title: Relationship of heart rate variability to parasympathetic effect.
abstract: BACKGROUND
  Baroreflex-mediated parasympathetic stimulation has variable effects on heart rate variability (HRV). We postulated that a quadratic function would describe the relationship between HRV and parasympathetic effect better than a linear function.
  
  
  RESULTS
  Twenty-nine normal volunteers (15 women; mean age 39+/-12 years) were studied after beta-adrenergic blockade with intravenous propranolol. Five-minute ECG recordings were made during graded infusions of phenylephrine and nitroprusside to achieve baroreflex-mediated increases and decreases in parasympathetic effect, respectively. Time- and frequency-domain measures of HRV were calculated from the R-R interval tachograms. The R-R interval and the vagal-sympathetic effect (VSE=R-R interval/intrinsic R-R interval) were used as indices of parasympathetic effect. The data were fit to both quadratic and linear models. In each case, the quadratic model (with a negative coefficient for the squared term) was superior to the linear model. There was some evidence that age influenced the responsiveness of the HRV parameters with changing parasympathetic effect, although the regression analysis was significant only in the models for MSSD (P<0.03) and pNN50 (P<0.001).
  
  
  CONCLUSIONS
  The relationship between HRV and parasympathetic effect is best described by a function in which there is an ascending limb where HRV increases as parasympathetic effect increases until it reaches a plateau level; HRV then decreases as parasympathetic effect increases. Because there is marked interindividual variation in this relationship, differences in HRV between individuals may reflect differences in this relationship and/or differences in autonomic effects.
authors: Division of Cardiology, Department of Medicine, Northwestern University, Chicago, Illinois, USA. goldberger@nwu.edu
authors: J J
authors: JJ
authors: Goldberger
authors: S
authors: S
authors: Challapalli
authors: R
authors: R
authors: Tung
authors: M A
authors: MA
authors: Parker
authors: A H
authors: AH
authors: Kadish
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage; D000328:Adult; D000367:Age Factors; D000368:Aged; D001285:Atropine / Q000008:administration & dosage; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D009599:Nitroprusside / Q000008:administration & dosage; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D010276:Parasympatholytics / Q000008:administration & dosage; D010656:Phenylephrine / Q000008:administration & dosage; D011433:Propranolol / Q000008:administration & dosage; D012044:Regression Analysis; D016683:Supine Position; D014662:Vasoconstrictor Agents / Q000008:administration & dosage; D014665:Vasodilator Agents / Q000008:administration & dosage
chemical_list: D000319:Adrenergic beta-Antagonists; D010276:Parasympatholytics; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D009599:Nitroprusside; D010656:Phenylephrine; D001285:Atropine; D011433:Propranolol