P6.16 PRONOUNCED INCREASE IN LONGITUDINAL DISPLACEMENT OF THE PORCINE CAROTID ARTERY WALL CAN TAKE PLACE INDEPENDENTLY OF WALL SHEAR RATE

Abstract

Objective and methods: We have recently shown that the longitudinal displacements of the arterial wall, i.e. the displacements along the artery during the cardiac cycle, undergo profound changes in response to catecholamines. The relations between longitudinal displacements of the arterial wall and wall shear rate (WSR) and wall shear stress (WSS), respectively, from the flowing blood are unexplored. To study this issue the common carotid artery of five anesthetized pigs was noninvasively investigated during different hemodynamic situations using ultrasound. The study protocol included intravenous infusion of epinephrine, as well as intravenous boluses of norepinephrine. Further, effects of β-blockade (metoprolol) were studied. Results: During infusion of epinephrine and following boluses of norepinephrine WSR increased. However, when catecholamines were administrated during β-blockade, β-blockade effectively counteracted increase in WSR. We found no correlation between longitudinal displacement of the intima-media complex and WSR. This was most obvious when boluses of norepinephrine were administrated during β-blockade; β-blockade effectively counteracted increase in WSR, whereas, at the same time, β-blockade was insufficient to counteract a sharp rise in pulse pressure and accompanying pronounced increase in longitudinal displacement of the intima-media complex. Conclusion: This study shows that a profound increase in longitudinal displacement of the arterial wall can take place independently of WSR, and thus, using the models of today, independently of WSS from the flowing blood. This strongly suggests that another force, or other forces, than WSS from the blood flow are also working in the direction of the blood flow; i.e. along the arteries.