MORE THAN 1 YEAR CONTINUOUS OPERATION OF A CENTRIFUGAL PUMP WITH A MAGNETICALLY SUSPENDED IMPELLER

The authors have been developing a centrifugal pump with a magneticall y suspended impeller (MSCP) designed for total artificial heart and lo ng-term ventricular support. The MSCP consists of a magnetic bearing, an impeller and housing, and a driving motor. The impeller is suspende d by a magnetic bearing, therefore providing contact free rotation of the impeller inside the pump. This study was designed to evaluate long -term durability and nonthrombogenicity of the MSCP in a chronic sheep model. The blood contacting surfaces of the pump and conduits were co mpletely modified by a heparin immobilization technique (Hepaface). Th e MSCP was placed paracorporeally as a left heart bypass between left ventricle and descending aorta in three adult sheep. Coumadin was give n orally to maintain prothrombin time at 15-20 sec. The coagulation an d hematologic parameters, including plasma free hemoglobin, were perio dically monitored throughout the experiment. Under daily movement in t he cage, the pump could produce average flow rates of 3-6 L/min (50-10 0 ml/kg) at 1,700-2,000 rpm. Although the arterial pulse contour decre ased, there was no physiologic deterioration. The axial impeller excur sion monitored by a position sensor was <25 mu m. Plasma free hemoglob in level remained at <5 mg/dl throughout the experiment. There was no increase in the motor current, which indicates no massive thrombus for mation around the impeller. One experiment was terminated at 70 days d ue to Hall sensor dysfunction of the motor. The retrieved pump was ent irely free from thrombus formation. There was no detectable thrombus f ormation inside the pump or the inflow and outflow conduits. Hematolog ic, renal, and hepatic parameters remained within the normal range thr oughout the experiment. The other two sheep have survived for more tha n 395 and 41 days without major complication. These studies demonstrat ed that the MSCP has significant potential for long-term use.