DOI: https://doi.org/10.15368/theses.2014.168
Available at: https://digitalcommons.calpoly.edu/theses/1311
Date of Award
12-2014
Degree Name
MS in Engineering - Biochemical Engineering
Department/Program
Biomedical and General Engineering
Advisor
David Clague
Abstract
Saccular aneurysms are the abnormal plastic deformation of veins and arteries that can lead to lethal thrombus genesis or internal hemorrhaging. Medication and surgery greatly reduce the mortality rates, but treatment is limited by predicting who will develop aneurysms. A common location for saccular aneurysm genesis is at the main middle cerebral artery (MCA) bifurcation. The main MCA bifurcation is comprised of the M1 MCA segment, parent artery, and two M2 segments, daughter arteries. Studies have found that the lateral angle (LA) ratio of the MCA bifurcation is correlated with aneurysm formation. The LA ratio is defined as the angle between the M1 and the larger M2 divided by the angle between the M1 and the smaller M2. When the LA ratio is equal to 1, perfectly symmetrical, no aneurysms are found at the MCA bifurcation. When the LA ratio is greater than 1.6, aneurysms are commonly found at the MCA bifurcation. In the research described here, varying MCA bifurcation angles were compared to uncover any changes to fluid flow and wall shear stress that could stimulate aneurysm growth. Eight pre-aneurysm MCA bifurcation models were created in SolidWorks® using 120 degrees, 90 degrees, and 60 degrees as the angle between the M1 and the larger M2. LA ratios of 1, 1.6 and 2.2 were then used to characterize the other branch angle (60 degrees with a LA ratio of 1 was excluded). These models were imported into COMSOL Multiphysics® where the laminar fluid flow module was used to simulate non-Newtonian blood flow. Fluid flow profiles showed little to no change between the models. Shear stress changed when the LA ratio was increased, but the changed varied between the 120, 90 and 60 degree models. 120 degree models had a 3.87% decrease in max shear stress with a LA ratio of 2.2 while the 90 degree models had 7.5% decrease in max shear stress with a LA ratio of 2.2. Each daughter artery had distinct areas of high shear stress when the LA ratio equaled 1. Increasing the LA ratio or decreasing the bifurcation angle caused the areas of shear stress to merge together. Increasing LA ratio caused shear stress to decrease and spread around the MCA bifurcation. The reduction in max wall shear stress for high LA ratios supports current aneurysm genesis hypothesizes, but additional testing is required before bifurcation geometries can be used to predicted aneurysm genesis.