Sustained vessel dilation induced by increased pulsatile perfusion of porcine carotid arteries in vitro

Arterial pulse pressure (PP) increases with exertional stress and ageing, and can modify vessel diameter in smaller vessels. To test if PP must exceed a certain range to influence vessel diameter, and determine if such effects are endothelium-dependent or intrinsic to vascular viscoelasticity, eight fresh excised porcine carotid artery segments were perfused with modified Krebs-Henseleit by a servo-controlled system generating physiological arterial pressure waveforms. In a separate group of vessels (n = 10), the endothelium was mechanically removed. Vessel external diameter was measured by video edge-detection. Vessels partially preconstricted with noradrenaline were perfused at 9 mL min^-1 mean flow, at mean pressure of 90 or 120 mmHg, and zero PP. PP alone was then increased to 40, 70, or 120 mmHg at 1 Hz cycling rate for 5 min, then returned to zero and vessel diameter measured immediately thereafter. The protocol was repeated after 10-20 min stabilization. Mean vessel diameter rose proportionally with PP only once PP exceeded 40 mm Hg, with maximal increases of 6-9% at a PP of 120 mmHg. Similar responses were obtained in vessels with and without a functional endothelium, at both mean pressures. Thus, when exposed to higher than normal resting PP, conduit arteries dilate owing to the stress-relaxation response of their viscoelastic wall. This mechanism of PP-mediated vascular dilatation may contribute to enhanced organ perfusion when small resistance arteries are already dilated.