The Research Of Test Method And System Of Lung Function Based On The Technology Of Bioelectrical Impedance

Bioelectrical impedance technology is a measurement technique which takes advantage of biological tissue and organs’electrical characteristics to fetch the information that contains physiological or abnormal status.Bioelectrical impedance technology is a good detection technology with the characteristics of safe,non-invasive,cheap and sustainable online monitoring.The physiological activity of the lung causes large changes of the chest bioelectrical impedance.The application of bioelectrical impedance to detect lung physiological activity has been a research hotspot.Based on the bioelectrical impedance technology,this paper made design and research about the lung function test system.The main work of this paper mainly includes these aspects:（1）Based on the introduction of the theoretical basis of bioelectrical impedance,the characteristics of bioelectrical impedance had been discussed.Through the introduction and analysis of the basic knowledge of lung function measurement,the relationship between the change value of chest bioelectrical impedance and the change of lung air was determined.The positive correlation was the key point to realize the measurement and calculation of lung function parameters based on bioelectric impedance technology.（2）The mathematical physical model of bioelectric impedance technology was briefly analyzed.The simulation model of chest bioelectrical impedance was established by using the finite source analysis software MAXWELL.The relationship between the air volume change of the lung and the change of the chest bioelectrical impedance was confirmed in the simulation level by modifying the parameters which represent the air volume in the lung.（3）According to the characteristics and requirements of bioelectrical impedance measurement,the system hardware design was completed.The hardware design was introduced by analyzing the key modules which contain constant current source module,switch array module,voltage and current acquisition module and communication module.After the hardware circuit design being completed,the software design was introduced by analyzing the software structure and process of ARM,FPGA and PC.The measurement of multi-frequency and multi-channel bioelectrical impedance based on the four-electrode method was realized after the hardware and software were designed and finished.The PC could obtain chest bioelectrical impedance through serial port and calculate lung function parameters.（4）Through the measurement experiment of the resistance capacity network,the measurement system was calibrated and the performance of the electrical impedance measurement system was specified.The system could achieve the electrical impedance measurement with accuracy of more than 1%under the excitation frequency of 50 kHz.Through the repeated and quantitative experiments which were performed on monomers,the relationship between the change value of the chest bioelectrical impedance and the air volume of the lung was determined.And the lung volume could be calculated by the change of the bioelectrical impedance of chest.In order to solve the problems of individual differences in the relationship between the change value of chest bioelectrical impedance and air volume of lung,this paper launched an experiment of 30 people and confirmed that the chest circumference was a significant factor affecting the relationship.The calculation of FVC and FEV₁ parameters were realized based on the change of the chest bioelectrical impedance after considering the factor of chest circumference.The method of this thesis was consistent with the standard method.The final accuracy was about 25%.