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Scheduled napping on the night shift : consequences for the performance and neurophysiological alertness of air traffic controllers : a thesis submitted for the degree of Doctor of Philosophy of the University of Otago, Dunedin New Zealand
Rapid technological change and increasing traffic volumes worldwide are adding to the safety challenges for air traffic control. The night shift has traditionally been a period of low workload and work practices have evolved to reflect this. Thus, despite the exemplary safety record, there is a need to consider further systemic defences for maintaining performance and safety on the night shift. One possible strategy is the provision of a scheduled nap at work. In order to investigate the consequences of a scheduled nap on the night shift, 28 operational air traffic controllers were monitored across four roster cycles. Each roster cycle included one of two night shifts. Air traffic controllers were given a nap opportunity on one night shift of each type, and did not nap on the other. Information on the timing, quantity, and quality of sleep during the work week and days off was collected using actigraphy, and supported with logbook data. Sleep during the nap was measured using polysomnography, and the EEG and EOG were further utilised to determine neurophysiological alertness over the latter part of the night shift. Reaction time performance was measured three times across the night shift (beginning, middle, and end) with the psychomotor vigilance test.Actigraphy data indicated that the backward, rapidly-rotating work schedule of air traffic controllers resulted in a progressive loss of sleep across the work week. The reduction in sleep lead to an increasing cumulative sleep debt that was at a maximum prior to the night shift. This sleep debt was not related to reaction time performance at the end of the night shift, but was found to influence neurophysiological alertness.It was determined that the large majority of air traffic controllers were able to sleep during the scheduled 40 minute nap opportunity. However, the latency to sleep onset was long, the sleep short, and of relatively poor quality. Circadian and homeostatic factors increased the likelihood of entry into, and waking from, slow wave sleep (SWS). They were also found to influence reaction time performance and neurophysiological alertness. More variable performance and lowered alertness were seen at the end of the later starting (and finishing) night shift, possibly due to the combined influence of circadian and time-on-task factors. Homeostatic variables had less influence on performance at the end of the night shift, but greater acute sleep loss and higher cumulative sleep debts were related to increased neurophysiological sleepiness.performance and greater neurophysiological alertness in a dose-dependent manner, with even small amounts of stage 1 sleep effecting a performance improvement. Performance improvement was consistent across a range of reaction time measures and consistent improvements were also evident in the neurophysiological data, with the occurrence of SEMs declining, and lower spectral power evident in all frequency bands and single frequencies.These findings clearly demonstrate that a minimal quantity of sleep benefits the performance and alertness of air traffic controllers despite the "noise" of a field setting, thus providing a link between laboratory studies of napping and the actual work environment. The findings also fully support management endorsing a 40 minute napping opportunity for air traffic controllers working the night shift.The short nap sleep had no measurable effect on sleep subsequent to the night shift. However, the amount of sleep obtained in the nap was related to improved reaction time.