Relationship Between Pump Speed Design and Hemolysis in an Axial Flow Blood Pump

In an attempt to reduce the hemolysis caused by axial flow blood pumps, we investigated whether the specific speed should be kept within the standard engineering range or whether pump speed should be minimized, thus making the specific speed beyond the standard range. Four pumps with 11.8 mm diameter impellers were designed to accommodate a flow of 5 L/min and a head of 100 mm Hg. The pumps were tested at 4 speeds: A, 14,000; B, 18,000; C, 22,000; and D, 26,000 rpm. Pump performance data were obtained, and the maximum point of total pump efficiency was found for each pump. The maximum efficiencies were A, 50%; B, 58%; C, 52%; and D, 53%. The specific speed of each pump recorded at the maximum efficiency point was calculated as A, 899; B, 954; C, 1,218; and D, 1,951 rpm. Hemolytic tests were performed with fresh goat blood in a closed, mock-loop circuit. Hemolytic indexes were A, 0.036; B, 0.22; C, 0.35; and D, 0.66. We have concluded that decreased hemolysis is correlated with a lower pump speed and that the specific speed for the lowest pump speed is less than the standard range. Having a specific speed outside the standard range was not correlated with reduced total pump efficiency.