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.

Extracorporeal membrane oxygenation (ECMO) is a life-saving support treat-ment in case of pulmonary and/or cardiac failure. An artificial extracorporealcircuit is used to offload the function of lungs and/or heart. Patient blood is drained through a drainage cannula, pumped with a centrifugal pump, oxygenated in a membrane lung and returned to the body through a reinfusion cannula. Tubing and connectors complete the circuit. However, its use canlead to thromboembolic and haemolytic complications, which are related to mechanical stresses arising in the flow of blood through its components. Numerical simulations of some of the pumps and cannulae used in the circuit were performed to investigate the flow structures developing in these components and their relation to measures of blood damage in the form of platelet activation state (PAS) and haemolysis index (HI). Simulations of two magnetically levitated centrifugal ECMO pumps were performed both in on- and off-label conditions with flow rates compatible with adult and neonatal use. The results showed that off-label low flow rate can be damaging due to an increase of residence time of the particles, which exposed them for longer to non-physiological stress. This held true for both passive tracers and inertial particles subjected to lift and drag. The neonatal pump showed a backflow structure with flow swirling back to the inlet tubing over its whole labelled range. Simulations of a lighthouse drainage cannula were undertaken to assess drainage characteristics at different haematocrits and flow rate ratios. The results indicated that the flow field was dominated by a jet in crossflow type of structure, with the most proximal holes draining the largest amount of fluid in all the studied cases and for all the considered haematocrits. The effects due to non-Newtonian behaviour of blood were less relevant in the drainage area, allowing to use a Reynolds number analogy to bridge between water and blood results.A lighthouse cannula in return configuration was also considered in both a centred and a tilted position. A characteristic confined jet configuration was found, with a backflow developing at the vessel wall, increasing residence time. In the tilted case, a group of small vortical structures developed at the holes close to the wall, which behaved as an obstacle to the vessel flow and increased both residence time and stress. This led to locally increased haemolysis which, however, did not impact haemolysis at large due to the low flow exposed to this area. The use of different viscosity models in this case led to small variations in the results, which were minor compared to the uncertainty introduced by the use of different model coefficients in the computation of the haemolysis index.

Extrakorporeal membranoxygenering (ECMO) är en livräddande stödbehandling vid lung- och/eller hjärtsvikt. En artificiell extrakorporeal krets används för att stödja hjärt-lungfunktion. Patientblod dräneras via en dräneringskanyl, pumpas med en centrifugalpump genom membranlunga (gasväxlare) för syresättning och koldioxidclearance, för att sedan återföras till patienten via en returkanyl. Slangar och konnektorer sammankopplar kretsen. Användning av ECMO kan leda till tromboemboliska och hemolytiska komplikationer relaterade till mekaniska skjuvkrafter som uppstår när blodet strömmar genom ECMO-systemetskomponenter. Numeriska simuleringar av några av de pumpar och kanyler som används vid ECMO utfördes för att undersöka flödesstrukturer som skapas i systemkomponenter och deras relation till blodtrauma skattat som Plateletactivation state (PAS) och Haemolysis index (HI). Simuleringar av två centrifugalpumpar utfördes både inom och utanför rekommenderade flödesvolymer kompatibla med vuxen och neonatal ECMO användning. Resultaten visade att låg flödeshastighet off-design kan vara skadlig på grund av en ökad uppehållstid (residence time) för partiklarna i undersökt område. Detta gällde både passiva och tröghetsberoende partiklar som utsätts för lift och drag. Neonatalpumpen visade en motströms flödesstruktur i form av virvel utefter pumpinloppets väg över hela rekommenderade flödesområdet. Simulering av en dränkanyl med sidohål genomfördes för att bedöma dränegenskaper vid olika hematokritvärden och flödeshastigheter. Resultaten indikerade att flödesmönster dominerades av en struktur “jet in crossflow”. De mest proximala hålen dränerade mest vätska i alla studerade fall inklusive hematokritfraktioner. Effekterna av blodets icke-Newtonska egenskaper var inte avgörande inom testområdet vilket möjliggjorde användande av Reynolds-tal för att koppla vatten och blodresultat. En returkanyl undersöktes både i centrerad och vinklad position i kärlet. En karakteristisk “confined jet”konfiguration sågs, med ett returflöde somutvecklades vid kärlväggen. Detta orsakade ökad residence time. I vinkladposition noterades en grupp små virvelstrukturer vid hålen nära kärlväggen vilka funktionellt betedde sig som hinder för blodflödet i kärlet men skapade också mera shear stress och förlängd residence time. Lokalt ökad hemolys avröda blodkroppar sågs, vilket dock inte var relevant i ett globalt perspektivp å grund av det lågt fraktionellt flödet vid sidohålen. Användningen av olika viskositetsmodeller gav små variationer i resultaten, vilka blev obetydliga med den osäkerhet som introducerades av användningen olika modellkoefficienter vid beräkning av hemolysindex.