title: Power spectral analysis of heart rate variability in obese subjects: evidence of decreased cardiac sympathetic responsiveness.
abstract: OBJECTIVE
  To investigate changes in sympathetic nervous system function in obesity.
  
  
  METHODS
  Cross-sectional clinical study.
  
  
  METHODS
  18 middle-aged obese patients (43-55 years, BMI > 33 kg/m2) and 26 age- and sex-matched normal-weight controls (44-56 years, BMI < 26 kg/m2).
  
  
  METHODS
  Post-synaptic sympathetic response studied by power spectral analysis of heart rate variability at rest and during sympathetic stimulus obtained through passive head-up tilt. Spectral analysis comprised two frequency domain components: high-frequency power (HF), reflecting parasympathetic activity and low-frequency power (LF), in particular the LF: HF ratio, reflecting sympathetic function. Pre-synaptic sympatho-adrenal function was assessed by measurement of 8.00 am plasma noradrenaline.
  
  
  RESULTS
  Obese patients had significantly lower spectral indexes of sympathetic response and higher spectral markers of parasympathetic activity than nonobese subjects both at rest (25.9 +/- 3.5 vs 38.6 +/- 1.7 LF NUs, P < 0.001) and after tilt (0.98 +/- 0.40 vs 2.30 +/- 0.39 LF: HF, P < 0.05; 62.7 +/- 6.9 vs 41.1 +/- 4.9 HF NUs, P < 0.05). By contrast, the obese subjects had higher noradrenaline levels (289.32 +/- 27.40 vs 159.80 +/- 19.20 pg/ml, P < 0.001). No relation was found between these neuroautonomic indexes and body mass index.
  
  
  CONCLUSIONS
  Obese subjects seem to have increased pre-synaptic sympatho-adrenal function but a depressed end-organ cardiovascular response.
authors.affiliation: Chair of Geriatrics, 1st Medical Clinic, University La Sapienza Rome, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Piccirillo
authors.forename: F
authors.initials: F
authors.lastname: Vetta
authors.forename: F L
authors.initials: FL
authors.lastname: Fimognari
authors.forename: S
authors.initials: S
authors.lastname: Ronzoni
authors.forename: J
authors.initials: J
authors.lastname: Lama
authors.forename: M
authors.initials: M
authors.lastname: Cacciafesta
authors.forename: V
authors.initials: V
authors.lastname: Marigliano
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000328:Adult; D015992:Body Mass Index; D005260:Female; D006321:Heart / Q000294:innervation*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood; D009765:Obesity / Q000503:physiopathology*; D011187:Posture; D011433:Propranolol / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000503:physiopathology*
chemical_list: D000319:Adrenergic beta-Antagonists; D011433:Propranolol; D009638:Norepinephrine