On the boundary conditions used in calculations of gas mixing in alveolar lungs.

The lung boundaries exhibit a tight barrier for any insoluble gas; hence boundary conditions for lung gas mixing have to account for the absence of both diffusive and convective fluxes across the lung walls. Scrimshire et al. (1978) have, in contrast, used the less rigid boundary condition that only the net flux be zero. As we believe this boundary condition to be inappropriate for the study of insoluble gases, the results derived appear to have no physiological significance.