Identical blood pressure levels and slower heart rates among nurses during night work and day work

To investigate the effects of shift work on circadian BP variation, ambulatory 24h BP monitoring was performed during the day shift and night shift on 17 normotensive nurses. On both shifts, BP and heart rate increased in the working phase and decreased during sleep. The mean 24h BP and heart rate were identical in the two shifts. During sleep, BP was lower and the heart rate was slower in the day shift (night sleep) perhaps because of deeper sleep than during daytime sleep associated with the night shift. During work, BP was identical but the heart rate was significantly slower during the night shift. These data suggest that the circadian BP variation is determined largely by the sleep-wakefulness cycle and that the heart rate is also influenced by the internal body clock.