Physiological control of a rotary left ventricular assist device: Robust control of pressure pulsatility with suction prevention and suppression

Abstract

A control method for rotary blood pumps is presented that operates the pump at a user-selectable operating point. In partial assist (PA) mode, the aortic valve opens predictably, and high ventricular strain rate and hence ventricular washout is achieved. In full assist (FA) mode, the level of unloading is maximized without inducing ventricular collapse. Emphasis is placed on a fast control action to prevent suction. A cascaded control loop that regulates the pulsatility of the pressure difference measured by the pump was designed. The reference pulsatility is automatically selected according to the operating mode and adapted continuously to changing physio-logical conditions. The pump speed is controlled by a robust predictive controller. Physiological and anatomical intra-patient and inter-patient variability is accounted for by a model of process uncertainties. To suppress possible suction events resulting from a sudden drop of preload, a suction detection and compensation mechanism that accelerates the controller action is added to the control loop. Stability and performance was guaranteed for the range of variation of physiological parameters and operating points. The response time to a sudden decrease of preload is between 5 and 20 s. Ventricular collapse is avoided for almost all scenarios. Only a step-wise drop of preload in mode FA may provoke suction, which is immediately suppressed by the controller. The control method showed promising results in computer simulations. Above all, the prevention of suction may have a positive effect on the therapy's outcome. In addition, the physician is relieved of the task of patient-specific tuning the controller settings. © 2009 Springer-Verlag.