The influence of split sleep-wake schedules and daytime sleep strategies on neurobehavioural performance
Creators: name: Kosmadopoulos, Anastasi
Publisher: name: Central Queensland University
Year: 2018
Subjects: Sleep
Circadian rhythms
Alertness
Behaviour
Fatigue
Shift work

description: Demand for 24-h access to services and goods has led to an increase in the number of employees engaged in shiftwork. However, while shiftwork has become necessary to meet community expectations, it has serious consequences for health and safety. The risk of fatigue-related accidents and injuries is a significant problem for the shift working population. This is because shiftwork places restrictions on the opportunities available for workers to obtain sleep. Shiftworkers, especially those who work night shifts, must often stay awake for long hours and sleep at times inconsistent with their body clocks, so sleep loss is common. This dissertation evaluates alternative options for arranging sleep that could potentially optimise neurobehavioural function in circumstances where long nocturnal sleep episodes are not possible. Two main approaches were used to address these aims. The first was to assess the effectiveness of split sleepwake schedules at sustaining neurobehavioural function around the clock – with and without sleep restriction – which could have implications for work rosters in certain safety-critical industries. The second approach was to assess the effectiveness of different arrangements of daytime sleep at ameliorating the decline of night-time performance, which could have implications for the sleep strategies shiftworkers employ before and after night shifts. It is important to ensure participants are well-rested prior to entering the laboratory. This is usually achieved with a combination of sleep diaries and actigraphy with wrist-worn accelerometers. The first two studies reported in this dissertation (Chapter 3 and Chapter 4) were conducted to validate several accelerometers for monitoring sleep/wake patterns and ensuring participant compliance with pre-study instructions. Splitting a shiftwork schedule into multiple short work-rest cycles per day could potentially sustain performance around the clock because it would: (i) reduce the time between rest breaks, and (ii) facilitate more opportunities for nocturnal sleep than would otherwise be available to night workers on a traditional schedule. There is converging evidence that the sleep-wake system is adaptable and splitting sleep into two or more shorter episodes per day is not inherently detrimental to performance. However, a limitation of previous investigations into split sleep-wake schedules is that they usually only assess daytime performance and confound the influence of homeostatic process and circadian processes. As such, this dissertation expanded on previous research by systematically comparing the circadian and homeostatic effects of split and consolidated sleep-wake schedules on neurobehavioural performance by means of forced desynchrony (Chapter 5). This study was then followed by an assessment of how severe sleep restriction affects simulated driving and performance on various different neurobehavioural tasks during another split sleep-wake forced desynchrony schedule (Chapter 6). To understand whether there is an ideal arrangement of daytime sleep for performance on consecutive night shifts, this dissertation compared the effects of three broad strategies for sleep timing between simulated 12-h night shifts in the laboratory (Chapter 7). These included (i) sleeping immediately after the night shift, (ii) delaying sleep for several hours in a manner similar to day workers, and (iii) splitting sleep episodes, obtaining some in the morning and some in the afternoon. Performance during the first night shift in a roster can be impaired by sleep deprivation associated with the transition to a night-time schedule because a long preceding daytime sleep is usually impractical. As such, the final study of this dissertation assessed whether a 1-h nap prior to a simulated first 12-h night shift was sufficient to mitigate significant performance deficits compared to a subsequent shift (Chapter 8). Several conclusions may be drawn from the results of this dissertation. First, the wrist-worn accelerometers used in the studies were suitable for monitoring sleep/wake behaviour (Chapter 3 and 4). Second, split sleep-wake schedules are not detrimental to performance and may even be beneficial for nocturnal performance (Chapter 5). The reduction of wakefulness required between sleep opportunities resulted in better performance at night during the split sleepwake schedule than in the consolidated schedule. Third, during severe sleep restriction, tasks requiring sustained vigilance exhibit the greatest circadian variation and the worst nocturnal deficits (Chapter 6). Fourth, daytime sleep strategies (immediate, delayed, split) have no significant effects during 12-h night shifts, where the “window” in which to differentiate them is limited (Chapter 7). Finally, a prophylactic 1-h nap is likely to be sufficient to ameliorate the effects of sleep deprivation on performance during the first night shift (Chapter 8).