CONSIDERATIONS AND PROBLEMS IN THE DEVELOPMENT OF THE MINI-SPINDLE PUMP

The premise for the development of the minispindle pump, planned as an implantable device for assisted circulation, was to transport 4 L of water/min in mock circulation with a speed of 12-15,000 rpm against an afterload of 90 mm Bg. After calculations, the resulting first protot ype had a spindle rotor with 3 threads (outer diameter, 18 mm; inner d iameter, 6.2 mm; length, 45 mm) in a U-shaped housing, driven by an el ectric motor with a cooling system. In mock circulation, this pump mov ed 7.8 L of water/min at 18,000 rpm. To avoid animal experiments, its influence on the blood was tested in a Maxima oxygenator. The device c irculated 4.2 L of blood/min with the same speed. Because of its high traumatic hemolysis rate (>250 mg% of free hemoglobin after 7 h of pum ping), the rotor was modified, first without effect at 2.5 threads and then at 4 threads. In addition, in this third prototype, the flow dir ection was reversed. This prototype was more effective (4.3 L of blood /min at 12,000 rpm in the oxygenator) and the hemolysis rate, after a pumping duration of 8 h, could only be reduced to 180 mg% of free hemo globin. As a result, a fourth prototype was developed (i.e., the U-sha pe of the housing was abandoned). This device functioned better than t he third prototype (4.5 L of blood/min at 12,000 rpm in the oxygenator ), but the blood trauma increased (220 mg% of free hemoglobin after 7 h of pumping). To find out if the oxygenator may be responsible for th e hemolysis problem, the 16th prototype of the large spindle pump was tested in the oxygenator. The result was expected, the level of free p lasma hemoglobin was high again (190 mg%). To verify the function of t he third and the fourth prototype of the mini-spindle pump, 4 animal e xperiments were performed. Under normal cardiac conditions, the device s emptied the left ventricle up to 70% with a speed between 10,500 and 11,200 rpm, moving about 6 L of blood/min (afterload between 65 and 9 0 mm Hg). The hemolysis rates were between 32 and 90 mg% of free hemog lobin in the plasma.