Heart rate patterns in sedentary shift work: influence of circadian rhythm, meals and personality.

Heart rate was recorded at regular intervals during the course of 8-h sessions of simulated sedentary shift work performed for 12 consecutive days. Separate groups of subjects were assigned to one of three shifts, commencing either at 0400 hours ("morning" shift), 0800 hours ("day" shift) or 2200 hours ("night" shift). A major meal was taken during a break in the middle of each shift. In all groups heart rate fell during the pre-break period, but rose after the break in response to the meal. This pattern remained constant over the 12-day period in the morning and day shift groups, but in the night shift group a progressive rise in the general level of the readings, caused mainly by the adjustment of the circadian rhythm to the altered sleep/wake cycle, was accompanied by systematic changes in the extent of both the pre-break fall and the post-meal rise. Comparison with the results of a control study of 24-h variation in base heart rate suggested that differential responses to the meal observed in the three shift groups may have been due, at least in part, to differences in their personality make-up. It is concluded that, although systematic patterns of heart rate can be observed in sedentary shift work, both the timing of the shift and the personality of the subject must be taken into account when assessing the changes in physiological state likely to occur during work sessions that include a major break for refreshment.