AN IMPLANTABLE CENTRIFUGAL BLOOD PUMP WITH A RECIRCULATING PURGE SYSTEM (COOL-SEAL SYSTEM)

A compact centrifugal blood pump has been developed as an implantable left ventricular assist system. The impeller diameter is 40 mm, and pu mp dimensions are 55 x 64 mm. This first prototype, fabricated from ti tanium alloy, resulted in a pump weight of 400 g including a brushless DC motor. The weight of a second prototype pump was reduced to 280 g. The entire blood contacting surface is coated with diamond like carbo n (DLC) to improve blood compatibility. Flow rates of over 7 L/min aga inst 100 mm Hg pressure at 2,500 rpm with 9 MI total power consumption have been measured. A newly designed mechanical seal with a recircula ting purge system (Cool-Seal) is used for the shaft seal. In this seal system, the seal temperature is kept under 40 degrees C to prevent he at denaturation of blood proteins. Purge fluid also cools the pump mot or coil and journal bearing. Purge fluid is continuously purified and sterilized by an ultrafiltration unit which is incorporated in the par acorporeal drive console. In vitro experiments with bovine blood demon strated an acceptably low hemolysis rate (normalized index of hemolysi s = 0.005 +/- 0.002 g/100 L). In vivo experiments are currently ongoin g using calves. Via left thoracotomy, left ventricular (LV) apex desce nding aorta bypass was performed utilizing an expanded polytetrafluoro ethylene (ePTFE) vascular graft with the pump placed in the left thora cic cavity, In 2 in vivo experiments, the pump flow I-ate was maintain ed at 5-9 L/min. and pump power consumption remained stable at 9-10 W. AIL plasma free Hb levels were measured at less than 15 mg/dl. The se al system has demonstrated good seal capability with negligible purge fluid consumption (<0.5 ml/day). In both calves, the pumps demon strat ed trouble free continuous function over 6 month (200 days and 222 day s).