Limiting role of stratification in alveolar exchange of oxygen.

On the basis of a simple lung model the limiting effects of stratification on tidal/alveolar transfer of O2 are calculated using values for diffusive conductance of distal airways previously obtained from analysis of wash-out kinetics of He and SF6. In particular it is shown that the alveolar-capillary transfer of O2 (neglected in a previous study) plays an important role in giving rise to stratificational gradients of O2 in distal airways. For 10 kg dogs breathing hypoxic mixtures the stratificational component of the alveolar-arterial Po2 difference is estimated at about 0.8 torr for resting conditions and at about 3.5 torr for medium level exercise.