Effects of decreased aortic compliance on performance of the left ventricle

Abstract

The effects of decreased aortic compliance on the performance of the left ventricle were studied in 8 dogs by diverting their aortic blood flow through a rigid bypass. Despite unchanged myocardial contractility, judged by the force-velocity relation during isovolumic systole, direction of blood into the rigid bypass caused increases in peak systolic pressure, duration of ejection, and left ventricular end-diastolic pressure. Stroke volume was unchanged and the ejection fraction therefore declined. Peak and integrated myocardial fiber tension rose as a result of the increases in left ventricular pressure and size and because of the increase in tension, circumferential fiber and contractile element velocities decreased. At any instant during ejection, the performance of the ventricle was dependent on the interrelations between myocardial fiber length, tension, velocity, and the impedance to ejection. In other experiments, aortic blood flow was diverted through the rigid bypass while preload was held constant. Under these circumstances, stroke volume fell and left ventricular tension rose to a smaller extent than when preload was allowed to rise. The mechanical performance of the left ventricle is altered by the physical characteristics of the arterial tree. Decreased aortic compliance, as occurs during aging in man, therefore increases the impedance to ejection and the tension load on the myocardium.