HEMODYNAMIC SYSTEM-ANALYSIS OF INTRAARTERIAL MICROAXIAL PUMPS IN-VITRO AND IN-VIVO

Because of the lack of a sophisticated pump management system, the per formance of the Hemopump in patients cannot be assessed successfully. To clarify the interrelationship between an intravascular nonpulsatile pump and a pulsating ventricle, an in vitro study was set up under co ntrolled conditions. Before these in vitro experiments, a series of in vivo experiments were performed in sheep using Hp31 cannulae. As anti cipated, the resulting pulsatile pump flow was a function of the momen tary pressure difference across the pump. This varying pump flow showe d a significant flow loop hysteresis, indicating that the pressure dif ference across the pump is not the only parameter governing momentary pump flow of a rotary pump operating at constant speed in a pulsatile environment. Furthermore, flow in the Hp31 was significantly influence d by the inflow situation, blood supply, size of the ventricular cavit y, and shape and position of the inflow cannula within the ventricle. Pulsatile flow conditions with good as well as impaired inflow into th e pump were accordingly simulated in vitro to verify the in vivo measu rements, to characterize the various inflow conditions, and to discuss methods of improved pump management. As a result of the in vivo and i n vitro experiments, one can rely on the measurement of nonpulsatile i n vitro flow and pressure differences across the pump to characterize the momentary pump flow for good inflow conditions into the pump. For these situations, the flow hysteresis produced, caused by fluid inerti a within the pump and cannula, can be neglected. In contrast, for an i mpaired inflow situation, the calculated pump flow based on pressure d ifference measurements can be misleading. Consequently, an improved pu mp management system is required to adjust the pump speed, the pump pe rformance, to any kind of impaired inflow.