Fluid-Dynamic Optimal Design of Helical Vascular Graft for Stenotic Disturbed Flow

Abstract

Although a helical configuration of a prosthetic vascular graft appears to be clinically beneficial in suppressing thrombosis and intimal hyperplasia, an optimization of a helical design has yet to be achieved because of the lack of a detailed understanding on hemodynamic features in helical grafts and their fluid dynamic influences. In the present study, the swirling flow in a helical graft was hypothesized to have beneficial influences on a disturbed flow structure such as stenotic flow. The characteristics of swirling flows generated by helical tubes with various helical pitches and curvatures were investigated to prove the hypothesis. The fluid dynamic influences of these helical tubes on stenotic flow were quantitatively analysed by using a particle image velocimetry technique. Results showed that the swirling intensity and helicity of the swirling flow have a linear relation with a modified Germano number (Gn*) of the helical pipe. In addition, the swirling flow generated a beneficial flow structure at the stenosis by reducing the size of the recirculation flow under steady and pulsatile flow conditions. Therefore, the beneficial effects of a helical graft on the flow field can be estimated by using the magnitude of Gn*. Finally, an optimized helical design with a maximum Gn* was suggested for the future design of a vascular graft.

Unraveling Endothelial Cell Phenotypic Regulation By Spatial Hemodynamic Flows With Microfluidics

“…stents, perfusion systems) that perturb flow profiles experienced by endothelial cells. Strutted stents or grafts are known to induce local disturbed flow that increases the risk of restenosis, thrombosis and neointimal hyperplasia (6), whereas flow helicity has been postulated to reduce flow disturbances and impede atheroprone flow signatures (7)(8)(9). Indeed, specific stents have been used to emulate physiological helical flows (7)(8)(9), and a recent clinical trial has demonstrated improved vessel patency, and therefore the clinical utility of reproducing helical SPF (10).…”

Fluid dynamics in helical geometries with applications for by-pass grafts

“…Starting from thermal [1] and chemical engineering [2] or medical applications [3] requirements, researches are conducted strongly related to process and phenomena optimization. A possibility for swirl flow development is described in the literature by using helical configurations [4]. The main advantage of this kind of geometries is the increase of particle mixing inside the specific zone associated for different applications or heat exchange efficiency, modifying the stagnation point or the particle residence time [1,2,4].…”

“…A possibility for swirl flow development is described in the literature by using helical configurations [4]. The main advantage of this kind of geometries is the increase of particle mixing inside the specific zone associated for different applications or heat exchange efficiency, modifying the stagnation point or the particle residence time [1,2,4].…”

“…straight, S-type, helical) used in by-pass surgery [5,[8][9][10][11]. As presented in the literature, graft patency increases in case of helical grafts [4,5]. Zhan et al [12] suggested that swirling blood flow improve the patency by suppressing acute thrombus formation, whereas Morbiducci et al [7] consider that swirl flow prevent the excessive dissipation of energy by limiting the flow instability in arteries.…”

“…[7] and oscillatory shear index [6]. Ha et al suggest both swirling intensity and helicity, and the Germano number [4]. Local variations of wall shear stress is associated with regions such as branching or bifurcations, where flow velocity and shear stress is reduced and flow departs from unidirectional patterns, favoring atherogenesis, by inducing the vascular response of the endothelium [6,13].…”