Exploration of the Mixing Phenomena during Interaction of Internal and External Circulations (EMPACs): Developing an in-vitro and in-silico Model of the Human Circulation

Objectives: In acute circulatory failure, extracorporeal life support (ECLS) can be used in a “bridge to recovery” intention. In this context, fluid-mechanical aspects of the interaction between the slowly recovering human circulation and ECLS are relevant but poorly understood. We aimed to generate a model out of components and with dimensions suitable for use in an MRI which can first be fully virtualized for CFD analyses, second reproduce physiological flow- and pressure parameters of the human circulation, and third can be used for study of different ECLS cannulation sites and techniques.

Methods: For reproducible and standardized fluid-mechanical studies using MRI, ultrasound and computational fluid dynamics- (CFD) measurements addressing these questions, we developed a combined in-vitro and in-silico model of the human circulation. Silicon-based life-sized dummies of the human aorta and vena cava (vascular module) were combined with a pulsatile artificial heart. The vascular module is placed in a table tray with all arterial branches merging in a venous reservoir and fluid (water-glycerin mixture) returning to the artificial heart through the venous dummy. ECLS-cannulation can be performed in the femoral and subclavian arteries as well as in the femoral and jugular vein position. DICOM-datasets of the model and cannulas were generated using CT scans and transformed into a virtual model for CFD analysis.

Results: The EMPACs-model provides a virtually physiological platform for simulation of the human circulation and its interaction with external circulation generated by ECLS. This set-up allows for precise characterization of fluid-mechanical aspects of this interaction.

Conclusion: The EMPACs-project was developed by a multidisciplinary team of perfusionists, fluid-mechanic engineers, radiologists, medical physicists and cardiac surgeons. With this platform, the interaction of autologous and external circulations will be better understood in the future. Data generated from this project could be useful to optimize recovery and weaning from ECLS in the future.