title: The impact of sleep timing and bright light exposure on attentional impairment during night work.
abstract: The prevalence of hazardous incidents induced by attentional impairment during night work and ensuing commute times is attributable to circadian misalignment and increased sleep pressure. In a 10-day shift work simulation protocol (4 day shifts and 3 night shifts), the efficacies of 2 countermeasures against nighttime (2300 to 0700 h) attentional impairment were compared: (1) Morning Sleep (0800 to 1600 h; n = 18) in conjunction with a phase-delaying light exposure (2300 to 0300 h), and (2) Evening Sleep (1400 to 2200 h; n = 17) in conjunction with a phase-advancing light exposure (0300 to 0700 h). Analysis of the dim light salivary melatonin onset indicated a modest but significant circadian realignment in both sleep groups (evening sleep: 2.27 +/- 0.6 h phase advance, p < 0.01; morning sleep: 4.98 +/- 0.43 h phase delay, p < 0.01). Daytime sleep efficiency and total sleep time did not differ between them or from their respective baseline sleep (2200 to 0600 h; p > 0.05). However, on the final night shift, the evening sleep subjects had 37% fewer episodes of attentional impairment (long response times: 22 +/- 4 vs. 35 +/- 4; p = 0.02) and quicker responses (p < 0.01) on the Psychomotor Vigilance Task than their morning sleep counterparts. Their response speed recovered to near daytime levels (p = 0.47), whereas those of the morning sleep subjects continued to be slower than their daytime levels (p = 0.008). It is concluded that partial circadian realignment to night work in combination with reduced homeostatic pressure contributed to the greater efficacy of a schedule of Evening Sleep with a phase-advancing light exposure as a countermeasure against attentional impairment, over a schedule of Morning Sleep with a phase-delaying light exposure. These results have important implications for managing patients with shift work disorder.
authors.affiliation: Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA. nsanthi@rics.bwh.harvard.edu
authors.forename: Nayantara
authors.initials: N
authors.lastname: Santhi
authors.forename: Daniel
authors.initials: D
authors.lastname: Aeschbach
authors.forename: Todd S
authors.initials: TS
authors.lastname: Horowitz
authors.forename: Charles A
authors.initials: CA
authors.lastname: Czeisler
mesh_terms: D000328:Adult; D001683:Biological Clocks; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000032:analysis; D012890:Sleep; D020178:Sleep Disorders, Circadian Rhythm; D013997:Time Factors; D014940:Work Schedule Tolerance
chemical_list: D008550:Melatonin