Continuing in vivo trials are being conducted at the University of Pittsburgh using the Nimbus axial flow blood pump (AxiPump). To date, 14 sheep experiments have been performed to address several issues related to short-term support. Six acute experiments (<6 hr) have been performed to assess hemodynamics related to speed regulation and to determine anatomic placement of the pump and cannulae. Eight short-term survival studies lasting up to 6 days have been performed to evaluate biocompatibility and system reliability, and to establish clinical management protocols. The AxiPump has been used as a left ventricular assist device (LVAD), right ventricular assist device (RVAD), and bi-ventricular assist device (BiVAD) with left ventricular and right atrial cannulation. The AxiPump has demonstrated the ability to assume complete support of either the pulmonary or systemic circulation, or both. We have determined that sufficient surgical access may be obtained through left lateral thoracotomy for both LVAD and RVAD insertion. In the absence of post operative anticoagulation therapy, we have detected subclinical renal cortical infarctions in 6 of 8 short-term animals. Thrombus deposition has been observed at the ventricular cannula tip in 4 of 8 cases—necessitating design changes. Two short-term experiments have been terminated because of bleeding—one due to inflow cannula obstruction and one due to cannula failure. Plasma free hemoglobin levels were all below 15 mg/dl, except for one case complicated by inflow obstruction. There has been no evidence of device failure; however, we have encountered some problems with the purge delivery circuit, which has motivated additional design and procedural changes. Future in vivo experiments will incorporate design changes identified in these early experiments and will concentrate on longer-term (12 week) performance.
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