DEVELOPMENT OF THE BAYLOR NASA AXIAL-FLOW VENTRICULAR ASSIST DEVICE -IN-VITRO PERFORMANCE AND SYSTEMATIC HEMOLYSIS TEST-RESULTS

Our newly developed axial flow pump consists of a flow tube, an intern al rotating impeller, and a fixed flow stator (we call the stator) beh ind the impeller. This pump produces a flow of 3 to 8 L/min against 50 to 150 mm Hg pressure difference, respectively, in the range of 10,00 0 to 16,000 rpm. An axial flow pump that will be used as a ventricular assist device (VAD) has to have low hemolytic and good antithrombogen ic characteristics. This paper will show how to decrease the hemolytic properties of this axial flow pump systematically using a test matrix . The test variables evaluated were impeller blade tip geometry, impel ler flow tube clearance (radial clearance), impeller stator clearance (axial clearance), impeller blade number, stator blade number, and imp eller length. All in vitro hemolysis tests were performed at 5.0 L/min against 100 mm Hg pressure difference using a total of 83 bags of fre sh bovine blood. The results were as follows: the impeller blade tip g eometry did not significantly effect hemolysis, a 0.005-inch and a 0.0 09-inch radial clearance were significantly (p < 0.01 or 0.001) less h emolytic than the other clearances, a 0.075-inch axial clearance was s ignificantly (p < 0.05) more hemolytic than the other clearances, two- and six-bladed impellers were significantly (p < 0.01 and 0.02, respe ctively) less hemolytic than a four-bladed impeller, a five-bladed sta tor was significantly (p < 0.05 or 0.01) less hemolytic than the other stators, and the impeller length did not make a significant differenc e. Currently, the best index of hemolysis is 0.031 +/- 0.018 g/100 L, and using parameters from these results, implantable devices are being fabricated.