Modeling and control of the heart left ventricle supported with a rotary assist device

A rotary left ventricular assist device (RLVAD) is a mechanical pump implanted in patients with congestive heart failure to assist their left ventricle in pumping blood through the circulatory system. This blood pump is controlled by varying the rotor speed to adjust the amount of blood flow pumped into the circulatory system. If the patient is in a health care facility, the pump speed can be adjusted manually by a trained clinician to meet the patient¿s blood needs depending on his or her activity level. However, an important challenge facing the increased use of the RLVAD is the desire to allow the patient to return home. The development of an appropriate feedback controller that is capable of automatically adjusting the pump speed is therefore a crucial step in meeting this challenge. In order to be able to develop such a controller an appropriate dynamic mathematical model of the combined cardiovascular system and RLVAD must first be developed. In this paper, we review progress on a state space model for this system that can be used to develop the controller. The model is 6th order, nonlinear, and time-varying and is a combination of a 5th order model of the left ventricle and circulatory system and a 1st order model of the RLVAD along with its inlet and outlet cannulae. The entire combined system is controlled by the rotational speed of the pump. Using this model we will discuss some of the challenges faced in the development of a useful feedback controller for this system. We will also present some preliminary results on a simple partial state feedback controller whose purpose is to prevent the occurrence of a dangerous phenomenon called ventricular suction.