In vitro flow visualization study within an outlet cannula of a rotary ventricular assist device

Rotary ventricular assist devices (VADs) are primarily used during surgery, bridge to recovery, and short-term post-operative assistance. Most hospitals today use a VAD that is based on a pusher plate principle for long-term assistance. However, rotary blood pumps require less energy for power and are less complex in design and have seen greater clinical application as of late. There are issues involving the use of rotary VADs for ventricular assistance including the behavior of flow emanating from the assist device, which might induce flow irregularities leading to an adverse host response with a potential outcome of strokes or cerebrovascular accidents.; An in vitro analysis of the flow fields using a particle image velocimetry system seeded with fluorescent particles was executed to visualize the flow occurring within the outlet cannula of a rotary ventricular assist device. Performing experiments over a wide range of operating conditions including physiologic situations, data was collected using glass cannulae with angles ranging from 30° to 75°. Axial flow fields at the bend and downstream of the bend were the primary focus. The results indicate that flow irregularities exist over all operating conditions and cannula angles, particularly at the higher flow rates and more acute angles. Stagnant zones as well as recirculation zones along the inner wall of the cannula are visible and vary with angle and operating condition. These stagnant or recirculation zones could lead to thrombus formation. Boundary layer shedding occurs downstream of the cannula bends while other flow irregularities become more pronounced with increasing cannula angle. These conditions may create hemolysis, thus exacerbating potential danger to the surgical patient. In conclusion, this study has indicated that acute angles of attack regarding the outflow tract of a VAD should be avoided during surgical implantation and device placement due to the potentially adverse conditions that might occur.