title: Relationship of heart rate variability to sleepiness in patients with obstructive sleep apnea with and without heart failure.
abstract: BACKGROUND
  Many patients with severe obstructive sleep apnea (OSA) do not complain of excessive daytime sleepiness (EDS), possibly due to increased sympathetic nervous activity (SNA) and accompanying heightened alertness. We hypothesized that in patients with OSA, those without subjective EDS (Epworth Sleepiness Scale, ESS score < 11) would have higher very low frequency (VLF) heart rate variability (HRV) during sleep, reflecting greater sympathetic heart rate modulation than patients with an ESS score ≥ 11.
  
  
  METHODS
  Patients with severe OSA (AHI ≥ 30: 26 with and 65 without heart failure) were divided into those with and without EDS. Heart rate (HR) signals were acquired in stage 2 sleep during periods of recurrent apneas and hypopneas and submitted to coarse graining spectral analysis, which extracts harmonic, neurally mediated contributions to HRV from total spectral power. Because the apnea-hyperpnea cycle entrains muscle SNA at VLF (0 to 0.04 Hz), VLF power was our principal between-group comparison.
  
  
  RESULTS
  Subjects without EDS had higher harmonic VLF power (944 ± 839 vs 447 ± 461 msec(2), p = 0.003) than those with EDS, irrespective of the presence or absence of heart failure (1218 ± 944 vs 426 ± 299 msec(2), p = 0.043, and 1029 ± 873 vs 503 ± 533 msec(2), p = 0.003, respectively). ESS scores correlated inversely with VLF power in all (r = -0.294, p = 0.005) and in heart failure subjects (r = -0.468, p = 0.016).
  
  
  CONCLUSIONS
  Patients with severe OSA but without EDS have higher VLF-HRV than those with EDS. This finding suggests that patients with severe OSA but without EDS have greater sympathetic modulation of HRV than those with EDS that may reflect elevated adrenergically mediated alertness.
  
  
  BACKGROUND
  Taranto Montemurro L; Floras JS; Picton P; Kasai T; Alshaer H; Gabriel JM; Bradley TD. Relationship of heart rate variability to sleepiness in patients with obstructive sleep apnea with and without heart failure.
authors.affiliation: Sleep Research Laboratory of the Toronto Rehabilitation Institute ; Centre for Sleep Medicine and Circadian Biology of the University of Toronto.
authors.forename: Luigi
authors.initials: L
authors.lastname: Taranto Montemurro
authors.affiliation: the Departments of Medicine of the University Health Network Toronto General Hospital ; Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: John S
authors.initials: JS
authors.lastname: Floras
authors.affiliation: the Departments of Medicine of the University Health Network Toronto General Hospital.
authors.forename: Peter
authors.initials: P
authors.lastname: Picton
authors.affiliation: Sleep Research Laboratory of the Toronto Rehabilitation Institute ; Centre for Sleep Medicine and Circadian Biology of the University of Toronto.
authors.forename: Takatoshi
authors.initials: T
authors.lastname: Kasai
authors.affiliation: Sleep Research Laboratory of the Toronto Rehabilitation Institute ; Centre for Sleep Medicine and Circadian Biology of the University of Toronto.
authors.forename: Hisham
authors.initials: H
authors.lastname: Alshaer
authors.affiliation: Sleep Research Laboratory of the Toronto Rehabilitation Institute ; Centre for Sleep Medicine and Circadian Biology of the University of Toronto.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Gabriel
authors.affiliation: Sleep Research Laboratory of the Toronto Rehabilitation Institute ; Centre for Sleep Medicine and Circadian Biology of the University of Toronto ; the Departments of Medicine of the University Health Network Toronto General Hospital.
authors.forename: T Douglas
authors.initials: TD
authors.lastname: Bradley
mesh_terms: D016022:Case-Control Studies; D006970:Disorders of Excessive Somnolence / Q000150:complications / Q000503:physiopathology*; D004562:Electrocardiography; D005260:Female; D006333:Heart Failure / Q000150:complications / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D020181:Sleep Apnea, Obstructive / Q000150:complications / Q000503:physiopathology*
keywords: Sleepiness; heart rate variability; obstructive sleep apnea; sympathetic activity