Achieving physiologic perfusion with ventricular assist devices: comparison of control strategies

Rotary blood pumps (RBP) are currently being used as a bridge to transplantation as well as for myocardial recovery and destination therapy for patients with heart failure. Physiologic control systems for RBP that can automatically and autonomously adjust the pump flow to match the physiologic requirement of the patient while avoiding suction for varying clinical and physical activity conditions are needed to reduce human intervention and error, and to improve the quality of life. For RBP used as left ventricular assist devices (LVAD), we hypothesize that maintaining a constant average pressure difference between the pulmonary vein and the aorta (ΔPa) or maintaining a constant average pressure difference between the left ventricle and the aorta (ΔP) would give rise to a physiologically adequate perfusion while avoiding LV suction. Using a mock circulatory system we tested the performance of the control strategy of maintaining a constant average ΔPa and a constant average pump pressure head (ΔP) and compared it with the results obtained when constant rpm is maintained. The comparison was made for normal, failing, and asystolic left heart during rest and at light exercise. The ΔPa was maintained at 95 ± 1 mmHg and ΔP was maintained at 75 ± 1 mmHg for all the scenarios. The results indicate that the ΔPa control strategy maintained or restored the total flow rate to that of the physiologically normal heart during rest (3.8 l/m) and light exercise (5.4 l/m) conditions. The ΔPa approach adapted to changing exercise and clinical conditions better than the constant rpm and constant ΔP control strategies. Our computer simulation studies indicate that the ΔP control strategy performs better than the constant rpm control strategy, especially at higher cardiac demand situations, which could not be tested experimentally due to the limitation of the mock circulatory system.