Some implications of ternary diffusion in the lung

Diffusion in the lung normally involves three gases and the governing laws are Stefan-Maxwell equations rather than the more familiar Fick's law. A simple gas film model is studied mathematically to (1) demonstrate that the rate of diffusion of a component gas may be zero even though its concentration gradient is not zero (known as "diffusion barrier"), that the rate of diffusion of a component gas may not be zero even though its concentration gradient is zero ("osmotic diffusion"), and that a component gas may diffuse against the gradient of its concentration ("reverse diffusion"); (2) compare the discrepancy between results obtained by binary and ternary laws separately; (3) determine the importance of ternary diffusion at high pressure. The findings from the model study suggest that the effects of ternary diffusion may not be pronounced when air is breathed under normal conditions, but the behavior of helium mixtures deviate significantly from that described by binary diffusion laws.