Classification of Unsteady Flow Patterns in a Rotodynamic Blood Pump: Introduction of Non-Dimensional Regime Map

Rotodynamic blood pumps (also known as rotary or continuous flow blood pumps) are commonly evaluated in vitro under steady flow conditions. However, when these devices are used clinically as ventricular assist devices (VADs), the flow is pulsatile due to the contribution of the native heart. This study investigated the influence of this unsteady flow upon the internal hemodynamics of a centrifugal blood pump. The flow field within the median axial plane of the flow path was visualized with particle image velocimetry (PIV) using a transparent replica of the Levacor VAD. The replica was inserted in a dynamic cardiovascular simulator that synchronized the image acquisition to the cardiac cycle. As compared to steady flow, pulsatile conditions produced periodic, transient recirculation regions within the impeller and separation in the outlet diffuser. Dimensional analysis revealed that the flow characteristics could be uniquely described by the non-dimensional flow coefficient (Φ) and its time derivative ( Φ ˙ ), thereby eliminating impeller speed from the experimental matrix. Four regimes within the Φ– Φ ˙ plane were found to classify the flow patterns, well-attached or disturbed. These results and methods can be generalized to provide insights for both design and operation of rotodynamic blood pumps for safety and efficacy.