Gas mixing in lung model ventilated by high frequency oscillation: effect of tidal volume, frequency and molecular diffusivity.

The efficiency of gas mixing during sinusoidal oscillatory flow in a model of human lung cast was assessed by using a multibreath carbon dioxide washout manoeuvre. The experiments were performed at high frequencies (5, 10, 15 and 20 Hz) and low tidal volumes (50, 90 and 120 cm3). A particular effort was made to analyse the influence of flow oscillation conditions (f and VT) as well as the effect of resident alveolar gas density (molecular diffusion) on the effective diffusion coefficient (Deff). This longitudinal mixing parameter was found to be strongly dependent on the tidal volume (approximately proportional to VT1.4) and weakly dependent on the frequency (approximately proportional to f0.5). However, molecular diffusion was not, in general, a limiting factor in the gas transport process during high-frequency oscillation (HFO).