Robust physiological control of left ventricular assist devices

Due to the increasing shortage of donor hearts, modern left ventricular assist devices (LVADs) have become a real alternative to heart transplantation in advanced heart failure therapy. In clinical practice, these devices are fixed speed controlled which causes an insufficient adaption of the pump flow to the varying blood flow demand of the patient. This problem is addressed by presenting a robust control concept that ensures an adjustable load distribution between the native heart and a blood pump by utilizing a novel control variable: the assistance ratio. By using this relative value as the control variable, the changes of the residual cardiac output are amplified. If these changes are initiated by the remaining native physiological control loops, the combination of the damaged heart and an LVAD restores the functionality comparable to a healthy heart. The assistance control strategy was successfully tested in vitro using a hydrodynamic cardiovascular system simulator as well as in vivo in two different animal studies with sheep suffering from acute heart failure. The evidence from these acute trials suggests that, if the native cardiac output control loops are still intact, the assistance control strategy adequately maintains the systemic circulation.