Sleep in Airplanes: a potential risk factor?

Kurzfassung

The baromedical laboratory at the DLR-Institute of Aerospace Medicine offers sophisticated facilities for experiments with humans in low pressure environment. It hosts a pressure chamber where subjects can be exposed for a long term to a prescribed set of atmospheric conditions (pressure, gas composition, temperature, humidity). Environmental conditions aboard airplanes are challenging for the human body. At cruising altitude the cabin pressure is equivalent to an altitude of 8000 ft. Consequently the oxygen partial-pressure (pO2) of cabin air is diminished by one-quarter as compared to ground level. The pO2 is the driving force of gas exchange in lungs since gas is transported across the alveolar membrane by passive diffusion. Although sleep is a common event on aircrafts, little is known of its physiological effects under hypobaric conditions. On long distance flights cabin- and flight deck crew work in shift rotations and off-duty crew members are expected to recreate in crew-rest-compartments which provide multiple bunk beds. As part of the Fitness for Duty study (FIT), which aims to detect fatigue symptoms amongst aircrew, 16 healthy subjects (8 female, 8 male), average age 28 years (± 4 SD), slept in the pressure chamber furnished as crew-rest-compartment. The time in bed was limited to 4h, simulating the resting period of off-duty crew. During this flight simulation with realistic atmospheric conditions and aircraft noise blood oxygen saturation (SpO2), heart rate, and Sleep-EEG were recorded. The next 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 for 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 time in bed an average SpO2 level of 96% (± 1 SD) and a mean heart rate of 62 bpm (± 8 SD) were measured under normobaric conditions, whereas mean SpO2 level in the pressure chamber was 88% (± 1 SD) with a mean heart rate of 74 bpm (± 6 SD). Under hypobaric conditions the average SpO2 dropped below 90% for 135 min (± 69 SD) and the mean minimum SpO2-level was 81% (± 3 SD). Performance was significantly more impaired in the experimental group (p<0.05). The recuperative function for crew members sleeping in a crew-rest-compartment during flight seems limited since performance is impaired and SpO2 drops considerably. Sleep aboard an airplane induced hypobaric hypoxia in young, healthy subjects. To date the degree of arterial hypoxemia which should be considered as being harmful remains unclear. However, passengers with a SpO2 below 85% in the hypoxic challenge test are recommended to receive supplemental oxygen during flight. Consequently, for risk groups sleep during flight should be regarded with care.