Frequency dependence of dynamic compliance analyzed from one cycle of breathing.

An analytical method for testing frequency dependence of dynamic compliance (Cdyn) from a Fourier-series analysis of flow and transpulmonary pressure in a single cycle of breathing was described and compared to the conventional method in an electrical model, in excised dog lobes and in human subjects. In the electrical model, the frequency dependence of Cdyn in the Fourier method corresponded exactly with the theoretical frequency dependence of Cdyn. A frequency dependence of Cdyn was evaluated by a ratio of Cdyn at 1 Hz to Cdyn at zero frequency, C1Hz/CoHz, from the regression line between Cdyn and the frequency in excised dog lobes and human subjects. In healthy nonsmokers, C1Hz/CoHz was significantly smaller in the Fourier method than in the conventional method. The discrepancy of frequency dependence of Cdyn between the two methods was thought to be possibly due to the effects of the nonsinusoidal breathing pattern on the conventional method, and due to the effects of a volume-dependent compliance on the Fourier method.