Heart failure is the number one cause of death in the United States and presents an increasing public burden of morbidity and mortality even as the mortality from coronary artery disease and hypertension is decreasing. While an estimated 40,000 congestive heart failure patients are candidates for heart transplantation, only 2,200 donor hearts are made available each year highlighting the need for mechanical circulatory support. In its efforts to develop new treatments of cardiovascular diseases, the NIH NHLBI has funded development of pulsatile and nonpulsatile mechanical circulatory assist devices (MCADs). While, current use of MCADs is increasing, many more patients would benefit if fully implantable and wearable devices with physiologic control systems were available. MiTi's ultimate goal is an implantable rotary Left Ventricular Assist Device (LVAD) with physiologic controller for destination therapy in adult heart failure patients. Key and novel features of the proposed self sensing physiologic controller are its ability to use motor and magnetic bearing signals to adjust LVAD output in response to cardiac output changes through the use of differential pressure and flow estimators all while avoiding suction. The specific goals of this project are to design, implement and demonstrate physiologic control of the MiTiHeart(R) LVAD output through computer simulations, in vitro and in vivo tests. Specifically, MiTi(R)'s Mock Circulator System (MCS) will be modified to more accurately model left ventricle hemodynamics, the physiologic control algorithms having differential pressure, flow and suction avoidance objective functions will be implemented in the MiTiHeart(R) LVAD controller and evaluated in the MCS. Electric analog computer simulations of the MCS and LVAD will be updated and tuned to match the measured data so that evaluations of additional control algorithms and system physical changes can be simulated including replacing the MCS model with a human cardiovascular system model. Finally, in vivo acute animal studies will be completed at Penn State Hershey Medical Center to demonstrate the ability of the physiologic controller to adjust LVAD output without entering suction. The following Specific Aims are planned: (1) Design and implement modifications to the MiTi(R) MCS to more accurately model left ventricle hemodynamics by incorporating improved simulation of left ventricle (LV) ejection flow and pressure. (2) Modify the mathematical model of the MCS developed in Phase I to accept an enhanced LVAD performance model including the physiologic control algorithm. Tune the integrated mathematical model to reflect the measured performance in the MCS. Use the optimized model to assess the ability of the LVAD and controller to respond to simulated changes first in the MCS model and then with a human cardiovascular system (CVS) model. Simulations with both MCS and CVS models will then be performed using the enhanced models to assess performance of the LVAD and physiologic control system under a wide variety of conditions to verify the ability of the controller to vary output with changing physiologic demand while also avoiding suction. (3) Evaluate the physiologic control system performance, suction avoidance and pump differential pressure and flow estimations via in vitro testing in the updated MCS. The physiologic control algorithms and architecture developed under Phase I will be implemented in a dSpace digital control hardware system. The control system will then be used with the MiTiHeart LVAD to characterize and verify the proposed control system in the updated MCS. MCS testing under different simulated heart conditions that encourage suction events will be conducted. (4) Conduct three in vivo acute animal studies to validate performance of the physiologic controller including estimating differential pressure and flow as well as detecting and avoiding suction where the animal heart CO will be pharmacologically modified.
According to the American Heart Association [1], approximately one million Americans die each year from heart disease and almost 4.7 million Americans have congestive heart failure (CHF), a chronic condition in which at least one chamber of the heart is not pumping well enough to meet the body's need. With more than half a million new cases of CHF and only 2,200 donor hearts available for almost 40,000 heart transplantation candidates every year, there is a pressing need for new treatment options such as mechanical circulatory assist devices or heart assist pumps [2]. The success of early developments has resulted in the use of circulatory assistance for short durations [2, 3, 4], however new developments are needed to make long duration use of these heart assist devices possible.
