DEVELOPMENT OF A MIXED-FLOW CARDIAC ASSIST DEVICE

Abstract

A new type of continuous flow pump, the mixed flow pump (MFP), featuring smaller size and higher efficiency than a centrifugal pump, while achieving lower hemolysis than an axial flow pump, was reported by us at the 44thASAIO congress. These advantages prompted us to develop a MFP for cardiopulmonary bypass (CPB), extracorporeal membrane oxygenation, or ventricular assistance. In an attempt to reduce the hemolysis of an MFP, we studied the influence on hemolysis of decreasing pump speed, by changes of impeller size. Four MFPs (A: 32-mm; B: 36-mm; C: 40-mm; and D: 44-mm impeller diameter) were compared in this study. These MFPs developed a pump flow of 51/min against a 100-mmHg pressure head, at 3450, 3000, 2550, and 2200 rpm, respectively. In vitro hemolysis tests were performed under three different driving conditions, defined by pressure heads of 100, 200, and 300 mmHg, all with a pump flow rate of 51/min, using fresh bovine blood.TableThese results showed that the lowest hemolysis was achieved in pump D at 100 mmHg, and in pump C at over 200 mmHg. It was concluded that a lower level of hemolysis is associated with decreasing pump speed, commensurate with enlargement of pump size; however, over-enlargement of the impeller increased hemolysis again. Among the pumps evaluated, the 40 mm-impeller MFP was deemed best-suited for CPB, because of its low hemolysis at afterloads over 200 mmHg, and is now thought to be the minimum size for commercial applications of the MFP as a CPB pump.