Sleep duration and efficiency predict heart rate variability during work hours in intensive care unit nurses

The aim of this study was to examine the associations between components of subjective sleep quality and parasympathetic nervous activity, as assessed by heart rate variability, in intensive care unit nurses during work hours. Sleep quality was assessed using the Pittsburgh Sleep Quality Index, which comprises seven components: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medications, and daytime dysfunction. Heart rate variability was measured using a Holter monitor, with high-frequency power used as an index of parasympathetic activity. Age, energy expenditure, and step count were included as covariates. Associations between each Pittsburgh Sleep Quality Index component and both raw and adjusted high-frequency power data were analyzed using Kruskal-Wallis tests followed by Bonferroni-adjusted post hoc comparisons. Twenty-four full-time intensive care unit nurses participated. Significant differences in high-frequency adjusted for age and step count were found for sleep duration, with post hoc comparisons revealing significantly lower high-frequency in those with short sleep durations than in those with moderate sleep durations. Significant differences in both raw and all high-frequency residuals were observed for habitual sleep efficiency, with lower high-frequency power in participants with moderate sleep efficiency than in those with optimal efficiency. Poor sleep efficiency and short sleep duration were associated with reduced parasympathetic nervous activity during work hours among intensive care unit nurses.