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Approximate Simulation of Acute Hypobaric Hypoxia with Normobaric HypoxiaINTRODUCTION. Some manufacturers of reduced oxygen (O2) breathing devices claim a comparable hypobaric hypoxia (HH) training experience by providing F(sub I) O2 < 0.209 at or near sea level pressure to match the ambient O2 partial pressure (iso-pO2) of the target altitude. METHODS. Literature from investigators and manufacturers indicate that these devices may not properly account for the 47 mmHg of water vapor partial pressure that reduces the inspired partial pressure of O2 (P(sub I) O2). Nor do they account for the complex reality of alveolar gas composition as defined by the Alveolar Gas Equation. In essence, by providing iso-pO2 conditions for normobaric hypoxia (NH) as for HH exposures the devices ignore P(sub A)O2 and P(sub A)CO2 as more direct agents to induce signs and symptoms of hypoxia during acute training exposures. RESULTS. There is not a sufficient integrated physiological understanding of the determinants of P(sub A)O2 and P(sub A)CO2 under acute NH and HH given the same hypoxic pO2 to claim a device that provides isohypoxia. Isohypoxia is defined as the same distribution of hypoxia signs and symptoms under any circumstances of equivalent hypoxic dose, and hypoxic pO2 is an incomplete hypoxic dose. Some devices that claim an equivalent HH experience under NH conditions significantly overestimate the HH condition, especially when simulating altitudes above 10,000 feet (3,048 m). CONCLUSIONS. At best, the claim should be that the devices provide an approximate HH experience since they only duplicate the ambient pO2 at sea level as at altitude (iso-pO2 machines). An approach to reduce the overestimation is to at least provide machines that create the same P(sub I)O2 (iso-P(sub I)O2 machines) conditions at sea level as at the target altitude, a simple software upgrade.
Document ID
20110015909
Acquisition Source
Johnson Space Center
Document Type
Presentation
Authors
Conkin, J. (Universities Space Research Association Houston, TX, United States)
Wessel, J. H., III (Wyle Integrated Science and Engineering Group Houston, TX, United States)
Date Acquired
August 25, 2013
Publication Date
January 1, 2011
Subject Category
Aerospace Medicine
Report/Patent Number
JSC-CN-24704
Meeting Information
Meeting: 83rd Annual Scientific Meeting of the Aerospace Medical Association
Location: Atlanta, GA
Country: United States
Start Date: May 13, 2012
End Date: May 17, 2012
Sponsors: Aerospace Medical Association
Distribution Limits
Public
Copyright
Public Use Permitted.

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