The nonlinear volume-dependent extended RIC model for Forced Oscillation Technique measurements

Abstract

The Forced Oscillation Technique (FOT) measures the respiratory impedance at different frequencies by applying sinusoidal oscillation on spontaneous breathing. Previously, we introduced an extension of the Forced Oscillation Technique in which the patients breathe slowly from residual volume to total lung capacity. The result of the measurement is a volume-dependent respiratory impedance Z(V,f). The nonlinear volume-dependent extended RIC model consists of two nonlinear volume-dependent resistances (central and peripheral), an inertia, and a bronchial compliance. Applying the nonlinear Least Squares parameter estimation and comparing to the original extended RIC model, the volume-dependent RIC model yields the best fit to the experimental data comparing to classical lung models such as the extended RIC model, the Mead-model, and the constant-phase model. The volume-dependency of the respiratory impedance can be approximated adequately with the non-linear model. The volume-dependent FOT measurement and the nonlinear extended RIC model provide a new tool for pulmonary testing with focus on the volume-dependency of the respiratory parameters. It has a high potential for the detection of obstructive lung diseases in early stages.