Intelligent control design for heart assist devices

Heart assist devices are blood pumps used to augment the cardiac output of patients with left ventricular failure. A new generation of devices being evaluated for human use is based on turbo-hydrodynamic methods of pumping, which offer several advantages over the reciprocating, pulsatile methods used in current devices. However, the new devices pose a more difficult control problem because of their sensitivity to circulatory load and other patient cardiovascular parameters. The paper describes the design of a control structure to regulate the operation of these devices. The controller has three different types of algorithm available: a model-based patient-adaptive algorithm; two heuristic algorithms that rely only on the device characteristics; and a default algorithm. The patient-adaptive algorithm uses a model of the patient's systemic circulation to determine the required cardiac output for a given level of activity. The heuristic algorithms use the known operating characteristics of the device to adjust the cardiac output to changes in demand without knowledge of patient-specific conditions. The default algorithm provides a fixed speed operation to be used in case of system or sensor failure. An intelligent supervisor determines the cardiac output required from the assist device and selects the control algorithm to use, based on a multidimensional measure of the patient's level of activity, available estimates of hemodynamic variables, reliability of the patient model, and the past history of the patient.