Effects of napping on fatigue and sleepiness during a 16-hour night shift among hospital nurses.-the influence of the start and length of nap-

This study aimed to identify effective ways of nap among nurses in order to achieve fatigue recovery and reduce sleepiness during 16-hour night shifts (15:15-8:45). Subjects were 12 nurses in their 20s, and their heart rate variability (HRV) was measured during the 16-hour night shift. Questionnaires were also completed at the following 6 time-points to investigate subjective sleepiness and fatigue: at the initiation of the night shift, at 21:00, before and after taking a nap, at 6:00, and at the end of the night shift. As the results, the subjects who took naps during the first half of the night shift (between 22:00 and 2:00) reported significantly increased sleepiness before the napping time until the end of the night shift compared to the initiation of the night shift, regardless of whether the nap time was more or less than 120 minutes. The subjects who took nap more than 120-min between 1:00 and 4:00 reported increased sleepiness before and after the nap, but their sleepiness was reduced after 6:00. They also reported significantly increased sense of fatigue before the nap time until the end of the night shift. Concerning the variation in HRV, the subjects who took nap more than 120-min showed increased high-frequency HRV after the nap compared to those who took nap less than 120-min. These results revealed that taking nap during the 16-hour night shift can reduce the physical burden, and that taking nap during the second half of the night shift can improve sleepiness in the morning.