Pulmonary gas exchange during exercise in athletes I. Ventilation- perfusion mismatch and diffusion limitation

To investigate pulmonary gas exchange during exercise in athletes, 10 high aerobic capacity athletes (maximal aerobic capacity = 5.15 ± 0.52 l/min) underwent testing on a cycle ergometer at rest, 150 W, 300 W, and maximal exercise (372 ± 22 W) while trace amounts of six inert gases were infused intravenously. Arterial blood samples, mixed expired gas samples, and metabolic data were obtained. Indexes of ventilation-perfusion (V̇A/Q̇) mismatch were calculated by the multiple inert gas elimination technique. The alveolar-arterial difference for O₂ (AaDO₂) was predicted from the inert gas model on the basis of the calculated V̇A/Q̇ mismatch V̇A/Q̇ heterogeneity increased significantly with exercise and was predicted to increase the AaDO₂ by > 17 Torr during heavy and maximal exercise. The observed AaDO₂ increased significantly more than that predicted by the inert gas technique during maximal exercise (10 ± 10 Torr). These data suggest that this population develops diffusion limitation during maximal exercise, but V̇A/Q̇ mismatch is the most important contributor (>60%) to the wide AaDO₂ observed.