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

Cherry AD; Forkner IF; Frederick HJ; Natoli MJ; Schinazi A; Longphre JP; Conard JL; White WD; Freiberger JJ; Stolp BW; Pollock NW; Doar PO; Boso AE; Alford EL; Walker AJ; Ma AC; Rhodes MA; Moon RE

J Appl Physiol 2009 Jan; 106(1):316-325

https://doi.org/10.1152/japplphysiol.00885.2007

20054121

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 49.9 +/- 5.4 (P < 0.001 vs. 1 ATA) during breathing with high external resistance. There was no significant effect of inspired Po2 or Ptr on PaCO2 or minute ventilation (Ve). Ve (l/min) decreased from 89.2 +/- 22.9 dry to 76.3 +/- 20.5 (P = 0.02) submersed, to 61.6 +/- 13.9 (P < 0.001) at 4.7 ATA during air breathing and to 49.2 +/- 7.3 (P < 0.001) during breathing with resistance. We conclude that the major contributors to increased PaCO2 during exercise at 4.7 ATA are increased depth and external respiratory resistance. HCVR and maximal O2 consumption were also weakly predictive. The effects of Ptr, inspired Po2, and O2 consumption during short-term exercise were not significant.

Diving; Divers; Psychomotor function; Breathing; Respiration; Respiratory function; Carbon dioxide; Author Keywords: transrespiratory pressure; respiratory resistance; hyperoxia; carbon dioxide response; diving

R. E. Moon, Dept. of Anesthesiology, Box 3094, Duke Univ. Medical Center, Durham, NC 27710

JAPHEV

124-38-9

20090101

Journal Article

moon0002@mc.duke.edu

Grant

2009

Grant-Number-T42-OH-008673

1

8750-7587

Journal of Applied Physiology

NC

University of North Carolina, Chapel Hill