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Occupational and neurophysiological deficits in shift work disorder relate to insomnia, not sleepiness.

Belcher-R; Roth-T; Gumenyuk-V; Mengel-HJ; Philport-J; Drake-CL
Sleep 2014 Mar; 37(Abstract Suppl):A169-A170
Introduction: We examine whether insomnia and excessive sleepiness, the two diagnostic symptoms of Shift Work Disorder (SWD), are differently related to evoked responses and work impairment. Methods: 34 night workers participated in an overnight MSLT and evoked potential assessment. Subjects had no sleep disorders prior to starting night work. At 17:00, each subject completed an Endicott Work Productivity Scale (EWPS), two Insomnia Severity Indices (ISI-Day, ISI-Night), and an Epworth Sleepiness Scale (ESS). Subjects with ISI-Day >/= 10 and ESS < 10 were classified "alert insomniacs" (AI, n = 12). Subjects with ISI-Day >/= 10 and ESS >/= 10 were classified "sleepy insomniacs" (SI, n = 11). Subjects reporting < 10 on both scales were classified controls (n = 11). At 18:00, subjects completed a test of attention to novelty and associated ERPs. Results: Neither the MSLT nor the ESS correlated with EWPS scores or ERP amplitudes (p > .10). However, the mean of the ISI measures correlated with the EWPS (r = .409, p < .01) and the attention-to-novelty P3a (r = -.410, p < .01). The AI group was most impaired on the EWPS, significantly more impaired than controls (25.8 +/- 14.8 vs. 12.3 +/- 9.4, p < .05). SI were not statistically different from controls (19.5 +/- 8.7 vs. 12.3+/- 9.4, p > .05). Interestingly, the fatigue subscale of the EWPS was significantly higher in AI than in controls (6.3 +/- 3.1 vs. 3.4 +/- 2.5, p < .05), while there was no significant difference between SI and controls (4.8 +/- 1.7 vs. 3.4 +/- 3.1, p > .10). Compared to controls, AI showed significantly attenuated P3a responses (Fcz, Czp, Cpz, MD 1.62-1.77, p < .05) and target-detection P3b responses (Fcz, Czp, Cpz, MD 1.28-1.64, p < .05). P3b in SI was not different from controls (p > .10) and P3a was only different at one electrode (Cpz, MD 1.43, p < .01). Conclusion: Insomnia is linked to functional and cognitive impairments in shift workers. Insomniacs with normal sleepiness showed more severe impairments than insomniacs who reported excessive sleepiness.
Sleep-deprivation; Sleep-disorders; Shift-work; Shift-workers; Work-intervals; Humans; Analytical-instruments; Analytical-models; Health-surveys; Physiological-fatigue; Physiological-response; Neurophysiological-effects; Neurophysiology; Work-performance; Brain-function
R. Belcher, Sleep Disorders and Research Center, Henry Ford Hospital, Detroit, MI, USA
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Grant-Number-K01-OH-009996; M122014
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Henry Ford Health System, Detroit, Michigan