Date on Master's Thesis/Doctoral Dissertation

12-2020

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Interdisciplinary and Graduate Studies

Degree Program

Interdisciplinary Studies (Individualized Degree), PhD

Committee Chair

Koenig, Steven

Committee Member

Dasse, Kurt

Committee Member

Slaughter, Mark

Committee Member

Roussel, Thomas

Committee Member

Kopechek, Jonathan

Committee Member

Williams, Stuart

Author's Keywords

mechanical circulatory support; ventricular assist device; rotary blood pump; computational fluid dynamics; heart failure; pump design

Abstract

Heart failure (HF) remains the leading cause of death, affecting 26 million adults worldwide and 6.5 million adults in the United States. Pediatric HF patients have been a historically underserved population with few options for mechanical circulatory support (MCS) therapy, a leading treatment as an alternative to heart transplantation. To address this clinical need, the Inspired Universal MagLev System is being developed; a low cost, universal magnetically levitated extracorporeal MCS system with interchangeable single-use pumps that will ultimately provide adult and pediatric patients ventricular and respiratory assist therapies. The Inspired Pediatric VAD is the first single-use pump application for this MCS system and is specifically designed for pediatric circulatory support. This dissertation describes the development efforts to design and evaluate iterative impeller and pump housings for the Inspired Pediatric VAD. Requirements for the Inspired Pediatric VAD design include the need to generate the appropriate hemodynamic parameters (pressures and flows) for pediatric patients, and miniaturization of the pump and impeller to accommodate the pediatric population. Traditional pump theory and design methods were applied to aid in the unique design of the VAD impeller and pump housing, resulting in multiple design iterations. Two impeller and pump designs (V1, V2) were virtually constructed using computer-aided design (CAD) software. Three-dimensional flow and pressure features were analyzed using computational fluid dynamics (CFD) analysis. Simulated pump designs (V1, V2) were operated at 15% higher rotational speeds (~5000 rpm) than initially estimated (4255 rpm) to achieve the desired operational point (3.5 L/min flow at 150 mmHg). V2 design outperformed V1 by generating up to 30% higher pressures at all simulated rotational speeds and with 5% lower priming volume. Simulated hydrodynamic performance (flow, pressure and hydraulic efficiency) of VAD V2 compared favorably to current commercially available MCS devices. A prototype of the Inspired Pediatric VAD V2 was fabricated, the magnitude and range of hydraulic torque and forces of the impeller were quantified, and the hydrodynamic performance benchmarked. A static mock flow loop model containing a heated blood analogue solution was created to test the pump over a range of rotational speeds (500 - 6000 RPM), flow rates (0 - 3.5 L/min), and pressures (0 to ~420 mmHg). The device was initially powered by a shaft driven DC motor, which was used to calculate the fluid torque acting on the impeller. Additional CFD simulations of VAD V2 were compared against the empirical bench-top data at select rotational speed and flow rate conditions. Empirically, the pediatric VAD produced flows as high as 4.3 L/min against a pressure of 127 mmHg at 6000 RPM. Based on the performance of the first two VAD design iterations, a final design iteration, VAD V3, was achieved. Hydrodynamic performance of VAD V3 was numerically assessed using CFD simulations. The results indicated no change in flow and pressure head performance compared to the previous device design (V2). Shear stress and flow residence time volumetric distributions were generated over a range of pump rotational speeds and flow rates. At the lowest pump operating point (3000 RPM, 0.50 L/min, 75 mmHg), 79% of the pump volume was in the shear stress range of 0 – 10 Pa with < 1% of the volume in the critical range of 150 – 1000 Pa associated with potential for increased risk of clinically-significant blood damage. At higher speed and flow (5000 RPM, 3.50 L/min, 176 mmHg), 65% of the volume resided in the 0 – 10 Pa range compared to 2.3% at 150 – 1000 Pa. The initial results from the computational characterization of the Inspired Pediatric VAD V3 were encouraging, and based on the overall research performed to date, future work will include pre-clinical testing of VAD V3 in static and dynamic mock flow loop and acute large animal model studies to further assess device function, hydrodynamic performance, hemodynamic response, and hemocompatibility.

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