ABSTRACT
OBJECTIVES: To investigate sleep-wake patterns and chronotype in rapidly rotating shift nurses (SRN). METHODS: We translated and back-translated the Korean Munich ChronoType for Shift-Workers (K-MCTQ(shift)) with original authors' permission. In this study, 353 full-time, SRN (age 28.7±3.95 years 341 females, mean shift–working duration=5 years 9 months) at one university hospital completed the K-MCTQ(shift) and the Morningness-Eveningness Questionnaire (MEQ). Time in bed, sleep duration, and mid-sleep time (sleep onset time+1/2 sleep duration) were evaluated on work days and free days. Social jet lag was computed for each shift. Chronotype was assessed based on the mid-sleep time on free days corrected for sleep debt accumulated over the workweek (MSF(SC)). RESULTS: Sleep duration on workdays were 5.2 hours (day shift, D), 7.7 hours (evening shift, E), and 5.7 hours (night shift, N), respectively. Alarm clock usage on workdays was the highest in day-shifts (92.4%). The chronotype of 166 SRN who did not use alarm on free days was 6:09 h. Social jet lag was the longest in day-shifts (3.3 hours), and the shortest in evening-shifts (0.3 hour). Mid-sleep after the evening-shift (MSW(E), MSF(E), MSF(E)(SC)) showed significant correlations with MEQ scores. CONCLUSIONS: The Korean MCTQ(shift) provides actual sleep-wake patterns per shift schedule and chronotype in shift workers. We suggest that the sleep-corrected version of mid-sleep on free days after evening shifts (MSF(E)(SC)) is suitable for assessing chronotype in shift workers.