Comprehensive detrimental effects of a simulated frequently shifting schedule on diurnal rhythms and vigilance

Jul 18, 2022Chronobiology international

Widespread negative effects of a frequently changing daily schedule on body rhythms and alertness

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Abstract

Elevated and decreased cortisol levels were observed at different stages during a 30-day shift work schedule.

Shift work is associated with disturbances in circadian rhythms, impacting physiology and performance.
Increased sleepiness and changes in sleepiness patterns were reported during the shift work schedule.
Alertness decreased continuously over the course of the shift, primarily due to slower reaction speeds in cognitive tasks.
Psychomotor Vigilance Task errors were significantly higher in the early period of the shift but decreased in the late period.
Changes in correlations between physiological and cognitive variables were noted, with varying relationships over different periods of the shift.

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Accumulating data have demonstrated that shift work causes a disturbance in circadian rhythms, which is detrimental to physiology and performance. However, the detailed effects of shift work and especially the underlying mechanisms remain to be further investigated. Frequently shifting schedules are widely used in industries, e.g., maritime tasks, oil mining, and aviation. In this work, we investigated the physiological changes and vigilance of 12 subjects who lived on a 30-day frequent shift working schedule in a confined environment, which mimics the common maritime schedules. Elevated and decreased cortisol levels were observed at different stages during the shift, suggesting the occurrence of stress and fatigue. The results of the Karolinska Sleepiness Scale (KSS) indicate increased sleepiness and a changed pattern of the rhythmicity of sleepiness during the shift. The tests of the Psychomotor Vigilance Task (PVT) reveal that the shift led to a continuously decreasing alertness as the shift working schedule progressed, which is prevalently due to the increasingly slower reaction speed. The PVT time-out errors were significantly increased in the early period but decreased in the late period. In addition, we found recoupling of the correlations between multiple physiological and cognitive variables. For instance, heartbeat rate (HR) and breath rate (BR) showed moderate correlations in the control and early periods but little in the late period. Together, these results reveal substantial alterations in diurnal rhythms, affected vigilance and changed coupling of the correlations of diurnal rhythms, physiology and cognition caused by a shift schedule. Our findings may help in the recognition of the detrimental effects of such working schedules and provide clues for the development of potential mitigations.

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Comprehensive detrimental effects of a simulated frequently shifting schedule on diurnal rhythms and vigilance

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