0167 Determinants Of Irregular Sleep On Different Work Schedules Using Mathematical Modeling

Abstract

Even on the same work schedule (regular or rotating), two individuals can differ in the regularity of their sleep patterns. Recent studies have reported a relationship between low day-to-day sleep regularity and a late circadian phase or late chronotype based on two novel metrics: Sleep Regularity Index (SRI) and Composite Phase Deviation (CPD). We aimed to identify possible mechanisms that underlie this relationship using a validated mathematical model of human sleep-wake regulation. Sleep-wake patterns were generated under realistic constraints on sleep timing for a range of circadian periods from short (τ = 23.8 h) to long (τ = 24.4 h). We simulated schedules of weekly daytime work and rotating shift-work by enforcing wakefulness during work times ± commute time. Light exposure was set to 800 lux during the day, 40 lux in the evening, and 0 lux during sleep. Sleep regularity was assessed by calculating two metrics: SRI (similarity of sleep-wake patterns between consecutive 24-h time intervals) and CPD (difference in midsleep timing between consecutive days and relative to chronotype). Work start times and intrinsic circadian period τ were varied to investigate the impact of exogenous vs. endogenous model factors on SRI and CPD. Longer τ-values resulted in later chronotypes independent of work schedule type and start times. Sleep regularity was lower (lower SRI, higher CPD) in most scenarios for longer τ-values and later chronotypes, particularly in the day-work schedule for early start times (before 7:00). It was possible to reverse this relationship (i.e., lower regularity for shorter τ-values and earlier chronotypes) in the rotational shift schedule by advancing shift times; such a schedule forces the earliest chronotypes to be awake at times when the latest chronotypes had to be awake at under standard shift times. Our findings suggest that irregular sleep patterns are the result of the interaction between external, environmental characteristics (i.e., imposed work schedules, self-selected light exposure) and individual, endogenous traits (i.e., circadian period), and are not only a characteristic of late chronotypes. R00HL119618, K24HL105664, R01HL114088, R01GM105018, R01HL128538, P01AG009975.