No abstract

Clinic encounters of dentists and otolaryngologists inherently expose these specialists to an enhanced risk of severe acute respiratory syndrome coronavirus 2 infection, thus threatening them, their patients, and their practices. In this study, we propose and simulate a helmet design that could be used by patients to minimize the transmission risk by retaining droplets created through coughing. The helmet has a port for accessing the mouth and nose and another port connected to a vacuum source to prevent droplets from exiting through the access port and contaminating the environment or clinical practitioners. We used computational fluid dynamics in conjunction with Lagrangian point-particle tracking to simulate droplet trajectories when a patient coughs while using this device. A range of droplet diameters and different operating conditions were simulated. The results show that 100% of the airborne droplets and 99.6% of all cough droplets are retained by the helmet.

Recently, the assisted bidirectional Glenn (ABG) procedure has been proposed as an alternative to the modified Blalock-Taussig shunt (mBTS) operation for neonates with single-ventricle physiology. Despite success in reducing heart workload and maintaining sufficient pulmonary flow, the ABG also raised the superior vena cava (SVC) pressure to a level that may not be tolerated by infants. To lower the SVC pressure, we propose a modified version of the ABG (mABG), in which a shunt with a slit-shaped nozzle exit is inserted at the junction of the right and left brachiocephalic veins. The proposed operation is compared against the ABG, the mBTS, and the bidirectional Glenn (BGD) operations at normal (2.3 Wood units-m^2) and high (7 Wood units-m^2) pulmonary vascular resistance (PVR) using closed-loop multiscale simulations. The results show that the mABG provides the highest oxygen saturation and oxygen delivery and also higher pulmonary flow rate in comparison to the BDG and the ABG. At normal PVR, the SVC pressure is significantly reduced below the ABG and the BDG (mABG: 4; ABG: 8; BDG: 6; mBTS: 3 mmHg). However, the SVC pressure remains high at high PVR (mABG: 15; ABG: 16; BDG: 12; mBTS: 3 mmHg), motivating an optimization study to improve the ABG hemodynamics efficiency for a broader range of conditions in the future. In overall, the mABG preserves all advantages of the original ABG procedure while reducing the SVC pressure at normal PVR.

No abstract

This study introduces an algebraic model informed by computational fluid dynamics (CFD) simulations to investigate the performance of the assisted bidirectional Glenn (ABG) operation on a broad range of conditions. The performance of this operation, as measured by the superior vena cava (SVC) pressure, depends on the nozzle area in its ejector pump and the patient’s pulmonary vascular resistance (PVR). Using the developed algebraic model to explore this two-dimensional parameter space shows that the ejector pump can create a pressure difference between the pulmonary artery and the SVC as high as 5 mmHg. The lowest SVC pressure is produced at a nozzle area that decreases linearly with the PVR such that, at PVR =4.2 (Wood units-m2), there is no added benefit in utilizing the ejector pump effect (optimal nozzle area is zero, corresponding to the bidirectional Glenn circulation). At PVR =2 (Wood units-m2), the SVC pressure can be lowered to less than 4 mmHg by using an optimal nozzle area of ≈2.5 mm2. Regardless of the PVR, adding a 2 mm2 nozzle to the baseline bidirectional Glenn boosts the oxygen saturation and delivery by at least 15%. The SVC pressure for that 2 mm2 nozzle remains below 14 mmHg for all PVRs less than 7 Wood units-m2. The mechanical efficiency of the optimal designs consistently remains below 30%, indicating the potential for improvement in the future. A good agreement is observed between the algebraic model and high-fidelity CFD simulations.