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Background: Acute mountain sickness occurs in some unacclimatized persons who travel to terrestrial altitudes at which barometric pressures are the same as those in commercial aircraft during flight. Whether the effects are similar in air travelers is unknown. Methods: We conducted a prospective, single-blind, controlled hypobaric-chamber study of adult volunteers to determine the effect of barometric pressures equivalent to terrestrial altitudes of 650, 4000, 6000, 7000, and 8000 ft (198, 1219, 1829, 2134, and 2438 m, respectively) above sea level on arterial oxygen saturation and the occurrence of acute mountain sickness and discomfort as measured by responses to the Environmental Symptoms Questionnaire IV during a 20-hour simulated flight. Results: Among the 502 study participants, the mean oxygen saturation decreased with increasing altitude, with a maximum decrease of 4.4 percentage points (95% confidence interval, 3.9 to 4.9) at 8000 ft. Overall, acute mountain sickness occurred in 7.4% of the participants, but its frequency did not vary significantly among the altitudes studied. The frequency of reported discomfort increased with increasing altitude and decreasing oxygen saturation and was greater at 7000 to 8000 ft than at all the lower altitudes combined. Differences became apparent after 3 to 9 hours of exposure. Persons older than 60 years of age were less likely than younger persons and men were less likely than women to report discomfort. Four serious adverse events, 1 of which may have been related to the study exposures, and 15 adverse events, 9 of which were related to study exposures, were reported. Conclusions: Ascent from ground level to the conditions of 7000 to 8000 ft lowered oxygen saturation by approximately 4 percentage points. This level of hypoxemia was insufficient to affect the occurrence of acute mountain sickness but did contribute to the increased frequency of reports of discomfort in unacclimatized participants after 3 to 9 hours. (ClinicalTrials.gov number, NCT00326703 [ClinicalTrials.gov].). [ABSTRACT FROM AUTHOR]

Acute mountain sickness is a syndrome that occurs when unacclimatized persons ascend rapidly to high altitudes. It is postulated that cerebral edema causes its symptoms. Since dexamethasone is useful in treating some forms of cerebral edema, we investigated its role in the prevention of acute mountain sickness. Using a double-blind crossover design, we exposed eight young men to a simulated altitude of 4570 m (15,000 ft) on two occasions. By random assignment, each subject received dexamethasone (4 mg every 6 hours) or placebo for 48 hours before and throughout the 42-hour exposure. The presence of symptoms of acute mountain sickness was established by two methods: a questionnaire and an interview by a physician. Dexamethasone significantly reduced the symptoms of acute mountain sickness. During dexamethasone treatment, the cerebral-symptom score (mean +/- S.E.) decreased from 1.09 +/- 0.18 to 0.26 +/- 0.08, and the respiratory-symptom score decreased from 0.64 +/- 0.09 to 0.31 +/- 0.06 (both, P less than 0.05). As judged by the interviewing physician, the symptom score decreased from 1.10 +/- 0.11 to 0.28 +/- 0.07 (P = 0.01). We conclude that dexamethasone may be effective in preventing the symptoms of acute mountain sickness.