Viscosity and density dependence during maximal flow in man

Abstract

Maximal expiratory flow curves were obtained from 10 healthy humans subjects while breathing air and 3 other gas mixtures with different densities and viscosities. From these data the magnitudes of the dependence of maximal flow on gas density and viscosity were obtained. The scaling laws of fluid mechanics, together with a model for the lung flow-limiting mechanism, were used to obtain a prediction of the relationship between the density dependence and the viscosity dependence of maximal flow. Although the data for individual subjects were too variable to allow a precise comparison with this prediction, the relationship between the mean density dependence and the mean viscosity dependence of all subjects agreed with the theoretical prediction. Apparently flow resistance rather than tissue viscoelasticity is the dominant contributor to peripheral resistance. Relationships between the pressure drop to the flow-limiting segment and flow, gas density and viscosity, and lung volume were studied.