Numerical Study of Purely Viscous Non-Newtonian Flow in an Abdominal Aortic Aneurysm

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
Victor L. Marrero ◽  
John A. Tichy ◽  
Onkar Sahni ◽  
Kenneth E. Jansen
Keyword(s):  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Shear Rate ◽  
Aortic Aneurysm ◽  
Computational Techniques ◽  
Newtonian Viscosity ◽  
Viscosity Models ◽  
Newtonian Model ◽  
Abdominal Aortic ◽  
Newtonian Case

It is well known that blood has non-Newtonian properties, but it is generally accepted that blood behaves as a Newtonian fluid at shear rates above 100 s−1. However, in transient conditions, there are times and locations where the shear rate is well below 100 s−1, and it is reasonable to infer that non-Newtonian effects could become important. In this study, purely viscous non-Newtonian (generalized Newtonian) properties of blood are incorporated into the simulation-based framework for cardiovascular surgery planning developed by Taylor et al. (1999, “Predictive Medicine: Computational Techniques in Therapeutic Decision Making,” Comput. Aided Surg., 4, pp. 231–247; 1998, “Finite Element Modeling of Blood Flow in Arteries,” Comput. Methods Appl. Mech. Eng., 158, pp. 155–196). Equations describing blood flow are solved in a patient-based abdominal aortic aneurysm model under steady and physiological flow conditions. Direct numerical simulation (DNS) is used, and the complex flow is found to be constantly transitioning between laminar and turbulent in both the spatial and temporal sense. It is found for the case simulated that using the non-Newtonian viscosity modifies the solution in subtle ways that yield a mesh-independent solution with fewer degrees of freedom than the Newtonian counterpart. It appears that in regions of separated flow, the lower shear rate produces higher viscosity with the non-Newtonian model, which reduces the associated resolution needs. When considering the real case of pulsatile flow, high shear layers lead to greater unsteadiness in the Newtonian case relative to the non-Newtonian case. This, in turn, results in a tendency for the non-Newtonian model to need fewer computational resources even though it has to perform additional calculations for the viscosity. It is also shown that both viscosity models predict comparable wall shear stress distribution. This work suggests that the use of a non-Newtonian viscosity models may be attractive to solve cardiovascular flows since it can provide simulation results that are presumably physically more realistic with at least comparable computational effort for a given level of accuracy.

scholarly journals Alterations of blood flow pattern after triple stent endovascular treatment of saccular abdominal aortic aneurysm: a porcine model.

2016 ◽  
Vol 43 (3) ◽  
pp. 154-159
Author(s):  
JAHIR RICHARD DE OLIVEIRA ◽  
MAURÍCIO DE AMORIM AQUINO ◽  
SVETLANA BARROS ◽  
GUILHERME BENJAMIN BRANDÃO PITTA ◽  
ADAMASTOR HUMBERTO PEREIRA
Keyword(s):  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Endovascular Treatment ◽  
Flow Pattern ◽  
Blood Flow Pattern ◽  
Large White ◽  
Abdominal Aortic ◽  
Before And After ◽  
Infrarenal Abdominal Aorta

ABSTRACT Objective: to determine the blood flow pattern changes after endovascular treatment of saccular abdominal aortic aneurysm with triple stent. Methods: we conducted a hemodynamic study of seven Landrace and Large White pigs with saccular aneurysms of the infrarenal abdominal aorta artificially produced according to the technique described. The animals were subjected to triple stenting for endovascular aneurysm. We evaluated the pattern of blood flow by duplex scan before and after stent implantation. We used the non-paired Mann-Whitney test for statistical analysis. Results: there was a significant decrease in the average systolic velocity, from 127.4cm/s in the pre-stent period to 69.81cm/s in the post-stent phase. There was also change in the flow pattern from turbulent in the aneurysmal sac to laminate intra-stent. Conclusion: there were changes in the blood flow pattern of saccular abdominal aortic aneurysm after endovascular treatment with triple stent.

Computational Modeling of the Effects of Transient Blood Flow Characteristics and Wall Thickness on the Rupture of Abdominal Aortic Aneurysm

2014 ◽  
Author(s):  
Pinaki Pal
Keyword(s):  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Thickness ◽  
Flow Model ◽  
Wall Stress ◽  
Flow Transition ◽  
Abdominal Aortic ◽  
Sst Model ◽  
Peak Wall Stress

Precise estimation of wall stress distribution within an abdominal aortic aneurysm (AAA) is clinically useful for prediction of its rupture. In this paper a computational fluid dynamic model incorporating two-way coupled fluid-structure interaction is employed to investigate the role of laminar-turbulent flow transition and wall thickness in altering the distribution and magnitude of wall stress in an AAA. Blood flow in axially symmetric aneurysm models governed by a compliant wall mechanics was simulated. Menter’s hybrid k-epsilon/k-omega shear stress transport (SST) model with a correlation-based transition model was used to capture laminar-turbulent transition in the blood flow. Realistic physiological transient boundary conditions were prescribed. The numerical model was validated against experimental data available from the literature. Fluid flow analysis showed the formation of recirculating vortices at the proximal end of the aneurysm after the peak systole which then, moved towards the distal end of the aneurysm along with the bulk flow and were dissipated eventually due to viscous effects. These vortices interacted with the aortic wall and led to local pressure rise. Von Mises stress distribution on the aneurysm wall and location of its peak value were computed and compared with those of a separate numerical simulation performed using a laminar viscous flow model. The predicted peak wall stress was found to be significantly higher for the SST model as compared to the laminar flow model. The location of maximum stress shifted more towards the posterior end of the aneurysm when laminar-turbulent flow transition was considered. In addition, a small reduction of 0.4 mm in wall thickness resulted in the elevation of peak wall stress by a factor of 1.4. The present study showed that capturing flow transition in an AAA is essential to accurate prediction of its rupture. The proposed numerical model provides a robust computational framework to gain more insight into AAA biomechanics and to accurately estimate wall stresses in realistic aneurysm configurations.

Three-Dimensional Simulation of Blood Flow in an Abdominal Aortic Aneurysm—Steady and Unsteady Flow Cases

1994 ◽  
Vol 116 (1) ◽  
pp. 89-97 ◽  
Author(s):  
Tad W. Taylor ◽  
Takami Yamaguchi
Keyword(s):  
High Pressure ◽  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Unsteady Flow ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Abdominal Aortic ◽  
Flow Cycle ◽  
Flow Case

Atherosclerosis and atherosclerotic aneurysms can occur in the abdominal aorta. Steady and unsteady three-dimensional flow cases were simulated in abdominal aortic aneurysm using a flow simulation package on a graphics workstation. In the steady case, three aneurysm models of 8.0 cm length were simulated using Reynolds numbers of 350 and 700. In the unsteady case, blood flow in a single asymmetric aneurysm of 8.0 cm length was simulated at Reynolds numbers of 350 and 700 and 1400. In the aneurysm center, two symmetric vortices were formed, and flow separation started at the aneurysm inlet. In the unsteady flow case, the main vortex appeared and disappeared and changed position in the unsteady flow case and induced vortices were formed. Although the centerline view shows the vortices change position with time, cross-sectional views show that two symmetric vortices are present or partially formed throughout the entire flow cycle. Regions of high pressure were observed at the aneurysm exit caused by the symmetric vortices that were formed, implying that this high-pressure region could be an area where rupture is most likely. In the unsteady case, regions of maximum pressure moved depending on the flow cycle time; at peak flow, local pressure maximums were observed at the distal aneurysm; these oscillated, tending to put an additional strain on the distal portion of the aneurysm. The shear stress was low in the aneurysm portion of the vessel, and local maximum values were observed at the distal aneurysm constriction.

The blood flow channel index as novel predictor of abdominal aortic aneurysm impending rupture based on the intraluminal thrombus angio-CT study

2015 ◽  
Vol 84 (4) ◽  
pp. 662-667 ◽  
Author(s):  
Ireneusz Wiernicki ◽  
Pawel Szumilowicz ◽  
Arkadiusz Kazimierczak ◽  
Aleksander Falkowski ◽  
Donald Rutkowski ◽  
...  
Keyword(s):  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Flow Channel ◽  
Intraluminal Thrombus ◽  
Impending Rupture ◽  
Abdominal Aortic ◽  
Angio Ct

Volumetric Flow at the Supraceliac and Infrarenal Levels in Patients With Abdominal Aortic Aneurysm: Waveforms and Allometric Scaling Relationships

2009 ◽  
Author(s):  
Andrea S. Les ◽  
Janice J. Yeung ◽  
Phillip M. Young ◽  
Robert J. Herfkens ◽  
Ronald L. Dalman ◽  
...  
Keyword(s):  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Boundary Conditions ◽  
Computational Simulation ◽  
Critical Role ◽  
Healthy Person ◽  
Patient Specific ◽  
Hemodynamic Forces ◽  
Abdominal Aortic

Hemodynamic forces are thought to play a critical role in abdominal aortic aneurysm (AAA) formation and growth, as well as in the migration and failure of aortic stent grafts. Computational simulation of blood flow enables the study of such hemodynamic forces; however, these simulations require accurate geometries and boundary conditions, usually in the form of flow and pressure data at specific locations. Although hundreds of computed tomography (CT) and magnetic resonance (MR) imaging studies of AAA geometry are performed daily in the clinical setting, flow information is difficult to obtain: It is not possible to reliably measure flow using CT, and while phase-contrast MRI (PC-MRI) can measure velocities, it is rarely used clinically for AAA patients. As a result, many AAA blood flow simulations use highly resolved patient-specific geometries, but may utilize literature-derived flows for inlet boundary conditions from a single, unrelated, sometimes healthy person of dissimilar body mass.

“Silent” thrombosis of an abdominal aortic aneurysm not producing acute limb ischemia

VASA ◽  
2010 ◽  
Vol 39 (3) ◽  
pp. 265-267 ◽  
Author(s):  
Moulakakis ◽  
Maras ◽  
Bountouris ◽  
Pomoni ◽  
Georgakis ◽  
...  
Keyword(s):  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Mortality Rate ◽  
Aortic Aneurysm ◽  
Acute Pain ◽  
Limb Ischemia ◽  
Lower Limbs ◽  
Acute Limb Ischemia ◽  
Abdominal Aortic ◽  
Flow Through

Thrombosis of an abdominal aortic aneurysm is a rare devastating complication with an estimated mortality rate of 50%. Simultaneous acute pain, pallor and coldness of the lower limbs, mottling from the level of iliac crests or umbilicus, paraplegia and absence of femoral pulses are all manifestations of a sudden and acute interruption of blood flow through the aneurysmatic aorta. We report a case of an occlusion of an abdominal aortic aneurysm during hospitalization which was not manifested with symptoms of limb ischemia. In this case we feature the rare and unusually “silent” presentation of the event.

Dynamic simulation and Doppler Ultrasonography validation of blood flow behavior in Abdominal Aortic Aneurysm

2017 ◽  
Vol 37 ◽  
pp. 1-8 ◽  
Author(s):  
Cristian C. Botar ◽  
Árpád Á. Tóth ◽  
Olivera R. Klisurić ◽  
Dijana D. Nićiforović ◽  
Viktorija A. Vučaj Ćirilović ◽  
...  
Keyword(s):  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Dynamic Simulation ◽  
Doppler Ultrasonography ◽  
Flow Behavior ◽  
Abdominal Aortic

Elevated Renal Oxygen Extraction During Open Abdominal Aortic Aneurysm Repair Is Related to Postoperative Renal Dysfunction

2018 ◽  
Vol 22 (4) ◽  
pp. 369-375 ◽  
Author(s):  
Niels Damkjær Olesen ◽  
Thomas Bech Jørgensen ◽  
Jonas Eiberg ◽  
Ulf Johan Vilhelm Helgstrand ◽  
Henrik Hegaard Sillesen ◽  
...  
Keyword(s):  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Frontal Lobe ◽  
Abdominal Aortic Aneurysm Repair ◽  
Oxygen Extraction ◽  
Abdominal Aortic ◽  
Aneurysm Repair ◽  
Aortic Aneurysm Repair ◽  
Renal Oxygen

Background. Open abdominal aortic aneurysm repair is often followed by elevated plasma creatinine, likely due to impaired renal blood flow. We evaluated whether postoperative elevation in creatinine relates to renal oxygen extraction during surgery as an index of renal blood flow and also monitored frontal lobe oxygenation. Methods. For 19 patients (66 ± 10 years; mean ± SD) undergoing open infrarenal abdominal aortic aneurysm repair, renal oxygen extraction was determined by arterial and renal vein catheterization. Near-infrared spectroscopy determined frontal lobe oxygenation. Results. During surgery mean arterial pressure (from 102 ± 14 to 65 ± 11 mm Hg; P < .0001), arterial hemoglobin (from 7.7 ± 0.7 to 6.6 ± 0.8 mmol/L; P < 0.0001), and frontal lobe oxygenation (from 74 ± 6% to 70 ± 6%; P = .0414) decreased, while renal oxygen extraction increased (from 5.3% [4.3-8.1]; median [interquartile range] to 10.8% [5.8-17.5]; P = .0405). Plasma creatinine became significantly elevated on the second day after the operation (from 83 [73-101] to 105 µmol/L [79-143]; P = .0062) with a peak increase observed after 2 days (1-2). The peak increase in creatinine correlated to intraoperative renal oxygen extraction ( r = 0.51; P = .026). Conclusion. Kidney function was affected after open abdominal aortic aneurysm repair likely related to limited renal blood flow. We take the increase in renal oxygen extraction and reduction in frontal lobe oxygenation to suggest that mean arterial pressure and hemoglobin were too low to maintain renal and cerebral circulation in vascular surgical patients.

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