EFFECT OF THE CURVATURE OF THE O-2 EQUILIBRIUM CURVE ON ALVEOLAR O-2 UPTAKE - THEORY

The effect of the curvature of the O2 equilibrium curve (OEC), in the range between mixed venous and alveolar P(O)2, on alveolar O2 uptake was quantitatively investigated in a simple homogeneous lung model. The O2 uptake achieved with a linear OEC (Mlin) was subtracted from the O2 uptake (M) attained with the physiologically curved, sigmoid OEC, and the relative difference was considered as the 'curvature effect', CE [= (M - Mlin)/M], indicating, if positive, the enhancement of O2 uptake by the non-linearity of the OEC. Calculations show CE to be close to nil (less than 1%) in normal lungs during rest both in normoxia and in hypoxia. CE is more important in heavy exercise both in normoxia (CE < 19%) or slight hypoxia (CE < 15%). In deep hypoxia, CE is negligible again even during exercise. Thus, the simplified approach to the analysis of alveolar O2 uptake using a linear OEC, in the mixed venous-to-alveolar P(O)2 range, constitutes in most cases a valid approximation.