Differences in alveolo-capillary equilibration in healthy subjects on facing O(2) demand

Oxygen diffusion across the air-blood barrier in the lung is commensurate with metabolic needs and ideally allows full equilibration between alveolar and blood partial oxygen pressures. We estimated the alveolo-capillary O(2) equilibration in 18 healthy subjects at sea level at rest and after exposure to increased O(2) demand, including work at sea level and on hypobaric hypoxia exposure at 3840 m (P(A) ~ 50 mmHg). For each subject we estimated O(2) diffusion capacity (DO(2)), pulmonary capillary blood volume (Vc) and cardiac output ([Formula: see text] ). We derived blood capillary transit time [Formula: see text] and the time constant of the equilibration process ([Formula: see text] , β being the slope of the hemoglobin dissociation curve). O(2) equilibration at the arterial end of the pulmonary capillary was defined as [Formula: see text] . L(eq) greately differed among subjects in the most demanding O(2) condition (work in hypoxia): lack of full equilibration was found to range from 5 to 42% of the alveolo-capillary PO(2) gradient at the venous end. The present analysis proves to be sensible enough to highlight inter-individual differences in alveolo-capillary equilibration among healthy subjects.