A Multiscale Computational Platform in the Design of a Geometrically Tunable Blood Shunt

Monday, July 24, 2023

8:45 AM-10:45 AM

BIOMED PhD Thesis Defense

Title:
A Multiscale Computational Platform in the Design of a Geometrically Tunable Blood Shunt
 
Speaker:
Ellen Garven, PhD Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University

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

Details:
Single ventricle malformations are a severe form of congenital heart defect in which one of the two normal ventricles of the heart is missing or malformed. In the first of several staged palliative surgeries, the Norwood procedure establishes a circulation with a single functional ventricle that delivers blood to both the lungs and the body. This is achieved through the implantation of an artificial graft called a shunt, which remains in place for approximately four to six months. The Norwood procedure is the riskiest stage of the single ventricle palliation plan, and the risk of morbidity and mortality extends throughout the period that the shunt remains in place. A delicate balance of flow is maintained through the shunt, which impacts the overall blood oxygenation of the patient. The task of maintaining that balance is further complicated by the duration of the interstage period. During the four to six months that the shunt remains in place, the infant should experience a significant period of growth and development. Given the numerous physiological changes that occur in the first few months of infancy, a fixed diameter shunt theoretically cannot maintain adequate blood oxygenation and stable hemodynamics across the entire period.
 
Motivated by this idea in the context of the clinical challenges, the BioCirc Laboratory at Drexel University and its collaborators have begun investigation into the design of a geometrically tunable blood shunt. This shunt would address the limitations of the current clinical design with an inner lumen diameter that could be adjusted over the duration of use. The inner diameter would be customized by modulating the cross-linking density of a hydrogel coating along the interior wall of the shunt, thereby altering the effective internal resistance of the shunt.
 
In this study, we sought to characterize how the inner lumen of the shunt should change over time in a Norwood patient to best maintain blood oxygenation. To accomplish that goal, computational models of blood flow were used to simulate the hemodynamics. First, we developed a multiscale modeling methodology that would capture all of the relevant variables surrounding the shunt, using a computational fluid dynamics model coupled to a lumped parameter model. The hemodynamic conditions were then characterized under the existing clinical design. Using patient-specific data, multiscale models were created that represented two points in time spanning the period between the Norwood and the next surgical stage. The resulting set of models captured growth related changes to the geometric and hemodynamic conditions within the patient. While the Norwood has been studied extensively using computational models, our simulations are among the first to study the Norwood at multiple timepoints and the results provided hemodynamic insights about a clinically complicated period.
 
Finally, the models of growth-related changes across the Norwood duration were leveraged to simulate the tunable shunt with the goal of maintaining reasonable hemodynamics, and therefore sufficient blood oxygenation. The diameters of the tunable shunt that positively impacted the hemodynamic balance were identified through iterative simulations. By comparing the identified diameters between timepoints, we established how the tunable shunt diameter could change over time.
 
This work established a computational platform of the Norwood across the interstage period in two patient-specific models. Given the heterogeneity in the Norwood patient population, the contrast in these models was used to study the tunable shunt in a range of clinical conditions and will help ensure a robust design. The results quantified how the inner lumen of the tunable shunt should adjust in geometry in order to better maintain the hemodynamic balance in a model of growth-related changes. With the ratio of flow through the shunt maintained at a specified level, the tunable shunt design should allow for sufficient blood oxygenation across infancy. Beyond the current research goals, the computational platform that was created will continue to serve as a valuable resource for future design and development investigations.

Contact Information

Natalia Broz
njb33@drexel.edu