DEVELOPMENT OF DESIGN METHODS OF A CENTRIFUGAL BLOOD PUMP WITH IN-VITRO TESTS, FLOW VISUALIZATION, AND COMPUTATIONAL FLUID-DYNAMICS - RESULTS IN HEMOLYSIS TESTS

There are few established engineering guidelines aimed at reducing hem olysis for the design of centrifugal blood pumps. In this study, a flu id dynamic approach was applied to investigate hemolysis in centrifuga l pumps. Three different strategies were integrated to examine the rel ationship between hemolysis and flow patterns. Hemolytic performances were evaluated in in vitro tests and compared with the flow patterns a nalyzed by flow visualization and computational fluid dynamic (CFD). T hen our group tried to establish engineering guidelines to reduce hemo lysis in the development of centrifugal blood pumps. The commercially available Nikkiso centrifugal blood pump (HPM-15) was used as a standa rd, and the dimensions of 2 types of gaps between the impeller and the casing, the axial and the radial gap, were varied. Four impellers wit h different vane outlet angles were also prepared and tested. Represen tative results of the hemolysis tests were as follows: The axial gaps of 0.5, 1.0, and 1.5 mm resulted in normalized index of hemolysis (NIH ) values of 0.0028, 0.0013 and 0.0008 g/100 L, respectively. The radia l gaps of 0.5 and 1.5 mm resulted in NIH values of 0.0012 and 0.0008 g /100 L, respectively. The backward type vane and the standard one resu lted in NIH values of 0.0013 and 0.0002 g/100 L, respectively. These r esults revealed that small gaps led to more hemolysis and that the bac kward type vane caused more hemolysis, Therefore, the design parameter s of centrifugal blood pumps could affect their hemolytic performances . In flow visualization tests, vortices around the impeller outer tip and tongue region were observed, and their patterns varied with the di mensions of the gaps. CFD analysis also predicted high shear stress co nsistent with the results of the hemolysis tests. Further investigatio n of the regional flow patterns is needed to discuss the cause of the hemolysis in centrifugal blood pumps.