title: Characterization of sleep stages by correlations in the magnitude and sign of heartbeat increments.
abstract: We study correlation properties of the magnitude and the sign of the increments in the time intervals between successive heartbeats during light sleep, deep sleep, and rapid eye movement (REM) sleep using the detrended fluctuation analysis method. We find short-range anticorrelations in the sign time series, which are strong during deep sleep, weaker during light sleep, and even weaker during REM sleep. In contrast, we find long-range positive correlations in the magnitude time series, which are strong during REM sleep and weaker during light sleep. We observe uncorrelated behavior for the magnitude during deep sleep. Since the magnitude series relates to the nonlinear properties of the original time series, while the sign series relates to the linear properties, our findings suggest that the nonlinear properties of the heartbeat dynamics are more pronounced during REM sleep. Thus, the sign and the magnitude series provide information which is useful in distinguishing between the sleep stages.
authors.affiliation: Center for Polymer Studies and Department of Physics, Boston University, Boston, Massachusetts 02215, USA.
authors.forename: Jan W
authors.initials: JW
authors.lastname: Kantelhardt
authors.forename: Yosef
authors.initials: Y
authors.lastname: Ashkenazy
authors.forename: Plamen Ch
authors.initials: PCh
authors.lastname: Ivanov
authors.forename: Armin
authors.initials: A
authors.lastname: Bunde
authors.forename: Shlomo
authors.initials: S
authors.lastname: Havlin
authors.forename: Thomas
authors.initials: T
authors.lastname: Penzel
authors.forename: Jörg-Hermann
authors.initials: JH
authors.lastname: Peter
authors.forename: H Eugene
authors.initials: HE
authors.lastname: Stanley
mesh_terms: D001703:Biophysics / Q000379:methods*; D006321:Heart / Q000502:physiology*; D006801:Humans; D015233:Models, Statistical; D012890:Sleep; D012895:Sleep, REM; D013997:Time Factors