Pulmonary gas mixing during spontaneous breathing and at high-frequency ventilation

This work is intended to estimate the contribution of either laminar or turbulent dispersion during spontaneous breathing on one hand, and at high-frequency pulmonary ventilation on the other. For that purpose, we performed a computer simulation of a mathematical model of gas transport in the human airways governed by a combination of axial convection and longitudinal dispersion. Calculations were carried out by incorporating two dispersion coefficients, proposed by Taylor and Scherer respectively, into the mathematical model. Moreover, computations were performed with five constant flow rates and two inert heavy (SF6) and light (He) gases to enhance the effect of mixing. It is concluded that Taylor laminar dispersion cannot play a significant role in the human airways; however, it seems that convective gas mixing with disturbed dispersion--corresponding to a regime of quasi-steady state--can account for most gas transport during spontaneous respiration and high-frequency ventilation.