Series ventilation, diffusion in airways, and stratified inhomogeneity.

Functional inhomogeneity in lungs, meaning local variance of PCO2 and PO2 in alveolar space, may be of parallel and/or series nature. The effects of both kinds of inhomogeneity are qualitatively similar (decrease of the efficiency of alveolar gas exchange) and difficult to differentiate by experimental analysis. As far as diffusive mixing is concerned, methods specifically suited for detection and quantification of stratified inhomogeneities are based on separation of multiple test gases of differing diffusivity. The results of studies by such methods indicate that for alveolar O2 exchange the resistance attributable to stratification is in most cases less than the reciprocal pulmonary diffusing capacity for O2. In the conventional analysis of alveolar gas exchange, effects of stratification would contribute to alveolar dead space ventilation or would be incorporated in the pulmonary diffusing capacity.