Puthettu M, et al. - During cardiac surgery, entry of micro-air emboli occur regularly into the bloodstream, which can cause cognitive impairment or stroke. In view of the uncertainty of the origin (the heart-lung machine (HLM) or the blood-air contact) of the most threatening air emboli when opening the heart, researchers herein carried out an in vitro study investigating, for the two sources, air emboli distribution in the arterial tree, especially in the brain region, during cardiac surgery with different cannulation sites. They 3D printed a model of the arterial tree and included it in a hydraulic circuit, divided such that flow going to the brain was separated from the rest of the circuit. To simulate the two sources, they injected air micro-emboli either in the HLM (“ECC Bubbles”) or in the mock left ventricle (“Heart Bubbles”). An ultrasonic bubble counter was used to perform measurement of emboli distribution. For each combination of injection site and cannulation site, where air bubble counts and volumes were recorded, they carried out five repetitions. Based on size, air bubbles were separated in three categories. As per outcomes from the in vitro model, the chosen cannulation site affects the portion of air bubbles traveling to the brain. Based on this observation, it is hypothesized that air embolic load in the brain may be reduced also in clinical cases by choosing an optimal cannulation site.