Development of a Small Animal Model to Improve Arterial Flow Profiles during Extracorporeal Circulation

Objectives: The impact of different extracorporeal circulation (ECC) scenarios on arterial blood flow profiles and resulting wall shear stress values remains yet unclear. To allow for exact blood flow profile measurements, magnetic resonance imaging during ECC is required. Therefore, the present feasibility study aimed at developing an animal model of ECC that can be examined by means of magnetic resonance imaging.

Methods: New Zealand White rabbits (n = 2; 4 kg body weight) were used to realize this model, since in rabbits, atherosclerosis can be additionally induced for future investigations. To enable high resolution magnetic resonance imaging, we developed an extracorporeal circuit of a total length of 20 m so that the blood pump and control unit of the heart lung machine can be placed outside of the strong magnetic field. The miniaturized ECC system via thoracic access comprised an infant oxygenator (Medtronic Affinity Pixie), a pulsatile centrifugal pump (Medos Deltastream DP3), 1/8” tubes, a 10 Fr aortic cannula and a 12 Fr venous two-stage cannula for vacuum-assisted drainage.

Results: We generated a miniaturized ECC system with a very low priming volume (240ml) to reduce the system-inherent hemodilution to ~1:1. Consequently, hemoglobin rates were higher than 6 g/dl and adequate oxygenation could be obtained. Optimized venous drainage by an additionally inserted pulmonary vein vent catheter (6 Fr) resulted in sufficient blood flow (300 ml/min) that was maintained for more than 60 minutes as either pulsatile or non-pulsatile flow.

Conclusions: The developed miniaturized extracorporeal circuit guarantees adequate perfusion in rabbits while allowing for simultaneous magnetic resonance imaging. Thus, for the first time, real time blood flow profile measurements during ECC would be possible. Furthermore, this model could be used for validating and optimizing blood flow simulation algorithms to compare the impact of different ECC scenarios without further animal experiments.