Sleep and recovery in airplanes

Abstract

Introduction: With the steadily increase in number and duration of long-haul flights crews’ on-board sleep, recovery, and performance is an important matter of safety. At cruising altitude passengers and crew sleep under hypobaric conditions in a cabin that is pressurized equivalent to an altitude of 8000 ft. Methods: In the DLR-pressure chamber, 24 healthy subjects (12 female, average age 27 years ± 4 SD) were investigated sleeping in a mock-up of a crew-rest-compartment. We simulated the ambient conditions of an airplane cabin at cruising altitude regarding the barometric pressure (75.3 kPa ~ 8000 ft), and the in-flight noise (70 dBA). Subjects spent 4h time in bed from midnight to 4am. Polysomnography, subjective sleep quality, and blood oxygen saturation (SpO2) were measured. A control group of 23 healthy subjects (9 female, average age 26 years ± 6 SD) had a sleep opportunity of 4h time in bed in private rooms of the DLR-sleep laboratory from midnight to 4am under normobaric environmental conditions without noise. Results: Under hypobaric conditions sleep efficiency (p<0.05) was decreased while wake after sleep onset (p<0.01) was increased. Deep sleep (p<0.05) and REM sleep (p<0.001) were reduced in favor of the light sleep phases (N1 and N2 p<0.05). Sleep period time (SPT) did not differ between groups. The subjective ratings (calmness of sleep: p<0.001; sleep depth: p<0.05) reflected the objective results. During sleep in the flight simulation, subjects spent 73% (± 29%) of SPT in a state of hypobaric hypoxia (<90% SpO2), 5% of SPT even below 85% SpO2. The mean SpO2 level in-flight was 88% (± 2 SD) with a mean minimum of 81% (± 3 SD). In contrast, the control group had a mean SpO2 level of 96% (± 1 SD) (p<0.0001) with a mean minimum of 91% (± 4%). Conclusion: Sleeping at cruising altitude caused hypobaric hypoxia. The recuperative value of sleep was reduced due to a decrease in sleep quality. Young and healthy subjects were clearly affected. Sleeping on board might present a risk factor for older flight crews or diseased passengers who might experience stronger effects.