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Research Papers

Computational Modeling of Shear-Based Hemolysis Caused by Renal Obstruction

[+] Author and Article Information
Polina A. Segalova1

 Department of Mechanical Engineering, Stanford University, Stanford, CA 94305; James H. Clark Center, E350,318 Campus Drive, Stanford, CA 94305polina@stanford.edu

K. T. Venkateswara Rao

 Nellix Endovascular, Palo Alto, CA 94303

Christopher K. Zarins

 Department of Surgery,Stanford University, Stanford, CA 94305

Charles A. Taylor

 Department of Bioengineering,Stanford University, Stanford, CA 94305

1

Corresponding author.

J Biomech Eng 134(2), 021003 (Mar 19, 2012) (7 pages) doi:10.1115/1.4005850 History: Received July 07, 2011; Revised January 16, 2012; Posted January 30, 2012; Published March 14, 2012; Online March 19, 2012

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.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Maximum intensity projection (MIP) renderings of the CTA data sets used in this study for the three patients

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Figure 2

Geometric models were created for each patient based on CTA data using 2D segmentation techniques. In this method, centerlines were created along the desired vessels, which allowed for vessel segmentation. Finally, the vessel cross sections were lofted together to generate the final geometric model.

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Figure 3

Each patient baseline model was altered to include a row of metal scaffold struts obstructing the renal ostia. The additional set of models is referred to as endoframe models and is depicted above.

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Figure 4

Pressure waveforms (solid line) at the inlet were computed for each patient anatomy. The measured systolic (dashed line) and diastolic (dotted line) patient blood pressures are also displayed. There was no noteworthy difference in the inlet blood pressure between the baseline and endoframe models for a given patient. The pressure waveform maximums and minimums (solid line) were within 5% of the measured systolic (dashed line) and diastolic (dotted line) blood pressure values, respectively.

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Figure 5

Volume rendering of the velocity magnitude (cm/s) in peak-systole for the baseline and endoframe models in all three patients. Velocities at a cross section immediately distal to the renal artery ostia are also illustrated in a magnified view.

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Figure 6

Volume rendering of the scalar stress field of the baseline and endoframe models for Patients A-C. Stress field at a cross-sectional level immediately distal to the renal artery ostia is also illustrated in a magnified view. Elevated levels of stress can be seen around the endoframe struts for all endoframe models.

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