MINIMIZATION OF HEMOLYSIS IN CENTRIFUGAL BLOOD PUMPS - INFLUENCE OF DIFFERENT GEOMETRIES

Centrifugal blood pumps are of substantial importance for intraoperati ve extracorporeal circulation and for temporary cardiac assist. Their development and improvement raises many specific questions, especially on mechanical blood properties, flow distribution, and the resulting biocompatibility. In this comprehensive study the influence of various pump geometries on blood trauma was investigated. For this purpose an alytical calculations, hydrodynamic performance, numerical simulation, in vitro hemolysis tests and in vivo experiments were used. The gap b etween rotor and housing was found to be crucial showing a distinct mi nimum of hemolysis at a gap of 1.5 mm (in vitro increase of plasma fre e hemoglobin per 100 ml plasma an hour: DELTAfHb/hour = 2.4+/-0.83 mg% /h at 1.5 mm versus 12 +/- 2.2 mg%/h at 2.5 mm; p < 0.05). Housing dia meter and shape of the vanes were of less importance for blood traumat ization (d = 60 mm: DELTAfHb/hour = 6.36 +/- 1.8 mg%/h; d = 70 mm: fHb = 7.1 +/- 1.9 mg%/h; straight radial vanes: 5.2 +/- 1.8 mg%/h; straig ht inclined vanes: 6.8 +/- 1.2 mg%/h; flexed vanes: 6.1 +/- 2.0 mg%/h) . Three animal experiments confirmed the optimization of geometry, wit h a mean fHb of 2.5 to 3.2 mg% in steady state. Hydrodynamic efficienc y revealed to be a necessary, but not a sufficient and sensitive crite rion for hemolysis minimization (e.g. changes of eta < 10% for changes of fHb > 500%). Numerical simulation gives an improved insight in flo w distribution, but can not yet be applied for quantification of blood trauma. The study supports theories on mechanical hemolysis predictin g a hemolysis at shear levels of less than 500N/m2 depending on exposu re time. With the methods used it was possible to develop a pump with very low hemolysis potential. For further reduction of blood trauma an d correlated thrombus formation basic studies on cell damage in recirc ulating blood and also advanced flow studies in rotary pumps would be desirable.