Impedance of intrathoracic airway models during low-frequency periodic flow.

The total pulmonary and lower airway impedances of the normal adult lung were simulated from 0.5 to 10 Hz using a distributed parameter model of the complete tracheobronchial tree. The model includes branching asymmetry; distributed representation of gas compliance, inertance, viscous effects, and inertial distortion of velocity profiles; and nonrigid airway walls. The model predicts closely similar resistance and frequency dependence of resistance but substantially greater reactances than observed by Finucane et al. (J. Appl. Physiol. 38: 517--530, 1975). Increases in resistance with frequency could be explained by changes in the distribution of flow among parallel inhomogeneities (47%), inertial distortion of velocity profiles (35%), changes in the serial distribution of flow due to gas compliance (11%), and airway wall compliance (7%). The disparity between measured and simulated reactance is attirbutable to artifact in the previously reported reactance measurement.