In vivo time-resolved echo-PIV measurement of cardiovascular flows with Extracorporeal Membrane Oxygenation

Extracorporeal Membrane Oxygenation (ECMO) is a life support technology used for patients with heart and lung failure by oxygenating the blood outside the body. The veno-arterial configuration is routinely used for providing both respiratory and hemodynamic support by delivering oxygenated blood through arteries and draining deoxygenated blood from the veins. However, the choice of the ECMO parameters, or the tradeoff between maintaining sufficient end-organ perfusion and reducing the afterload of the native left ventricle, is challenging without a non-invasive monitoring approach of the hemodynamics. Therefore, the current study applies PIV and PTV to determine the timeresolved velocity field from contrast-enhanced (micro-bubble seeded) ultrasonographic images in order to study the interaction between the cardiac flow of a severely injured pig’s heart and the flow induced by an external ECMO machine. The measurements focus on the pig’s aortic root, where the external ECMO flow impinges directly on the cardiac outflow. Prior to PIV/PTV analysis, image processing including blind deconvolution, and local background removal is performed to overcome the undesirable blur and to segment the bubble traces. In addition, active contouring is applied to define the boundaries of the aorta and the moving aortic valves. Phase-averaged vorticity field and velocity-time integral are presented to help estimate the transitional point, which is the divide between well-oxygenated ECMO flow and oxygen deficient cardiac flow, and the cardiac functions. The results suggest that for the present conditions, an ECMO flow rate of 3 L/min is optimal, under which the transitional point is located 0.8-1cm downstream the sinotubular junction, with a maximum cardiac ejection speed of 14 cm/s.