title: Calibration of an objective alertness scale.
abstract: In order to establish validity of an objective scale of alertness-sleepiness, one is forced to somehow calibrate it using subjective scales, such as the Karolinska Sleepiness Scale (KSS). We evaluated the effects of prolonged wakefulness on the extent of disagreement between objective and subjective KSS assessments, and tested whether calibration of an objective alertness-sleepiness scale can be established despite the limited reliability of subjective reports. Starting from 7p.m., the resting electroencephalogram (EEG) was recorded at 2-hour intervals over the last 32-50 h of 44-61-hour wakefulness of 15 healthy study participants. Frontal and occipital scores on the 2nd principal component of the EEG spectrum and occipital alpha-theta power difference were computed for 1-min intervals of 5-min eyes-closed EEG recordings. To obtain alertness scale scores in the range from 5 to 0, positive and negative values of these EEG indexes were assigned to 1 and 0, respectively, and then summed. Although correlation between time courses of objective and subjective (KSS) scores was very strong, evidence for systematic errors in both the mean and the calibration was also found. Correction of these errors resulted in strengthening of correlation (r = 0.99) and establishing one-to-one correspondence between the steps of objective and subjective scales. The results indicate that scores from 5 to 0 on the objective alertness scale can be anchored to minimal, mild, moderate, marked, severe, and disabling levels of sleepiness.
authors.affiliation: Research Institute for Molecular Biology and Biophysics, Siberian Branch of the Russian Academy of Medical Sciences, 2, Timakova Street, Novosibirsk 630117, Russia. Electronic address: putilov@ngs.ru.
authors.forename: Arcady A
authors.initials: AA
authors.lastname: Putilov
authors.affiliation: Research Institute for Molecular Biology and Biophysics, Siberian Branch of the Russian Academy of Medical Sciences, 2, Timakova Street, Novosibirsk 630117, Russia.
authors.forename: Olga G
authors.initials: OG
authors.lastname: Donskaya
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001288:Attention / Q000502:physiology*; D058256:Brain Waves / Q000502:physiology*; D002138:Calibration; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D025341:Principal Component Analysis; D015203:Reproducibility of Results; D012890:Sleep / Q000502:physiology; D012892:Sleep Deprivation; D014851:Wakefulness / Q000502:physiology*; D055815:Young Adult
keywords: Calibration; EEG spectrum; Karolinska Sleepiness Scale; Principal component analysis; Sleep deprivation; Subjective sleepiness