| Description |
Heart disease is the leading cause of death in the United States. Mechanical circulatory support by ventricular assist devices (VADs) is a means by which deteriorating heart function can be supplemented, and is a leading therapy for latestage heart failure patients. The devices are commonly connected to the apex of the left ventricle (LV) to move oxygenated blood to the body via the aorta. Recent developments have made continuous-flow pumps commonplace in the clinical environment when compared to their pulsatile-flow predecessors. Typically, continuous-flow VADs are designed with axial- or centrifugal- (radial) configurations. The pressures and flow rates vary dramatically in the native heart as blood is moved from the LV to the aorta. This dissertation presents pressure-flow characteristics for both axial- and centrifugal-flow VADs within a wide range of pressure differential values under uniform conditions, by means of a novel, open-loop flow system. Current techniques employ a closed-loop system to determine pump performance. A closed-loop system does not allow pressure differentials less than or equal to zero to be achieved. The native heart experiences pressure gradients near zero across the aortic valve during systole, which is essentially where the VAD is placed. Thus, an open-loop flow system with independently adjustable preload and afterload pressures is required to reach physiologically-relevant pressure differential regions that approximate the pressure gradient across the aortic valve during systole. Additional modifications made to the open-loop flow system generate pulsatile flow type conditions, which mimic those of the native LV. With this type of in vitro test system, not only can general hydrodynamic performance and hydraulic efficiency of VADs be measured, but also off-design operational performance under dynamic flow conditions can be characterized. This research explores hydrodynamic performance characteristics of axial- and centrifugal-flow VADs to determine design advantages that each have. Device characteristics include pressure-flow performance curves, pressure sensitivity, pulsatility index, and pulsatility ratio. Performance curves and other relevant attributes are investigated at previously unreported pressure-flow regions. Performance is evaluated theoretically, computationally, and experimentally under both steady-state, continuous-flow and pulsatile-flow circumstances. |
