In Vivo Evaluation of an Intraventricular Axial Flow Blood Pump

Abstract

A miniature intraventricular axial flow blood pump (IVAP) is undergoing in vivo evaluation in calves. The IVAP system consists of a miniature (13.9-mm diameter) axial flow pump which resides within the left ventricular 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 51/min against 100 mmHg pressure at 9000 rpm with 8W total power consumption. The maximum total efficiency exceeds 17%. A purged-lip seal system is used in prototype no. 8, and a newly developed “cool seal” (low-temperature mechanical seal) is used in prototype no. 9, respectively. In the cool-seal system, a large amount of purge flow is introduced behind the seal faces to augment convective heat transfer to keep the seal face temperature at a low level for the prevention of heat denaturation of blood proteins. The cool-seal system consumes less than 10 ml purge fluid per day and has greatly extended the seal life. These pumps were implanted in 3 calves (26, 30, and 150+ days of support). The pump was inserted through a left thoracotomy at the 5th intercostal space. Two purse-string sutures were placed on the left ventricular apex, and the apex was cored with a myocardial punch. The pump was inserted into the left ventricle, with the outlet cannula smoothly passing through the aortic valve without any difficulty. Only 5 minutes elapsed between the time of chest opening and the initiation of pumping. Pump function remained stable throughout in all experiments. No cardiac arrhythmias were detected, even during treadmill exercise tests. The plasma free hemoglobin level remained in an acceptable range. Postmortem examination did not reveal any interference between the pump and the mitral apparatus. No major thromboembolism was detected in the vital organs.