The Interest of Microsleeps Recording during Real Long Haul Flight: An Index of Hypovigilance

Abstract

Involuntary microsleeps period may occur during long haul flight, that may increase the risk of accidents and decrease pilots' performances. Microsleeps are temporary episode (1 to 30 sec) of sleep, associated with a brief lapse in consciousness, considered as an objective parameter of sleepiness. Miniaturized ambulatory EEG/EOG recorders allow continuous assessment of pilots' microsleeps on-board. The aim of this study was to assess the risk factors of microsleeps for pilots during long haul military flights with a recent tactical airlifter, with strategic capabilities. 11 voluntary pilots were recorded (18 flights, mean duration 6.4 h, ranged 2.5-9.6 h) for a total of 130 hours of flight. Sleep/wake activities were recorded over 8 days before each flight using a wrist actimeter. Subjective Karolinska sleepiness scale (KSS) and sustained attentional performance (Psychomotor vigilance test, PVT) were studied every 2-hours during the flights. Electrical signals from two electro-encephalogram (EEG) and electro-occulogram (EMG) derivations were continuously recorded during the flights using a miniaturized device fixed on the pilots' skull. Microsleep episodes were detected off-line by visual inspection. Microsleeps number and cumulative duration were quantified per hours of flight. At least one microsleep occurred during each flight (mean duration: 6 ± 4 sec, ranged: 4-29 sec). Pilots habitual total sleep time (TST) was 7.0 ± 1.3 h. TST during the night before the flight was 5.8 ± 1.6 h. Multiple regression analysis showed that the increase of microsleeps occurrence and the decrease of attentional performances were associated with the decrease of TST before the flight (p=0.01), cumulative sleep debt during the week (p