AN IMPLANTABLE CENTRIFUGAL BLOOD PUMP FOR LONG-TERM CIRCULATORY SUPPORT

A compact centrifugal blood pump was developed as an implantable left ventricular assist system. The impeller diameter is 40 mm and the pump dimensions are 55 x 64 mm. This first prototype was fabricated from t itanium alloy, resulting in a pump weight of 400 g including a brushle ss DC motor. Weight of the second prototype pump was reduced to 280 g. The entire blood contacting surface is coated with diamond like carbo n to improve blood compatibility. Flow rates of over 7 L/min against 1 00 mmHg pressure at 2,500 rpm with 9 W total power consumption have be en measured. A newly designed mechanical seal with a recirculating pur ge system (''Cool-Seal'') is used as a shaft seal. In this seal system , seal temperature is kept under 40 degrees C to prevent heat denatura tion of blood proteins. Purge fluid also cools the pump motor coil and journal bearing. The purge fluid is continuously purified and sterili zed by an ultrafiltration filter incorporated into the paracorporeal d rive console. In vitro experiments with bovine blood demonstrated an a cceptably low hemolysis rate (normalized index of hemolysis = 0.005 +/ - 0.002 g/100 L). In vivo experiments are currently ongoing using calv es. Via left thoracotomy, left ventricular apex-descending aorta bypas s was performed utilizing a PTFE (Polytetrafluoroethylene) vascular gr aft, with the pump placed in the left thoracic cavity. In two in vivo experiments, pump flow rate was maintained at 5-8 L/min, and pump powe r consumption remained stable at 9-10 W. All plasma free hemoglobin le vels were measured at <15 mg/dl. The seal system has demonstrated good seal capability with negligible purge fluid consumption (<0.5 ml/day) . Both animals remain under observation after 162 and 91 days of conti nuous pump function.