The acute effects of experimental short-term evening and night shifts on human circadian rhythm: the oral temperature, heart rate, serum cortisol and urinary catecholamines levels

Abstract

This study was designed to examine the temporal changes in circadian rhythm of oral temperature, heart rate, serum cortisol and urinary catecholamines levels due to experimental short-term shifts. The six subjects were assigned to consecutive day (work 0800-1600 hours; sleep 0000-0800 hours), evening (1600-2400 hours; 0400-1200 hours), and night (0000-0800 hours; 1200-2000 hours) shifts of 2 days each scheduled as hospital shiftwork by nurses, in random order, during which data were collected every 4 h throughout the experimental periods. According to acrophases of a fitted cosine curve and visual inspection on chronograms, the phases of circadian rhythms were delayed to different degrees in the evening shifts with a minimum of about 1 h for oral temperature and a maximum of about 4 h for urinary free noradrenaline. The corresponding phase delays were larger in the night shift for oral temperature (about 3 h), resting heart rate (about 5 h) and urinary free noradrenaline (about 13 h); the diurnal variations of serum cortisol and urinary free adrenaline were greatly modified, and their circadian rhythmicities disappeared, indicating that the normal circadian phase relations of these variables were disrupted more by the night shift. The comparison of chronograms and correlation analyses revealed that the 4-h mean heart rate and urinary free noradrenaline were largely affected by rest-activity level in connection with shifts, while the resting heart rate and urinary free adrenaline were less affected. On the other hand, the sleep factor (time of onset and/or period) seemed to be more potent in modifying the circadian rhythm of serum cortisol, especially with the night shifts.