Interstitial transmural flow and shear stress in a blood vessel wall

Alterations in shear stress exerted on vascular smooth muscle cells (VSMCs) may result in abnormal VSMC proliferation and migration, which may result in cardiovascular disease progression. In this dissertation, the effect of age on mechanical circumferential stress, interstitial fluid velocity, and fluid shear stress in the human common carotid artery (CCA) is investigated computationally in two complementary studies using FEBio software. The effect of age is adapted via changes in material properties and geometry. In the arterial ring model of the human common carotid artery (CCA) with three distinct biphasic layers with anisotropic fiber-reinforced materials, the mechanical response and the interstitial fluid flows are calculated as the lumen is pressurized. Since the model is homogenous and doesn't consider VSMCs, the shear stress is calculated in the second study incorporating a biphasic medial lamellar unit as a representative volume unit of media layer consisting of an anisotropic single VSMC, elastin layers, and collagenous domain. The resulting fluid velocity of the arterial ring is applied as an inlet fluid velocity to the lamellar unit. As a result, the mechanical responses show strongly nonlinear behavior. Younger models exhibit less circumferential stretch. The radial compression of the arterial layers resulted in a decrease in hydraulic conductivity of the whole artery as the lumen pressure increases in the physiological pressure range (PPR). The total hydraulic conductivity is reduced by 48% in the young and 16% in the aged arterial walls. Consequently, the average radial interstitial flux increases with pressure by 14% in the young and 91% in the aged arteries. The average fluid flux is found to be around 4 times higher in young CCA. Accordingly, the average shear stresses on VSMCs are found to be 0.2 and 0.8 dyne/cm² in the aged and young lamellar units. The maximum local shear stresses are found to be 2.5 and 7 dyne/cm², respectively. These amounts of shear stress experienced by the VSMCs are more significant in aged arteries and may accelerate cardiovascular disease progression more than in young arteries.