Clinical success of pediatric veno‐venous (VV) extracorporeal membrane oxygenation (ECMO) is associated with the double lumen cannula cardiovascular device design as well as its anatomic orientation in the atrium. The positions of cannula ports with respect to the vena cavae and the tricuspid valve are believed to play a significant role on device hemodynamics. Despite various improvements in ECMO catheters, especially for the neonatal and congenital heart patients, it is still challenging to select a catalogue size that would fit to most patients optimally. In effect, the local unfavorable blood flow characteristics of the cannula would translate to an overall loss of efficiency of the ECMO circuit. In this study, the complex flow regime of a neonatal double lumen cannula, positioned in a patient‐specific right atrium, is presented for the first time in literature. A pulsatile computational fluid dynamics (CFD) solver that is validated for cardiovascular device flow regimes was used to perform the detailed flow, oxygenated blood transport, and site‐specific blood damage analysis using an integrated cannula and right atrium model. A standard 13Fr double lumen cannula was scanned using micro‐CT, reconstructed and simulated under physiologic flow conditions. User defined scalar transport equations allowed the quantification of the mixing and convection of oxygenated and deoxygenated blood as well as blood residence times and hemolysis build‐up. Site‐specific CFD analysis provided key insight into the hemodynamic challenges encountered in cannula design and the associated intra‐atrial flow patterns. Due to neonatal flow conditions, an ultra high velocity infusion jet emanated from the infusion port and created a zone of major recirculation in the atrium. This flow regime influenced the delivery of the oxygenated blood to the tricuspid valve. Elevated velocities and complex gradients resulted in higher wall shear stresses (WSS) particularly at the infusion port having the highest value followed by the aspiration hole closest to the drainage port. Our results show that, in a cannula that is perfectly oriented in the atrium, almost 38% of the oxygenated blood is lost to the atrial circulation while only half of the blood from inferior vena cava (IVC) can reach to the tricuspid valve. As such, approximately 6% of venous blood from superior vena cava (SVC) can be delivered to tricuspid. High values of hemolysis index were observed with blood damage encountered around infusion hole (0.025%). These results warrant further improvements in the cannula design to achieve optimal performance of ECMO and better patient outcomes.

Objective: Malposition of dual lumen cannula is a frequent and challenging complication in neonates and plays a significant role in shaping the in vitro device hemodynamics. This study aims to analyze the effect of the dual lumen cannula malposition on right-atrial hemodynamics in neonatal patients using an experimentally validated computational fluid dynamics model. Methods: A computer model was developed for clinically approved dual lumen cannula (13Fr Origen Biomedical, Austin, Texas, USA) oriented inside the atrium of a 3-kg neonate with normal venous return. Atrial hemodynamics and dual lumen cannula malposition were systematically simulated for two rotations (antero-atrial and atrio-septal) and four translations (two intravascular movements along inferior vena cava and two dislodged configurations in the atrium). A multi-domain compartmentalized mesh was prepared to allow the site-specific evaluation of important hemodynamic parameters. Transport of each blood stream, blood damage levels, and recirculation times are quantified and compared to dual lumen cannula in proper position. Results: High recirculation levels (39 ± 4%) in malpositioned cases resulted in poor oxygen saturation where maximum recirculation of up to 42% was observed. Apparently, Origen dual lumen cannula showed poor inferior vena cava blood–capturing efficiency (48 ± 8%) but high superior vena cava blood–capturing efficiency (86 ± 10%). Dual lumen cannula malposition resulted in corresponding changes in residence time (1.7 ± 0.5 seconds through the tricuspid). No significant differences in blood damage were observed among the simulated cases compared to normal orientation. Compared to the correct dual lumen cannula position, both rotational and translational displacements of the dual lumen cannula resulted in significant hemodynamic differences. Conclusion: Rotational or translational movement of dual lumen cannula is the determining factor for atrial hemodynamics, venous capturing efficiency, blood residence time, and oxygenated blood delivery. Results obtained through computational fluid dynamics methodology can provide valuable foresight in assessing the performance of the dual lumen cannula in patient-specific configurations.

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In this paper the Volume-of-Fluid (VOF) method is used to simulate Newtonian and non-Newtonian fluid flow within simplex (pressure-swirl) atomizers. The two-dimensional axisymmetric swirl Navier-Stokes equations coupled with the VOF method is employed for accounting the formation mechanism of the liquid film inside the swirl chamber and the orifice hole of the pressure swirl atomizer. For verification of the code, the numerical results were compared with experimental data for large scale prototype injector with water (Newtonian fluid) as injection fluid in various constant inlet mass flow rate. By using power-law equation to calculate shear stress terms in the Navier-Stokes equations, the code is extended to compute Newtonian and non-Newtonian fluid flow inside the atomizer. The time-independent purely viscous power-law fluids flow in pressure-swirl atomizers is simulated. The effects of shear-thinning fluids (0.5 < n <1), viscous Newtonian (n = 1) fluids and shear thickening fluids (1< n < 1.5) on atomizers performance (discharge coefficient and spray cone angle) were investigated. Results were shown that with increasing the power-law index the spray cone angle decreases and the discharge coefficient increases.

doi: medRxiv preprint NOTE: This preprint reports new research that has not been certified by peer review and should not be used to guide clinical practice.

In this paper, the effects of various geometric parameters of a high pressure swirl Gasoline Direct Injector (GDI) on the injection flow quality are investigated. The two-dimensional axisymmetric Navier-Stokes equations coupled with the Volume-of-Fluid (VOF) method were employed for simulation of the formation mechanism of the liquid film inside the swirl chamber and the orifice hole of the pressure swirl atomizer. To validate the model, results for base injector were compared in the steady state operation with those of available experiments in the literature. Good agreements were obtained for discharge coefficient (Cd) and cone angle (θ) with experimental data. The effects of five characteristic geometric parameters of swirl injectors such as orifice ratio (orifice length to orifice diameter), angle of swirl chamber, orifice diameter, needle lift and needle head angle (assumed to be cone) were investigated. The results show that increasing the swirl chamber angle leads to an increase in mass flow rate and a decrease of the cone angle of liquid sheet. Through extensive simulations, geometric parameters of an optimum injector were obtained.

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