Sleeping aboard airplanes: unknown risks

Little is known about the physiological effects for crew and passenger when sleeping in airplanes under hypobaric conditions. At cruising altitude the cabin pressure equals an altitude of 8000 ft. At the DLR-Institute of Aerospace Medicine, 16 healthy subjects (8 female, average age 28 years ± 4 SD), slept in a pressure chamber furnished as crew-rest-compartment during a realistic flight simulation concerning atmospheric conditions and noise. Blood oxygen saturation (SpO2), heart rate, and Sleep-EEG were recorded during the 4h sleep period. Morning performance was tested using an unstable tracking task reflecting typical operator demands. A control group of 16 subjects (8 female, average age 26 years ± 6 SD), slept 4h in private sleeping rooms of the DLR-isolation unit in normobaric conditions.SpO2 and heart rate differed significantly between groups (p<0.0001). During sleep period time (SPT) a mean SpO2 level of 96% (± 1 SD) and a mean heart rate of 62 bpm (± 8 SD) were measured in normobaric conditions, whereas mean SpO2 level in the pressure chamber was 88% (± 1 SD) with a mean heart rate of 73 bpm (± 7 SD). In hypobaric conditions for 83% (± 5%) of SPT the average SpO2 dropped below 90% and for 4% of SPT even below 85% SpO2. The mean minimum SpO2-level was 81% (± 3 SD). SPT and sleep efficiency did not differ between groups, but deep sleep (p<0.05) and REM sleep (p<0.01) were significantly reduced in hypobaric conditions in favor of the light sleep phases (N1 p<0.05, N2 p<0.01). Performance was significantly impaired in the experimental group (p