Impact of Stents and Flow Diverters on Hemodynamics in Idealized Aneurysm Models

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Santhosh Seshadhri ◽  
Gábor Janiga ◽  
Oliver Beuing ◽  
Martin Skalej ◽  
Dominique Thévenin
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Residence Time ◽  
Exchange Flow ◽  
Invasive Treatment ◽  
Mean Velocity ◽  
Brain Aneurysm ◽  
Geometrical Properties ◽  
Wall Shear ◽  
Flow Diverters

Cerebral aneurysms constitute a major medical challenge as treatment options are limited and often associated with high risks. Statistically, up to 3% of patients with a brain aneurysm may suffer from bleeding for each year of life. Eight percent of all strokes are caused by ruptured aneurysms. In order to prevent this rupture, endovascular stenting using so called flow diverters is increasingly being regarded as an alternative to the established coil occlusion method in minimally invasive treatment. Covering the neck of an aneurysm with a flow diverter has the potential to alter the hemodynamics in such a way as to induce thrombosis within the aneurysm sac, stopping its further growth, preventing its rupture and possibly leading to complete resorption. In the present study the influence of different flow diverters is quantified considering idealized patient configurations, with a spherical sidewall aneurysm placed on either a straight or a curved parent vessel. All important hemodynamic parameters (exchange flow rate, velocity, and wall shear stress) are determined in a quantitative and accurate manner using computational fluid dynamics when varying the key geometrical properties of the aneurysm. All simulations are carried out using an incompressible, Newtonian fluid with steady conditions. As a whole, 72 different cases have been considered in this systematic study. In this manner, it becomes possible to compare the efficiency of different stents and flow diverters as a function of wire density and thickness. The results show that the intra-aneurysmal flow velocity, wall shear stress, mean velocity, and vortex topology can be considerably modified thanks to insertion of a suitable implant. Intra-aneurysmal residence time is found to increase rapidly with decreasing stent porosity. Of the three different implants considered in this study, the one with the highest wire density shows the highest increase of intra-aneurysmal residence time for both the straight and the curved parent vessels. The best hemodynamic modifications are always obtained for a small aneurysm diameter.

Plaque Progression in a Human Coronary Artery is Associated With Low Wall Shear Stress and Extended Particle Residence Time

2010 ◽  
Author(s):  
Jin Suo ◽  
Michael McDaniel ◽  
Parham Eshtehardi ◽  
Saurabh Dhawan ◽  
Ravi Prasad Avati Nanjundappa ◽  
...  
Keyword(s):  
Shear Stress ◽  
Coronary Artery ◽  
Wall Shear Stress ◽  
Residence Time ◽  
Vigorous Physical Activity ◽  
Region Of Interest ◽  
Reconstruction Technique ◽  
Plaque Progression ◽  
Human Coronary Artery ◽  
Wall Shear

Intravascular ultrasound (IVUS) evaluation was performed in the coronary arteries of a 45-year-old patient with stable angina during vigorous physical activity. Concurrent angiography demonstrated a mild plaque in the proximal left anterior descending artery (LAD), with obvious lumen dilatation immediately distal to the plaque. Blood velocity was measured by a catheter Doppler transducer at proximal and distal segments of the left coronary artery, and the left main artery (LM) and LAD were reconstructed using a 3D-IVUS reconstruction technique based on biplanar angiography and IVUS images, enabling simulation of the flow field in the artery employing computational fluid dynamics (CFD). Wall shear stress (WSS) and particle path lines were determined from the CFD studies. The patient returned for a follow up evaluation after 6 months, and plaque progression during this period was evaluated from the IVUS data. Results showed that low WSS, less than 5 dynes/cm2, which occurs in the region immediately distal to the plaque, correlates with localized progression of the lesion over the 6 month interval. The path line tracking computations showed that particles near the vessel surface where plaque progression was observed resided near the artery wall longer than one complete cardiac cycle, whereas in other areas particles were flushed through the region of interest rapidly. These observations in a specific individual are consistent with the hypothesis that plaque progression is related to low WSS and relatively long residence time of atherogenic blood-borne substances.

scholarly journals Fluid-induced wall shear stress in anthropomorphic brain aneurysm models: MR phase-contrast study at 3 T

2007 ◽  
Vol 25 (6) ◽  
pp. 1120-1130 ◽  
Author(s):  
Sinyeob Ahn ◽  
Dongsuk Shin ◽  
Satoshi Tateshima ◽  
Kazuo Tanishita ◽  
Fernando Vinuela ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Phase Contrast ◽  
Contrast Study ◽  
Brain Aneurysm ◽  
Wall Shear

Supplementary Boundary-Layer Approximations for Turbulent Flow

1989 ◽  
Vol 111 (4) ◽  
pp. 420-427 ◽  
Author(s):  
L. C. Thomas ◽  
S. M. F. Hasani
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Boundary Layer Flows ◽  
Mean Velocity ◽  
Wide Range ◽  
The Mean ◽  
Wall Shear

Approximations for total stress τ and mean velocity u are developed in this paper for transpired turbulent boundary layer flows. These supplementary boundary-layer approximations are tested for a wide range of near equilibrium flows and are incorporated into an inner law method for evaluating the mean wall shear stress τ0. The testing of the proposed approximations for τ and u indicates good agreement with well-documented data for moderate rates of blowing and suction and pressure gradient. These evaluations also reveal limitations in the familiar logarithmic law that has traditionally been used in the determination of wall shear stress for non-transpired boundary-layer flows. The calculations for τ0 obtained by the inner law method developed in this paper are found to be consistent with results obtained by the modern Reynolds stress method for a broad range of near equilibrium conditions. However, the use of the proposed inner law method in evaluating the mean wall shear stress for early classic near equilibrium flow brings to question the reliability of the results for τ0 reported for adverse pressure gradient flows in the 1968 Stanford Conference Proceedings.

Near-Wall Measurements in Turbulent Boundary Layers Using Laser Doppler Anemometry

2002 ◽  
Author(s):  
T. Gunnar Johansson ◽  
Luciano Castillo
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Pressure Gradient ◽  
Laser Doppler Anemometry ◽  
Reynolds Numbers ◽  
Mean Velocity ◽  
The Mean ◽  
Wall Shear ◽  
Near Wall

Near wall measurements have been performed in a zero pressure gradient turbulent boundary layer at low to moderate local Reynolds numbers using Laser-Doppler Anemometry in order to investigate how accurately the wall shear stress can be determined. Also, scaling problems are particularly difficult at low Reynolds numbers since they involve simultaneous influences of both inner and outer scales and this is most clearly observed in the near-wall region. In order to fully describe the zero pressure gradient turbulent boundary layer at low to moderate local Reynolds numbers it is necessary to accurately measure a number of quantities. These include the mean velocity and Reynolds stresses, and their spatial derivatives all the way down to the wall (y+∼1). Integral parameters that need to be measured are the wall shear stress and boundary layer thickness, particularly the momentum thickness. Problems with the measurement of field properties get worse close to a wall, and they get worse for increasing local Reynolds number. Three different approaches to measure the wall shear stress were examined. It was found that small measurement errors in the mean velocity close to the wall significantly reduced the accuracy in determining the wall shear stress by measuring the velocity gradient at the wall. The constant stress layer was found to be affected by the advection terms. However, it was found that taking the small pressure gradient into account and improving on the spatial resolution in the outer part of the boundary layer made the momentum integral method reliable.

scholarly journals Numerical insights into the determinants of stent performance for the management of aneurysm with a visceral vessel attached

2021 ◽  
Vol 23 (2) ◽  
Author(s):  
Zhongyou Li ◽  
Chong Chen ◽  
Yu Chen ◽  
Zhenze Wang ◽  
Wentao Jiang ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Pore Size ◽  
Residence Time ◽  
Single Layer ◽  
Oscillatory Shear ◽  
Bending Test ◽  
Oscillatory Shear Index ◽  
Relative Residence Time ◽  
Wall Shear

Purpose: As the factors affecting the efficacy of the bare-metal stent in the treatment of aneurysm with a visceral vessel attached were not fully understood, we aimed to discuss the effects of different characteristics of the stent on the hemodynamics and flexibility in the treatment of the aneurysm. Methods: Single-layer (with different strut widths) and multi-layer (with a different number of struts) stent models divided into three porosity groups, with porosities of 72.3, 60.5, and 52.4%, were modeled for a comparison of their hemodynamic isolation and flexibility performance via computational fluid dynamics and finite element methods. Results: The velocity and timeaveraged wall shear stress decreased more noticeably with multi-layer stent interventions. A higher oscillatory shear index and relative residence time occurred at the aneurysmal sac wall after multi-layer stents were employed. Time-averaged wall shear stress on the aneurysmal wall decreased with an increase in the number of struts or a decrease in pore size, but oscillatory shear index and relative residence time increased as the number of struts increased or the pore size decreased. Besides, all stents affect the branch patency slightly. In the bending test, when the porosity exceeded 60.5%, multi-layer stents were more flexible. Conclusion: The number of struts or pore size of stent dominated the isolation in the management of the aneurysm and affected the flexibility significantly when the porosity was below 60.5%. These findings may contribute to the special design of the stent in the treatment of such types of aneurysms.

Wall shear stress determination from near-wall mean velocity data in turbulent pipe and channel flows

1996 ◽  
Vol 20 (6) ◽  
pp. 417-428 ◽  
Author(s):  
F. Durst ◽  
H. Kikura ◽  
I. Lekakis ◽  
J. Jovanović ◽  
Q. Ye
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Channel Flows ◽  
Stress Determination ◽  
Velocity Data ◽  
Mean Velocity ◽  
Wall Shear ◽  
Near Wall

Direct numerical simulations of turbulent flows over superhydrophobic surfaces

2009 ◽  
Vol 620 ◽  
pp. 31-41 ◽  
Author(s):  
MICHAEL B. MARTELL ◽  
J. BLAIR PEROT ◽  
JONATHAN P. ROTHSTEIN
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Numerical Simulations ◽  
Slip Velocity ◽  
Direct Numerical Simulations ◽  
Superhydrophobic Surfaces ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Wall Shear

Direct numerical simulations (DNSs) are used to investigate the drag-reducing performance of superhydrophobic surfaces (SHSs) in turbulent channel flow. SHSs combine surface roughness with hydrophobicity and can, in some cases, support a shear-free air–water interface. Slip velocities, wall shear stresses and Reynolds stresses are considered for a variety of SHS microfeature geometry configurations at a friction Reynolds number of Reτ ≈ 180. For the largest microfeature spacing studied, an average slip velocity over 75% of the bulk velocity is obtained, and the wall shear stress reduction is found to be nearly 40%. The simulation results suggest that the mean velocity profile near the superhydrophobic wall continues to scale with the wall shear stress but is offset by a slip velocity that increases with increasing microfeature spacing.

scholarly journals Phase Averaged Wall Shear Stress, Wall Pressure and Near Wall Velocity Field Measurements in a Whirling Annular Seal

1995 ◽  
Author(s):  
Gerald L. Morrison ◽  
Robert B. Winslow ◽  
H. Davis Thames
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Field Measurements ◽  
Wall Pressure ◽  
Mean Velocity ◽  
Annular Seal ◽  
Mean Pressure ◽  
Wall Shear ◽  
Anemometer System ◽  
Velocity Turbulence

The flow field inside a 50% eccentric whirling annular seal operating at a Reynolds number of 24,000 and a Taylor number of 6,600 has been measured using a 3-D laser Doppler anemometer system. Flush mount pressure and wall shear stress probes have been used to measure the stresses (normal and shear) along the length of the stator. The rotor was mounted eccentrically on the shaft so that the rotor orbit was circular and rotated at the same speed as the shaft (a whirl ratio of 1.0). This paper presents mean pressure, mean wall shear stress magnitude and mean wall shear stress direction distributions along the length of the seal. Phase averaged wall pressure and wall shear stress are presented along with phase averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure and wall shear stress are very complex and do not follow simple bulk flow predictions.

Sign in / Sign up

Export Citation Format

Share Document