Assessment of aortic wall distensibility in acute heart failure by aortic pressure-diameter relation

To estimate the changes of impedance of the aorta to the left ventricular (LV) ejection in acute heart failure, thoracic aortic pressure (AoP : micromanometer) - diameter (AoD : sonomicrometry) relation was evaluated at control and during failing heart led by injection of carbon powder into the main trunk of the left coronary artery in 7 anesthetized dogs. After the recording at rest (operating point), AoP-AoD relation over a wide AoP range was obtained by squential inferior vena caval and sortic occlusions. After the injection of carbon powder, cardiac output and LV dP/dt were significantly decreased, and total systemic resistance and aortic characteristic impedance were significantly increased compaired with control, indicated that acute failing heart was successfully prepared. In all animals, AoP-AoD relation under the wide AoP range was well fitted to a cubic regression curve (r≧0.98) at both control and failing heart. The dP/dD value, the first derivative of the AoP-AoD relation, was calculated as a stiffness index of the aortic wall. And the dP/dD value was minimum at the inflection point of AoP-AoD relation curve. At failing heart, AoP-AoD relation curve shifted left-upward and became more steeper than at control. At control rest, the operating ponit (mean AoD, 13.3±2.0mm, mean AoP, 89.8±12.1mmHg) was significantly shifted to the right-upward from the inflection point. However, at failing heart, the operating point (12.9±1.8mm, 82.9±10.6mmHg) was seen at near the inflecion point. Thus the aortic wall distensibility was significantly impaired during acute heart failure, however, ventrcle-aortic coupling might be operating at the adequate point on the AoP-AoD relation curve, where aortic wall showed most compliant. These findings suggest that the distensibility of the aorta may play an important role for reducing aortic impedance to LV ejection at acute heart failure.