CARD33: Analyzing Off-Design Point Operation for LVADs Using Flexible Rotor Blades

Abstract

Introduction: The use of left ventricular assist devices (LVADs) has exhibited clinical success in both destination and bridge-to-transplant therapy for patients suffering from end stage heart failure (HF). However, the operating speeds of the LVAD are often tuned to accommodate patient variability which might lead to operating the LVAD at off design points. This could cause a potential loss in efficiency and an increased risk of thrombosis/hemolysis. The flexible rotor blades will deform in response to the complex inflow conditions, and with an appropriate geometry and flexibility generate a flatter performance curve. This would not only improve the preload sensitivity of the LVAD but also offer a wider range of operation with optimal efficiencies. In this study, we investigate the hydraulic performance of varied impeller geometries for a centrifugal LVAD with flexible rotor blades at pediatric and adult pressure/flow conditions. Methods: The flexible rotor blades are manufactured by casting polyurethane resin (Easton, PA) of shore hardness 60A in a four-piece mold. These mold pieces were 3D printed using a J850 Pro (Stratasys Ltd, MN, USA). The inlet angle of the blades was set at 20o and the outlet angle was varied from 10o to 70o. The blade thickness was 1.2 mm and the blade height was 7 mm. These flexible rotor blades were evaluated on a hydrodynamic test setup with 40%wt glycerin solution as the working fluid. This setup consisted of a motor to drive the rotor, a flow probe, pressure transducers upstream and downstream of the rotor and a pinch valve to vary the downstream resistance. The mounted rotor is driven at 3000 RPM, and the flow produced by the rotor is measured as the pinch valve incrementally increases downstream resistance. The hydrodynamic results were then scaled to achieve pediatric and adult pressure/flow conditions of 70mmHg-2L/min and 90mmHg-5L/min respectively. To analyze the off-design point operation, the gradient of the pressure/flow curve at two operating conditions was calculated using the equation in Figure 1. Results: For a flexible rotor blade with an outlet angle of 30o, the operating speed for pediatric and adult pressure/flow conditions was found to be 2550 RPM and 3230 RPM respectively. The gradient at the pediatric and adult operating conditions was – 6.14 mmHg/ (L/min)-1 and – 11.12 mmHg/ (L/min)-1. Results for the remaining flexible rotor blades is currently being generated and will be presented at the conference. Conclusion: We successfully analyzed the hydraulic performance of a centrifugal LVAD with flexible rotor blades. The flexible rotor blades proposed in this study will be a positive step towards improving the off-design point operation of LVADs and thereby, reducing the blood damage associated with it.Figure 1. Equation used to calculate the gradient of the pressure/flow curve at two operating conditionsFigure 2. Hydrodynamic Test Setup SchematicFigure 3. Hydrodynamic Performance Results for Flexible Rotor Blade with 30o Outlet Angle