IN-VITRO INVESTIGATION OF THE ST-JUDE-MEDICAL-ISOFLOW-CENTRIFUGAL-PUMP - FLOW VISUALIZATION AND HEMOLYSIS STUDIES

Centrifugal blood pumps have become valuable therapeutic tools for car diopulmonary bypass surgery. In addition, surgeons have used them as t emporary ventricular assist devices, and this type of pump is also bei ng developed for use as a permanent assist device and total artificial heart. However, centrifugal pumps create flow patterns that are signi ficantly different from those the blood experiences physiologically. T he St. Jude Medical Isoflow centrifugal pump has been used clinically during cardiopulmonary bypass surgery, yet no experimental results hav e been reported that describe the flow patterns within this pump or th at quantify the hemolysis generated over a range of operating conditio ns. The purpose of this study was to investigate the flow patterns and hemolysis during 4 operating conditions. The experimental operating c onditions included the design condition (6 L/min, 2,500 rpm, 350 mm Hg ), a high flow condition (10 L/min, 2,500 rpm, 330 mm Hg), a low flow condition (2 L/min, 2,500 rpm, 370 mm Hg), and a near surge condition (2 L/min, 3,000 rpm, 550 mm Hg). The flow visualization results demons trated that the flow within the impeller was well aligned with the imp eller blades except near the inlet at the high flow condition. In cont rast, the flow through the outlet was well aligned at the high flow co ndition while there was evidence of particle impact at the design cond ition, and the flow was disturbed at the low flow and near surge condi tions. The indices of hemolysis (IH) for the 3 operating conditions at 2,500 rpm were 0.0082 +/- 0.0026 (mean +/- SD) for the design conditi on, 0.0035 +/- 0.0014 for the high flow condition, and 0.0326 +/- 0.00 50 for the low flow condition. The indices for high and low flow were significantly different from that for the design condition (p < 0.05). The IH for the near surge condition (0.0748 +/- 0.0039) was significa ntly higher than that for all other conditions (p < 0.05). In addition to describing the flow patterns within the Isoflow, this study indepe ndently validated St. Jude Medical's reported IH at the design conditi on and showed how that IH significantly changed based on operating con ditions.