Objective: The hydraulic properties of implantable rotary blood pumps (RBPs) determine their interaction with the cardiovascular system. A systematic comparison in this regard has not yet been performed for different clinically used RBPs. Aim of this study was to describe the hydraulic characteristics of four RBPs with a universal mathematical model and to compare their behavior under clinical operating conditions. Methods: First, static and dynamic pump properties of four RBPs (HVAD, Heartmate II, Heartmate 3 and Incor) including their peripheral components were identified in an in-vitro setup; results were translated into mathematical models based on principles of turbomachinery including the low and backflow region. Second, the four hydraulic models were compared in a numerical simulation of the cardiovascular system for full and partial support conditions. Results: A model structure applicable to each of the investigated RBPs was developed. Deviations between simulated and measured signals for static and dynamic properties were small (2.6 $\pm$ 0.5 mmHg, 0.38 $\pm$ 0.14 L/min, respectively). For a simulated partial support condition, flow pulsatility ranged from 4.1 (Incor) to 9.1 L/min (HVAD). Negative flow rates during diastole were observed in 3 out of 4 pumps. Conclusion: Hydraulic properties differ greatly between the investigated RBPs, with flat characteristics for the HVAD and Heartmate II and steeper curves for the Heartmate 3 and especially the Incor. Significance: Hydraulic characteristics of implantable RBPs are particularly important at lower pump flow rates if backflow is to be avoided. For further research we provide dynamic hydraulic models of the four RBPs including their periphery.

Contemporary centrifugal continuous-flow left ventricular assist devices (LVADs) incorporate dynamic speed modulation algorithms. Hemocompatibility of these periodic unsteady pump operating conditions has been only partially explored. We evaluated whether speed modulation induces flow alterations associated with detrimental prothrombotic effects. For this aim, we evaluated the thrombogenic profile of the HeartWare ventricular assist device (HVAD) Lavare Cycle (LC) and HeartMate3 (HM3) artificial pulse (AP) via comprehensive numerical evaluation of (i) pump washout, (ii) stagnation zones, (iii) shear stress regimens, and (iv) modeling of platelet activation status via the platelet activity state (PAS) model. Data were compared between different simulated operating scenarios, including: (i) constant rotational speed and pump pressure head, used as reference; (ii) unsteady pump pressure head as induced by cardiac pulsatility; and (iii) unsteady rotor speed modulation of the LC (HVAD) and AP (HM3). Our results show that pump washout did not improve across the different simulated scenarios in neither the HVAD nor the HM3. The LC reduced but did not eliminate flow stagnation (–57%) and did not impact metrics of HVAD platelet activation (median PAS: +0.4%). The AP reduced HM3 flow stagnation by up to 91% but increased prothrombotic shear stress and simulated platelet activation (median PAS: +124%). Our study advances understanding of the pathogenesis of LVAD thrombosis, suggesting mechanistic implications of rotor speed modulation. Our data provide rationale criteria for the future design optimization of next generation LVADs to further reduce hemocompatibility-related adverse events.