Comparison of heart rate variability of the nurses working in intensive care unit during working and nonworking days

Aim There are significant effects of the autonomic nervous system in the regulation of the body's functions. Autonomic nervous system is composed of sympathetic and parasympathetic nervous system that balances each other's work. This autonomy is disturbed by the daytime stress and sleepless at night in the health personnel working with the night shift system. Especially the parasympathetic system, which is supposed to dominate the night, is suppressed, resulting in a stress environment in the body. Heart rate variability is an easy and noninvasive method demonstrating sympathetic and parasympathetic systems function. Heart rate variability measurements come from 24 hour electrocardiography(ECG) holter monitoring. In this study, we planned to measure the difference in heart rate variability between 2 days by wearing ECG Holter in nurses of intensive care unit on 2 different days as working and nonworknig day. Thus, we aimed to show the negative situations and the risks that night shifts create on the body. Methods 51 nurses working in intensive care unit were included into the study. The study was performed when the subjects were on 24-hour weekend shift. Subjects was underwent 24 hours 3 channel ambulatory rhythm Holter from 09.00-09.00 o'clock twice, once during their 24 hours shift and once during normal nonwork day. We chose 24 hours working shift as study group and 24 hours nonworking day as control group. From these holter records, heart rate variability parameters which 5 time domain and 7 frequency domain values were obtained. Findings Mean heart rate and minimum heart rate parameters were statistical significantly higher in working day whereas total mean NN, daytime mean NN and night mean NN were statistical significantly higher in nonworking day. Heart rate parameters including SDNN, SDANN, pNN50, TP, VLF, rMSSD, HF and Hfnu which are indirect indicators of parasympathetic system were statistical significantly higher in nonworking day. On the other hand, LFnu and LF/HF ratio which are indirect indicators of sympatic system were statistical significantly higher in work shift. Compared to daytime and nighttime heart rate variability parameters, sympathetic dominance was observed at working day. In addition, when the heart rate parameters were compared at 24-hour intervals, it was seen that the sympathetic system was higher at the day of the working than the day of nonworking. Both working and nonworking day, the sympahetic dominance is higher at daytime than nighttime. It was also seen that sympathetic dominance at shift nights began earlier than at nonworking nights. Results In conclusion, sympathetic activation is increased during shift days. This effect lasts for 24 hours. Regardless of shift or nonworking day, daytime sympathetic dominance is much more than night. This was interpreted as a sign of the fact that it was a circadian effect. It was also thought that the early onset of sympathetic activity on working days may be related to the earlier onset of cortisol release time compared with nonworking day. One of the important limitations of this study is the small number of participants and there is a need for new studies with large groups of participants for more ideal results. Keywords: Heart rate variability, autonomic nerve system, shift and nonworking day, nurses of the intensive care unit