Circadian rhythm of heart rate and physical activity in nurses during day and night shifts

The study investigates if the circadian rhythm of heart rate is apparent during the working periods of day and night shifts in Swiss and Japanese nurses and if it is influenced by work organization. For a better interpretation of the heart rate, the activity profile over these working periods was monitored. Heart rate and activity profile of 18 Swiss and 24 Japanese nurses were measured during one day and one night shift. The day and the night shift data of each subject were combined, resulting in an approximately 18-h working period. A significant time effect of the mean hourly value of the heart rate was found in Swiss nurses (change in amplitude 7.1 bpm) as well as in Japanese nurses (11.8 bpm). These effects could be modeled with cosine curves for the Swiss and Japanese subjects. For the activity level significant time effects, similar to the ones in heart rate, were found in Swiss nurses (87 % of SD) but not in Japanese nurses (26 % of SD). We found a significant time effect in heart rate similar to the known circadian rhythm under normal sleep-wake conditions while working in the studied shift work schedules. In the Japanese nurses, studied heart rate followed a circadian rhythm independently of the level of physical activity. Therefore, an activity profile following the circadian rhythm, especially a reduced workload from 2 to 4 a.m., is proposed. The proposed activity profile could be reached with an adapted work organization.