Doctoral Dissertations
Date of Award
12-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Biomedical Engineering
Major Professor
Dr. Bryan C. Good
Committee Members
Dr. Omer San, Dr. A. Colleen Crouch, Dr. Haochen Li
Abstract
Cardiopulmonary bypass (CPB) is essential for modern cardiac surgery, yet it remains closely linked to acute ischemic stroke, acute kidney injury, and other organ complications. Many of these adverse events arise from emboli that are generated and transported through disturbed flow fields during CPB. Despite extensive clinical use, the hemodynamic mechanisms that govern embolic transport are not fully understood, particularly how cannula orientation, flow conditions, blood viscosity, embolus properties, and patient specific anatomy interact to shape embolic trajectories.
This dissertation develops and validates an experimental and computational framework to investigate embolic transport across the thoracic aorta, abdominal branches, and cerebral arteries under realistic CPB conditions. A patient-specific mock circulatory flow loop with a silicone aortic model was constructed to reproduce CPB perfusion and was coupled with computational fluid dynamics (CFD) and Lagrangian particle tracking (LPT) simulations in OpenFOAM.
The results reveal that flow rate and hemodilution are primary drivers of embolic dispersion. Increased pump flow and reduced viscosity amplify turbulence and weaken viscous damping, which together promote cross-stream migration and increase embolic delivery to cerebral and visceral branches. Also, cannula orientation emerged as a dominant control variable. Perpendicular cannulation generated a high-momentum jet that impinged on the posterior ascending aorta, increasing recirculation, embolic entry into supra-aortic branches, and local wall stress. Embolus size and density further modulated transport through a clear Stokes-number-based mechanism. Aging and geometric variability of the aorta amplified these trends.
Extending the framework to a complete thoracic aorta, Circle of Willis, and abdominal aorta configuration yielded, to our knowledge, the first experimentally validated cerebral embolic and abdominal transport model under CPB conditions. The validated CFD and LPT platform provides a mechanistic basis for patient-tailored perfusion planning, including optimization of cannula placement, pump-flow limits, and hemodilution targets to jointly reduce cerebral and visceral embolic risk while controlling wall loading in vulnerable aortas. By connecting detailed flow physics to clinically relevant embolic outcomes, this work advances the development of precision perfusion strategies aimed at minimizing CPB-related neurological and multi-organ injury.
Recommended Citation
Arefin, Nafis Mahdi, "Embolic Transport Dynamics and Aortic Hemodynamics During Cardiopulmonary Bypass to Assess Risk of Stroke and Organ Injury. " PhD diss., University of Tennessee, 2025.
https://trace.tennessee.edu/utk_graddiss/13580