Involuntary sleep during civil air operations: wrist activity and the prevention of sleep.

BACKGROUND

During air operations, aircrew may encounter sleepiness that can arise from the length of duty periods, working during the circadian low of alertness, and circadian dysrhythmia arising from time-zone change. A previous study investigated physiological and physical measures that could be used to identify sleep and provide the basis of an alertness alarm. Eye movements were sensitive indicators of sleepiness and sleep, and wrist inactivity identified sleep episodes lasting longer than 5 min.

HYPOTHESIS

Wrist inactivity can provide the basis of a practical alertness device for use by aircrew.

METHODS

The electrical activity of the brain (electroencephalogram, EEG), eye movements, and wrist activity were recorded continuously from the Captain and First Officer during six return flights between London and Chicago. The route comprised an outward daytime and overnight return flight, each lasting approximately 9 h. The EEG and eye movements were used to identify sleepiness and sleep, and these episodes were correlated with periods of wrist inactivity. A software simulation based on the data collected during the study was conducted in order to determine the number of errors generated by an alertness alarm based on wrist inactivity lasting 3, 4, or 5 min.

RESULTS

Sleepiness or sleep was observed in 8 of the 12 subjects. All periods of sustained sleep in excess of 5 min were associated with at least 5 min of wrist inactivity. The simulated alertness alarm using a wrist inactivity setting of 5 min gave only one false alarm, and in this respect performed better than a device based on a shorter time interval (3 or 4 min).

CONCLUSIONS

An alertness device based on wrist inactivity would prevent sustained periods of sleep lasting longer than 5 min. It would not, however, reliably detect sleepiness and brief episodes of sleep. The anticipated use of the device is in support of the management of alertness in aircrew, where it could be used to ensure that unintended or unauthorized napping does not occur or is detected in a timely manner.