Cyclic flow characteristics in an idealized asymmetric abdominal aortic aneurysm model

2003 ◽  
Vol 217 (1) ◽  
pp. 27-39 ◽  
Author(s):  
T H Yip ◽  
S C M Yu
Keyword(s):  
Shear Stress ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Flow Characteristics ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Cyclic Flow ◽  
Turbulent Shear Stress ◽  
Abdominal Aortic ◽  
Flow Cycle

The flow characteristics and the corresponding hydrodynamic stability in an idealized asymmetric abdominal aortic aneurysm (AAA) model have been investigated using a laser Doppler anemometer. A rectified sine waveform was used to simulate aortic flow conditions (Reδ = 806 and α = 12.2). The flow around the distal neck of the AAA model undergoes transition and becomes turbulent for a fraction of time shortly after the commencement of the deceleration phases at every flow cycle while the rest of the flow inside the model stayed laminar throughout the cycle. As a result of non-symmetric vortical structure development inside the model, the distribution of turbulent shear stresses was found to be highly uneven along the radial direction of the model; this is in contrast to results found by the present authors in the symmetrical AAA model. The maximum turbulent shear stress found at the straight side of the distal neck are four times more than the maximum turbulent shear stress measured at the most dilated side of the distal neck. One of the interesting biological implications of the results is that the outward dilation of the arterial wall may be a physiological response to avoid the high turbulent shear load from the momentarily turbulent blood flow.

scholarly journals Comprehensive mechanical & metabolic imaging of abdominal aortic aneurysm with 4D flow/ FDG PET on an integrated PETMRI: a feasibility study

2021 ◽  
Vol 22 (Supplement_3) ◽  
Author(s):  
S Wan ◽  
J Steeden ◽  
M Rega ◽  
L Hoy ◽  
D Walls ◽  
...  
Keyword(s):  
Shear Stress ◽  
Abdominal Aortic Aneurysm ◽  
Image Quality ◽  
Aortic Aneurysm ◽  
Wall Shear Stress ◽  
Fdg Pet ◽  
Metabolic Imaging ◽  
Research Centre ◽  
Abdominal Aortic ◽  
Wall Shear

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): NIHR Biomedical Research Centre, University College London Hospitals. Background A number of non-invasive imaging derived parameters have been implicated in the development and progression of abdominal aortic aneurysm, although the mechanism, and relationships of many of these are yet to be precisely determined.  Mechanical parameters can now be studied using 4D phase contrast magnetic resonance (PCMR), and inflammatory cellular activity can be detected with FDG PET. Purpose It may be postulated that inflammation of the aortic wall may be the intermediary at the tissue level linking mechanical wall shear stress (WSS) to aneurysm progression. It may be feasible to study 4D PCMR and FDG PET at the same patient visit on a PETMRI platform, with the potential to enhance temporal and spatial co-registration and improving the understanding of any relationship between these two parameters.  Our study aims to assess feasibility of studying these on an integrated PETMRI system. Methods 7 patients with known aortic aneurysm were recruited in a vascular ultrasound screening follow up clinic.  During a single visit following 6 hours fasting, all patients underwent FDG injection and 60 minutes uptake period.  With quiet breathing, list mode PET acquisition and concurrent 4D PCMR was acquired using stacks of spiral acquisition, with ECG trace information for retrospective gating.  Images from the 4D PCMR and FDG PET were assessed qualitatively for image quality and visual matching. Results All 7 patients completed the study.  Overall image quality was adequate to good.  There is qualitatively a good concordance with impression of positive correlation between wall shear stress and inflammatory signal (see attached image). Conclusion We have demonstrated feasibility of combined assessment of mechanical and metabolic imaging parameters using an integrated PETMRI system.  Initial findings show there to be a broad concordance of wall shear stress and inflammatory signal in the abdominal aneurysm.

scholarly journals Combining Volumetric and Wall Shear Stress Analysis from CT to Assess Risk of Abdominal Aortic Aneurysm Progression

Radiology ◽  
2020 ◽  
Vol 295 (3) ◽  
pp. 722-729
Author(s):  
Olivier Meyrignac ◽  
Laurence Bal ◽  
Charline Zadro ◽  
Adrien Vavasseur ◽  
Anou Sewonu ◽  
...  
Keyword(s):  
Shear Stress ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Shear Stress ◽  
Stress Analysis ◽  
Abdominal Aortic ◽  
Wall Shear

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.

Low Shear Stress at Baseline Predicts Expansion and Aneurysm-Related Events in Patients With Abdominal Aortic Aneurysm

2021 ◽  
Author(s):  
Nikhilesh Bappoo ◽  
Maaz B.J. Syed ◽  
Georgia Khinsoe ◽  
Lachlan J. Kelsey ◽  
Rachael O. Forsythe ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Shear Stress ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Computed Tomography Angiography ◽  
Interquartile Range ◽  
Expansion Rate ◽  
Abdominal Aortic ◽  
Low Shear Stress ◽  
Low Shear

Background: Low shear stress has been implicated in abdominal aortic aneurysm (AAA) expansion and clinical events. We tested the hypothesis that low shear stress in AAA at baseline is a marker of expansion rate and future aneurysm-related events. Methods: Patients were imaged with computed tomography angiography at baseline and followed up every 6 months >24 months with ultrasound measurements of maximum diameter. From baseline computed tomography angiography, we reconstructed 3-dimensional models for automated computational fluid dynamics simulations and computed luminal shear stress. The primary composite end point was aneurysm repair and/or rupture, and the secondary end point was aneurysm expansion rate. Results: We included 295 patients with median AAA diameter of 49 mm (interquartile range, 43–54 mm) and median follow-up of 914 (interquartile range, 670–1112) days. There were 114 (39%) aneurysm-related events, with 13 AAA ruptures and 98 repairs (one rupture was repaired). Patients with low shear stress (<0.4 Pa) experienced a higher number of aneurysm-related events (44%) compared with medium (0.4–0.6 Pa; 27%) and high (>0.6 Pa; 29%) shear stress groups ( P =0.010). This association was independent of known risk factors (adjusted hazard ratio, 1.72 [95% CI, 1.08–2.73]; P =0.023). Low shear stress was also independently associated with AAA expansion rate (β=+0.28 mm/y [95% CI, 0.02–0.53]; P =0.037). Conclusions: We show for the first time that low shear stress (<0.4 Pa) at baseline is associated with both AAA expansion and future aneurysm-related events. Aneurysms within the lowest tertile of shear stress, versus those with higher shear stress, were more likely to rupture or reach thresholds for elective repair. Larger prospective validation trials are needed to confirm these findings and translate them into clinical management.

scholarly journals Hemodynamic Study of Flow Remodeling Stent Graft for the Treatment of Highly Angulated Abdominal Aortic Aneurysm

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Siang Lin Yeow ◽  
Hwa Liang Leo
Keyword(s):  
Shear Stress ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Shear Stress ◽  
Stent Graft ◽  
Thrombus Formation ◽  
Flow Recirculation ◽  
Aortic Neck ◽  
Abdominal Aortic ◽  
Wall Shear

This study investigates the effect of a novel flow remodeling stent graft (FRSG) on the hemodynamic characteristics in highly angulated abdominal aortic aneurysm based on computational fluid dynamics (CFD) approach. An idealized aortic aneurysm with varying aortic neck angulations was constructed and CFD simulations were performed on nonstented models and stented models with FRSG. The influence of FRSG intervention on the hemodynamic performance is analyzed and compared in terms of flow patterns, wall shear stress (WSS), and pressure distribution in the aneurysm. The findings showed that aortic neck angulations significantly influence the velocity flow field in nonstented models, with larger angulations shifting the mainstream blood flow towards the center of the aorta. By introducing FRSG treatment into the aneurysm, erratic flow recirculation pattern in the aneurysm sac diminishes while the average velocity magnitude in the aneurysm sac was reduced in the range of 39% to 53%. FRSG intervention protects the aneurysm against the impacts of high velocity concentrated flow and decreases wall shear stress by more than 50%. The simulation results highlighted that FRSG may effectively treat aneurysm with high aortic neck angulations via the mechanism of promoting thrombus formation and subsequently led to the resorption of the aneurysm.

scholarly journals Imaging Predictive Factors of Abdominal Aortic Aneurysm Growth

2021 ◽  
Vol 10 (9) ◽  
pp. 1917
Author(s):  
Petroula Nana ◽  
Konstantinos Spanos ◽  
Konstantinos Dakis ◽  
Alexandros Brodis ◽  
George Kouvelos
Keyword(s):  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Flow Characteristics ◽  
Wall Stress ◽  
Background Variable ◽  
Factors Associated ◽  
Initial Diameter ◽  
Abdominal Aortic ◽  
Newcastle Ottawa Scale ◽  
Diagnostic Modalities

Background: Variable imaging methods may add important information about abdominal aortic aneurysm (AAA) progression. The aim of this study is to assess available literature data regarding the predictive imaging factors of AAA growth. Methods: This systematic review was conducted using the PRISMA guidelines. A review of the literature was conducted, using PubMed, EMBASE and CENTRAL databases. The quality of the studies was assessed using the Newcastle-Ottawa Scale. Primary outcomes were defined as AAA growth rate and factors associated to sac expansion. Results: The analysis included 23 studies. All patients (2244; mean age; 69.8 years, males; 85%) underwent imaging with different modalities; the initial evaluation was followed by one or more studies to assess aortic expansion. AAA initial diameter was reported in 13 studies (range 19.9–50.9 mm). Mean follow-up was 34.5 months. AAA diameter at the end was ranging between 20.3 and 55 mm. The initial diameter and intraluminal thrombus were characterized as prognostic factors associated to aneurysm expansion. A negative association between atherosclerosis and AAA expansion was documented. Conclusions: Aneurysm diameter is the most studied factor to be associated with expansion and the main indication for intervention. Appropriate diagnostic modalities may account for different anatomical characteristics and identify aneurysms with rapid growth and higher rupture risk. Future perspectives, including computed mathematical models that will assess wall stress and elasticity and further flow characteristics, may offer valuable alternatives in AAA growth prediction.

Steady Flow in Abdominal Aortic Aneurysm Models

1993 ◽  
Vol 115 (4A) ◽  
pp. 418-423 ◽  
Author(s):  
R. Budwig ◽  
D. Elger ◽  
H. Hooper ◽  
J. Slippy
Keyword(s):  
Shear Stress ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Laminar Flow ◽  
Wall Shear Stress ◽  
Steady Flow ◽  
Recirculation Zone ◽  
Abdominal Aortic ◽  
Onset Of Turbulence ◽  
Wall Shear

Steady flow in abdominal aortic aneurysm models has been examined for four aneurysm sizes over Reynolds numbers from 500 to 2600. The Reynolds number is based on entrance tube diameter, and the inlet condition is fully developed flow. Experimental and numerical methods have been used to determine: (i) the overall features of the flow, (ii) the stresses on the aneurysm walls in laminar flow, and (iii) the onset and characteristics of turbulent flow. The laminar flow field is characterized by a jet of fluid (passing directly through the aneurysm) surrounded by a recirculating vortex. The wall shear stress magnitude in the recirculation zone is about ten times less than in the entrance tube. Both wall shear stress and wall normal stress profiles exhibit large magnitude peaks near the reattachment point at the distal end of the aneurysm. The onset of turbulence in the model is intermittent for 2000 < Re < 2500. The results demonstrate that a slug of turbulence in the entrance tube grows much more rapidly in the aneurysm than in a corresponding length of uniform cross section pipe. When turbulence is present in the aneurysm the recirculation zone breaks down and the wall shear stress returns to a magnitude comparable to that in the entrance tube.

Sign in / Sign up

Export Citation Format

Share Document