Increased aortic compliance maintains left ventricular performance at lower energetic cost

Objective: The aim of this study was to investigate left ventricular contra ctility and energetic cost of cardiac ejection under conditions of acute in crease in aortic compliance. Methods: In six anaesthetized pigs, ascending aortic compliance was increased by adding a volume chamber in parallel to t he ascending aorta. Systemic vascular parameters, including characteristic impedance, peripheral resistance, total vascular compliance, and inertance, were estimated with a four-clement windkessel model. Arterial elastance wa s derived from these parameters. Left ventricular systolic function was ass essed by end-systolic pressure-volume relationship tend-systolic elastance) , and stroke work. Pressure-volume area was used as a measure of myocardial oxygen consumption. Heart rate remained constant during the experimentatio n. Results: Adding the aortic volume chamber significantly increased vascul ar compliance from 0.95 +/- 0.08 to 1.17 +/- 0.06 ml/ mmHg (P < 0.01), whil e inductance, characteristic impedance, peripheral resistance, and arterial elastance remained statistically at basal values, respectively 0.0020 +/- 0.0003 mmHg.s(2)/ml, 0.105 +/- 0.009 mmHg.s/ml, 1.27 +/- 0.12. mmHg.s/ml, a nd 2.43 +/- 0.21 mmHg/ml. During the same interval, stroke work and pressur e-volume area decreased respectively from 2700 +/- 242 to 2256 +/- 75 mmHg. ml (P < 0.01), and from 3806 +/- 427 to 3179 +/- 167 mmHg.ml (P < 0.01). st roke work and pressure-volume area decreased at matched end-diastolic volum es. In contrast, end-systolic elastance, ejection fraction, and stroke volu me remained statistically unchanged, respectively at 2.29 +/- 0.14 mmHg/ ml , 48.1 +/- 2.1 %, and 32.4 +/- 1.7 ml. Conclusions: These data suggest that , when facing an increased aortic compliance, the left ventricle displays u nchanged contractility, bur the energetic cost of cardiac ejection is signi ficantly decreased. These data may be of clinical importance when choosing an artificial prosthesis for ascending aortic replacement. (C) 2000 Elsevie r Science B.V. All rights reserved.