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Computational Modeling of a Geometrically Tunable Blood Shunt for Norwood Recipients

Tuesday, September 18, 2018

2:00 PM-4:00 PM

BIOMED Master's Thesis Defense

Computational Modeling of a Geometrically Tunable Blood Shunt for Norwood Recipients

Ellen Garven, MS Candidate, School of Biomedical Engineering, Science and Health Systems, Drexel University

Amy Throckmorton, PhD, Associate Professor, School of Biomedical Engineering, Science and Health Systems, Drexel University

The low availability of suitable heart transplants requires the use of palliative treatments for infants with severe congenital heart defects. Out of every 10,000 live births, 2-4 infants have a severe form of congenital heart defect characterized by a single functional ventricle. In order to survive, these infants require the first of a series of palliative surgeries---the Norwood procedure---within hours or days after birth. The modified Blalock-Taussig shunt (MBTS) is one type of shunt used in the Norwood procedure to redirect blood flow. With this shunt, the single functional ventricle performs the work of two ventricles. The proper growth and development of the infant depends on a delicate balance of blood flow between the body and the lungs, the ratio of which is determined by the size, orientation, and conditions of the shunt.

A model of the MBTS in a neonatal aortic arch is developed and evaluated using computational fluid dynamics. Parameters are modified individually to study their effect in steady-state, including multiple shunt geometries and a range of physiological conditions. Additionally, time-variant simulations are conducted to simulate the dynamics over the duration of a heartbeat.

In comparison to a model of the healthy anatomy, the MBTS model creates more complex fluid patterns that have higher amounts of shear stress. These factors indicate less overall cardiac efficiency. Variations to the shunt diameter are used to validate the model against well-established concepts. Geometry variations with additional curvature and flaring had more pulmonary flow, which suggested more favorable uniform flow behaviors. Results of the physiological variations connect the significance of low cardiac output with blood oxygenation and poor clinical outcomes. The impact of moderate shunt dysfunction is found to be relatively minor. The inlet behavior of the time-variant simulations corresponds to a neonatal heartbeat, but the results do not mimic realistic fluid behavior over the entire duration because of limitations in the boundary conditions.

These findings establish the first part of a computational framework for the evaluation of a new type of shunt design–a geometrically tunable shunt–that would adjust in geometric shape in proportion to growth. The parameters studied in this research, especially the diameter and time-variant analyses, lay the groundwork for the modeling and development of the new shunt design.

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