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

Jun 23, 2015Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine

Eye Signs of Sleepiness Increase in Night Shift Workers During Simulated Night Work Near Melatonin Peak

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Abstract

Participants tested within the 6-sulphatoxymelatonin (aMT6s) acrophase range showed higher levels of sleepiness.

Higher sleepiness levels were observed in ocular measures, including the percentage of eye closure and blink duration, for those within the aMT6s acrophase range.
Objective sleepiness, as measured by EEG delta power, was greater in participants within the aMT6s acrophase range.
Subjective sleepiness ratings were elevated in those tested during the aMT6s acrophase compared to those outside this range.
Neurobehavioral performance was negatively impacted in participants within the aMT6s acrophase range.

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STUDY OBJECTIVE: 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 classified as being within range of 6-sulphatoxymelatonin (aMT6s) acrophase--defined as 3 hours before or after aMT6s peak--and 8 were classified 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 reflectance 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.

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

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