BME PhD Defense: Sucheta Tamragouri: "Assessment of Growth Adaptive Pediatric Heart Valves through Milli-PIV and Dye Injection”

"Assessment of Growth Adaptive Pediatric Heart Valves through Milli-PIV and Dye Injection” 

Sucheta Tamragouri  

Abstract: Congenital heart defects are the most common birth defects and often involve heart valve abnormalities. In pediatric patients, heart valve replacement remains challenging because most prosthetic valves are fixed in size and cannot accommodate somatic growth. As a child grows, the implanted valve may no longer meet the patient’s physiological needs, necessitating repeated invasive interventions. Growth-adaptive pediatric heart valves (GAP-HVs) are being developed to address this problem. However, because these valves are intended to change geometry with growth, evaluation is not straightforward; and moreover, testing approaches for pediatric valves remain limited. Current valve testing mainly focuses on global measurements such as pressure drop, effective orifice area, and leakage. These measurements are necessary, but they do not fully describe how flow behaves in and around the valve. Regions of slow-moving flow, concentrated jets, recirculation, or elevated shear may still occur even when overall valve function appears acceptable. These features are especially important at pediatric scales, where small geometric changes can have a large effect on flow structure. The objective of this dissertation was to develop, validate, and apply a pediatric-scale experimental workflow for evaluating pediatric prosthetic valves. The workflow combined dye-based flow visualization with millimeter-scale particle image velocimetry (milli-PIV). Dye injection was used to quantify how quickly fluid cleared from a region, while milli-PIV was used to measure velocity fields and shear-related flow behavior. The methods were first developed in a simplified model which allowed the parameters to be optimized before being applied to valve testing. After validation, the workflow was used to evaluate pediatric prosthetic valves across growth-relevant size states. A GAP-HV prototype and a clinically used valve were tested under pediatric-relevant flow conditions. Standard measurements showed that larger valve sizes were generally associated with improved forward-flow performance. The workflow measurements, however, showed differences that were not captured by global values alone: larger valve states had faster clearance from sinus-like regions, while downstream flow patterns and shear behavior depended on both valve size and geometry. These findings support the need for flow measurements when evaluating GAP-HVs. Finally, the workflow was applied in a patient-specific pulmonary artery model to study how valve placement affects downstream flow. A pediatric valve was tested in two rotational positions. Changing the valve orientation altered branch flow distribution, downstream jet structure, recirculation patterns, and wall shear stress. One orientation produced a more organized downstream flow pattern, while the other produced a more diffuse flow field with greater curvature and local flow reversal. This showed that placement, in addition to valve geometry, can influence the local flow environment. Overall, this dissertation establishes an experimental workflow for pediatric prosthetic valve assessment that combines standard measurements with flow visualization and velocity-field analysis. The results showed that growth-related changes in valve geometry can affect local flow structure and clearance behavior in ways that are not fully described by the current standard measurements. By providing a way to measure how valve geometry and placement affect local flow, this workflow can support future preclinical valve testing, patient-specific placement studies, and design refinement for pediatric valve technologies. 

For a zoom link, please email kharrison@wpi.edu