title: Discordance between microneurographic and heart-rate spectral indices of sympathetic activity in pulmonary arterial hypertension.
abstract: OBJECTIVE
  To determine, in patients with pulmonary arterial hypertension (PAH), whether there is a relationship: (1) between sympathetic nerve firing rate and spectral indices of sympathetic neural heart rate modulation; and (2) between heart rate variability (HRV) and right atrial pressure, a stimulus to sinoatrial node stretch.
  
  
  METHODS
  Characterisation of patients and healthy controls.
  
  
  METHODS
  Teaching hospital-based study.
  
  
  METHODS
  9 PAH patients without elevated pulmonary capillary wedge pressure and nine age-matched control subjects.
  
  
  METHODS
  Heart rate (HR) and muscle sympathetic nerve activity (MSNA) were recorded during 10 min of supine rest in both PAH patients studied after right heart catheterisation, and healthy volunteers. Coarse-graining spectral analysis determined HR spectral power.
  
  
  METHODS
  (1) Low-frequency (PL) spectral component of HRV; (2) MSNA burst frequency; and in PAH patients: (3) right atrial pressure.
  
  
  RESULTS
  MSNA burst frequency was higher in PAH patients (48 (24) and 29 (11) bursts/min, respectively; mean (SD); p = 0.05), whereas total power (p = 0.01), its fractal (p<0.01) and harmonic (p = 0.04) components, and PL (p = 0.01) were all reduced. PL related inversely to both MSNA burst frequency (r = -0.86, p = 0.005) and right atrial systolic pressure (r = -0.77, p = 0.04).
  
  
  CONCLUSIONS
  Thus, in PAH (as in patients with left ventricular systolic dysfunction) loss of PL relates inversely to gain in MSNA burst frequency. Diminished sympathetic neural heart rate modulation and increased right atrial stretch may combine to attenuate HRV, an adverse prognostic marker.
authors.affiliation: Department of Medicine, University Health Network, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada.
authors.forename: C L
authors.initials: CL
authors.lastname: McGowan
authors.forename: J S
authors.initials: JS
authors.lastname: Swiston
authors.forename: C F
authors.initials: CF
authors.lastname: Notarius
authors.forename: S
authors.initials: S
authors.lastname: Mak
authors.forename: B L
authors.initials: BL
authors.lastname: Morris
authors.forename: P E
authors.initials: PE
authors.lastname: Picton
authors.forename: J T
authors.initials: JT
authors.lastname: Granton
authors.forename: J S
authors.initials: JS
authors.lastname: Floras
mesh_terms: D016280:Atrial Function, Right / Q000502:physiology*; D005260:Female; D006333:Heart Failure / Q000209:etiology* / Q000401:mortality / Q000503:physiopathology; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D006976:Hypertension, Pulmonary / Q000150:complications / Q000401:mortality / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012044:Regression Analysis; D012849:Sinoatrial Node / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000503:physiopathology*