Pulmonary mechanisms and work of breathing at maximal ventilation and raised air pressure

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Abstract
Pulmonary ventilation (.ovrhdot.V) and the interrelationships of airflow, transpulmonary pressure and lung volume during inspiration and expiration were studied in 8 healthy men who performed maximal exercise (MEx; 140% .ovrhdot.VO2 max), 15-s maximal voluntary ventilation (MVV) and forced inspiratory and expiratory vital capacity (FVC) maneuvers at 1, 3 and 6 ATA [atmosphere absolute]. Maximal exercise ventilation and MVV amounted to 149 .+-. 7 (mean .+-. SE) and 193 .+-. 9 l .cntdot. 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; inspiratory peak flows during MEx were 20% less than the FVC flows. Despite 6-fold 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. Depletion of energy stores in the inspiratory muscles contributed to limiting .ovrhdot.V during MEx at raised air pressure.

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