Consecutive nights of moderate sleep restriction exacerbate sleep inertia

Sleep inertia is a temporary period after awakening that impairs functional abilities and alertness, thought to be exacerbated by sleep restriction. Many Australians perform safety critical tasks such as operating a vehicle in the first two hours after awakening and many do no obtain sufficient sleep on a regular basis. The aim of this study was to assess the impact of consecutive nights of sleep restriction on the severity of sleep inertia—particularly in terms of the safety implications of impaired performance and alertness.

Male participants (n=33) were randomly allocated to a sleep restriction (5-hour time in bed) or control (8-hour time in bed) condition for seven consecutive nights. Assessment of attentiveness (90-second Psychomotor Vigilance Task-192) and subjective alertness (Visual Analogue Scale-alertness) were administered at eight intervals during the first 4 hours after awakening at baseline and following five nights of sleep manipulation.

Mixed-linear effects models revealed a significant effect of time in bed on reaction time (F1,31=7.65, p=.01) and number of lapses (F1,31=5.04, p=.03). After five nights of sleep restriction, response time was slower (d=0.61), and the number of lapses was greater (d=0.53), than after five nights of 8 hours time in bed. There was no effect of time in bed on VAS-alertness (F1,31=0.16, p=.69, d=0.11).

Consecutive nights of sleep restriction increases the impact of sleep inertia on attentiveness, but does not affect subjective alertness. Slower response times and lapses of attention while performing safety critical tasks shortly after awakening could result in increased errors, incidents and accidents.