Invitation:PhD Proposal Defense of Nadeem Shah

Thursday, May 21, 2026 · 10 - 11:30 AM

Hello ME Community,
You are invited to join the PhD Proposal Defense of Nadeem Shah, on Thursday, May 21, beginning at 10:00am. The defense will be presented in person in the Engineering Building room 210-I. (the Mechanical Engineering Conference room)

Co-Advisors: Dr. Sayantan Bhattacharya, and Dr. Charles Eggleton

Title: IN VITRO ASSESSMENT OF BICUSPID AORTIC VALVE HYDRODYNAMICS:
EFFECTS OF LEAFLET STIFFNESS, MORPHOLOGY, AND HEART RATE

Abstract:
Aortic valve defects significantly affect cardiovascular health, and nationally, more than 100,000 people undergo valve replacement each year. Bicuspid aortic valve (BAV) is a congenital defect in which two leaflets are fused together, compared to a normal tricuspid aortic valve (TAV) with three leaflets. The incidence of BAV is 1–2% of the population. However, BAV presents a higher risk for valvular defects and aortopathy, with an average age of valve replacement 20 years younger than that of TAV patients. The heterogeneity in BAV phenotype also complicates patient assessment. Additionally, BAV patients have a higher risk of bacterial infections in the valve leaflets, which can alter valve rigidity and functionality. In vivo measurements with 4D flow MRI have shown that BAV alters aortic hemodynamics and increases shear stress on the aortic wall, leading to aneurysm and dissection. Wall shear stress has been established as a biomarker for BAV patients. However, 4D flow MRI lacks sufficient spatial resolution near the wall, and BAV replacement decisions are still based on an aortic annulus diameter threshold, which is difficult to know a priori without regular check-ups or until symptoms appear. The effect of physical activities or exercises that increase heart rate is also unknown in relation to BAV disease progression. Our objective is to quantify BAV hydrodynamics with high spatial and temporal resolution to understand changes in cardiac flow patterns under elevated heart rate, reduced leaflet mobility, and a combination of both.

We tested this in an in vitro mock circulatory loop with pulsatile flow conditions. Flow waveforms were generated using an Avantor gear pump, matching systolic and diastolic times for 60, 90, and 120 bpm. Patient-mimicking 3D-printed BAV models with right-left cusp fusion morphologies were tested. A TAV served as a reference. Time-resolved planar particle image velocimetry (PIV) was performed downstream of the valve to capture instantaneous velocity fields over multiple cardiac cycles. To minimize optical distortion, refractive-index matched fluid was used within the test section and the surrounding chamber. High-speed imaging at 1.1 kHz enabled quantitative assessment of peak jet velocity, recirculation zones, vortical structures, and wall shear stress metrics. Preliminary results demonstrated clear differences in jet orientation and velocity magnitude for BAV model with different heart rates, with faster jet breakup and dissipation for lower cycle time. We also plan to test leaflets with different stiffnesses to quantify peak shear stress locations under reduced valve opening. This work addresses an important gap in understanding the influence of heart rate and valve leaflet stiffness on BAV hydrodynamics. The findings may improve risk assessment for aortic remodeling, support patient-specific treatment planning, and provide high-quality benchmark data for validating computational cardiovascular models.