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Hemodynamics of artificial devices used in extracorporeal life support

Time: Tue 2021-09-28 14.00

Location: Sal F3 and via live-stream, Lindstedtsvägen 26, Stockholm (English)

Subject area: Engineering Mechanics

Doctoral student: Francesco Fiusco , Teknisk mekanik

Opponent: Dr., Lecturer Katharine Fraser, University of Bath, Department of Mechanical Engineering

Supervisor: Docent Lisa Prahl Wittberg, Teknisk mekanik

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Extracorporeal Membrane Oxygenation (ECMO) is a life-saving therapy usedfor support in critical heart and/or lung failure. Patient’s blood is pumped viaan artificial lung for oxygenation outside of the body. The circuit is composedof a blood pump, cannulae for drainage and reinfusion, a membrane lung,tubing and connectors. Its use is associated with thromboembolic complicationsand hemolytic damage. Detailed numerical studies of two blood pumps anda lighthouse tip drainage cannula were undertaken to characterize the flowstructures in different scenarios and their link to platelet activation. The pumpsimulations were modelled according to manufacturer’s proclaimed use but alsoin off-design conditions with flow rates used in adult and neonatal patients.Lagrangian Particle Tracking (LPT) was used to simulate the injection ofparticles similar in size to platelets to compute platelet activation state (PAS).The results indicated that low flow rates impacted PAS similarly to high flowrates due to increased residence time leading to prolonged exposure to shearstress despite the fact that shear per se was lower at low flow rate. Regardingthe cannula, the results showed that a flow pattern similar to a jet in crossflowdeveloped at the side holes. A parameter study was conducted to quantifydrainage characteristics in terms of flow rate distribution across the holes wheninput variables of flow rate, modelled fluid, and hematocrit were altered. Thefindings showed, across all the cases, that the most proximal hole row drainedthe largest fraction of fluid. The effects due to the non-Newtonian nature ofblood were confined to regions far from the cannula holes and the flow structuresshowed very limited dependence on the hematocrit. A scaling law was found tobridge the global drainage performance of fluid between water and blood.