Vigilance on the civil flight deck: incidence of sleepiness and sleep during long-haul flights and associated changes in physiological parameters

The study investigated sleepiness and sleep in aircrew during long-haul fli ghts. The objectives were to identify loss of alertness and to recommend a practical approach to the design of an alerting system to be used by aircre w to prevent involuntary sleep. The flights were between London and Miami, covering both day- and nighttime sectors, each with a duration of similar t o9 h. The subjects were 12 British Airways pilots. Various physiological va riables were measured that could potentially be used to indicate the presen ce of drowsiness and involuntary sleep: brain electrical activity (electroe ncephalogram, EEG), eye movements via the electro-oculogram (EOG), wrist ac tivity, head movements and galvanic skin resistance. The EEG and EOG identi fied sleepiness and sleep, as well as being potential measures on which to base an alarm system. Ten pilots either slept or showed evidence of sleepin ess as assessed by the EEG and EOG. Many of the episodes of sleepiness last ed <20 s, which could mean that the subjects were unaware of their occurren ce and of the potential consequences on performance and vigilance. All phys iological parameters showed changes during sleep, although only the EEG and EOG were modified by sleepiness. During sleep, skin resistance was increas ed, and wrist activity and head movements were absent for long periods. The study indicated that the measurement of eye movements (either alone or in combination with the EEG), wrist activity or head movement may be used as t he basis of an alarm system to prevent involuntary sleep. Skin resistance i s considered to be unsuitable, however, being related in a more general way to fatigue rather than to sleep episodes. The optimal way to monitor the o nset of sleep would be to measure eye movements; however, this is not feasi ble in the flight deck environment at the present time due to the intrusive nature of the recording methodology. Wrist activity is therefore recommend ed as the basis of an alertness alarm. Such a device would alert the pilot after <similar to>4-5 min of wrist inactivity, since this duration has been shown by the present study to be associated with sleep. The possibility th at sleep inertia (reduced alertness immediately after awakening from sleep) could follow periods of sleep lasting 5 min needs to be considered. The fi ndings reported here might be applicable to other occupational environments where fatigue and sleepiness are known to occur.