Sleep and wakefulness in aircrew before and after transoceanic flights.

Aircrew were studied before and after flying one of two routes: San Francisco (SFO) to London (LHR) or SFO to Tokyo (NRT). After an adaptation night, sleep and daytime sleepiness were objectively measured in SFO and during the first layover (L/O) of the target trip. Baseline sleep was slightly shorter than normally reported for similar age subjects and, for several reasons, is not an ideal basis for subsequent comparison. Nevertheless, L/O sleep periods tended to provide either less total sleep or less efficient sleep. Crewmembers' estimates of their sleep duration correlated well with objective measures, but their estimates of daytime sleepiness correlated poorly with objectively measured sleepiness. During baseline there was a significant midday sleep tendency as measured by the Multiple Sleep Latency Test. This tendency occurred at almost the same time (GMT) on the second L/O day in LHR. Since sleepiness has a persistent rhythm which is maximal twice per day, it is suggested that L/O sleep periods be taken at these times of maximal sleepiness and that peak workload should coincide with the subsequent periods of maximal alertness. Although the overall quality of sleep diminished only slightly on this L/O, it is possible that if this relatively small loss accumulated over successive L/Os, the effects on daytime sleepiness could be measurable.