Methods for determination of stagnation in pneumatic ventricular assist devices

Abstract

Background:A pneumatic paediatric ventricular assist device developed at the Foundation of Cardiac Surgery Development, Zabrze, equipped with valves based on J. Moll’s design, with later modifications introduced at the Institute of Turbomachinery, Lodz University of Technology, was tested numerically and experimentally. The main aim of those investigations was to detect stagnation zones within the ventricular assist device and indicate advantages and limitations of both approaches.Methods:In the numerical transient test, a motion of the diaphragm and discs was simulated. Two different methods were used to illustrate stagnation zones in the ventricular assist device. The flow pattern inside the chamber was represented by velocity contours and vectors to validate the results using images obtained in the laser particle image velocimetry experiment.Results:The experimental light-based method implied problems with proper illumination of regions in the wall vicinity. High-resolution flow data and other important parameters as stagnation regions or flow patterns in regions not accessible for light in the particle image velocimetry method are derived in the numerical solution. However, computations of a single case are much more time-consuming if compared to a single experiment conducted on a well-calibrated stand.Conclusion:The resulting main vortexes in the central part of the pump chamber and the velocity magnitudes are correlated in both methods, which are complementary and when used together offer better insight into the flow structure inside the ventricular assist device and enable a deeper analysis of the results.

Effect of the bileaflet inlet valve angle on the flow of a pediatric ventricular assist device: Experimental analysis

“…In bio‐flows as is the case of blood, this threshold is based on the blood coagulation cascade. In this work, all regions with velocities lower than 0.01 m/s 8 were highlighted. The specific areas where the stagnation occurs are depicted.…”

“…For example, there are two approaches to estimate thrombus formation from the velocity field: stagnation zones and shear stress/rates. Stagnations zones are based on fluid regions where the velocities are lower than a threshold, 7,8 while shear stress/rates are based on a threshold of a derivative of the velocity in relation to a wall. 9 Existing devices form thrombus in between 38% and 63% of the cases for infants, while the rate in adults is around 18%.…”

Optimizing cerebral perfusion and hemodynamics during cardiopulmonary bypass through cannula design combining in silico, in vitro and in vivo input

“…Regions of stagnating blood flow with velocities v < 0.01 m/s are prone to thrombus formation 37 . This can even occur for well heparinized patients, if the heparin boluses do not advance into the respective areas due to stagnating blood flow.…”

Fluid‐structure interaction analysis of a collapsible axial flow blood pump impeller and protective cage for Fontan patients

“…Therefore, the k-ω based SST turbulence model was used because of its ability to reasonably predict and resolve flow both at the wall and in the bulk flow regime. The SST turbulence model, developed by Menter, 14 was selected and is commonly used within the field [15][16][17][18][19] because it has been shown to be more accurate near the wall and in the bulk flow. It leverages blending equations that use distance from wall to determine the correct two-equation model formulation (k-ε or k-ω).…”