title: Abnormal awake respiratory patterns are common in chronic heart failure and may prevent evaluation of autonomic tone by measures of heart rate variability.
abstract: BACKGROUND
  Reduced heart rate variability, particularly in the Very-low-frequency (VLF) spectral band, has been found to be a marker for poor prognosis in patients after myocardial infarction, but the origin of the VLF oscillations is unclear. In this study, we demonstrate that the power of cardiovascular oscillations in the VLF band in awake patients with mild to severe chronic heart failure is greatly increased by the common occurrence of unrecognized irregularity of breathing, which may confound the use of heart rate variability measures as indexes of autonomic tone or prognosis.
  
  
  RESULTS
  Among 110 consecutive patients referred for consideration of transplantation, 90 were in sinus rhythm, of whom 10 were excluded as unstable. The remaining 80 patients underwent recordings of ECG, beat-to-beat arterial oxygen saturation (SaO2), and respiration during both spontaneous and controlled breathing. During spontaneous awake breathing, 64% showed periodic breathing or Cheyne-Stokes respiration (CSR), which was associated with dominant power in the VLF band of all signals. This VLF power accounted for 55%, 77%, and 87% of heart rate variability, respectively, in patients with normal breathing, periodic breathing, and CSR. It was reduced by 48% and 62%, respectively, during controlled breathing in patients with periodic breathing or CSR. Controlled ventilation also improved oxygen saturation and markedly reduced its variability.
  
  
  CONCLUSIONS
  Breathing disorders are surprisingly common in awake patients with poor left ventricular function and produce large VLF oscillations in heart rate variability. If measures of heart rate variability are used for prognostic purposes during both short-term and long-term recordings, the confounding effects of variable respiratory patterns should be excluded. Respiratory rehabilitation might help control potentially hazardous surges in sympathetic tone.
authors.affiliation: Division of Cardiology, Centro Medico di Montescano, S. Maugeri Foundation, IRCCS, Pavia, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Mortara
authors.forename: P
authors.initials: P
authors.lastname: Sleight
authors.forename: G D
authors.initials: GD
authors.lastname: Pinna
authors.forename: R
authors.initials: R
authors.lastname: Maestri
authors.forename: A
authors.initials: A
authors.lastname: Prpa
authors.forename: M T
authors.initials: MT
authors.lastname: La Rovere
authors.forename: F
authors.initials: F
authors.lastname: Cobelli
authors.forename: L
authors.initials: L
authors.lastname: Tavazzi
mesh_terms: D000328:Adult; D001049:Apnea / Q000503:physiopathology / Q000517:prevention & control; D002311:Cardiomyopathy, Dilated / Q000503:physiopathology*; D002639:Cheyne-Stokes Respiration / Q000453:epidemiology / Q000503:physiopathology* / Q000517:prevention & control; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D011379:Prognosis; D018487:Ventricular Dysfunction, Left / Q000503:physiopathology*
chemical_list: D010100:Oxygen