Do night naps impact driving performance and daytime recovery sleep?

Short, nighttime naps are used as a fatigue countermeasure in night shift work, and may offer protective benefits on the morning commute. However, there is a concern that nighttime napping may impact upon the quality of daytime sleep. The aim of the current project was to investigate the influence of short nighttime naps (<30 min) on simulated driving performance and subsequent daytime recovery sleep. Thirty-one healthy subjects (aged 21-35 y; 18 females) participated in a 3-day laboratory study. After a 9-h baseline sleep opportunity (22:00 h-07:00 h), subjects were kept awake the following night with random assignment to: a 10-min nap ending at 04:00 h plus a 10-min nap at 07:00 h; a 30-min nap ending at 04:00 h; or a no-nap control. A 40-min driving simulator task was administered at 07:00 h and 18:30 h post-recovery sleep. All conditions had a 6-h daytime recovery sleep opportunity (10:00 h-16:00 h) the next day. All sleep periods were recorded polysomnographically. Compared to control, the napping conditions did not significantly impact upon simulated driving lane variability, percentage of time in a safe zone, or time to first crash on morning or evening drives (p > 0.05). Short nighttime naps did not significantly affect daytime recovery total sleep time (p > 0.05). Slow wave sleep (SWS) obtained during the 30-min nighttime nap resulted in a significant reduction in SWS during subsequent daytime recovery sleep (p < 0.05), such that the total amount of SWS in 24-h was preserved. Therefore, short naps did not protect against performance decrements during a simulated morning commute, but they also did not adversely affect daytime recovery sleep following a night shift. Further investigation is needed to examine the optimal timing, length or combination of naps for reducing performance decrements on the morning commute, whilst still preserving daytime sleep quality.