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Eur J Cardiothorac Surg 2003;24:912-919
© 2003 Elsevier Science NL

Effects of increased afterload on left ventricular performance and mechanical efficiency are not baroreflex-mediated

Haemodynamic Research Center (HemoLiege), University of Liege, Liege, Belgium

Received 18 April 2003; received in revised form 27 August 2003; accepted 16 September 2003.

^* Corresponding author. Department of Medicine, Medical Intensive Care Unit, University Hospital of Liege, CHU Sart Tilman (B35), 4000 Liege, Belgium. Tel.: +32-4-3667191; fax: +32-4-3667723
e-mail: b.lambermont{at}chu.ulg.ac.be

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.

Key Words: Autonomic nervous system • Baroreflex • Hemodynamics • Left ventricular function