Flow Features and Device-Induced Blood Trauma in CF-VADs under a pulsatile blood flow condition: A CFD Comparative Study

Abstract

In this study, the flow features and device-associated blood trauma in four clinical ventricular assist devices (VADs) (two implantable axial VADs, one implantable centrifugal VAD, and one extracorporeal VAD) were computationally analyzed under clinically relevant pulsatile flow conditions. The four VADs were operated at fixed pump speed at a mean rate of 4.5 L/min. Mean pressure difference, wall shear stress (WSS), volume distribution of scalar shear stress (SSS), and shear-induced hemolysis index (HI) were derived from the flow field of each VAD and were compared. The computationally predicted mean pressure difference across the three implantable VADs was ~ 70mm Hg and the extracorporeal VAD was ~ 345 mmHg, which matched well with their reported pressure-flow curves. The axial VADs had higher mean WSS and SSS compared to the centrifugal VADs. However, the residence time of the centrifugal VADs was much longer compared to the axial VADs because of the large volume of the centrifugal VADs. The highest SSS was observed in one axial VAD and the longest exposure time was observed in one centrifugal VAD. These two VADs generated the highest HI. The shear-induced HI varied as a function of flow rate within each cardiac cycle. At fixed pump speed, the HI was greatest at low flow rate due to longer exposure time to shear stress compared to at high flow rate. Subsequently, we hypothesize that in order to reduce the risk of blood trauma during VAD support, shear stress magnitude and exposure time need to be minimized.

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