FLOW VISUALIZATION STUDY OF WORLDHEART LEVACOR TM VAD UNDER SYNCHRONOUS PULSATILE CONDITIONS

1. C A B C D A B C D D 4 1 5 A B Camera C D Smooth flow & separated flow in the outlet under low and high flow coefficient 2 1 3 A 2 5 5 1 4 2 1 3 3 4 B FLOW VISUALIZATION STUDY OF WORLDHEART LEVACORTM VAD UNDER SYNCHRONOUS PULSATILE CONDITIONS Fangjun Shu,♥ Stijn Vandenberghe,♥ Philip J Millerand James F Antaki ♥ ♥ BioMedical Engineering, Carnegie Mellon University Bioengineering, University of Pittsburgh,  WorldHeart, Inc. FLOW VISUALIZATION: The fluid dynamics within the outlet diffuser and part of the blade to blade region of the impeller was investigated using a 2D PIV system. Glycerol/water (35/65 V%) mixture seeded with 7 μm fluorescent particles was used as working fluid. The camera was triggered using pump encoder and ventricle volume signals, giving image pairs of 16 cardiac phases with the impeller in a fixed position. PULSATILE CONDITIONS: INTRODUCTION CONCLUSIONS Results of two representative conditions (low and nominal pump speed) are presented. • PIV measurements were conducted for the prototype WorldHeart LevacorTM pump in both steady state and pulsatile conditions. • Steady State • Under steady state conditions, the flow field within the critical regions of interest exhibited similitude according to the non-dimensional flow coefficient. • Steady state nominal flow conditions at all three speeds demonstrated well-behaved velocity fields, absent of separation and recirculation. • Pulsatile • At low RPM, the (mock) ventricular contribution to the velocity field was relatively strong, inducing transient regurgitation, flow separation (outlet diffuser) and flow recirculation (blade-blade region). • At nominal RPM, regurgitation and flow recirculation no longer exist. • Rotary (Turbodynamic) blood pumps are typically designed for a single “best efficiency” operating point; however in practice they must operate over a wide dynamic range of flow and pressure conditions: due to the varying demands of the body, and due to the pulsations caused by the native heart. • Pulsatility causes very complicated time-dependent fluid dynamics within the pump. • Time-varying CFD analyses over the full range of operating conditions are prohibitive. • These studies were performed to characterize the time-varying hemodynamics experimentally through flow visualization. PIV measurement region RESULTS STEADY STATE: Condition 2 Condition 1 NOMINAL (2250 rpm) Absolute velocity Relative velocity METHODS LOW (1500 rpm)Absolute velocity Relative velocity PUMP AND FLOW LOOP: The experimental version of the pump was shaft-driven and was fitted with a transparent (acrylic) housing to permit visualization of the flow path. PIV was conducted at 5 steady-state conditions including 3 pump speeds and 3 flow coefficients. No flow separation was observed within the outlet diffuser at nominal flow coefficient. At fixed flow coefficient, flow similarity is apparent. Levacore VAD 2 3 The pump was interposed into a modified Vivitro cardiovascular simulator, comprised of a reciprocating positive displacement pump, reservoir, ventricle, compliance chamber, and flow restrictor, connected by PVC tubing. The velocity field relative to the impeller was acquired by subtracting the circumferential velocity (ωr) from the absolute velocity field. Flow recirculation was observed within the blade-blade region at low flow coefficient. • At 1500 rpm, intermittent flow recirculation was observed in the blade to blade region. • For both speeds, intermittent flow separations were observed within the outlet diffuser. Experimental setup