Abstract
Decreasing hemolysis and thrombogenesis is a major problem to realize the long-term use of blood pumps. In this study, we investigated the effect of discharge angle on pump properties of a monopivot centrifugal blood pump. Compared impellers had the same diameter, and they varied the discharge angle of the impeller which were 22.5°, 45°, 67.5°, and 90°. The axial thrust on the impeller, the estimated hemolysis index and the stagnation area around the pivot were calculated using computational fluid dynamics analysis. The pump driving condition was set at a flow rate of 4 L/min and a pressure head of 200 mmHg to simulate an extracorporeal circulatory condition. As a result, the rotational speed of the impeller was the lowest when the discharge angle was 90°. Although the axial thrust was the negative largest when the discharge angle was 22.5°, it was also kept negative for the other models, which indicated that all impellers will never lift off. The estimated hemolysis index was the lowest when the discharge angle was 22.5°, because high shear stress region around the outlet of the flow path was the smallest despite the rotational speed of the impeller was the highest. The stagnation area around the pivot was the smallest when the discharge angle was 22.5° because the flow rate through the washout holes was the largest due to the highest rotational speed of the impeller. Therefore, it was predicted that low discharge angle of the impeller improves both hemolytic and anti-thrombogenetic properties in the blood pump without considering other factors such as sliding of bearing and so on.
