Correlation of Intimal Hyperplasia Development and Shear Stress Distribution at the Distal End-side-anastomosis, in vitro Study Using Particle Image Velocimetry

Abstract

Low shear areas at the distal anastomosis of peripheral bypasses are thought to promote neointimal hyperplasia. In this study we evaluated the fluid dynamic environment at the distal anastomosis of peripheral bypasses by means of a new method for in vitro flow visualization and quantitative velocity field measurement. A silastic model of a distal end-side anastomosis was attached to a mock circulation loop driven by an artificial heart. High resolution velocity fields were measured by means of particle image velocimetry (PIV). The velocity vector data were used to calculate vorticity omega, strain rates ex, shear rates h and shear stresses tau. Two separations and a stagnation zone were identified by means of flow visualization. Measured velocities inside the three zones were significantly lower than in the high velocity mainstream. Calculated shear rates and shear stresses inside the zones were significantly lower than human wall shear rates. At the transition between the effective mainstream and the boundary layers high vorticity and compressive strain fields existed, indicating the presence of high shear forces. The locations of these areas corresponded to the well known zones of intimal hyperplasia. The high resolution shear stress analysis supports the low shear theory of intimal hyperplasia development. A wall diversion angle greater than 6 degrees leads to flow separation and presumed IH promotion until high shear transition areas are reached.

Vascular Adaptation: Pattern Formation and Cross Validation between an Agent Based Model and a Dynamical System

“…As largely described in this section, it is clear how low shear stress promotes the neointimal generation fostering intimal hyperplasia, and favoring in this way the restenosis of the graft. This outcome is largely confirmed with experimental evidences presented in literature, where many works address that the uncontrolled proliferation of SMC within tunica intima is favored by low shear stress (Heise M et al 2003; Ojha M 1984; Salam TA et al 1996; Jackson M et al 2009; Huynh TTT et al 1999). …”

Flow Patterns in Carotid Bifurcation Models Using Pulsed Doppler Ultrasound: Effect of Concentric vs. Eccentric Stenosis on Turbulence and Recirculation

“…Note the CFD studies were not performed in the 70%-stenosed models due to the anticipated presence of turbulence, which is not easily handled in CFD. However, future shear-stress and turbulence measurements are planned using a high-resolution digital particle image velocimetry (DPIV) system (e.g., see Adrian 1991;Bluestein et al 2000;Heise et al 2003), as opposed to the qualitative imaging (i.e., DPI) performed here due to the low-intensity lasers requiring large particles and low frame rates (i.e., long exposures). Additionally, it is noted that DPI serves to qualitatively observe the large-scale flow structure and may not accurately represent smallscale velocity fluctuations due to the relatively large size of the reflective particles (as required with the lowintensity lasers), although the corresponding Stokes time is very small at ,0.02 s. Previous studies have demonstrated that stenosis asymmetry leads to higher shear stress and a larger flow separation region (Tang et al 2003) and increased intensity of turbulent pressure fluctuations (Loree et al 1991).…”

Why Patencies of Femoropopliteal Bypass Grafts with Distal End-to-End Anastomosis are Comparable with End-to-Side Anastomosis

“…The majority of these studies have focused on flow patterns in ETS anastomosis. [20][21][22] Although ETE anastomoses are theoretically considered to have better patencies, clinical studies lack the evidence for this assumption. By using high-resolution CT angiography, six different but representative ETS and ETE models were constructed from in vivo anastomosis and used to investigate local hemodynamics in this study.…”