Sleep inertia during a simulated 6-h on/6-h off fixed split duty schedule

ABSTRACT

Sleep inertia is a safety concern for shift workers returning to work soon after waking up. Split duty schedules offer an alternative to longer shift periods, but introduce additional wake-ups and may therefore increase risk of sleep inertia. This study investigated sleep inertia across a split duty schedule. Sixteen participants (age range 21–36 years; 10 females) participated in a 9-day laboratory study with two baseline nights (10 h time in bed, [TIB]), four 24-h periods of a 6-h on/6-h off split duty schedule (5-h TIB in off period; 10-h TIB per 24 h) and two recovery nights. Two complementary rosters were evaluated, with the timing of sleep and wake alternating between the two rosters (2 am/2 pm wake-up roster versus 8 am/8 pm wake-up roster). At 2, 17, 32 and 47 min after scheduled awakening, participants completed an 8-min inertia test bout, which included a 3-min psychomotor vigilance test (PVT-B), a 3-min Digit-Symbol Substitution Task (DSST), the Karolinska Sleepiness Scale (KSS), and the Samn–Perelli Fatigue Scale (SP-Fatigue). Further testing occurred every 2 h during scheduled wakefulness. Performance was consistently degraded and subjective sleepiness/fatigue was consistently increased during the inertia testing period as compared to other testing times. Morning wake-ups (2 am and 8 am) were associated with higher levels of sleep inertia than later wake-ups (2 pm and 8 pm). These results suggest that split duty workers should recognise the potential for sleep inertia after waking, especially during the morning hours.

KEYWORDS:

• Psychomotor vigilance test (PVT)
• subjective fatigue
• shift work roster
• split shifts
• split sleep
• subjective sleepiness

Acknowledgements

The authors would like to thank Alexandra Agostini, Bartholomew Pawlik, Rachel Hadcroft, Amanda Santamaria, Jasper Wolfe, Mia Louca, Daniel Feuerriegel, Pam Singh, Professor Gary Wittert and all our volunteers for their assistance with implementing this study.

Declaration of interest

The authors have no conflicts of interest to declare. This work was supported by the Bushfire Cooperative Research Council. This research was financially supported by the Bushfire Cooperative Research Council. Hans Van Dongen was supported by ONR [grant no. N00014-13-1-0302].

Supplemental Material

Supplemental data for this article can be accessed at www.tandfonline.com/icbi.