Diameter and Elasticity of the Ascending Aorta during Infusion of Noradrenaline

The effect of smooth muscle contraction on diameter and elasticity of the ascending aorta was examined in 18 anesthetized rabbits. Aortic diameter was measured with ultrasonic technique inside the intact thorax, and blood pressure was recorded from a catheter in the right common carotid artery. Control observations were obtained at various blood pressure levels by producing stepwise changes of the blood volume. At diastolic pressures from 40–90 mm Hg, i.v. infusion of noradrenaline (4–6 μg/kg · min) caused a 6.6% average reduction in diastolic aortic diameter. Noradrenaline at low pressures increased the aortic pressure‐strain elastic modulus (E p ) and theoretical pulse‐wave velocity (PWV) by 30–67%. Control values of Ep and PWV were slightly higher for rabbits than those usually found in dogs. It is concluded that at comparable pressures, contraction of aortic smooth muscle tissue, induced by infusion of noradrenaline, produces a small but significant constriction of the ascending aorta, and, at low pressures only, increases dynamic stiffness of the vessel.