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Browne LD, Griffin P, Bashar K, Walsh SR, Kavanagh EG, Walsh MT. In vivo validation of the in silico predicted pressure drop across an arteriovenous fistula. Ann Biomed Eng 2015; 43:1275-86. [PMID: 25753016 DOI: 10.1007/s10439-015-1295-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2014] [Accepted: 02/28/2015] [Indexed: 10/23/2022]
Abstract
The creation of an arteriovenous fistula offers a unique example of vascular remodelling and adaption. Yet, the specific factors which elicit remodelling events which determine successful maturation or failure have not been unambiguously determined. Computational fluid dynamic (CFD) simulations are increasingly been employed to investigate the interaction between local hemodynamics and remodelling and can potentially be used to assist in clinical risk assessment of maturation or failure. However, these simulations are inextricably linked to their prescribed boundary conditions and are reliant on in vivo measurements of flow and pressure to ensure their validity. The study compares in vivo measurements of the pressure distribution across arteriovenous fistulae against a representative numerical model. The results of the study indicate relative agreement (error ≈ 8-10%) between the in vivo and CFD prediction of the mean pressure drop across the AVFs. The large pressure drop across the AVFs coincided with a palpable thrill (perivascular vibration) in vivo and fluctuations were observed in the numerical pressure drop signal due to flow instabilities arising at the anastomosis. This study provides a benchmark of the pressure distribution within an AVF and validates that CFD solutions are capable of replicating the abnormal physiological flow conditions induced by fistula creation.
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Affiliation(s)
- Leonard D Browne
- Centre for Applied Biomedical Engineering Research (CABER), Department of Mechanical, Aeronautical and Biomedical Engineering, Materials and Surface Science Institute, University of Limerick, Limerick, Ireland
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Validation of Computational Fluid Dynamics-Based Analysis to Evaluate Hemodynamic Significance of access Stenosis. J Vasc Access 2014; 15:409-14. [DOI: 10.5301/jva.5000226] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/12/2014] [Indexed: 11/20/2022] Open
Abstract
Purpose Stenosis in a vascular access circuit is the predominant cause of access dysfunction. Hemodynamic significance of a stenosis identified by angiography in an access circuit is uncertain. This study utilizes computational fluid dynamics (CFD) to model flow through arteriovenous fistula to predict the functional significance of stenosis in vascular access circuits. Methods Three-dimensional models of fistulas were created with a range of clinically relevant stenoses using SolidWorks. Stenoses diameters ranged from 1.0 to 3.0 mm and lengths from 5 to 60 mm within a fistula diameter of 7 mm. CFD analyses were performed using a blood model over a range of blood pressures. Eight patient-specific stenoses were also modeled and analyzed with CFD and the resulting blood flow calculations were validated by comparison with brachial artery flow measured by duplex ultrasound. Results Predicted flow rates were derived from CFD analysis of a range of stenoses. These stenoses were modeled by CFD and correlated with the ultrasound measured flow rate through the fistula of eight patients. The calculated flow rate using CFD correlated within 20% of ultrasound measured flow for five of eight patients. The mean difference was 17.2% (ranged from 1.3% to 30.1%). Conclusions CFD analysis-generated flow rate tables provide valuable information to assess the functional significance of stenosis detected during imaging studies. The CFD study can help in determining the clinical relevance of a stenosis in access dysfunction and guide the need for intervention.
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Fitts MK, Pike DB, Anderson K, Shiu YT. Hemodynamic Shear Stress and Endothelial Dysfunction in Hemodialysis Access. ACTA ACUST UNITED AC 2014; 7:33-44. [PMID: 25309636 DOI: 10.2174/1874303x01407010033] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Surgically-created blood conduits used for chronic hemodialysis, including native arteriovenous fistulas (AVFs) and synthetic AV grafts (AVGs), are the lifeline for kidney failure patients. Unfortunately, each has its own limitations: AVFs often fail to mature to become useful for dialysis and AVGs often fail due to stenosis as a result of neointimal hyperplasia, which preferentially forms at the graft-venous anastomosis. No clinical therapies are currently available to significantly promote AVF maturation or prevent neointimal hyperplasia in AVGs. Central to devising strategies to solve these problems is a complete mechanistic understanding of the pathophysiological processes. The pathology of arteriovenous access problems is likely multi-factorial. This review focuses on the roles of fluid-wall shear stress (WSS) and endothelial cells (ECs). In arteriovenous access, shunting of arterial blood flow directly into the vein drastically alters the hemodynamics in the vein. These hemodynamic changes are likely major contributors to non-maturation of an AVF vein and/or formation of neointimal hyperplasia at the venous anastomosis of an AVG. ECs separate blood from other vascular wall cells and also influence the phenotype of these other cells. In arteriovenous access, the responses of ECs to aberrant WSS may subsequently lead to AVF non-maturation and/or AVG stenosis. This review provides an overview of the methods for characterizing blood flow and calculating WSS in arteriovenous access and discusses EC responses to arteriovenous hemodynamics. This review also discusses the role of WSS in the pathology of arteriovenous access, as well as confounding factors that modulate the impact of WSS.
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Affiliation(s)
- Michelle K Fitts
- Department of Bioengineering, University of Utah, Salt Lake City, Utah, USA
| | - Daniel B Pike
- Department of Bioengineering, University of Utah, Salt Lake City, Utah, USA
| | - Kasey Anderson
- Department of Bioengineering, University of Utah, Salt Lake City, Utah, USA
| | - Yan-Ting Shiu
- Department of Medicine, Division of Nephrology and Hypertension, University of Utah, Salt Lake City, Utah, USA
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Boghosian M, Cassel K, Hammes M, Funaki B, Kim S, Qian X, Wang X, Dhar P, Hines J. Hemodynamics in the cephalic arch of a brachiocephalic fistula. Med Eng Phys 2014; 36:822-30. [PMID: 24695337 DOI: 10.1016/j.medengphy.2014.03.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Revised: 01/22/2014] [Accepted: 03/08/2014] [Indexed: 12/01/2022]
Abstract
The care and outcome of patients with end stage renal disease (ESRD) on chronic hemodialysis is directly dependent on their hemodialysis access. A brachiocephalic fistula (BCF) is commonly placed in the elderly and in patients with a failed lower-arm, or radiocephalic, fistula. However, there are numerous complications such that the BCF has an average patency of only 3.6 years. A leading cause of BCF dysfunction and failure is stenosis in the arch of the cephalic vein near its junction with the axillary vein, which is called cephalic arch stenosis (CAS). Using a combined clinical and computational investigation, we seek to improve our understanding of the cause of CAS, and to develop a means of predicting CAS risk in patients with a planned BCF access. This paper details the methodology used to determine the hemodynamic consequences of the post-fistula environment and illustrates detailed results for a representative sample of patient-specific anatomies, including a single, bifurcated, and trifurcated arch. It is found that the high flows present due to fistula creation lead to secondary flows in the arch owing to its curvature with corresponding low wall shear stresses. The abnormally low wall shear stress locations correlate with the development of stenosis in the singular case that is tracked in time for a period of one year.
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Affiliation(s)
- M Boghosian
- Mechanical, Materials, and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, IL, United States.
| | - K Cassel
- Mechanical, Materials, and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, IL, United States
| | - M Hammes
- Nephrology, Department of Medicine, University of Chicago, Chicago, IL, United States
| | - B Funaki
- Vascular and Interventional Radiology, Department of Medicine, University of Chicago Medical Center, Chicago, IL, United States
| | - S Kim
- Vascular and Interventional Radiology, Department of Medicine, University of Chicago Medical Center, Chicago, IL, United States
| | - X Qian
- Mechanical, Materials, and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, IL, United States
| | - X Wang
- Mechanical, Materials, and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, IL, United States
| | - P Dhar
- Biomedical Engineering Department, Illinois Institute of Technology, Chicago, IL, United States
| | - J Hines
- Nephrology, Department of Medicine, University of Chicago, Chicago, IL, United States
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Remuzzi A, Ene-Iordache B. Novel paradigms for dialysis vascular access: upstream hemodynamics and vascular remodeling in dialysis access stenosis. Clin J Am Soc Nephrol 2013; 8:2186-93. [PMID: 23990161 PMCID: PMC3848396 DOI: 10.2215/cjn.03450413] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Failure of hemodialysis access is caused mostly by venous intimal hyperplasia, a fibro-muscular thickening of the vessel wall. The pathogenesis of venous neointimal hyperplasia in primary arteriovenous fistulae consists of processes that have been identified as upstream and downstream events. Upstream events are the initial events producing injury of the endothelial layer (surgical trauma, hemodynamic shear stress, vessel wall injury due to needle punctures, etc.). Downstream events are the responses of the vascular wall at the endothelial injury that consist of a cascade of processes including leukocyte adhesion, migration of smooth muscle cells from the media to the intimal layer, and proliferation. In arteriovenous fistulae, the stenoses occur in specific sites, consistently related to the local hemodynamics determined by the vessel geometry and blood flow pattern. Recent findings that the localization of these sites matches areas of disturbed flow may add new insights into the pathogenesis of neointimal hyperplasia in the venous side of vascular access after the creation of the anastomosis. The detailed study of fluid flow motion acting on the vascular wall in anastomosed vessels and in the arm vasculature at the patient-specific level may help to elucidate the role of hemodynamics in vascular remodeling and neointimal hyperplasia formation. These computational approaches may also help in surgical planning for the amelioration of clinical outcome. This review aims to discuss the role of the disturbed flow condition in acting as upstream event in the pathogenesis of venous intimal hyperplasia and in producing subsequent local vascular remodeling in autogenous arteriovenous fistulae used for hemodialysis access. The potential use of blood flow analysis in the management of vascular access is also discussed.
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Affiliation(s)
- Andrea Remuzzi
- Biomedical Engineering Department, IRCCS - Istituto di Ricerche Farmacologiche “Mario Negri,” Bergamo, Italy; and
- Engineering Department, University of Bergamo, Bergamo, Italy
| | - Bogdan Ene-Iordache
- Biomedical Engineering Department, IRCCS - Istituto di Ricerche Farmacologiche “Mario Negri,” Bergamo, Italy; and
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Rajabi-Jagahrgh E, Roy-Chaudhury P, Wang Y, Al-Rjoub M, Campos-Naciff B, Choe A, Dumoulin C, Banerjee RK. New techniques for determining the longitudinal effects of local hemodynamics on the intima-media thickness in arteriovenous fistulae in an animal model. Semin Dial 2013; 27:424-35. [PMID: 24261988 DOI: 10.1111/sdi.12162] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Remodeling in the arteriovenous fistulas (AVFs) is believed to be a hemodynamic-driven process, which results in extreme changes in the diameter and intima-media thickening (IMT) of vessels over time. This study aims to describe the successful development of techniques that enabled correlation of changes in local and longitudinal wall shear stress (WSS) with the temporal variations of the diameter and IMT in the venous segment of AVFs. An AVF was created between the femoral artery and vein of a 50-kg pig. We have previously shown the successful use of CT-scan and ultrasound techniques for anatomical and flow measurements in AVFs, respectively. In this study, we developed new techniques involving markers (both in vivo and ex vivo), casting (ex vivo), and micro-MRI (ex vivo; 7 Tesla). A radiopaque marker (ROM) was sutured to the AVF at the day of surgery, which was visible in the CT-scan images, micro-MRI, and histology sections. Therefore, ROM served as a fixed local reference for both in vivo and ex vivo states of AVFs. Immediately after sacrificing the pig, a procedure was developed to create a cast from the AVF and thus, maintaining the in vivo state of the AVF during the histology process. Then, micro-MRI and histology techniques were conducted on the AVF to measure IMT in the vein. Along the ROM, the local changes in WSS levels for two cross-sections were tracked at 2D (D: days) and 28D post surgery. WSS levels reduced from 2D to 28D for both cross-sections. Also, the recirculation zones, which formed at 2D for both sections, became smaller in size at 28D. These hemodynamic changes were then mapped onto the corresponding IMT measurements from histology and micro-MRI. It was observed that the recirculation zones at 2D and 28D corresponded to the largest IMT in the two sections. In summary, the new methodologies allowed us to define a fixed local reference at all time points in the AVF, which enabled accurate tracking of local changes in hemodynamics (WSS), configuration (diameter), and structure (IMT) of the venous segment over time. This also empowered study of the interactions between these parameters, which could improve our understanding about the hemodynamic-driven remodeling in AVFs. From a clinical point of view, this information could be translated into local and early therapeutic interventions for dialysis patients.
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Affiliation(s)
- Ehsan Rajabi-Jagahrgh
- Mechanical Engineering Program, School of Dynamic Systems, University of Cincinnati, Cincinnati, Ohio
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