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Ventilation during simulated altitude, normobaric hypoxia and normoxic hypobariaTo investigate the possible effect of hypobaria on ventilation (VE) 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 VE was increased similarly by altitude and normobaric hypoxia. The was 38% above post-test values and end-tidal CO2 (PET(CO2) was lower by 4 mmHg. After 3, 6 and 9 h, the average VE in normobaric hypoxia was 26% higher than at altitude (p < 0.01), resulting primarily from a decline in VE at altitude. The difference between altitude and normobaric hypoxia was greatest at 3 h (+ 39%). In spite of the higher VE during normobaric hypoxia, the PET(CO2) was higher than at altitude. Changes in VE and PET(CO2) in normoxic hypobaria were minimal relative to normobaric normoxia post-test measurements. One possible explanation for the lower VE 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 VE 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.
Document ID
20040173010
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Loeppky, J. A.
(Lovelace Institutes Albuquerque, NM 87108, United States)
Icenogle, M.
Scotto, P.
Robergs, R.
Hinghofer-Szalkay, H.
Roach, R. C.
Leoppky, J. A.
Date Acquired
August 22, 2013
Publication Date
March 1, 1997
Publication Information
Publication: Respiration physiology
Volume: 107
Issue: 3
ISSN: 0034-5687
Subject Category
Aerospace Medicine
Funding Number(s)
CONTRACT_GRANT: 5M01 RR00997
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Environmental Health
Non-NASA Center

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