scholarly journals Computational Fluid Dynamics Modeling of Redundant Stent-Graft Configurations in Endovascular Aneurysm Repair

2010 ◽  
Author(s):  
Leonard W. Tse ◽  
Tina L. T. Shek ◽  
Aydin Nabovati ◽  
Cristina H. Amon
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Blood Flow ◽  
Steady State ◽  
Stent Graft ◽  
Endovascular Aneurysm Repair ◽  
Clinical Consequence ◽  
Dynamics Modeling ◽  
Aneurysm Wall ◽  
Aneurysm Repair

An aneurysm is a bulge or localized dilation of an artery that can result in rupture, rapid blood loss, and death. Endovascular aneurysm repair (EVAR) is a minimally-invasive surgical technique that involves delivery of a stent-graft from within the blood vessels. The metallic stents anchor and support the graft (fabric tube), through which blood flow is contained and directed. This relieves the pressure on the weakened aneurysm wall. When the stent-graft is too long for a given patient, the redundant (extra) length adopts a convex configuration in the aneurysm. Based on clinical experience, we hypothesize that redundant stent-graft configurations increase the downward force acting on the device thereby increasing the risk of device dislodgement and failure. This work numerically studies both steady-state and physiologic pulsatile blood flow in redundant stent-graft configurations. Computational fluid dynamics simulations predicted peak downward displacement force for the zero-, moderate- and severe-redundancy configurations of 7.49, 7.65 and 8.04 N, respectively for steady-state flow; and 7.55, 7.70 and 8.31 N, respectively for physiologic pulsatile flow. These results suggest that redundant stent-graft configurations in EVAR do increase the downward force acting on the device, but the clinical consequence depends significantly on device-specific resistance to dislodgement.

Computational Fluid Dynamics Evaluation of the Cross-Limb Stent Graft Configuration for Endovascular Aneurysm Repair

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Tina L. T. Shek ◽  
Leonard W. Tse ◽  
Aydin Nabovati ◽  
Cristina H. Amon
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Stent Graft ◽  
Endovascular Aneurysm Repair ◽  
Planar Geometry ◽  
Short Term ◽  
Out Of Plane ◽  
Transient Simulations ◽  
The Cross ◽  
Aneurysm Repair

The technique of crossing the limbs of bifurcated modular stent grafts for endovascular aneurysm repair (EVAR) is often employed in the face of splayed aortic bifurcations to facilitate cannulation and prevent device kinking. However, little has been reported about the implications of cross-limb EVAR, especially in comparison to conventional EVAR. Previous computational fluid dynamics studies of conventional EVAR grafts have mostly utilized simplified planar stent graft geometries. We herein examined the differences between conventional and cross-limb EVAR by comparing their hemodynamic flow fields (i.e., in the “direct” and “cross” configurations, respectively). We also added a “planar” configuration, which is commonly found in the literature, to identify how well this configuration compares to out-of-plane stent graft configurations from a hemodynamic perspective. A representative patient’s cross-limb stent graft geometry was segmented using computed tomography imaging in Mimics software. The cross-limb graft geometry was used to build its direct and planar counterparts in SolidWorks. Physiologic velocity and mass flow boundary conditions and blood properties were implemented for steady-state and pulsatile transient simulations in ANSYS CFX. Displacement forces, wall shear stress (WSS), and oscillatory shear index (OSI) were all comparable between the direct and cross configurations, whereas the planar geometry yielded very different predictions of hemodynamics compared to the out-of-plane stent graft configurations, particularly for displacement forces. This single-patient study suggests that the short-term hemodynamics involved in crossing the limbs is as safe as conventional EVAR. Higher helicity and improved WSS distribution of the cross-limb configuration suggest improved flow-related thrombosis resistance in the short term. However, there may be long-term fatigue implications to stent graft use in the cross configuration when compared to the direct configuration.

Push-Up Technique and Anatomical Deployment With the Endurant Stent-Graft System for Severely Angulated Aneurysm Necks

2017 ◽  
Vol 24 (3) ◽  
pp. 435-439 ◽  
Author(s):  
Shizuyuki Dohi ◽  
Yasutaka Yokoyama ◽  
Taira Yamamoto ◽  
Kenji Kuwaki ◽  
Akifusa Hariya ◽  
...  
Keyword(s):  
Blood Flow ◽  
Stent Graft ◽  
Endovascular Aneurysm Repair ◽  
Stent Deployment ◽  
Proximal Neck ◽  
Aneurysm Repair ◽  
Angulated Neck ◽  
Stent Graft Implantation ◽  
Graft Implantation ◽  
Push Up

Purpose: To describe a technique suitable for treating severely angulated (>75°) necks during endovascular aneurysm repair using the Endurant stent-graft. Technique: In the push-up technique, the suprarenal stent is released early to fix the proximal stent-graft in place so that each stent in the neck can be deployed individually without displacing the device upward. It is important to push the delivery system up after each stent deployment to allow the fabric between the stents to fold up circumferentially. By doing so, there is minimal upward force applied to the suprarenal stent. Because the stents expand along the angulated neck while catching blood flow, this anatomical deployment is feasible, with hardly any change to the proximal neck shape after stent-graft implantation. Conclusion: The push-up technique and anatomical deployment with the Endurant stent-graft system are effective and safe methods for treating aneurysms with severely angulated necks.

Computational Fluid Dynamics Modeling on Steady-State Friction Stir Welding of Aluminum Alloy 6061 to TRIP Steel

2016 ◽  
Vol 139 (5) ◽  
Author(s):  
Xun Liu ◽  
Gaoqiang Chen ◽  
Jun Ni ◽  
Zhili Feng
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Steady State ◽  
Friction Stir Welding ◽  
Steel Strip ◽  
Thermal Response ◽  
Physical And Mechanical Properties ◽  
Dynamics Modeling ◽  
Friction Stir ◽  
Computational Fluid Dynamics Analysis

A coupled thermal–mechanical model based on the Eulerian formulation is developed for the steady-state dissimilar friction stir welding (FSW) process. Multiple phase flow theories are adopted in deriving analytical formulations, which are further implemented into the fluent software for computational fluid dynamics analysis. A shear stress boundary at the tool/workpiece interface yields a much more reasonable material distribution compared with a velocity boundary condition when the involved two materials have quite different physical and mechanical properties. The model can capture the feature of embedded steel strip in aluminum side, as observed in weld cross sections from experiments. For further evaluation, the calculated flow and thermal response are compared with experimental results in three welding conditions, which generally show good agreements.

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