Diffusion in lung gas and across alveolar membrane in mammalian lungs.

The relative importance of stratified inhomogeneity in the mammalian lung has been considered both theoretically and experimentally. Calculations show that alveolar-capillary diffusion resistance is not limiting for inert gas exchange. Previous model calculations have concluded that stratified inhomogeneity is not likely to be an important mechanism in limiting gas exchange. Experimental data with inspired boluses of inert gas show the presence of stratified inhomogeneity. However, another possible mechanism, related to interaction of diffusion and convection, remains as a possible explanation for these findings. Stratified inhomogeneity appears to play a role in gas exchange in the normal rat, but the role of stratified inhomogeneity in humans and other animals is yet to be determined.