Reducing the frequency of short intervals between shifts improved nurses' ability to recover from work, according to a study published online June 2 and in the September issue of Clinical Nursing Studies.

After nurses switched to a more ergonomic schedule, in line with recommendations governing short intervals between shifts, heart rate variability recordings showed "an increase in the parasympathetic with relation to sympathetic activation of the [autonomic nervous system] occurring during the first four hours of sleep," write Susanna Järvelin-Pasanen, PhD, from the Institute of Public Health and Clinical Nutrition, University of Eastern Finland in Kuopio, and colleagues.

"The results of this study indicated that a reduced number of short intervals between work-shifts was associated with beneficial changes in [heart rate variability]," they continue. "In particular, the reduced number of short intervals resulted in increased sleep time [root mean square of the successive differences, high-frequency (HF)] power and HF power in normalized units."

The researchers gathered 24-hour heart rate variability recordings and questionnaires from 39 female nurses, average age 45 years, whose schedules included irregular two-shift or three-shift work. For example, a morning shift, starting at 7 a.m., might frequently follow an evening shift, ending at 9 p.m.

After the collection of baseline data, the nurses' schedules were changed on the basis of recommended guidelines in which the number of quick returns was reduced, thereby reducing the number of intervals shorter than 11 hours between shifts. Starting and ending times for shifts did not change. The average number of these quick-return shifts then dropped 55%, from an average of 28 per year at baseline to an average 15 per year 1 year later. Total working hours, amount of weekend work, and total amount of evening and night work did not change.

One year after adjusting the shifts, the nurses underwent 24-hour heart rate variability recordings and filled out the questionnaires again. At follow-up, the researchers identified a significant increase in six positive attributes of heart rate variability.

The mean difference from baseline to follow-up in the mean of the selected beat-to-beat RR interval series, inversely proportional to mean heart rate, was 1.33 ms (95% confidence interval, 0.81 - 1.85). The mean difference in root mean square of the successive differences was 1.45 ms (95% confidence interval, 1.00 - 1.91).

"The changes in the numbers of short intervals between work-shifts increased the available time for recovery between successive work shifts and this is hypothesized to account for the positive effects on [heart rate variability] at the beginning of the sleep, i.e., a decrease in the sympathovagal balance," Dr Järvelin-Pasanen and colleagues write.

"In addition, our earlier results based on the partially same dataset indicated that the beginning of the work shift was less stressful and the psychophysiological strain of nurses was lower in the more ergonomic shift schedule as compared to the conventional shift schedule."

Established risks of shift work include increased risk for cardiovascular disease, sleep disturbance, impaired alertness, and reduced recovery from work. Past research has revealed improved quality and quantity of sleep and perceived alertness and well-being in home, work, and social spheres, but this study found no correlation between sleep time heart rate variability and sleep quality or duration.

These findings did indicate that recovery of the autonomic nervous system from shift work occurs more efficiently when schedules follow ergonomic recommendations, the authors conclude.

The research was funded by the Finnish Work Environment Fund, the city of Helsinki, and the Finnish Work Environment Fund grants. The authors have disclosed no relevant financial relationships.

Clin Nurs Stud. 2015;3:118-126. Full text