Effects of the length and timing of nighttime naps on task performance and physiological function

Abstract

ObjectiveTo examine the effects of the length and timing of nighttime naps on performance and physiological functions, an experimental study was carried out under simulated night shift schedules. Methods Six students were recruited for this study that was composed of 5 experiments. Each experiment involved 3 consecutive days with one night shift (22:00-8:00) followed by daytime sleep and night sleep. The experiments had 5 conditions in which the length and timing of naps were manipulated: 0:00-1:00 (E60), 0:00-2:00 (E120), 4:00-5:00 (L60), 4:00-6:00 (L120), and no nap (No-nap). During the night shifts, participants underwent performance tests. A questionnaire on subjective fatigue and a critical flicker fusion frequency test were administered after the performance tests. Heart rate variability and rectal temperature were recorded continuously during the experiments. Polysomnography was also recorded during the nap. Results Sleep latency was shorter and sleep efficiency was higher in the nap in L60 and L120 than that in E60 and E120. Slow wave sleep in the naps in E120 and L120 was longer than that in E60 and L60. The mean reaction time in L60 became longer after the nap, and faster in E60 and E120. Earlier naps serve to counteract the decrement in performance and physiological functions during night shifts. Performance was somewhat improved by taking a 2-hour nap later in the shift, but deteriorated after a one-hour nap. Conclusions Naps in the latter half of the night shift were superior to earlier naps in terms of sleep quality. However performance declined after a 1-hour nap taken later in the night shift due to sleep inertia. This study suggests that appropriate timing of a short nap must be carefully considered, such as a 60-min nap during the night shift. Resumo ObjetivoPara investigar os efeitos da duração e horário de cochilos noturnos sobre o desempenho e as funções fisiológicas foi realizado um estudo experimental por meio do trabalho noturno simulado.

Napping During Night Shift: Practices, Preferences, and Perceptions of Critical Care and Emergency Department Nurses

“…However, findings related to the duration and severity of sleep inertia and the relationship of sleep inertia to both nap length and timing remain controversial and are based on modest sample sizes. [59][60][61] Symptoms of sleep inertia measured as sleepiness, fatigue, and dullness have been reported to increase in the first hour immediately after a night-shift nap with subsequent decreases in reported symptoms over time to prenap levels. 59 Impairments in cognitive performance upon awakening even after a full night's sleep are not consistent, with severe impairment ranging from the first 3 minutes of awakening 61 to up to 10 minutes.…”

“…In terms of timing, naps taken earlier in the night shift (between midnight and 2 AM) have greater performance and physiological benefit than do naps taken later in the night (4 AM-6 AM). 60 Lewis reviewed the literature in this area (16 studies with a high level of evidence) and found that the evidence suggests that a 40-to 60-minute nap between 2 AM and 4 AM was superior to a longer nap (>60 minutes) earlier in the shift. 63 This evidence poses an organizational challenge for health care, where coverage is required throughout the shift period.…”

Aspectos cronobiológicos do sono de enfermeiras de um hospital universitário

“…Porém, o cochilo noturno pode ter um efeito negativo sobre a atuação dos trabalhadores, uma vez que, ao acordar, a pessoa pode ser afetada pela "inércia do sono", caracterizada pela falta de disposição ao despertar, que pode durar de três minutos até duas horas, que causaria mais danos do que benefícios ao desempenho (15) . Canopus faz uso do artifício do cochilo e refere que "o meu horário de sono, que é sagrado, é das 4:00 as 6:00".…”

The Nighttime Nap Strategies for Improving Night Shift Work in Workplace

“…Recently, we also examined the effects of 5 different nap conditions during night duty regarding nap length and timing under laboratory conditions 32) . In short, the effects of naps taken at 0:00 for 60 and 120 min, naps taken at 4:00 for 60 and 120 min, and no-nap conditions on alertness and performances were investigated.…”