PULMONARY GAS-EXCHANGE DURING EXERCISE IN ATHLETES .1. 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 I/min) underwent testing on a cycle ergometer at rest, 150 SIT, 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 (VA/Q) mismatch were calculated by the multiple inert gas elimination technique. The alveoiar-arterial difference for O-2 (AaDo(2)) was predicted from the inert gas model on the basis of the calculated VA/Q mismatch. VA/Q heterogeneity increased significantly with exercise and was predicted to increase the AaDo, by >17 Torr during heavy and maximal exercise. The observed AaDo(2) 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 VA/Q mismatch is the most important contributor (>60%) to the wide AaDo(2) observed.