Fluorescent image tracking velocimetry of the Nimbus AxiPump

High shear rates and extended residence times causing hemolysis and platelet activation can develop in an assist pump or cannula when inferior flow conditions exist. The high volume output of a miniature axial flow pump presents challenges in avoiding these adverse conditions. To assess the hemodynamics within the continuous flow Nimbus Axi-Pump, vector flow fields inside a translucent inflow cannula and a modified 12 mm AxiPump were mapped. Fluorescent image tracking velocimetry was used to track the motion of neutrally buoyant fluorescent particles (30 microns) using pulsed laser light, high resolution video cameras, and computer image analysis. An acrylic pump housing and cannula were integrated into a mock circulatory loop filled with a Newtonian, optically clear blood analog fluid. The flow parameters were controlled to yield known, physiologic loading conditions, including varying degrees of pulsatility. Cannula flow visualization results exhibited critical recirculation patterns at the bend. These results will be used to further optimize the design of the inflow. Particle impact was seen at the pump inlet in the inducer region of the rotor. Very good attachment of flow from the rotor to stator was observed when the pump operated at normal operating speeds. Intermittent regurgitant flow fields were evident in the presence of increased pulsatility and low pump speed. These results have lead to improvements in impeller design and speed control criteria to avoid potential deleterious flows.