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Pulsatile flows in a Curved Artery Model Open Access

Due to the importance of understanding behavior of blood flow in curved arteries, we experimentally modeled the flow of blood analog fluids through curved vessels. The curvature deviates the primary flow and causes the formation of helical motions inside the vessels, i.e. vortices. These vortices play important roles in hemodynamics and can affect mixing of different blood components and wall shear stress inside the artery. Therefore, understanding of the dynamics of these vortices is important. There are some characteristics that can affect the vortices in vessels e.g. rheological properties of the blood analog, vessel wall properties (rigid/elastic), and geometry of vessel. We investigate the morphology of vortical structures inside curved vessels under different conditions and aim to portray a complete picture of their evolution in 3D space. In order to investigate the effect of different parameters on vortices we used a canonical 180˚ curved vessel geometry. The rigid models were machined from an acrylic block. To fabricate the more complex elastic models we developed an injection molding method to produce optically clear elastic vessels from silicone. Our working blood-analog fluid is a mixture of water and glycerin to match the viscosity of blood. Viscoelastic and shear-thinning properties of blood were simulated by adding Xanthan gum. The refractive index was perfectly matched to that of the vessel to minimize distortion for imaging with our optical diagnostics. To produce the required variable pulsatile flow rates, an adaptive feedback PID controller was developed that automatically adjusts the input to the pump to match the desired flow rate waveform. Particle image velocimetry (PIV) was used in all experiments to measure the velocity fields inside the curved vessel. After obtaining the velocity data, vortices were detected using the d2 vortex identification method with an in-house Fortran code and vortex circulation analysis was performed. Our findings have resolved conflicting viewpoints in the scientific literature concerning the effects of complex fluids and effect of vessel wall elasticity. Our published results provide justification for using simple Newtonian fluids in rigid geometries as opposed to using more complex fluids in elastic vessels. These simpler models capture all the relevant flow physics and are simpler to construct, and are more amenable to optically-based measurements. Also, we showed that the effects of local elasticity on morphology of vortices are less important compared to dominant effect of geometry and torsion. Therefore, this justifies the use of simple rigid models with realistic geometry.

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