LONG-TERM ANIMAL-EXPERIMENTS WITH AN INTRAVENTRICULAR AXIAL-FLOW BLOOD PUMP

A miniature intraventricular axial flow blood pump (IVAP) is undergoin g in vivo evaluation in calves. The IVAP system consists of a miniatur e (phi 13.9 mm) axial flow pump that resides within the left ventricul ar (LV) chamber and a brushless DC motor. The pump is fabricated from titanium alloy, and the pump weight is 170 g. It produces a flow rate of over 5 L/min against 100 mmHg pressure at 9,000 rpm with an 8 W tot al power consumption. The maximum total efficiency exceeds 17%. A purg ed lip seal system is used in prototype no. 8, and a newly developed ' 'Cool-Seal'' (a low temperature mechanical seal) is used in prototype no. 9. In the Cool-Seal system, a large amount of purge flow is introd uced behind the seal faces to augment convective heat transfer, keepin g the seal face temperature at a low level for prevention of heat dena turation of blood proteins. The Cool-Seal system consumes <10 cc purge fluid per day and has greatly extended seal life. The pumps were impl anted in three calves (26, 30, and 168 days of support). The pump was inserted through a left thoracotomy at the fifth intercostal space. Tw o pursestring sutures were placed on the LV apex, and the apex was cor ed with a myocardial punch. The pump was inserted into the LV with the outlet cannula smoothly passing through the aortic valve without any difficulty. Only 5 min elapsed between the time of chest opening and i nitiation of pumping. Pump function remained stable throughout in all experiments. No cardiac arrhythmias were detected, even at treadmill e xercise tests. The plasma free hemoglobin level remained in the accept able range. Post mortem examination did not reveal any interference be tween the pump and the mitral apparatus. No major thromboembolism was detected in the vital organs in Cases 1 or 2, but a few small renal in farcts were detected in Case 3.