Predictors of increased PaCO2 during immersed prone exercise at 4.7 ATA.

During diving, arterial Pco2 (PaCO2) levels can increase and contribute to psychomotor impairment and unconsciousness. This study was designed to investigate the effects of the hypercapnic ventilatory response (HCVR), exercise, inspired Po2, and externally applied transrespiratory pressure (Ptr) on PaCO2 during immersed prone exercise in subjects breathing oxygen-nitrogen mixes at 4.7 ATA. Twenty-five subjects were studied at rest and during 6 min of exercise while dry and submersed at 1 ATA and during exercise submersed at 4.7 ATA. At 4.7 ATA, subsets of the 25 subjects (9–10 for each condition) exercised as Ptr was varied between +10, 0, and −10 cmH2O; breathing gas Po2 was 0.7, 1.0, and 1.3 ATA; and inspiratory and expiratory breathing resistances were varied using 14.9-, 11.6-, and 10.2-mm-diameter-aperture disks. During exercise, PaCO2 (Torr) increased from 31.5 ± 4.1 (mean ± SD for all subjects) dry to 34.2 ± 4.8 (P = 0.02) submersed, to 46.1 ± 5.9 (P < 0.001) at 4.7 ATA during air breathing and to ...