Ventilation during simulated altitude, normobaric hypoxia and normoxic hypobaria

Loeppky, J.A., Icenogle, M., Scotto, P., Robergs, R.A., Hinghofer-Szalkay, H., & Roach, R.C. (1997) Ventilation during simulated altitude, normobaric hypoxia and normoxic hypobaria. Respiration Physiology, 107(3), pp. 231-239.

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Abstract

To investigate the possible effect of hypobaria on ventilation (V̇e) at high altitude, we exposed nine men to three conditions for 10 h in a chamber on separate occasions at least 1 week apart. These three conditions were: altitude (Pb=432, FiO2=0.207), normobaric hypoxia (Pb=614, FiO2=0.142) and normoxic hypobaria (Pb=434, FiO2=0.296). In addition, post-test measurements were made 2 h after returning to ambient conditions at normobaric normoxia (Pb=636, FiO2=0.204). In the first hour of exposure V̇e was increased similarly by altitude and normobaric hypoxia. The was 38% above post-test values and end-tidal CO2 (PetCO2) was lower by 4 mmHg. After 3, 6 and 9 h, the average V̇e in normobaric hypoxia was 26% higher than at altitude (p<0.01), resulting primarily from a decline in V̇e at altitude. The difference between altitude and normobaric hypoxia was greatest at 3 h (+39%). In spite of the higher V̇e during normobaric hypoxia, the PetCO2 was higher than at altitude. Changes in V̇e and PetCO2 in normoxic hypobaria were minimal relative to normobaric normoxia post-test measurements. One possible explanation for the lower V̇e at altitude is that CO2 elimination is relatively less at altitude because of a reduction in inspired gas density compared to normobaric hypoxia; this may reduce the work of breathing or alveolar deadspace. The greater V̇e during the first hour at altitude, relative to subsequent measurements, may be related to the appearance of microbubbles in the pulmonary circulation acting to transiently worsen matching. Results indicate that hypobaria per se effects ventilation under altitude conditions.

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ID Code: 96949
Item Type: Journal Article
Refereed: Yes
Keywords: adult; air conditioning; altitude; article; breathing pattern; controlled study; human; human experiment; hypobarism; hypoxia; male; mammal; normal human; priority journal; respiration control, NASA Discipline Environmental Health; Non-NASA Center, Adult; Air Pressure; Altitude; Altitude Sickness; Carbon Dioxide; Humans; Male; Oxygen Consumption; Pulmonary Ventilation; Tidal Volume; Water-Electrolyte Balance
DOI: 10.1016/S0034-5687(97)02523-1
ISSN: 0034-5687
Divisions: Current > QUT Faculties and Divisions > Faculty of Health
Current > Schools > School of Exercise & Nutrition Sciences
Deposited On: 19 Jul 2016 01:40
Last Modified: 19 Jul 2016 01:40

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