Simulation of respiratory impedance variations during normal breathing using a morphometric model of the lung

Abstract

The forced oscillations technique (FOT) enables a non-invasive monitoring of respiratory mechanics, returning the impedance of the respiratory system (Zrs) at chosen frequencies. Recently it has been shown that the intrabreath variations of Zrs are correlated with respiratory diseases, mainly due to the sensitivity of Zrs to morphological changes in the respiratory system. The aim of this study was to develop a morphology-based computational model able to simulate the variations of airway dimensions during normal breathing and the resulting temporal changes in Zrs. The model counts the symmetric structure of the bronchial tree, lung and thorax wall viscoelasticity, and properties of the upper airways. It takes into account the distributed character of pressure loss along the airways and flow-limiting mechanisms. Quasi-dynamic simulations are performed, and for each time instant the distributed properties of airways are recalculated to a lumped parameter net corresponding to the momentary Zrs. The implemented model enabled simulations of primary signals characterising quiet breathing and the intrabreath variations in Zrs for both the normal case and small airways constriction. The simulation results recovered the flow- and volume-dependent variations of Zrs observed in healthy subjects and their alterations associated with uniform bronchial obstruction. However, testing specific hypotheses about the manifestation of inhomogeneous lung diseases in the intrabreath FOT data involves future incorporation of structural heterogeneity into the model.