N.H. Lovell and P.J. Ayre (Australia)
Implantable rotary blood pump, pumping states, control strategy, left ventricular assist device.
In a clinical setting it is necessary to control the speed of rotary blood pumps used as left ventricular assist devices (LVADs) to prevent possible severe complications associated with over- or under-pumping. 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 physiologically significant pumping states (without the need for additional implantable sensors). 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. These states are described in detail and a strategy for non invasive detection developed in a pulsatile mock loop and validated in (N=3) ex vivo sheep experiments. The strategy was based on a classification and regression tree. It was possible to detect pump states with 100% accuracy (0% false-positives and 0% false-negatives) in both the mock loop and in the ex vivo experiments (under pharmacological and other interventions).
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