Pulmonary ventilation (V) and the interrelationships of airflow, transpulmonary pressure, and lung volume during inspiration and expiration were studied in eight healthy subjects who performed maximal exercise (MEx; 140% VO2 max), 15-s maximal voluntary ventilation (MVV), and forced inspiratory and expiratory vital capacity (FVC) maneuvers at 1, 3, and 6 ATA. Maximal exercise ventilation and MVV amounted to 149 +/- 7 (mean +/- SE) and 193 +/- 9 l . min-1, respectively, at 1 ATA and were both reduced by approximately 37% at 3 ATA and by 50% at 6 ATA. Expiratory peak flows during MEx and MVV were equal to the maximal flows obtained during FVC at comparable lung volumes, whereas inspiratory peak flows during MEx were 20% less than the FVC flows. Despite a sixfold increase in gas density, the rate of mechanical work of breathing decreased when the pressure was raised to 6 ATA, during MEx from 8 +/- 1 to 6 +/- 1 W, and during MVV from 28 +/- 5 to 18 +/- 3 W. With increasing gas density there was a shift of lung volumes in the inspiratory direction with consequent reductions of inspiratory-to-expiratory flow ratios. We conclude that depletion of energy stores in the inspiratory muscles contributed to limiting V during MEx at raised air pressure.
