Time-related Changes in Sleep-Wake Pattern as Correlates of Controlled Shift Work Rotating Directions

Abstract

In order to elaborate the sleep-wake pattern changes manifested during controlled shift working of counterclockwise and clockwise rotations, eleven subjects were studied. A baseline sleep survey during uncontrolled shift working using a sleep questionnaire revealed that day and night shifts were found to have less total sleep time compared with evening and off duties, with delayed retire time in the evening shifts and advanced rise time in the day shifts. In analyses of data from controlled shift work schedules of opposite directions, difference in rise time appeared to be a crucial factor determining the total sleep time. This finding is compatible with the theory that rise time is one of the most powerful factors in resetting the biological clock. Retire time seemed to be determined more by the subjects' sleep habits and/or the socioenvironmental stimuli. Off-duty allocation was found to be an important variable in sleep-wake pattern modulation in shift working.