title: Effects of increased afterload on left ventricular performance and mechanical efficiency are not baroreflex-mediated.
abstract: OBJECTIVE
  To assess baroreflex intervention during increase in left ventricular afterload, we compared the effects of aortic banding on the intact cardiovascular system and under hexamethonium infusion.
  
  
  METHODS
  Six open-chest pigs, instrumented for measurement of aortic pressure and flow, left ventricular pressure and volume, were studied under pentobarbital-sufentanil anesthesia. Vascular arterial properties were estimated with a four-element windkessel model. Left ventricular contractility was assessed by the slope of end-systolic pressure-volume relationship.
  
  
  RESULTS
  The effects of aortic banding on mechanical aortic properties were unaffected by autonomic nervous system inhibition. However, increase in peripheral arterial vascular resistance and in heart rate were prevented by hexamethonium. Aortic banding increased left ventricular contractility and stroke work. Left ventricular-arterial coupling remained unchanged, but mechanical efficiency was impaired. These ventricular changes were independent of baroreflex integrity.
  
  
  CONCLUSIONS
  Our results demonstrate that an augmentation in afterload has a composite effect on left ventricular function. Left ventricular performance is increased, as demonstrated by increase in contractility and stroke work, but mechanical efficiency is decreased. These changes are observed independently of baroreflex integrity. Such mechanisms of autoregulation, independent of the autonomic nervous system, are of paramount importance in heart transplant patients.
authors.affiliation: Haemodynamic Research Center (HemoLiege), University of Liege, Liege, Belgium. b.lambermont@chu.ulg.ac.be
authors.forename: Philippe
authors.initials: P
authors.lastname: Kolh
authors.forename: Alexandre
authors.initials: A
authors.lastname: Ghuysen
authors.forename: Vincent
authors.initials: V
authors.lastname: Tchana-Sato
authors.forename: Vincent
authors.initials: V
authors.lastname: D'Orio
authors.forename: Paul
authors.initials: P
authors.lastname: Gerard
authors.forename: Philippe
authors.initials: P
authors.lastname: Morimont
authors.forename: Raymond
authors.initials: R
authors.lastname: Limet
authors.forename: Bernard
authors.initials: B
authors.lastname: Lambermont
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000502:physiology; D001341:Autonomic Nervous System / Q000502:physiology; D017704:Baroreflex / Q000502:physiology*; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006706:Homeostasis / Q000502:physiology; D008297:Male; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000502:physiology; D013552:Swine; D016277:Ventricular Function, Left / Q000502:physiology*