Pitfalls in the development of a rotary blood pump controller

The controller presents a major obstacle in the development of the rotary b lood pump as a left ventricular assist device (LVAD). Clinically, LVAD flow is a good indicator in the regulation of circulatory conditions and pump f low changes, depending on pump preload and afterload. Many investigators ha ve tried estimating pump flow by referencing the motor current. There have been pitfalls in in vitro experimental settings, however. Using a test loop with a pneumatically driven LV chamber and a centrifugal pump as an LVAD, we monitored pump flow and pressure head to evaluate the pump performance c urve (H-Q curve). Under pulsatile LV conditions, the H-Q curve was a loop t hat changed, depending on LV contractility. The pneumatically driven LV cha mber cannot mimic the Starling phenomenon, so the developed LV pressure doe s not change according to the LV preload. Rotary pump flow estimation is th e most effective control method. in pulsatile conditions, however, the H-Q curve is a loop that changes under various LV contractility conditions, com plicating determination of linear equation for calculating flow. In additio n, the LV chamber in the test loop cannot mimic native heart contractility as described by Starling's law. This finding can lead to a misanalysis of t he H-Q curve under pulsatile conditions.