Numerical simulation of pulmonary O2 and CO2 exchange.

The process of gas exchange leading to the oxygenation of blood in pulmonary capillaries is simulated numerically, taking into account the main transport mechanisms of molecular diffusion, convection and the facilitated diffusion due to the presence of haemoglobin, as well as physiologically relevant boundary conditions and variable initial data. An algorithmic program to solve the relevant equations is run on a computer. It is found that, in the immediate neighbourhood of the entry, the amount of dissolved oxygen decreases, whereas the amount of carbaminohaemoglobin increases and the facilitated diffusion is more dominant over the molecular diffusion. Further, it is shown that (i) O2 takes longest and CO2 is the fastest to attain equilibration, (ii) the blood is completely oxygenated with one fifth part of its transit. Finally, the effect of various physiological parameters on equilibration length is examined.