The Effects of Brief Naps During Night Shift on Fatigue, Sleepiness and Performance on a Simulated Driving Task

Fatigue leads to reduced vigilance and reaction time as well as increased sleepiness. These are major contributory factors in road and work place accidents and are a particular problem for night shift workers. A brief nap has been found to reduce the effects of fatigue in sleep deprived individuals. Naps taken during a night shift or immediately before a night shift may improve vigilance and alleviate sleepiness both at work and on the road after work. A problem associated with naps is sleep inertia, a period of grogginess and confusion after waking. One of the leading causes of death and disability in developed nations is motor vehicle accidents (Connor, Whitlock, Norton & Jackson, 2001; Philip & Mitler, 2000). Fatigue is considered to be the second most frequent cause of motor vehicle accidents, after alcohol (Arnedt, Wilde, Munt & Maclean, 2000; Philip, Taillard, Guilleminault, Quera-Salva, Bioulac & Ohayon, 1999). Fatigue leads to reduced vigilance and reaction time and has also been shown to be a major cause of work place accidents (Dorrian, Lamond & Dawson, 2000). Time of day, hours awake and previous sleep duration are all factors that cause fatigue and sleepiness (Bonnet & Arand, 1999; Feyer, 2001; Johnson, Spinweber, Gomez & Matteson, 1990). Night shift workers often suffer from partial sleep deprivation. In addition to this the bodies circadian rhythm promotes sleepiness during the night when workers are operating (Akerstedt, 1988). Fatigue and sleepiness appear to be major problems associated with night shift work, placing workers at a high risk of accidents in the work place and on the roads. (Akerstedt, 1991; Akerstedt, Torsvall & Gillberg, 1987). A higher than expected proportion of shift workers are involved in fatigue related motor vehicle accidents (Fell & Black, 1997). This makes night shift workers an important target group for interventions to reduce fatigue related accidents. Naps have been promoted as a possible countermeasure to fatigue. Studies (Gillberg, Kecklund, Axelsson & Akerstedt 1996; Lumley, Roehrs, Zorick, Lamphere & Roth, 1986; Reyner & Horne, 1997; Takahashi & Arito, 2000) have shown that brief naps of between 15 and 120 minutes are effective in reducing sleepiness and improving function in sleep deprived individuals. Similarly, naps taken during long periods of continuous work have shown positive effects on fatigue symptoms (Bonnet & Arand, 1995; Haslam, 1985; Naitoh, Kelly & Babkoff, 1992). A number of studies (Gillberg, 1984; Matsumoto & Harada, 1994; Sallinen, Harma, Akerstedt, Rosa & Lillqvist, 1998) have shown that a nap during the night reduces the effects of fatigue. However, conflicting results have been reported in studies assessing the benefits of naps taken prior to a night shift (Bonnet, 1991; Bonnet & Arand, 1995; Harma, Knauth & Ilmarinen, 1989; Naitoh, Englund & Ryman, 1982; Rosa, 1993). Thus, the timing of a nap may be of particular importance. A problem associated with naps is that a period of grogginess, or sleep inertia, may follow (Dinges, Orne & Orne, 1985). The degree of sleep inertia experienced may be related to the sleep stage individuals are awakened from (Bruck & Pisani, 1999). Few studies have examined the effects of napping on driving performance at the end of a night shift. Similarly, there has been little research assessing the positive and negative effects of napping opportunities prior to or during an actual night shift (Rosa, 1993). In this study shift-workers' driving performance was monitored on three separate first night shifts where participants either had no sleep or were given a 30-minute napping opportunity at either 20:15 hours (before the shift) or 04:00 hours (during the shift). Subjective sleepiness, vigilance and sustained attention were measured at the start end and during the night shift, to monitor fatigue and sleep inertia. Driving performance was also measured before and after the shift to monitor the effects of fatigue at the time the worker would be driving home. The results of this study indicated that a nap taken at 04:00 hours had positive effects on fatigue related symptoms. Future research should examine the effects of a nap on the next day’s sleep and during subsequent night shifts