APPARENT INCREASE OF O2 DIFFUSING CAPACITY WITH INCREASED O2 UPTAKE IN INHOMOGENEOUS LUNGS - THEORY

In order to interpret measurements of the pulmonary diffusing capacity for O2 (DO2) in conditions of increased O2 uptake in inhomogeneous lungs, calculations of DO2 based on experimental data were performed for simplified two-compartment lung models representing unequal distribution of alveolar ventilation and of diffusing capacity to blood flow, alveolar dead space ventilation and venous admixture. DO2 was found to be underestimated in all cases, but at increased O2 uptake levels to a lesser degree than with basal O2 uptake. Therefore the calculated, apparent DO2 tended to increase with increasing O2 uptake, although the diffusing conditions and the inequality of distribution were kept unchanged. Increases of DO2 experimentally found in conditions of heightened O2 uptake, particularly in muscular exercise, may be partly due to such effects. © 1969.