The Implications of Coarctation and Indentation of the Aorta on Blood Flow Characteristics in Pediatric Patients

• Author / Creator

  Jia, Yuxi

• Aorta coarctation is one of the most common geometrical anomalies observed in children that requires intervention in an early stage. Another equally important, but less common, anomaly of the aorta involves the indentation of the aortic arc. This study examines the blood flow characteristics in the presence of these geometrical anomalies by comparing the flow to a normal aorta model. The primary research objective of this thesis is to model the discrepancies between the blood flow characteristics of a normal and abnormal aorta, then conduct preliminary modifications to resolve key abnormal flow patterns using flow manipulators, e.g. vortex generators. Using two sets of patient-specific boundary conditions with the normal aorta model, the simulation setup was validated using experimental measurements, which only showed inaccuracies up to 5%. An abnormal aorta with a bicuspid aortic valve, aortic coarctation, and arch narrowing due to an indentation in the inferior aspect of the mid aortic arch was modeled using Direct Numerical Simulations and Fluid Structure Interaction. Moreover, the effect of boundary condition on blood flow in a normal and abnormal aorta were evaluated using a combination of Neumann and Dirichlet (patient specific) boundary conditions. Using the most optimum model setup, key regions of flow disturbance due to the geometrical anomalies of the abnormal aorta were found in the inferior aspect of the mid aortic arch and in the coarctation. These regions showed increased vorticity, large pressure drops, and high peak wall shear stress, suggesting the presence of recirculation zones. By implementing flow manipulators prior to the onset of these flow discrepancies, the optimum location of which was determined empirically, the size of the recirculation region decreased, and peak wall shear stresses declined up to 70%. The peak wall shear stress in the abnormal aorta is significantly greater than the magnitudes of wall shear stress in the normal aorta. This acts as a possible explanation for the decreased flow rate through the abnormal aorta. A decreased flow rate thereby decreases wall shear stress, and it could proactively prevent high stresses in the aorta, and lower the risk of rupture. With a decreased peak wall shear stress with the implementation of flow manipulators, the blood flow shows recovery towards normal flow rates. The coarctation also resulted in a larger pressure drop of 19 mmHg compared to the same segment in the normal aorta. The lower flow rate leads to pressure adjustments that increases the risk of low blood pressure in the lower body of patients with such anomalies. This pressure drop is remedied slightly by the installation of flow manipulators, which help to alleviate potential problems associated with low blood pressure. Thus, the implementation of flow manipulators in the abnormal aorta did alleviate undesirable blood flow characteristics towards those of a normal aorta. This serves as a proof of concept for such an approach in the development of better treatment techniques to replace surgical reconstruction of the aorta geometry.

• Subjects / Keywords

  • Coarctation
  • Flow Manipulator
  • Fluid Structure Interaction
  • Direct Numerical Simulation

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-ajq3-nn63

• License

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