Endothelium-dependent arterial wall tone elasticity modulated by blood viscosity

The role of blood viscosity on arterial wall elasticity before and after deendothelization (DE) was studied. Seven ovine brachiocephalic arteries were studied in vitro under physiological pulsatile flow conditions achieved by a mock circulation loop. Instantaneous pressure and diameter signals were assessed in each arterial segment. Incremental elastic modulus (E(inc)) was calculated using the slope of the pure elastic stress-strain relationship. There was no significant difference between E(inc) values before and after DE (3.11 vs. 3.16 10(7) dyn/cm(2)) at a blood viscosity of 2.00 mPa. s. Increases in blood viscosity (2.50, 3.00, 3.50, and 4.00 mPa. s) always resulted in decreases of E(inc) before DE; inversely, increases in blood viscosity resulted in increases of E(inc) after DE. These values of E(inc), for identical levels of blood viscosity, were always significantly lower (P < 0.05) before DE than those obtained after DE. Arterial wall elasticity assessed through E(inc) was strongly influenced by blood viscosity, probably due to presence or absence of endothelium relaxing factors or to direct shear smooth muscle activation when endothelial cells are removed.