DFT algorithm to obtain the complex impedance Z of the biological being tested. X After collecting the voltage signal with high precision and high speed, the two core parameters of the bioimpedance 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 on it REF And the impedance Z of the organism to be measured X The voltage V on it X The sampling frequency fs, select a frequency component f0, and at the same time select the number of points N for the discrete Fourier transform DFT. The sampling frequency fs and the number of points N for the discrete 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 on it REF The impedance Z of the organism to be measured X The voltage V on it X The frequency components a*f0, b*f0, c*f0 (a, b, c are natural numbers) in it happen to fall at the points M*a + 1, M*b + 1, M*c + 1 after the discrete Fourier transform DFT;

[0078] Calculate the discrete Fourier transform DFT components of the selected number of points N for the discrete Fourier transform DFT, and then the voltage V on the selected reference resistor R REF The voltage V on it REF The impedance Z of the organism to be measured X The amplitudes and phases of the frequency components a*f0, b*f0, c*f0 in the voltage Vx on it, and then obtain the impedance Z of the organism to be measured X The amplitudes and phases at the frequencies a*f0, b*f0, c*f0;

[0079] Select new frequency components f1, f2…fi (i < n), and repeat the calculation process n times to obtain the impedance Z of the organism X A series of impedance characteristic parameters from low frequency to high frequency;

[0080] Based on this series of impedance characteristic parameters and the organism impedance model, calculate the real part and imaginary part of the impedance Z of the organism X Of the real part and the imaginary part.

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

[0082]

[0083] e(-jω) = cosω - j sinω

[0084] After calculating the amplitude corresponding to this frequency, demodulate V based on the IQ demodulation principle f0_X Perform demodulation. Let 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, which is proportional to the phase difference between the input signal and the reference signal. Figure 7 The figure shows the schematic diagram of the IQ demodulation system. The impedance Z of the biological body to be measured can be calculated through IQ demodulation. X The 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 them.

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 to 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.

2. A multi-frequency synchronous bioelectrical impedance real-time acquisition method according to claim 1, characterized in that: The multi-frequency synchronous signal excitation source V IN The generation method is: An initial square wave signal is generated by the PWM source; Modulating 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 .

3. A multi-frequency synchronous bioelectrical impedance real-time acquisition method according to claim 2, 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 Select the measured frequency component f0 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 corresponding to the frequency point f0REF and V X The amplitude V corresponding to the frequency point f0_X ; Based on V f0_REF and amplitude V f0_X Calculate the bioimpedance Z X The magnitude of |Z X | and phase angle θ.

4. A multi-frequency synchronous bioelectrical impedance real-time acquisition method according to claim 3, characterized in that: Based on V f0_REF and amplitude V f0_X Calculate the bioimpedance Z X The magnitude 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 bioimpedance Z is calculated based on the following formula: X The magnitude of |Z X | and phase angle θ; 5. A multi-frequency synchronous bioelectrical impedance real-time acquisition method according to any one of claims 1 to 5, characterized in that: The multi-frequency synchronous bioelectrical impedance real-time acquisition method is applied to an acquisition system, and the acquisition system comprises: Host computer; An excitation square wave generator, the excitation square wave generator being electrically connected to a host machine; Reference resistance R REF , the reference resistor R REF electrically connected to an excitation square wave generator; An AD reference signal sampler, wherein the input end of the AD reference signal sampler is connected to a 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 is 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 respectively.

6. The multi-frequency synchronous bioelectrical impedance real-time acquisition method according to claim 1, characterized in that: The excitation square wave generator comprises: MCU, generates the initial square wave signal; A high-speed analog switch, which is electrically connected to the MCU, modulates the initial square wave signal to reduce the rise time, increase the equivalent bandwidth, and output a second square wave signal; An RC high-pass filter, the RC high-pass filter is electrically connected to the high-speed analog switch, performs high-pass filtering, increases the proportion of high-frequency components in the signal, and outputs a third signal; An active differential amplifier circuit is electrically connected to the RC high-pass filter to enhance the signal amplitude and improve the signal waveform, and output a multi-frequency synchronous signal excitation source V IN .

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