Cardiogenic oscillation and phase III caused by pressure-volume heterogeneity: a model.

The effect of heterogeneity of pressure-volume (PV) behavior of lung units and the effect of the pulsations of the heart on expired N2 following a single breath of O2 were studied mathematically in a model of the lung. The lung was pictured as consisting of three compartments, one of high compliance (HC) and another of low compliance (LC), both affected by cardiac pulsations, and a third, nonoscillatory compartment (NC). Three sigmoid PV curves were assigned to the three compartments, for both acini and airway (generation 10-23), so that total compliance summed up to 200 ml/cmH2O. Bifurcation of NC was at generation 5/6 and that of HC and LC at any chosen generation. A steepness constant, K, was defined to characterize the sharply descending portion of the sigmoid PV curve. For a ratio of the steepness constant for the oscillatory compartments, KHC/KLC = 1, a sloping alveolar plateau was produced. The plateau was concave for KHC/KLC greater than 1 and slightly convex for KHC/KLC less than 1. Cardiogenic oscillations (CO) of the expired N2 were produced by alternate flows from either NC or HC and LC. CO diminished in fast expiration, and a phase shift between the heart pulsation and the CO was seen; both agree with experimental findings.