Examining initial sleep onset in primary insomnia: a case-control study using 4-second epochs

• Published in: Journal of clinical sleep medicine Vol. 3; no. 5; pp. 479 - 488
• Main Authors: Moul, Douglas E, Germain, Anne, Cashmere, J David, Quigley, Michael, Miewald, Jean M, Buysse, Daniel J
• Format: Journal Article
• Language: English
• Published: United States American Academy of Sleep Medicine 15-08-2007
• Subjects: Case-Control Studies; Chi-Square Distribution; Female; Humans; Male; New Research; Polysomnography - methods; Reproducibility of Results; Sleep Initiation and Maintenance Disorders - diagnosis; Sleep Stages; Wakefulness
• ISSN: 1550-9389; 1550-9397
• DOI: 10.5664/jcsm.26912

To explore the sleep onset process in primary insomnia patients, new rules for scoring 4-second epochs were implemented to score sleep and artifacts during initial sleep onset. Conventional scorings in 20-second and 60-second epochs were also obtained.
The start of the initial 60-second epoch of stage 1 was used to define "time zero" (t0). Sleep onset periods from 11 patients and 11 individually age- and sex-matched controls spanned from 5 minutes before t0 through 29 minutes after t0. Using the new rules, the periods were scored blind to group assignment. This t0 time-referenced the data analysis to one plausible midpoint in the sleep onset process. In parallel, latencies were time-referenced from good night time.
Reliability in scoring sleep and artifacts was adequate (kappa = 0.68 & 0.63, respectively, p <0.001). Group differences in sleep latencies were marginal in 60-second and 20-second scoring but significant with a definition of 4-second sleep latency. Patients had more 4-second epochs scored as awake (Mantel-Haenszel chi2 = 271, d.f. = 1, p <0.001) and containing artifact (M-H chi2 = 143, p <0.001). Patients took longer to achieve 30 continuous 4-second epochs of NREM sleep (Breslow chi2 = 4.03, d.f. = 1, p = 0.045) after t0. Patients accumulated sleep more slowly with all 3 scoring rules after t0. A slower rate of accumulating sleep after t0 was detected only with the 4-second scoring (p = 0.047).
Evidence was present for momentary state-switching instabilities in the patients during the initial sleep onset process. Using rules for scoring small epochs may reveal such instabilities more readily than traditional scoring methods.