Night shifts in interns: Effects of daytime napping on autonomic activity and cognitive function

Abstract

ObjectiveNight shifts have adverse cognitive outcomes that might be attenuated by daytime napping. The neurovisceral integration model suggests that resting vagally mediated heart rate variability (vmHRV) is linked with cognitive function. This study investigated the relationship between resting vmHRV and cognitive function after different nap durations in interns after shift work.MethodsA total of 105 interns were randomly allocated to one of three groups (non-nap, n = 35; 15-min nap, n = 35; 45-min nap, n = 35) to perform cognitive tests and resting vmHRV at 12:00, 15:00 and 18:00. Information processing (digit symbol substitution test; DSST), motor speed (finger tapping test; FTT), response selection (choice reaction time; CRT), and attention shifts (shifting attention test; SAT) were assessed. Resting vmHRV was assessed at baseline and during each cognitive task across groups.ResultsCompared with the non-nap control, the 15-min and 45-min naps improved all outcome measures (including subjective sleepiness and cognitive performance) at 15:00, with some benefits maintained at 18:00. The 15-min nap produced significantly greater benefits on the FTT at 15:00 after napping than did the 45-min nap. Resting vmHRV was significantly correlated with DSST and SAT performance. In addition, FTT performance was the only significant predictor of DSST performance across different nap durations.ConclusionOur results demonstrate links between daytime napping (in particular, a 15-min nap) and improved cognitive control in relation to autonomic activity after shift work in interns. These results indicated that autonomic activity when awake plays a crucial role in DSST and SAT performance and facilitated the understanding of differences in neurocognitive mechanisms underlying information processing after different nap durations.

Causal relationship between sleep traits and cognitive impairment: A Mendelian randomization study

“…First, the duration of the benefits of daytime napping should be further studied, and we could not ignore the existence of sleep laziness 67 . Second, for shift workers, there was a link between daytime napping after work and improvements in cognitive control, 68 but this relationship might not necessarily hold for elderly people with low activity and work intensity 66,69 . Third, observation research introduced bias and confounding variables.…”

“…First, the duration of the benefits of daytime napping should be further studied, and we could not ignore the existence of sleep laziness. 67 Second, for shift workers, there was a link between daytime napping after work and improvements in cognitive control, 68 and daytime sleepiness) on AD risk and found that evidence for a link between sleep interruption and Alzheimer's risk was limited. 18 Similar to another previous MR study, 19 no causal effect of sleep pattern disorders on AD was found.…”