Sleep, sleepiness, and circadian rhythmicity in aircrews operating on transatlantic routes

This study was performed on B-747 aircrews operating on regular passenger flights between Frankfurt and the U.S. west coast (9 h time difference). In an initial phase, sleep behavior was surveyed by daily logs in 38 crewmembers. The results for the layover period indicate congruent sleep patterns with shifts in sleep onset distinctly less than 9 h. In comparison with preflight control data, sleep duration was significantly prolonged and, on average, no sleep deficits were experienced before commencing the return flight. The main part of the study consisted of polygraphic sleep recordings and multiple sleep latency tests (MSLT) applied to four complete cockpit crews (12 members total) in a baseline period, during layover, and after return to homebase. In addition, body temperature and ECG were continuously recorded. During layover, mean bed times were shifted by 4.5 h at maximum. Sleep was disturbed by early and prolonged awakenings which led to a reduction of sleep efficiency. In contrast, no sleep deficits nor increases in daytime sleepiness occurred. Night duty associated with the return flight caused sleep deprivation which conversely resulted in good sleep during the first night back in Germany. However, during the second night after return, impaired sleep was observed, at least in part caused by the rhythm disturbances. As predicted by our resynchronization model, ECG and rectal temperature recordings gave evidence for a desynchronization of the circadian system and an internal dissociation of different body functions.