Computational Study on the Effects of Peripheral Vessel Network on Blood Flow in the Arterial Circle of Willis

2007 ◽  
Author(s):  
Shigefumi Tokuda ◽  
Takeshi Unemura ◽  
Marie Oshima
Keyword(s):  
Numerical Simulation ◽  
Blood Flow ◽  
Boundary Conditions ◽  
Vascular System ◽  
Computational Study ◽  
Circulatory System ◽  
Biological Data ◽  
Patient Specific ◽  
Peripheral Vessel

Cerebrovascular disorder such as subarachnoid hemorrhage (SAH) is 3rd position of the cause of death in Japan [1]. Its initiation and growth are reported to depend on hemodynamic factors, particularly on wall shear stress or blood pressure induced by blood flow. In order to investigate the information on the hemodynamic quantities in the cerebral vascular system, the authors have been developing a computational tool using patient-specific modeling and numerical simulation [2]. In order to achieve an in vivo simulation of living organisms, it is important to apply appropriate physiological conditions such as physical properties, models, and boundary conditions. Generally, the numerical simulation using a patient-specific model is conducted for a localized region near the research target. Although the analysis region is only a part of the circulatory system, the simulation has to include the effects from the entire circulatory system. Many studies have carried out to derive the boundary conditions to model in vivo environment [3–5]. However, it is not easy to obtain the biological data of cerebral arteries due to head capsule.

On the Use of In Vivo Measured Flow Rates as Boundary Conditions for Image-Based Hemodynamic Models of the Human Aorta

2011 ◽  
Author(s):  
Diego Gallo ◽  
Gianluca De Santis ◽  
Federica Negri ◽  
Daniele Tresoldi ◽  
Giovanna Rizzo ◽  
...  
Keyword(s):  
Blood Flow ◽  
Boundary Conditions ◽  
Rigid Wall ◽  
Patient Specific ◽  
Human Aorta ◽  
Computational Domain ◽  
Healthy Human ◽  
Flow Rates ◽  
Measured Flow

It has been demonstrated that computational fluid dynamics (CFD) have the potential to enhance the comprehension of the role played by hemodynamic factors involved in atherosclerosis. Recently, phase-contrast magnetic resonance imaging (PC-MRI) has emerged as an effective tool for providing accurate vascular geometries for CFD simulations and quantitative data on blood flow rates, which can be used to specify realistic boundary conditions (BCs). However, the application of acquired flow waveforms at boundaries is not straightforward, mainly (i) due to possible occurrences of phase shifts and attenuations of outflow with respect to inflow rate and (ii) due to the instantaneous mass conservation constraint, which is required in hemodynamic simulations with rigid wall models, but is not guaranteed in in vivo measurements. As an alternative, new boundary conditions schemes have been developed in an effort to consider the interaction between the computational domain and the upstream/downstream vasculature by coupling through-scale hemodynamic models [1]. However, the identification of the parameters of these simplified vascular models on a subject-specific base involves both pressure and flow rates measurements [2]. In this context, it is clear that the direct application of individual PC-MRI measured flow rates waveforms as BCs in patient-specific simulations should be preferred [3]. In order to overcome the limitations mentioned above, measured flow rates should be combined with stress-free conditions or fixed mass flow ratio (derived from the same set of PC-MRI data) between inlet and multiple outlet sections. However, prescribing different BCs at boundaries can affect the solutions of the equations governing blood flow [1]. For this reason, different strategies in combining outlet BCs could lead to different simulated hemodynamics. This work analyzes the influence of different possible strategies of applying PC-MRI measured flow rates on an image-based hemodynamic model of a healthy human aortic arch with supra-aortic vessels. A total of six flow simulations was carried out applying six different schemes for treating BCs at outlets. Three common wall shear stress (WSS)-based indicators of abnormal flow were considered and the sensitivity of these indicators to the outlet treatment strategy was evaluated.

scholarly journals Patient-specific computational haemodynamics associated with surgical creation of an arteriovenous fistula

2021 ◽  
Author(s):  
George Hyde-Linaker ◽  
Pauline Hall Barrientos ◽  
Sokratis Stoumpos ◽  
Asimina Kazakidi
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Disease Patient ◽  
Blood Flow Rate ◽  
Fold Increase ◽  
Transitional Flow ◽  
Patient Specific ◽  
Venous Anastomosis ◽  
End Stage

Abstract Despite arteriovenous fistulae (AVF) being the preferred vascular access for haemodialysis, high primary failure rates (30-70%) and low one-year patency rates (40-70%) hamper their use. The haemodynamics within the vessels of the fistula change significantly following surgical creation of the anastomosis and can be a surrogate of AVF success or failure. Computational fluid dynamics (CFD) can crucially predict AVF outcomes through robust analysis of a fistula’s haemodynamic patterns, which is impractical in-vivo. We present a proof-of-concept CFD framework for characterising the AVF blood flow prior and following surgical creation of a successful left radiocephalic AVF in a 20-year-old end-stage kidney disease patient. The reconstructed vasculature was generated utilising multiple contrast-enhanced magnetic resonance imaging (MRI) datasets. Large eddy simulations were conducted for establishing the extent of arterial and venous remodelling. Following anastomosis creation, a significant 2-3-fold increase in blood flow rate was induced downstream of the left subclavian artery. This was validated through comparison with post-AVF patient-specific phase-contrast data. The increased flow rate yielded an increase in time-averaged wall shear stress (TAWSS), a key marker of adaptive vascular remodelling. We have demonstrated TAWSS and oscillatory shear distributions of the transitional-flow in the venous anastomosis are predictive of AVF remodelling.

Numerical simulation of blood flow and plaque progression in carotid–carotid bypass patient specific case

2015 ◽  
Vol 20 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Nenad Filipovic ◽  
Igor Saveljic ◽  
Dalibor Nikolic ◽  
Zarko Milosevic ◽  
Pavle Kovacevic ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Blood Flow ◽  
Patient Specific ◽  
Plaque Progression ◽  
Bypass Patient

Computational Modeling of Shear-Based Hemolysis Caused by Renal Obstruction

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Polina A. Segalova ◽  
K. T. Venkateswara Rao ◽  
Christopher K. Zarins ◽  
Charles A. Taylor
Keyword(s):  
Blood Flow ◽  
Boundary Conditions ◽  
Renal Artery ◽  
Aortic Aneurysms ◽  
Cfd Modeling ◽  
Patient Specific ◽  
Shear Stresses ◽  
Baseline Model ◽  
Implantable Medical Devices ◽  
Renal Obstruction

As endovascular treatment of abdominal aortic aneurysms (AAAs) gains popularity, it is becoming possible to treat certain challenging aneurysmal anatomies with endografts relying on suprarenal fixation. In such anatomies, the bare struts of the device may be placed across the renal artery ostia, causing partial obstruction to renal artery blood flow. Computational fluid dynamics (CFD) was used to simulate blood flow from the aorta to the renal arteries, utilizing patient-specific boundary conditions, in three patient models and calculate the degree of shear-based blood damage (hemolysis). We used contrast-enhanced computed tomography angiography (CTA) data from three AAA patients who were treated with a novel endograft to build patient-specific models. For each of the three patients, we constructed a baseline model and endoframe model. The baseline model was a direct representation of the patient’s 30-day post-operative CTA data. This model was then altered to create the endoframe model, which included a ring of metallic struts across the renal artery ostia. CFD was used to simulate blood flow, utilizing patient-specific boundary conditions. Pressures, flows, shear stresses, and the normalized index of hemolysis (NIH) were quantified for all patients. The overall differences between the baseline and endoframe models for all three patients were minimal, as measured though pressure, volumetric flow, velocity, and shear stress. The average NIH across the three baseline and endoframe models was 0.002 and 0.004, respectively. Results of CFD modeling show that the overall disturbance to flow caused by the presence of the endoframe struts is minimal. The magnitude of the NIH in all models was well below the accepted design and safety threshold for implantable medical devices that interact with blood flow.

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.

Effect of Local Coil Density on Blood Flow Stagnation in Densely Coiled Cerebral Aneurysms: A Computational Study Using a Cartesian Grid Method

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Tomohiro Otani ◽  
Takuya Shindo ◽  
Satoshi Ii ◽  
Masayuki Hirata ◽  
Shigeo Wada
Keyword(s):  
Blood Flow ◽  
Computational Study ◽  
Grid Method ◽  
Neck Region ◽  
Cartesian Grid ◽  
Dense Packing ◽  
Patient Specific ◽  
Local Flow ◽  
Cartesian Grid Method ◽  
Flow Stagnation

Aneurysm recurrence is the most critical concern following coil embolization of a cerebral aneurysm. Adequate packing density (PD) and coil uniformity are believed necessary to achieve sufficient flow stagnation, which decreases the risk of aneurysm recurrence. The effect of coil distribution on the extent of flow stagnation, however, especially in cases of dense packing (high PD), has received less attention. Thus, the cause of aneurysm recurrence despite dense packing is still an open question. The primary aim of this study is to evaluate the effect of local coil density on the extent of blood flow stagnation in densely coiled aneurysms. For this purpose, we developed a robust computational framework to determine blood flow using a Cartesian grid method, by which the complex fluid pathways in coiled aneurysms could be flexibly treated using an implicit function. This tool allowed us to conduct blood flow analyses in two patient-specific geometries with 50 coil distribution patterns in each aneurysm at clinically adequate PD. The results demonstrated that dense packing in the aneurysm may not necessarily block completely the inflow into the aneurysm and local flow that formed in the neck region, whose strength was inversely related to this local PD. This finding suggests that local coil density in the neck region still plays an important role in disturbing the remaining local flow, which possibly prevents thrombus formation in a whole aneurysm sac, increasing the risk of aneurysm regrowth and subsequent recurrence.

Sensitivity of patient-specific numerical simulation of cerebal aneurysm hemodynamics to inflow boundary conditions

2007 ◽  
Vol 106 (6) ◽  
pp. 1051-1060 ◽  
Author(s):  
Prem Venugopal ◽  
Daniel Valentino ◽  
Holger Schmitt ◽  
J. Pablo Villablanca ◽  
Fernando Viñuela ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Boundary Conditions ◽  
Numerical Simulations ◽  
Flow Rate ◽  
Artery Aneurysm ◽  
Blood Flow Rate ◽  
Patient Specific ◽  
Stress Distributions ◽  
Flow Rates

Object Due to the difficulty of obtaining patient-specific velocity measurements during imaging, many assumptions have to be made while imposing inflow boundary conditions in numerical simulations conducted using patient-specific, imaging-based cerebral aneurysm models. These assumptions can introduce errors, resulting in lack of agreement between the computed flow fields and the true blood flow in the patient. The purpose of this study is to evaluate the effect of the assumptions made while imposing inflow boundary conditions on aneurysmal hemodynamics. Methods A patient-based anterior communicating artery aneurysm model was selected for this study. The effects of various inflow parameters on numerical simulations conducted using this model were then investigated by varying these parameters over ranges reported in the literature. Specifically, we investigated the effects of heart and blood flow rates as well as the distribution of flow rates in the A1 segments of the anterior cerebral artery. The simulations revealed that the shear stress distributions on the aneurysm surface were largely unaffected by changes in heart rate except at locations where the shear stress magnitudes were small. On the other hand, the shear stress distributions were found to be sensitive to the ratio of the flow rates in the feeding arteries as well as to variations in the blood flow rate. Conclusions Measurement of the blood flow rate as well as the distribution of the flow rates in the patient's feeding arteries may be needed for numerical simulations to accurately reproduce the intraaneurysmal hemodynamics in a specific aneurysm in the clinical setting.

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