Journal of Applied Physiology, Vol 48, Issue 1 147-153, Copyright © 1980 by American Physiological Society
Effect of altered gas diffusivity on alveolar gas exchange-a theoretical study
W. Nixon and A. Pack
Experimental studies have established that alveolar gas exchange is
inversely relation to the molecular diffusivity of gas in the lung airways.
The mechanism underlying this relationship is, however, unclear. To
investigate this phenomenon, the conditions relevant to the experimental
studies are simulated using a computational model of pulmonary gas
transport. Results from these simulations suggest that the inverse
relationship found experimentally can largely be explained on the basis of
the intra-acinar stratification of blood flow and gas concentrations. Gas
having a relatively low molecular diffusivity is not transported as far
into the acinus as gas having a higher diffusivity. When these relative
intra-acinar gas distributions interact with the blood flow distribution,
which has been shown experimentally to be weighted towards the proximal
alveoli, more gas exchange occurs in the low molecular diffusivity mixture.
Consideration of the various other mechanisms that have been proposed to
explain the experimental findings.he inverse dependence suggests that they
are of little significance. In particular, our studies remove the need to
invoke Taylor diffusion to explain the experimental findings.
