In-Vitro study of Arterial Vessel Stiffness on Wall Shear Stress Under Physiological Pulsatile Flow Conditions

Wall shear stress (WSS) exerted on the vessel wall by flowing blood is believed to play an important role in the adaptive processes of the vascular wall by inducing the production of substances such as nitric oxide, prostacyclin, and endothelin by endothelial cells. Studies in humans have shown increased vessel stiffness with advancing age. However, the influences of vessel stiffness on the WSS under physiological pulsatile flow conditions are not clear. It is hypothesized that vessel stiffness can induce transient negative (reversed) WSS in pulsatile flow conditions. High-resolution PIV measurements were conducted in an in-vitro setup using a programmable gear pump to generate pulsatile flow. Transparent PVC tubings with different stiffness were tested under various flow conditions. Time-resolved WSS results were extracted from the PIV velocity profile. Although the flow rate is positive throughout the pulse, flow reversal and negative WSS near the wall were observed during the deceleration phase when using stiff tubings. The duration and magnitude of the negative WSS were found to increase with tubing stiffness. A theoretical model was also developed to predict the time-dependent WSS in rigid tubing under the same pulsatile flow conditions. We believe that increased stiffness, and thus reversed WSS, can possibly influence the orientation of endothelial cells and be partially responsible for artery diseases such as atherosclerosis and aneurysm.