Sleep, fatigue and sleepiness in shift-workers and sleep-disordered individuals

Results. The first investigation demonstrated a significant improvement in subjective and objective measures of sleep and performance on the new 10-hour night-shift schedule. Moreover, there was a remarkable reduction of time lost due to accidental injuries at the workplace after the shift schedule change. The second investigation showed a significantly increased rate of underlying sleep pathology and disrupted sleep architecture in highly fatigued subjects compared with the non-fatigued subjects. The third investigation showed a significantly increased frequency of sleep-disordered patients with pathological-fatigue compared with pathological-sleepiness. All three studies demonstrated a weak correlation between subjective measures of fatigue and sleepiness. Introduction. The three studies comprising this thesis carefully examined sleep from different perspectives. Sleep is one of the basic physiologic need-states and is known to have restorative functions. Extended hours of shift-work and sleep disorders have the potential of causing sleep-wake disruption and non-restorative sleep. This may impact negatively on sleepiness, fatigue and performance in the affected individuals. In this thesis, I have performed three independent but inter-linked research studies to explore the central theme of inter-dependence between sleep, fatigue and sleepiness. Methods. The first study was conducted in two phases. Phase-1 was a prospective evaluation of subjective sleep and performance in a group of shift-workers who underwent a schedule change from an 8-hour backward rotating to a 10-hour forward rotating schedule. Phase-2 was a cross-sectional study of objective evaluation of sleep and performance in a group of randomly selected shift-workers from the first phase. The second study was a cross-sectional study of subjective assessment of fatigue and objective assessment of sleep and underlying sleep pathology in a group of fatigued and non-fatigued shift-workers. The third study was a prospective evaluation of subjective fatigue versus sleepiness as independent manifestations of disordered sleep in a group of sleep-disordered patients. Rationale. The increasing prevalence of shift-work and the complex and inconclusive consequences of shift duration and sleep timing necessitate the examination of the impact of a shift schedule change on worker's sleep and performance. This new knowledge will lead to better working conditions, worker productivity and reduction of shift-work-related health and safety concerns. Excessive fatigue is a very common complaint in shift-workers and sleep-disordered individuals. However, fatigue is often equated with excessive sleepiness and thus rarely studied as an independent symptom of disordered sleep. Distinguishing between fatigue and sleepiness is important because etiology and treatment of these two states may differ. Conclusions. These are some of the first data to show significant benefits associated with longer night shifts. This is probably due to the forward rotating schedule and a new shift timing that does not encompass the entire night period. Subjective rating scales seem to be able to distinguish the apparent incongruence between sleepiness and fatigue. The findings support the notion that subjective fatigue can be an independent and central consequence of disordered-sleep in shift-workers and sleep-disordered patients and likely to require independent assessment.