Characterization of Shear-Induced Hemolysis in Rotational Medical Devices

The implantation of a Left Ventricular Assist Device (LVAD) is a rapidly growing means of treatment for a large variety of heart ailments. These blood pumps necessarily exert some degree of shear stress on blood passing through them, which, over time, may cause the rupture of red blood cells, coagulation, thromboses, and bleeding. This limits their use as long term treatment and therapy. While the relationship of fluid shear to blood damage has been demonstrated previously, there is significant variance in the reported levels of damage. Were these stresses and subsequent damage to be well understood and related, existing and future VADs, as well as other blood contacting devices, could be more quantitatively designed to apply shear stresses below some damage threshold, thus allowing for longer effective treatment for an implanted patient. The aim of this thesis has been to construct a robust, Couette-flow shearing device in order to expose blood to a known shear stress under well controlled experimental conditions and to evaluate the subsequent damage. This shearing device has been constructed from an existing axial flow LVAD design that uses a novel magnetic bearing system to levitate the pump’s rotor. This technology gives the shearing device a uniquely simplified flow path and avoids any stresses contributed by conventional bearings. Both ovine and porcine blood has been investigated in the course of this work over a stress range of 0-350Pa and exposure time ranging from 200-1200ms. Extremely low levels of damage relative to studies in the literature were observed below 200Pa for both species over any exposure time. Above those conditions, porcine blood shows signs of higher fragility than ovine, seeing as much as 1% red blood cell damage within the investigated range, while ovine damage under identical conditions remained below 0.2%