CN112022123B - Exercise lung function measuring system based on thoracic impedance - Google Patents

Abstract

The invention relates to a moving lung function measuring system based on thoracic impedance, which comprises a microcontroller (1), a wireless communication module (2), a thoracic impedance measuring module (3) and a special electrode array (4), wherein the thoracic impedance measuring module (3) is respectively connected with the special electrode array (4) and the microcontroller (1), the microcontroller (1) is connected with the wireless communication module (2), and the microcontroller (1) calls a pre-stored computer program to execute the following steps: acquiring a thoracic impedance signal acquired by a thoracic impedance measurement module (3); performing interference removal processing on the thoracic impedance signal to obtain a respiratory signal in the movement process; and obtaining local lung ventilation information and lung capacity information based on the respiratory signal to realize lung function evaluation. Compared with the prior art, the invention has the advantages of effectively overcoming interference, high accuracy, suitability for motion state detection, no disturbance to respiratory tract and the like.

Description

Exercise lung function measuring system based on thoracic impedance

Technical Field

The invention relates to the field of medical detection, in particular to a moving lung function measuring system based on thoracic impedance.

Background

Chronic Obstructive Pulmonary Disease (COPD), a common chronic disease of the respiratory system, as an important public health problem, relies on screening for lung function in its early diagnosis, which is considered to be the gold standard for lung function examination using a spirometer, and after inhalation of bronchodilators, a forced expiratory volume (FEV 1)/Forced Vital Capacity (FVC) < 70% in the first second indicates that airflow limitation is present and cannot be completely reversed. However, the lung function screening based on the spirometer has limited popularity and strong compensatory ability of the lung, 85% of COPD patients are sick in 5 years before diagnosis, and most patients lose more than 50% of lung function when diagnosis is confirmed.

Because the oxygen consumption of the human body is increased by exercise, early lesions of the chronic obstructive lung are more easily found in the exercise state. The heart-lung exercise test (CPET) is one of the lung function tests which are commonly used internationally at present and used for measuring the respiratory and circulatory function levels of human bodies, and can be used for evaluating functional exercise capacity, diagnosing diseases and judging and treating diseases. Unlike static pulmonary function examination which only reflects ventilation or air exchange conditions in a rest state, CPET firstly measures the whole set of pulmonary functions of a human body in the rest state, continuously and dynamically monitors and records air flow, oxygen and carbon dioxide in and out under different loads, detects dynamic changes of parameters such as oxygen consumption and carbon dioxide discharge of the body in real time, can reflect the movement limitation and labor dyspnea conditions of patients in daily life, and can also be used for prognosis evaluation of COPD patients. However, since the CPET has a high cost and requires special equipment and professional operators, the measurement result is easily affected by the proficiency of the test of the subject and the auxiliary tools, which is not favorable for popularization.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a system for measuring the function of the moving lung based on thoracic impedance, which can effectively overcome interference, has high accuracy, is suitable for detecting a moving state and has no disturbance to a respiratory tract.

The purpose of the invention can be realized by the following technical scheme:

a moving lung function measuring system based on thoracic impedance comprises a microcontroller, a wireless communication module, a thoracic impedance measuring module and a special electrode array, wherein the thoracic impedance measuring module is respectively connected with the special electrode array and the microcontroller, the microcontroller is connected with the wireless communication module, wherein,

the microcontroller calls a pre-stored computer program to execute the following steps:

acquiring a thoracic impedance signal acquired by a thoracic impedance measurement module;

performing interference removal processing on the thoracic impedance signal to obtain a respiratory signal in the movement process;

and obtaining local lung ventilation information and lung capacity information based on the respiratory signal to realize lung function evaluation.

Furthermore, the chest impedance measuring module comprises a multi-way switch, a human body impedance measuring chip, a self-correcting circuit and a peripheral circuit, wherein the human body impedance measuring chip is respectively connected with the multi-way switch, the self-correcting circuit, the peripheral circuit and the microcontroller, and the multi-way switch is connected with the special electrode array.

Further, the human body impedance measurement chip adopts an AFE4300 chip.

Further, the interference elimination processing comprises the following steps:

1) performing wavelet filtering and smoothing on the thoracic impedance signal, and removing baseline drift by a polynomial fitting method;

2) extracting human body movement signals from the threshold and the slope of the amplitude change of the signals obtained in the step 1);

3) subtracting the signals obtained in the step 1) and the step 2), and smoothing to obtain a respiratory signal in the motion process.

Further, the interference elimination processing further includes: and performing band-pass filtering on the thoracic impedance signal to extract a heart rate signal.

Further, a butterworth filter based band pass filter implements the band pass filtering.

Further, the smoothing processing in step 1) and step 3) is realized based on a five-point cubic smoothing filtering method.

Further, in the step 2), based on the threshold and the slope of the amplitude change, a small-amplitude pulse signal which is smaller than a set value and represents the chest impedance change generated by movement is obtained from the signal obtained in the step 1) and is used as the human movement signal.

Further, the obtaining of the local lung ventilation information and the vital capacity information based on the respiratory signal specifically includes:

and calculating local lung ventilation and lung capacity by taking the respiratory signal as an accurate thoracic impedance signal according to an impedance-lung ventilation fitting formula.

Further, the wireless communication module adopts a bluetooth communication module.

The bioelectrical impedance technology is a detection technology for acquiring biomedical information related to human physiological conditions by using electrical characteristics and change rules of biological tissues, organs and the like. Because the electrical characteristics of lung tissues and the gas in the lung have obvious difference, the impedance characteristic measured by the outside of the chest of a human body is sensitive to the change of the inflation state in the lung, so the impedance change of the chest of a patient with lung obstruction can be detected by an impedance method, and the lung function condition is reflected. Compared with the traditional airflow type spirometer, the impedance method adopted by the invention is simple to operate, safe, reliable, portable and wearable, a testee can be accepted by the testee more easily without breathing and inhaling through an instrument, the patient coordination is good, and the impedance method is suitable for monitoring the pulmonary ventilation condition of the patient in a resting state or a moving state, so that the impedance method can be used as an effective supplement for routine pulmonary function examination, and has important diagnostic value and clinical significance for COPD early screening.

Compared with the prior art, the invention is different from the motion lung function monitoring limited to indoor instrument motion, can monitor the lung ventilation condition in indoor and outdoor motion, diagnose the lung function, is convenient to use in daily exercise training, provides reference information for the diagnosis and treatment of the lung function, and has the following beneficial effects:

1. the invention adopts the AFE4300 chip to measure the human body impedance, compared with the human body impedance measurement system which is realized by the design of a separate element, the integration level is high, the volume of the measurement system is obviously reduced, and the wearing is convenient; the lung function evaluation result is sent to equipment such as a mobile phone or a computer through Bluetooth without being in hard connection with the mobile phone or the computer, so that the lung function measurement can be carried out in the moving process of running, walking and the like.

2. The invention adopts the precise resistor and capacitor to calibrate AF4300, overcomes the difference between different chip performances and the drift of the same chip performance, and realizes high-precision thoracic impedance measurement.

3. The chest impedance data measured in the movement process also contains information such as measurement noise, movement noise, heartbeat and the like besides the breathing information, the invention adopts data processing processes such as band-pass filtering, wavelet filtering, five-point cubic smoothing filtering, polynomial fitting and the like to remove the movement noise, the measurement noise, the heartbeat noise and baseline drift from the measured chest impedance so as to obtain signals related to breathing, thereby being capable of extracting the chest impedance data related to breathing in the movement process.

4. According to the invention, the thoracic impedance signal related to respiration extracted in the exercise process is processed to obtain the local lung ventilation information and the lung capacity information in the exercise process, and the lung function is evaluated, so that the lung function evaluation based on the thoracic impedance characteristic can be used for detecting the lung function in the exercise process.

5. The invention can detect the lung function in the process of non-fixed-point movement, is wearable, has no disturbance and resistance increase to the respiratory tract of a detected person, has no cross infection risk, is easier to be accepted by the detected person, and is convenient for detection and use in the daily body building and training processes.

6. The invention detects the lung ventilation condition in the exercise process of increasing the oxygen demand of the human body, is beneficial to finding out the early decline of the lung function, is convenient for screening and finding COPD symptoms at the early stage, and realizes the early diagnosis and early treatment of COPD.

Drawings

FIG. 1 is a schematic diagram of a lung function measuring system according to the present invention;

FIG. 2 is a schematic flow chart of the present invention;

FIG. 3 is an example of a waveform of an originally sampled thoracic impedance signal;

FIG. 4 is an example of an extracted heart rate signal;

FIG. 5 is an example of a signal after filtering and smoothing denoising;

FIG. 6 is an example of a human motion signal extracted by threshold determination;

fig. 7 is an example of the signals finally obtained in relation to the respiration of a human being.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.

Example 1

As shown in fig. 1, the present embodiment provides a system for measuring a function of a moving lung based on thoracic impedance, which includes a microcontroller 1, a wireless communication module 2, a thoracic impedance measuring module 3 and a dedicated electrode array 4, wherein the thoracic impedance measuring module 3 is connected to the dedicated electrode array 4 and the microcontroller 1, respectively, and the microcontroller 1 is connected to the wireless communication module 2. The special electrode array 4 is in contact with the surface of the chest of a human body, the chest impedance measuring module 3 collects measuring voltage through the special electrode array 4, the microcontroller 1 controls the chest impedance measuring module 3 to carry out self-correction and chest impedance measuring processes, measured chest impedance information is processed to obtain signals related to respiration, local lung ventilation condition and lung capacity are further calculated, lung function evaluation is carried out, and evaluation results can be transmitted to external equipment (such as a mobile phone, a computer and the like) through the wireless communication module 2.

In this embodiment, the special electrode array 4 includes 8 special composite electrodes attached to the surface of the chest, 4 electrodes on the upper, lower, left and right sides of the chest, 4 electrodes attached to the back opposite to the back, the electrodes opposite to the chest form an electrode pair, and the 4 pairs of electrodes measure 4 thoracic impedances on the upper left, upper right, lower left and lower right, respectively; each composite electrode comprises two concentric but insulated electrodes, the outer large electrode being used for applying an excitation current and the inner small electrode being used for measuring a response voltage. And applying excitation current through a current electrode in the composite electrode, detecting response voltage through a voltage electrode in the composite electrode, and performing signal conditioning and analog-to-digital conversion in the chip to obtain measurement voltage.

The chest impedance measuring module 3 comprises a multi-way switch 301, a human body impedance measuring chip 302, a self-correcting circuit 301 and a peripheral circuit 304, wherein the human body impedance measuring chip 302 is respectively connected with the multi-way switch 301, the self-correcting circuit 301, the peripheral circuit 304 and the microcontroller 1, and the multi-way switch 301 is connected with the special electrode array 4 to realize the measurement of different position information. During measurement, the microcontroller controls the multi-way switch to sequentially select different electrode pairs, the excitation current generated by the AFE4300 is applied to the excitation electrode pairs, the response voltage is transmitted to the voltage measurement channel of the AFE4300 through the multi-way switch, and 4 thoracic impedances of the upper left, the upper right, the lower left and the lower right are sequentially measured.

In the chest impedance measurement module 3, the human body impedance measurement chip 302 adopts an AFE4300 chip; the self-correcting circuit 301 comprises a precise resistor and capacitor network and is used for calibrating the AFE4300 measurement performance; the peripheral circuits 304 are used to provide clock signals, parameter settings, etc. to the AFE 4300. The human body impedance measurement chip AFE4300 gates one pair of current excitation channels and voltage measurement channels from the four pairs of composite electrodes to the AFE4300 in sequence through a multi-channel analog switch to measure impedance.

The microcontroller 1 invokes a pre-stored computer program to perform the following steps: acquiring a thoracic impedance signal acquired by the thoracic impedance measuring module 3; performing interference removal processing on the thoracic impedance signal to obtain a respiratory signal in the movement process; local lung ventilation information and lung capacity information are obtained based on the respiratory signals, and lung function assessment is achieved.

In this embodiment, the wireless communication module 2 is a bluetooth communication module.

The specific measurement process of the moving lung function measurement system based on the thoracic impedance comprises the following steps:

1) and calibrating the AFE4300 chip by using a self-calibration circuit to obtain a fitting relation between the measured voltage data and the measured impedance.

2) The AFE4300 chip generates 50kHz excitation current with the amplitude of 0.3500mA, weak excitation current is applied to the human thorax by sequentially gating one current electrode pair of four pairs of composite electrodes attached to the surface of the thorax of the object to be tested through a multi-path selection switch, response voltage is measured through voltage electrodes in the composite electrodes, and thoracic impedance data are obtained according to the voltage/impedance fitting relation obtained in the step 1). Obtaining a continuously monitored respiratory signal s during movement using an electrical impedance measurement system₀(n) at a sampling rate of 128sps, i.e., 128 samples per second, the original sampled signal is shown in fig. 3. The normal respiration frequency of an adult is 12-20 times/minute in rest, the normal heart rate is 60-100 times/minute, and the adult can increase during exercise.

3) Subjecting the thoracic impedance signal to a Butterworth filter-based bandpass filter to extract a heart rate signal s₁(n) for center rate monitoring during exercise, the heart rate can be used for exercise intensity assessment to prevent hyperkinesia, as shown in fig. 4.

4) Wavelet filtering and smoothing are carried out on the thoracic impedance signal, and baseline drift is removed by a polynomial fitting method. In particular, the most common model of the measurement signal has the following form:

s(n)＝f(n)+e(n) (1)

where time n is equidistant. The purpose of denoising is to suppress the noisy portion e (n) of the signal s (n) and recover the useful signal f (n). The principle is that the signal has certain continuity in space (or time domain), and the modulus of a wavelet coefficient generated by a valid signal in the wavelet domain is often larger; while the Gaussian white noise has no continuity in space (or time domain), the noise still shows strong randomness in the wavelet domain after wavelet transformation, and still meets the Gaussian white noise distribution. In the wavelet domain, if the variance corresponding to the wavelet coefficient of the noise is σ, most of the noise coefficients are located in the range of [ -3 σ, 3 σ ] according to the characteristics of gaussian distribution. Therefore, by simply setting the coefficients in the interval [ -3 σ, 3 σ ] to zero, the noise can be suppressed to the maximum extent while the effective signal is retained. And reconstructing the wavelet coefficient after threshold processing to obtain a denoised useful signal.

The smoothing process used is a five-point cubic smoothing filtering method. The five-point cubic smoothing filter is a low-pass filter, and performs smoothing filtering on sampling points by utilizing polynomial least square approximation, and the algorithm is as follows:

let the observed value of known n (n ≧ 5) equidistant points be x₀<x₁<…<x_n-1Then, two adjacent points before and after each data point can be respectively taken, and approximation is performed by a cubic polynomial:

y＝a₀+a₁x+a₂x²+a₃x³ (2)

from the least squares principle, a can be determined₀，a₁，a₂，a₃Finally, a five-point cubic smoothing formula is obtained as follows:

and finally, removing the baseline drift by adopting a polynomial fitting method. First, polynomial fitting is carried out on the signals containing the linear trend to obtain fitted baselines, and then the baseline fitting signals are subtracted from the original signals to obtain signals with baseline drift removed.

In order to extract the respiratory signal, the human heart rate signal and the high-frequency noise introduced by the environment need to be filtered. The method combining the wavelet threshold filtering and the five-point cubic smoothing method can effectively filter high-frequency noise interference and keep a reconstructed respiratory signal, so that a higher signal-to-noise ratio is obtained. Wherein, the wavelet threshold filtering adopts a fixed hard threshold and is adjusted according to the noise level estimation of the first layer wavelet decomposition. The coefficient of the five-point cubic smoothing filter is 5, i.e. 5 iterations are performed. Meanwhile, a certain baseline drift phenomenon of the measured signal is detected, a polynomial fitting method is used for generally carrying out cubic polynomial fitting on the signal with linear trend to obtain a fitted baseline, and then the fitted signal is subtracted from the original signal to obtain a signal s with the baseline removed₂(n) as shown in FIG. 5.

5) And (4) carrying out threshold judgment on the amplitude and slope change of the obtained signal, and extracting a human motion signal.

When the human body does walking or running exercise, the chest impedance value measured by the electrical impedance measurement system changes along with the muscle movement and the change of the diaphragm position. Compared with the conventional respiratory signal, the chest impedance change generated by movement is small in amplitude, generally below 2 omega, fast in increase and decrease and high in frequency, and appears as a small-amplitude pulse signal superposed on a respiratory signal. Therefore, the resistance value change s caused by the human body motion can be judged and extracted according to the threshold value and the slope of the amplitude value change₃(n) as shown in FIG. 6.

6) And (4) subtracting the signals obtained in the step (5) from the signals obtained in the step (4), and smoothing to obtain a respiratory signal.

Will s₂(n) subtracting s₃(n) then using five-point cubic smoothing filtering to obtain a respiratory signal s reflecting the lung ventilation status₄(n) as shown in FIG. 7. By judging the lung ventilation condition in the human body movement process, the method provides basis for the lung function diagnosisAccordingly.

7) For respiratory signal s₄(n) carrying out characteristic analysis to obtain local lung ventilation information and lung capacity information and evaluating lung function.

8) And returning to the step 1) until the movement is finished or a finishing measurement instruction is received.

9) And sending the lung function real-time evaluation result to equipment such as a mobile phone or a computer through Bluetooth.

The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims (4)

1. A moving lung function measuring system based on thoracic impedance is characterized by comprising a microcontroller, a wireless communication module, a thoracic impedance measuring module and a special electrode array, wherein the thoracic impedance measuring module is respectively connected with the special electrode array and the microcontroller, the microcontroller is connected with the wireless communication module,

the chest impedance measuring module comprises a multi-way change-over switch, a human body impedance measuring chip, a self-correcting circuit and a peripheral circuit, wherein the human body impedance measuring chip is respectively connected with the multi-way change-over switch, the self-correcting circuit, the peripheral circuit and a microcontroller, the multi-way change-over switch is connected with a special electrode array, and the human body impedance measuring chip adopts an AFE4300 chip;

the special electrode array comprises four pairs of composite electrodes;

the specific measurement process of the moving lung function measurement system based on the thoracic impedance comprises the following steps:

1) calibrating the AFE4300 chip by using a self-calibration circuit to obtain a fitting relation between measured voltage data and the impedance to be measured;

2) the AFE4300 chip generates 50kHz excitation current with the amplitude of 0.3500mA, sequentially gates a current electrode pair attached to one pair of four pairs of composite electrodes on the surface of the chest of a measured object by a multi-channel change-over switch to apply the excitation current to the chest of a human body, measures response voltage by a voltage electrode pair in the composite electrodes, and obtains chest impedance data according to the voltage/impedance fitting relation obtained in the step 1);

3) performing band-pass filtering based on a Butterworth filter on the thoracic impedance data, extracting a heart rate signal for monitoring the center rate in the exercise process, wherein the heart rate can be used for evaluating exercise intensity to prevent excessive exercise;

4) performing wavelet filtering and smoothing on the thoracic impedance signal, and removing baseline drift by a polynomial fitting method;

5) judging the threshold value of the amplitude and slope change of the obtained signal, extracting a human body movement signal, and obtaining a small-amplitude pulse signal which is smaller than the set value in the threshold value and represents the chest impedance change generated by movement from the signal obtained in the step 4) based on the threshold value and slope of the amplitude change, wherein the small-amplitude pulse signal is used as the human body movement signal;

6) subtracting the signals obtained in the step 4) and the step 5), and smoothing to obtain a respiratory signal;

7) and performing characteristic analysis on the respiratory signal to obtain local lung ventilation information and vital capacity information and evaluate the lung function.

2. A system for measuring motor lung function based on thoracic impedance as claimed in claim 1, wherein the smoothing process in step 4) and step 6) is implemented based on a five-point cubic smoothing filtering method.

3. The system of claim 1, wherein the obtaining of the local lung ventilation information and the lung capacity information based on the respiration signal is specifically:

and calculating local lung ventilation and lung capacity by taking the respiratory signal as an accurate thoracic impedance signal according to an impedance-lung ventilation fitting formula.

4. The system of claim 1, wherein the wireless communication module is a bluetooth communication module.

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