title: Is there a chronic sleep stage-dependent linear and nonlinear cardiac autonomic impairment in obstructive sleep apnea?
abstract: BACKGROUND
  Obstructive sleep apnea (OSA) is a respiratory disorder that has the potential to negatively impact heart rate variability (HRV) during the sleep cycle. However, it is uncertain whether there is a chronic sleep stage-dependent linear and nonlinear cardiac autonomic impairment in OSA. The aim of this study was to perform HRV analysis in apnea-free samples as well as during stage 2 and rapid eye movement (REM) sleep in mild and moderate OSA (MiOSA and MOSA, respectively) subjects as well as health controls (NonOSA).
  
  
  METHODS
  This study included 20 MiOSA (37 ± 14 years), 20 MOSA (39 ± 8 years), and 18 NonOSA (36 ± 8 years) subjects. Subjects underwent in-laboratory overnight polysomnography with electrocardiography recording. HRV indices were obtained by analyzing the R-R intervals (RRis) in 5-min apnea-free samples by the linear frequency domain [low frequency (LF), high frequency (HF) and LF/HF], Poincaré plot [standard deviation (SD1) and (SD2)], recurrence plot [mean line length (Lmean)], recurrence rate (REC), determinism (DET), and Shannon entropy (ShanEn).
  
  
  RESULTS
  The MOSA group presented with higher LF, LF/HF, and DET indices compared to NonOSA as well as a lower parasympathetic index (HF), suggesting sympathetic hyperactivity in MOSA subjects. Interestingly, MiOSA subjects failed to show the expected linear HRV difference between sleep stages, as observed in NonOSA, which may represent an early onset of autonomic impairment at this stage of OSA.
  
  
  CONCLUSIONS
  In OSA patients, there is a chronic sleep stage-dependent impairment of linear and nonlinear cardiac autonomic modulation. Interestingly, this impairment may be identifiable during the early stages of the disease.
authors.affiliation: Cardiopulmonary Physiotherapy Laboratory, Federal University of São Carlos, São Paulo, Brazil, retrimer@hotmail.com.
authors.forename: R
authors.initials: R
authors.lastname: Trimer
authors.forename: R G
authors.initials: RG
authors.lastname: Mendes
authors.forename: F S M
authors.initials: FS
authors.lastname: Costa
authors.forename: L M M
authors.initials: LM
authors.lastname: Sampaio
authors.forename: A
authors.initials: A
authors.lastname: Delfino
authors.forename: R
authors.initials: R
authors.lastname: Arena
authors.forename: F
authors.initials: F
authors.lastname: Aletti
authors.forename: M
authors.initials: M
authors.lastname: Ferrario
authors.forename: A
authors.initials: A
authors.lastname: Borghi-Silva
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D005260:Female; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D017711:Nonlinear Dynamics; D017286:Polysomnography; D012189:Retrospective Studies; D020181:Sleep Apnea, Obstructive / Q000145:classification / Q000175:diagnosis / Q000503:physiopathology*; D012894:Sleep Stages / Q000502:physiology*; D012895:Sleep, REM / Q000502:physiology