ABSTRACT
Blood compatibility of a ventricular assist device (VAD) depends on the dynamics of blood flow. The focus in most previous studies was on blood flow in the VAD. However, the tip shape and position of the VAD inflow cannula influence the dynamics of intraventricular blood flow and thus thrombus formation in the ventricle. In this study, blood flow in the left ventricle (LV) under support with a catheter-type continuous flow blood pump was investigated. The flow field was analyzed both numerically and experimentally to investigate the effects of catheter tip shape and its insertion depth on intraventricular flow patterns. A computational model of the LV cavity with a simplified shape was constructed using computer-aided design software. Models of catheters with three different tip shapes were constructed and each was integrated to the LV model. In addition, three variations of insertion depth were prepared for all models. The fully supported intraventricular flow field was calculated by computational fluid dynamics (CFD). A transparent LV model made of silicone was also fabricated to analyze the intraventricular flow field by the particle image velocimetry technique. A mock circulation loop was constructed and water containing tracer particles was circulated in the loop. The motion of particles in the LV model was recorded with a digital high-speed video camera and analyzed to reveal the flow field. The results of numerical and experimental analyses indicated the formation of two large vortices in the bisector plane of the mitral and aortic valve planes. The shape and positioning of the catheter tip affected the flow distribution in the LV, and some of these combinations elongated the upper vortex toward the ventricular apex. Assessment based on average wall shear stress on the LV wall indicated that the flow distribution improved the washout effect. The flow patterns obtained from flow visualization coincided with those calculated by CFD analysis. Through these comparisons, the numerical analysis was validated. In conclusion, results of these numerical and experimental analyses of flow field in the LV cavity provide useful information when designing catheter-type VADs.
