Interpretation of inert gas retention and excretion in the presence of stratified inhomogeneity.

The effects of diffusion limitation in alveolar space (stratification) for inert gas retention and excretion by lungs with log-normal VA/Q distribution are calculated using the approach of Scheid et al. (Respir. Physiol. 44, 299-309, 1981). Since gases used in the multiple inert gas elimination technique have widely varying molecular weights (between 30 and 197), and therefore varying diffusivities, the effects of stratification are different for each gas. The result is a perturbation in the recovered VA/Q distributions that is calculated neglecting stratification effects. Application to inert gas elimination data obtained in the anesthetized rat by Truog et al. (J. Appl. Physiol. 47, 1112-1117, 1979) yields a value for the diffusion resistance in alveolar gas which would give rise to a PO2 difference of 5 Torr, suggesting that stratification may exert a significant limitation to pulmonary O2 transfer in rats.