Identifying physiologically significant pumping states in implantable rotary blood pumps using non-invasive system observers

The VentraCor implantable rotary blood pump (IRBP) is a centrifugal pump that uses a hydrodynamic bearing to support its impeller. The speed of the pump may be controlled externally. However, under- or over-pumping can result in severe complications to the patient, so a means to control pump flow within a predefined range is clinically important. In vitro (mock loop) and ex vivo experiments in the sheep (n=3) were conducted. By varying pump speed in the mock loop, five physiologically significant states were identified: regurgitant pump flow, ventricular ejection, full aortic valve closure over the cardiac cycle, intermittent collapse of the ventricle wall, and total collapse of the ventricle. The hypothesis is that by using only the non-invasive measure of instantaneous pump impeller speed to assess flow dynamics and an average flow estimate developed from speed and input power, it is possible to detect the afore-mentioned states. Using a classification and regression tree derived in the mock loop, it was possible to detect pump states with 100% accuracy (0% false-positives and 0% false-negatives) in both the mock loop (under the same and different loading conditions) and in the ex vivo experiments (under pharmacological and other interventions).