Method of Calculating FVC and FEV1 Based on Integrated Transfer Impedance With Higher-Order Modified Parameter Matrix

Lung function parameters are important reference for evaluating lung health. Compared with the flow vital capacity measurement method, the bioimpedance method has been widely concerned as a detection method with non-respiratory contact, strong comfort, and continuous monitoring. However, the current bioimpedance method still has the problems of large measurement error. To achieve accurate calculation of lung function parameters, this article first established a six-port circuit network model of the thoracic cross-section with the four-electrode fitting position as the node, calculated the transfer impedances in different measurement modes, and the mutual correction mathematical relationship of them is deduced. Furthermore, the calculated expression for the integrated transfer impedance is obtained. Second, the refined simulation model of the thoracic cross-section is constructed. The simulation results prove that the conclusions of the theoretical analysis are applicable for any respiratory moment. Then, 300 samples were measured, the experimental data were analyzed, and the parameters that correlate most strongly with lung function parameters were selected as independent variables for the binary functions used to calculate forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1). The coefficients of the function analytic formula are corrected by means of a higher-order parameter matrix, the elements of which are fitted from the experimental data. Finally, 20 samples were measured, and the calculated lung function parameters were compared with the standard values. The results showed that the difference between the two data was within the confidence range of 95%, and the maximum relative errors of FVC and FEV1 were 1.44% and 1.97%, respectively.