The influence of day and night work on the circadian variations of cardiovascular performance.

Circadian variations of the pre-ejection period, Q-T interval, heart rate and oral temperature at rest and in day and night shift work were investigated. At rest, pronounced circadian variation was found in heart rate, pre-ejection period and Q-T interval. The ratio between Q-T interval and heart rate also shows a distinct circadian variation. When working, the rest rhythms of the variables were obscured. The physiological implications for shift work are discussed.