title: 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: 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.
authors.affiliation: School of Psychological Sciences, Monash University, Clayton, Victoria, Australia.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Ftouni
authors.affiliation: School of Psychological Sciences, Monash University, Clayton, Victoria, Australia.
authors.forename: Tracey L
authors.initials: TL
authors.lastname: Sletten
authors.affiliation: Sleep Research Laboratory, Melbourne School of Psychological Sciences, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Christian L
authors.initials: CL
authors.lastname: Nicholas
authors.affiliation: Robinson Research Institute, School of Paediatrics and Reproductive Health, University of Adelaide, Adelaide, South Australia, Australia.
authors.forename: David J
authors.initials: DJ
authors.lastname: Kennaway
authors.affiliation: School of Psychological Sciences, Monash University, Clayton, Victoria, Australia.|Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, Massachusetts.|Division of Sleep Medicine, Department of Medicine, Harvard Medical School, Boston, Massachusetts.
authors.forename: Steven W
authors.initials: SW
authors.lastname: Lockley
authors.affiliation: School of Psychological Sciences, Monash University, Clayton, Victoria, Australia.|Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, Massachusetts.|Division of Sleep Medicine, Department of Medicine, Harvard Medical School, Boston, Massachusetts.
authors.forename: Shantha M W
authors.initials: SM
authors.lastname: Rajaratnam
mesh_terms: D000293:Adolescent; D000328:Adult; D001767:Blinking / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D008875:Middle Aged; D011597:Psychomotor Performance / Q000502:physiology*; D020178:Sleep Disorders, Circadian Rhythm / Q000503:physiopathology* / Q000652:urine; D012894:Sleep Stages / Q000502:physiology*; D014940:Work Schedule Tolerance / Q000502:physiology; D055815:Young Adult
chemical_list: C054513:6-sulfatoxymelatonin; D008550:Melatonin
keywords: circadian misalignment; oculometrics; performance; shift work; sleepiness