Prediction of shiftworker alertness, sleep, and circadian phase using a model of arousal dynamics constrained by shift schedules and light exposure

Study Objectives: The study aimed to, for the first time, (1) compare sleep, circadian phase, and alertness of intensive care unit (ICU) nurses working rotating shifts with those predicted by a model of arousal dynamics; and (2) investigate how different environmental constraints affect predictions and agreement with data. Methods: The model was used to simulate individual sleep-wake cycles, urinary 6-sulphatoxymelatonin (aMT6s) profiles, subjective sleepiness on the Karolinska Sleepiness Scale (KSS), and performance on a Psychomotor Vigilance Task (PVT) of 21 ICU nurses working day, evening, and night shifts. Combinations of individual shift schedules, forced wake time before/after work and lighting, were used as inputs to the model. Predictions were compared to empirical data. Simulations with self-reported sleep as an input were performed for comparison. Results: All input constraints produced similar prediction for KSS, with 56%-60% of KSS scores predicted within +/- 1 on a day and 48%-52% on a night shift. Accurate prediction of an individual's circadian phase required individualized light input. Combinations including light information predicted aMT6s acrophase within +/- 1 h of the study data for 65% and 35%-47% of nurses on diurnal and nocturnal schedules. Minute-by-minute sleep-wake state overlap between the model and the data was between 81 +/- 6% and 87 +/- 5% depending on choice of input constraint. Conclusions: The use of individualized environmental constraints in the model of arousal dynamics allowed for accurate prediction of alertness, circadian phase, and sleep for more than half of the nurses. Individual differences in physiological parameters will need to be accounted for in the future to further improve predictions. Statement of Significance The current work examines how well a physiologically based model of arousal dynamics can predict sleep, circadian phase, and alertness of nurses working rotating shifts in intensive care unit (ICU). We show that the mean error in prediction of alertness during shifts is similar in the model using individual shift schedules to constrain sleep dynamics and that using self-reported sleep as an input. This is an important finding for making prospective predictions of alertness during shiftwork and optimization of shift schedules. Further work is needed to test the model against larger datasets and to incorporate inter-individual variability in physiological parameters to make more accurate individual predictions.