title: Evaluation of an automated single-channel sleep staging algorithm.
abstract: BACKGROUND
  We previously published the performance evaluation of an automated electroencephalography (EEG)-based single-channel sleep-wake detection algorithm called Z-ALG used by the Zmachine(®) sleep monitoring system. The objective of this paper is to evaluate the performance of a new algorithm called Z-PLUS, which further differentiates sleep as detected by Z-ALG into Light Sleep, Deep Sleep, and Rapid Eye Movement (REM) Sleep, against laboratory polysomnography (PSG) using a consensus of expert visual scorers.
  
  
  METHODS
  Single night, in-lab PSG recordings from 99 subjects (52F/47M, 18-60 years, median age 32.7 years), including both normal sleepers and those reporting a variety of sleep complaints consistent with chronic insomnia, sleep apnea, and restless leg syndrome, as well as those taking selective serotonin reuptake inhibitor/serotonin-norepinephrine reuptake inhibitor antidepressant medications, previously evaluated using Z-ALG were re-examined using Z-PLUS. EEG data collected from electrodes placed at the differential-mastoids (A1-A2) were processed by Z-ALG to determine wake and sleep, then those epochs detected as sleep were further processed by Z-PLUS to differentiate into Light Sleep, Deep Sleep, and REM. EEG data were visually scored by multiple certified polysomnographic technologists according to the Rechtschaffen and Kales criterion, and then combined using a majority-voting rule to create a PSG Consensus score file for each of the 99 subjects. Z-PLUS output was compared to the PSG Consensus score files for both epoch-by-epoch (eg, sensitivity, specificity, and kappa) and sleep stage-related statistics (eg, Latency to Deep Sleep, Latency to REM, Total Deep Sleep, and Total REM).
  
  
  RESULTS
  Sensitivities of Z-PLUS compared to the PSG Consensus were 0.84 for Light Sleep, 0.74 for Deep Sleep, and 0.72 for REM. Similarly, positive predictive values were 0.85 for Light Sleep, 0.78 for Deep Sleep, and 0.73 for REM. Overall, kappa agreement of 0.72 is indicative of substantial agreement.
  
  
  CONCLUSIONS
  This study demonstrates that Z-PLUS can automatically assess sleep stage using a single A1-A2 EEG channel when compared to the sleep stage scoring by a consensus of polysomnographic technologists. Our findings suggest that Z-PLUS may be used in conjunction with Z-ALG for single-channel EEG-based sleep staging.
authors.affiliation: General Sleep Corporation, Euclid, OH, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.affiliation: General Sleep Corporation, Euclid, OH, USA ; Department of Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, OH, USA.
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Loparo
authors.affiliation: Department of Psychology, University of Arizona, Tucson, AZ, USA.
authors.forename: Monica R
authors.initials: MR
authors.lastname: Kelly
authors.affiliation: General Sleep Corporation, Euclid, OH, USA.
authors.forename: Richard F
authors.initials: RF
authors.lastname: Kaplan
keywords: EEG; Zmachine; algorithm; automatic sleep scoring; single channel; sleep detection; sleep staging