Transport by gas-phase diffusion: lessons learned from the hen's egg.

Diffusive gas transport obeys laws which differ from those of convective transport. Diffusive gas transport can be described as an elite transport system because it not only distinguishes between O2, CO2, and water vapor molecules, but it is also influenced by barometric pressure and the presence of particular inert gas species. In the presence of air binary diffusion coefficients are applicable, but in the presence of He or SF6 effective diffusion coefficients must be used. By contrast, convective transport is an egalitarian transport system which conveys O2, CO2, and water vapor without discrimination at any altitude or in the presence of any inert gas mixture. Experiments in progress offer the opportunity to delineate for the first time precise diffusion-perfusion ratios and their effects upon the gas-space O2 and CO2 tensions.