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INTRODUCTION: Crewmembers on ultra long-range commercial flights have the opportunity for rest and sleep in onboard areas in which the barometric pressure is 75.3 kPa (565 mmHg) or higher, equivalent to a terrestrial altitude of 2438 m (8000 ft) or lower. Sleep at higher altitudes is known to be disturbed, resulting in postsleep neurobehavioral performance decrements. We investigated the effects of sleep at 2438 m on oxygen saturation, heart rate, sleep quantity, sleep quality, postsleep neurobehavioral performance, and mood. METHODS: Twenty men, 30-56 yr of age, participated in a blinded cross-over investigation conducted in a hypobaric chamber to compare the effects of sleep at altitude (ALT, 2438 m) and ground level (GND, 305 m). RESULTS: SpO2 measured before sleep was significantly lower at ALT than at GND, 90.7 +/- 2.0% (average +/- SD) and 96.2 +/- 2.0%, respectively. During sleep, SpO2 decreased further to 86.1 +/- 2.0% at ALT, and 92.3% +/- 2.0% at GND. The percent of time during which SpO2 was below 90% was 44.4% (3.6-86.9%) at ALT and 0.1% (0.0-22.9%) at GND. Objective and subjective measurements of sleep quantity and quality did not differ significantly with altitude, nor did postsleep neurobehavioral performance or mood. DISCUSSION: The absence of significant changes in sleep and post-sleep neurobehavioral performance associated with pronounced oxygen desaturation during sleep was unexpected. Further study is needed to determine if the same effects occur in women and to characterize the changes in respiratory physiology that occur during sleep at 2438 m in both sexes.

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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].).

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INTRODUCTION: The degree of hypoxia manifested by airline passengers during flight is not well characterized. Statistical models to predict age-specific levels of Pao2 manifest at altitudes between sea level and 8000 ft (Pao2alt) are described. METHODS: The relationship between age and Pao2 at sea level (Pao2sl) and the relationship between Pao2alt, and Pao2sl, Pco2 at sea level (Pco2sl), and pulmonary health status were investigated using linear regression techniques to analyze previously published data. RESULTS: In persons with normal pulmonary health, the relationship between Pao2sl (mmHg) and age (yr) was Pao2sl = 105.9 - 0.44 * age (R2 = 0.582, MSE = 25.314); Pco2sl (38.1 +/- 2.8 mmHg) was not related to age over the range 18-75 yr. In persons with chronic obstructive lung disease (COPD), neither Pao2sl (78.2 +/- 11.3 mmHg) nor Pco2sl (40.5 +/- 5.7 mmHg) were related to age (77.0 +/- 9.0 yrs).The relationship between PaO2alt and Pao2sl, Pco2sl and altitude (ft) was: Pao2alt = 1.59 + 0.98 * Pao2sl + 0.0031 * Alt - 0.000061 * Pao2sl * Alt - 0.000065 * PCO(2)sl [corrected] * Alt + 0.000000092 * Alt2 (R2 = 0.932, MSE = 22.774). DISCUSSION: Pao2sl declines with age in persons with normal pulmonary health; Pco2sl remains constant. Neither vary with age in persons with COPD. Pao2alt can be estimated with acceptable precision from knowledge of Pao2sl, Pco2sl, and altitude. These models predict a substantial proportion of older passengers will manifest a Pao2alt at 8000 ft below the threshold at which supplemental oxygen is recommended.

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