Alveolar-capillary gas transfer in lungs: development of concepts and current state.

Progress in research on pulmonary gas exchange, with special reference to the contribution of Gerhard Thews and associates, is reviewed. In particular, the following aspects are considered. (1) Oxygen transfer kinetics of red blood cells. Recent measurements, particularly on red blood cells in thin blood films, yield more rapid equilibration kinetics than previously recorded. A reevaluation of the roles of diffusion and chemical reaction in alveolar O2 uptake may become necessary. (2) Gas exchange in functionally inhomogeneous lungs. Besides the classical ventilation/perfusion (VA/Q) inequality, a variation of the diffusing capacity-to-perfusion ratio (DL/Q) appears to be of importance. The combination of VA/Q and DL 1Q inequalities may lead to a better understanding of alveolar gas exchange, particularly in diseased lungs. (3) Pulmonary diffusing capacity (DL) for oxygen. The rebreathing technique, which strongly reduces the effects of inequal VA/Q distribution effects, appears to be particularly suited for measurement of overall alveolar-capillary diffusion. But neither the factors determining DL, obtained by rebreathing or other methods, nor the relationships between DL for various gases are yet fully understood.