The Hemodynamics of the Berlin Pulsatile VAD and the Role of its MHV Configuration

Abstract

The 3D flow in a model of the Berlin ventricular assist device (VAD) chamber with monoleaflet valves placed in S-shape conduits was simulated numerically. The blood flow dynamics were described in terms of flow patterns, velocity, pressure, and shear stress. The hemodynamic properties and the VAD's potential risk for thrombosis were evaluated in terms of mixing and washout properties, and global estimations of platelet level of activation (LOA). In order to evaluate the role of valves on the flow in the chamber, the flow in a model with bileaflet valves in straight conduits was simulated and compared with the original case. The results showed that in both models a large rotating flow was developed in the chamber during filling. This vortex filled the entire chamber and moved constantly up to the peak ejection phase, resulting in relatively low shear stress (up to 0.4 Pa) and no lasting stagnation regions. Significant shear stresses were found near the valves with higher values near the outlet valve in both models. The configuration of valves and conduits had a large effect on VAD washout and mixing properties, with advantage to the bileaflet model. However, since the bileaflet valves exhibited higher shear stresses, higher LOA were found for the bileaflet model.

Lagrangian Postprocessing of Computational Hemodynamics

“…(10) alternatively. This has been used in several computational studies to calculate AP [9, 1, 133]. It should be noted however that for incompressible flow, ${\sigma }_{\nu }=\sqrt{2}\mu {\mathbf{e}}_F$, and the two measures provide equivalent results.…”

“…It should be noted however that for incompressible flow, ${\sigma }_{\nu }=\sqrt{2}\mu {\mathbf{e}}_F$, and the two measures provide equivalent results. Some experimental studies have suggested that stress and exposure time should not be “weighted equally,” but AP is better expressed as a power law of stress and exposure time [53, 2, 55, 106], which has been applied in several computational studies [9, 1, 102, 153, 132, 133, 12, 93]. …”

Validation of a CFD Methodology for Positive Displacement LVAD Analysis Using PIV Data

“…For this research, valve closure is modeled using the variable viscosity model employed by Avrahami et al [20][21][22] and Stijnen [23,24]. The valve grids are fixed at the fully opened position for the duration of the analysis.…”

“…Avrahami et al [20][21][22] performed an unsteady 3D analysis of a complete pumping cycle for several LVADs. The analysis assumed incompressible, Newtonian, and laminar fluid behaviors.…”

Flow Visualization of the Penn State Pulsatile Pediatric Ventricular Assist Device Cannulae and Change in Outlet Valve Placement

“…Changes to valve type and orientation have been established as methods to improve flow throughout VADs. 1,3,12,20 In a previous study by our lab we found that the blockage remained at all valve orientations, therefore we chose to move the valve position. The rationale of moving the valve downstream is that the flow can move from the body of the device to the smaller outlet port without the interference of the mechanical heart valve strut and disc.…”