Ocular Measures of Sleepiness Are Increased in Night Shift Workers Undergoing a Simulated Night Shift Near the Peak Time of the 6-Sulfatoxymelatonin Rhythm

Abstract

Study Objectives:The study examined the relationship between the circadian rhythm of 6-sulphatoxymelatonin (aMT6s) and ocular measures of sleepiness and neurobehavioral performance in shift workers undergoing a simulated night shift. Methods: Twenty-two shift workers (mean age 33.4, SD 11.8 years) were tested at approximately the beginning (20:00) and the end (05:55) of a simulated night shift in the laboratory. At the time point corresponding to the end of the simulated shift, 14 participants were classifi ed as being within range of 6-sulphatoxymelatonin (aMT6s) acrophasedefi ned as 3 hours before or after aMT6s peak-and 8 were classifi ed as outside aMT6s acrophase range. Participants completed the Karolinska Sleepiness Scale (KSS) and the auditory psychomotor vigilance task (aPVT). Waking electroencephalography (EEG) was recorded and infrared refl ectance oculography was used to collect ocular measures of sleepiness: positive and negative amplitude/velocity ratio (PosAVR, NegAVR), mean blink total duration (BTD), the percentage of eye closure (%TEC), and a composite score of sleepiness levels (Johns Drowsiness Scale; JDS).Results: Participants who were tested within aMT6s acrophase range displayed higher levels of sleepiness on ocular measures (%TEC, BTD, PosAVR, JDS), objective sleepiness (EEG delta power frequency band), subjective ratings of sleepiness, and neurobehavioral performance, compared to those who were outside aMT6s acrophase range. Conclusions:The study demonstrated that objective ocular measures of sleepiness are sensitive to circadian rhythm misalignment in shift workers. Keywords: oculometrics, circadian misalignment, shift work, performance, sleepiness Citation: Ftouni S, Sletten TL, Nicholas CL, Kennaway DJ, Lockley SW, Rajaratnam SM. Ocular measures of sleepiness are increased in night shift workers undergoing a simulated night shift near the peak time of the 6-sulfatoxymelatonin rhythm. J Clin Sleep Med 2015;11(10):1131 -1141 .pii: jc-00268-14 http://dx.doi.org/10.5664/jcsm.5086 S hift work has become a ubiquitous part of labor practices due to the increasing pressure for 24-hour provision of goods and services. This drive for round-the-clock productivity, however, has resulted in negative consequences to health, safety, and performance.1 Such consequences have been welldocumented in a number of occupational sectors in which peak functioning during the night shift is critical, for example, commercial transport, mining, emergency services, and health care. The impairment to alertness that occurs during night shift work is mainly attributed to misalignment of the imposed sleep-wake cycle from the internally generated circadian (~24-hour) rhythm of sleepiness, 3 often against a background of chronic sleep defi ciency and prolonged periods of wakefulness. Alertness and neurobehavioral performance peak when the circadian pacemaker promotes wakefulness during the daytime, and decline markedly during the night, particularly between 03:00 and 06:00, 4 as the circadian pacemaker strongly promotes...

Jet Lag and Shift Work Disorder

“…In a recent study, the use of ocular measures with a new device was predictive of sleepiness and circadian alignment in simulated shift work. 104 These devices could be another tool to measure the impact of new interventions on waking function.…”

Temporal dynamics of circadian phase shifting response to consecutive night shifts in healthcare workers: role of light–dark exposure

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“…; Ftouni et al . ). As the circadian response to light is phase‐dependent, the substantial inter‐individual variability that exists in circadian phase in night workers means that circadian phase adjustment in response to night shift work is likely to differ between individuals irrespective of exposure to the same light–dark cycle.…”

Randomised controlled trial of the efficacy of a blue-enriched light intervention to improve alertness and performance in night shift workers

“…In the 48 hours prior to the laboratory visit, participants collected urine samples in approximately 4–8 hourly intervals for determination of circadian phase via measurement of the urinary metabolite of melatonin, 6-sulphatoxymelatonin (aMT6s), as described previously 23. Participants recorded the timing and volume of each collection to permit calculation of aMT6s excretion rate.…”

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