In vitro and in vivo evaluations of the antithrombogenic properties of the spiral vortex pump for temporary left heart bypass

From conception to realization, the design emphasis of the spiral vortex diaphragm pump has been on promoting efficient blood flow patterns in order to lower thrombogenicity. The tracer method was used to visualize flow patterns in this pump and the results were compared with those of a conventional diaphragm pump with paraxial inlet and outlet ports. During diastole, the flow through a 45° angled inlet is tangential to the axis of the pump forming a continuous vortex central along the pump axis. During systole, the vortex converges to pass through the apically located outlet. No areas of turbulence or stasis could be found, whilst in the conventional pump only random flow with recirculation could be demonstrated. Dye washout tests confirmed good washout at the periphery of this pump with no signs of stasis. However, large areas of stagnation with incomplete washout at diaphragm-housing (D-H) junctions were observed in the conventional pump. The comparative in vitro haemolysis test revealed that the level of free plasma haemoglobin was doubled in a commercially available pump compared with that of the spiral vortex pump. No thrombus formed within the pump housing after up to 50 hours of pumping in five acute animal experiments without postoperative anticoagulants. However, thrombi were found at the D-H junction of this pump due to imperfect fabrication techniques in one of the four sheep that survived 14-21 days. Neither thrombus in the pump nor infarcts in either kidneys were found in the last two sheep after 14 days of uneventful partial left heart bypass with this pump following improved fabrication methods.