Patient-Adaptive Feedback Controllers for Heart Assist Devices

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Patient-Adaptive Feedback Controllers for Heart Assist DevicesA. Project SummaryHeart transplant candidates often wait long periods (300 days or more on the average) before a suitabledonor heart becomes available, and many of these candidate die while awaiting heart transplantation.Consequently, the medical community has been placing increased emphasis on the use of mechanicaldevices that can substitute for, or enhance, the function of the natural heart. A Ventricular Assist Device(VAD) is such a device. This device if often used as a bridge to mechanically support a patient whileawaiting heart transplantation, or while their natural heart recovers. But the ultimate use of this device is asa long-term iocurelr for heart failure. In either case, the goal of a VAD is to provide the patient with as closeto a normal lifestyle as possible. The goal for all concerned is to allow patients to return home and returnto the workforce.An important challenge facing the increased use of VADs is the development of an appropriate controllerfor these devices. The latest generation of VADs, based on turbo-dynamic pumps, requires a controller thatcan adjust the speed of the rotor (pump impeller) to meet the circulatory demand of the patient. Therefore,in addition to being robust and reliable, such a controller should be able to adapt to the daily activities andthe physiological changes of the patient. In this project we propose to investigate the theoretical andfundamental issues associated with the development of such a controller. More specifically, (1) we willcontinue our ongoing work on the development of a generalized model of a rotary blood pump that, whencoupled to existing model of the human cardiovascular system, will serve as a simulation model for furtherdevelopment; (2) we will develop a robust optimal feedback control algorithm that provides the flexibilityto incorporate various sensor inputs as available, and (3) we will implement the control algorithm into a PCplatform and test its responsiveness in a mock circulating flow loop. The principal functions of thisfeedback controller will be: (1) to determine and maintain appropriate cardiac output, subject to constraintsimposed by the device and the patients condition including avoiding ventricular suction; (2) to identifysystem variables and parameters to monitor the patient's condition, indicating when the patient'scardiovascular status is improving or deteriorating and detecting component failures; (3) to recognizedifferent operating conditions and data environments, responding to changes in the signals available formeasurement from the patient and the assist device; (4) to monitor the control strategy (algorithm) itself toavoid uncontrollable situations and inappropriate or dangerous control actions; and (5) to provide a fail-safemode of operation by entering a preset open-loop operating mode when a hardware or algorithmic failureoccurs.The primary intellectual merit of the proposed research will be to increase our understanding offundamental technical issues related to the control of non-conventional complex systems, such as theVADs, that involve both electromechanical as well as physiological components. A truly interdisciplinaryapproach, with expertise coming from the electrical, mechanical, and biomedical engineering fields as wellas the medical profession, is needed to develop the mathematical framework needed to be able toeffectively control such systems.The broader impact of the proposed research will primarily be in improving the quality of life forcardiovascular patients awaiting heart transplantation. Any improvement in the existing technology of theventricular assist devices will have a tremendous effect on the physical condition and ultimately therecovery of patients suffering from congestive heart failure. It is hoped that this study, leading to thedevelopment of a patient adaptive feedback controller, will provide an opportunity for these patients toleave the hospital, return home, and re-enter the work force while awaiting for a donor heart. Anotherimportant impact of this project is in training engineering graduate (and a few undergraduate) studentsfrom the electrical, mechanical, and biomedical, departments to work together as a team in this highlyinterdisciplinary field. This project will provide an opportunity for students to apply what they havelearned in the control and signal processing courses to a realistic (but not very well defined mathematically)problem that has a tremendous societal impact.