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Wilderness Environ Med. 2014 Jun;25(2):143-51. doi: 10.1016/j.wem.2013.11.007. Epub 2014 Mar 13.

Acute mountain sickness is not repeatable across two 12-hour normobaric hypoxia exposures.

Author information

  • 1School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada. Electronic address: martin@alumni.ubc.ca.
  • 2School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
  • 3Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada; School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.

Abstract

OBJECTIVE:

The purposes of this experiment were to determine the repeatability of acute mountain sickness (AMS), AMS symptoms, and physiological responses across 2 identical hypoxic exposures.

METHODS:

Subjects (n = 25) spent 3 nights at simulated altitude in a normobaric hypoxia chamber: twice at a partial pressure of inspired oxygen (PIO2) of 90mmHg (4000 m equivalent; "hypoxia") and once at a PIO2 of 132 mmHg (1000 m equivalent; "sham") with 14 or more days between exposures. The following variables were measured at hours 0 and 12 of each exposure: AMS severity (ie, Lake Louise score [LLS]), AMS incidence (LLS ≥3), heart rate, oxygen saturation, blood pressure, and the fraction of exhaled nitric oxide. Oxygen saturation and heart rate were also measured while subjects slept.

RESULTS:

The incidence of AMS was not statistically different between the 2 exposures (84% vs 56%, P > .05), but the severity of AMS (ie, LLS) was significantly lower on the second hypoxic exposure (mean [SD], 3.1 [1.8]) relative to the first hypoxic exposure (4.8 [2.3]; P < .001). Headache was the only AMS symptom to have a significantly greater severity on both hypoxic exposures (relative to the sham exposure, P < .05). Physiological variables were moderately to strongly repeatable (intraclass correlation range 0.39 to 0.86) but were not associated with AMS susceptibility (P > .05).

CONCLUSIONS:

The LLS was not repeatable across 2 identical hypoxic exposures. Increased familiarity with the environment (not acclimation) could explain the reduced AMS severity on the second hypoxic exposure. Headache was the most reliable AMS symptom.

Copyright © 2014 Wilderness Medical Society. Published by Elsevier Inc. All rights reserved.

KEYWORDS:

acclimation; acclimatization; high altitude; previous history; reproducibility

[PubMed - indexed for MEDLINE]
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