title: Low frequency power of heart rate variability reflects baroreflex function, not cardiac sympathetic innervation.
abstract: BACKGROUND
  Power spectral analysis of heart rate variability is used to assess cardiac autonomic function. The relationship of low frequency (LF) power to cardiac sympathetic tone has been unclear. We reported previously that LF power may reflect baroreflex modulation. In this study we attempted to replicate our findings in additional subject cohorts, taking into account possible influences of respiration and using different methods to measure baroreflex-cardiovagal gain (BCG).
  
  
  OBJECTIVE
  We assessed relationships of LF power, including respiration-adjusted LF power (LFa), with cardiac sympathetic innervation and baroreflex function in subjects with or without neuroimaging evidence of cardiac sympathetic denervation.
  
  
  METHODS
  Values for LF power at baseline supine, seated, and during the Valsalva maneuver were compared between subject groups with low or normal myocardial concentrations of 6-[(18)F]fluorodopamine-derived radioactivity. BCG was calculated from the slope of cardiac interbeat interval vs. systolic pressure during Phase II of the Valsalva maneuver or after i.v. nitroglycerine injection (the Oxford technique).
  
  
  RESULTS
  LF and LFa were unrelated to myocardial 6-[(18)F]fluorodopamine-derived radioactivity. During sitting rest and the Valsalva maneuver logs of LF and LFa correlated positively with the log of Phase II BCG (r = 0.61, p = 0.0005; r = 0.47, p = 0.009; r = 0.69, p < 0.0001; r = 0.60, p = 0.0006). Groups with Low BCG (≤ 3 ms/mmHg) had low LF and LFa regardless of cardiac innervation. The log of LF power during supine rest correlated with the log of Oxford BCG (r = 0.74, p < 0.0001).
  
  
  CONCLUSIONS
  LF power, with or without respiratory adjustment, reflects baroreflex modulation and not cardiac sympathetic tone.
authors.affiliation: Clinical Neurocardiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 10 Center Drive MSC-1620, Bethesda, MD 20892-1620, USA.
authors.forename: Faisal
authors.initials: F
authors.lastname: Rahman
authors.forename: Sandra
authors.initials: S
authors.lastname: Pechnik
authors.forename: Daniel
authors.initials: D
authors.lastname: Gross
authors.forename: LaToya
authors.initials: L
authors.lastname: Sewell
authors.forename: David S
authors.initials: DS
authors.lastname: Goldstein
mesh_terms: D017704:Baroreflex / Q000502:physiology*; D016022:Case-Control Studies; D022062:Electrophysiologic Techniques, Cardiac / Q000379:methods*; D006321:Heart / Q000294:innervation* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007024:Hypotension, Orthostatic / Q000503:physiopathology; D019578:Multiple System Atrophy / Q000503:physiopathology; D005996:Nitroglycerin / Q000494:pharmacology; D010300:Parkinson Disease / Q000503:physiopathology; D054970:Pure Autonomic Failure / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000502:physiology*; D014055:Tomography, Emission-Computed; D014636:Valsalva Maneuver / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D014665:Vasodilator Agents; D005996:Nitroglycerin