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1 Center for Hyperbaric Medicine and Environmental Physiology, Duke University, Durham, North Carolina, United States
2 Center for Hyperbaric Medicine and Environmental Physiology, Duke University, Durham, North Carolina, United States; Department of Anesthesiology, Duke University, Durham, North Carolina, United States
3 Senior Statistician, Department of Anesthesiology, Duke University, Durham, North Carolina, United States
4 Department of Anesthesiology, Duke University, Durham, North Carolina, United States; Center for Hyperbaric Medicine and Environmental Physiology, Duke University, Durham, North Carolina, United States
5 Anesthesiology, Duke University, Durham, North Carolina, United States; Center for Hyperbaric Medicine and Environmental Physiology, Duke University, Durham, North Carolina, United States
* To whom correspondence should be addressed. E-mail: moon0002{at}mc.duke.edu.
During diving, arterial PCO2 (PaCO2) levels can increase and contribute to psychomotor impairment and unconsciousness. This study was designed to investigate the effects of hypercapnic ventilatory response (HCVR), exercise, inspired PO2, and externally applied transrespiratory pressure (Ptr) on PaCO2 during immersed prone exercise breathing oxygen-nitrogen mixes at 4.7 ATA. Methods: Twenty-five subjects were studied at rest and during 6 minutes 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 cm H2O; breathing gas PO2 was 0.7, 1.0 and 1.3 ATA; and inspiratory and expiratory breathing resistances were varied using disks with three differrent sizes of circular apertures. During exercise, PaCO2 (mmHg) 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 breathing air, and to 49.9±5.4 (P<0.001 vs. 1 ATA) with high external breathing resistance. There was no significant effect of inspired PO2 or Ptr on PaCO2 or minute ventilation (VE). VE (l·min-1) 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 breathing air, and to 49.2±7.3 (P<0.001) with resistance. We conclude that the major contributors to increased PaCO2 during exercise at 4.7 ATA are the increased depth and external respiratory resistance. HCVR and VO2 max values were also weakly predictive. The effects of Ptr, inspired PO2, and VO2 during short term exercise were not significant.
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  R. E. Moon, A. D. Cherry, B. W. Stolp, and E. M. Camporesi Pulmonary gas exchange in diving J Appl Physiol, February 1, 2009; 106(2): 668 - 677. [Abstract] [Full Text] [PDF]
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T. E. Wester, A. D. Cherry, N. W. Pollock, J. J. Freiberger, M. J. Natoli, E. A. Schinazi, P. O. Doar, A. E. Boso, E. L. Alford, A. J. Walker, et al. Effects of head and body cooling on hemodynamics during immersed prone exercise at 1 ATA J Appl Physiol, February 1, 2009; 106(2): 691 - 700. [Abstract] [Full Text] [PDF]
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