Industrial healthDec 3, 2013

Two 15-Minute Naps and Their Effects on Sleepiness, Fatigue, and Heart Rate Variability in Night Shift Nurses

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Updated Apr 6, 2026

Abstract

Taking two 15-minute naps may significantly lower the low- to high-frequency heart rate variability ratio compared to no naps.

Both sleepiness and fatigue levels increased between 4:00 and 5:00 in all participants.
No significant differences in subjective sleepiness and fatigue were observed between the nap and no-nap groups.
The Nap condition group showed a significantly lower low- to high-frequency heart rate variability ratio than the No-nap condition group.
A sudden increase in high-frequency heart rate values was recorded in the No-nap condition group in the morning.
Two short naps may help reduce tension and prevent a spike in high-frequency heart rate values.

Simplified

The purpose of this study was to examine the effects of two 15-min naps on nurses who work at night in a three-shift system. Of the 15 nurses who were included as study subjects on a night shift, eight took two short naps (the Nap condition), and seven worked without taking a nap (the No-nap condition) during the night shift. We measured sublingual temperature and the bispectral index (BIS), obtained heart rate and heart rate variability measures from an electrocardiogram (ECG), and evaluated sleepiness and fatigue levels every hour using the Visual Analog Scale (VAS). Both subjective sleepiness and fatigue increased between 4:00 and 5:00, with no significant differences observed between the two groups. However, the low- to high-frequency ratio (LF/HF) in the Nap condition group was found to be significantly lower than in the No-nap condition group. Furthermore, a sudden, brief increase in HF values was observed in the No-nap condition group in the morning. The results of this study suggest that taking two short naps may effectively reduce tension and prevent a brief increase in HF values by suppressing sympathetic nervous activity in the morning.

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Two 15-Minute Naps and Their Effects on Sleepiness, Fatigue, and Heart Rate Variability in Night Shift Nurses

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