Resolving Flow Properties of Spiral Groove Bearings to Improve Mechanical Circulatory Support Hemocompatibility
Bieritz, Shelby A
Doctor of Philosophy
Rotary blood pumps are utilized as bridge to transplant, bridge to destination, and bridge to recovery devices to support a failing heart. These pumps unload the ventricles (ventricular assist devices) or replace the heart entirely (total artificial hearts), using impellers, or a rotating set of blades, to drive blood flow to the systemic and/or pulmonary circulation. These pumps have been used in the clinic for decades, supporting patients for 1.5 years on average, but the complication rate while on pump support remains high, with 60% of patients returning to the hospital with a major adverse event within 6 months. Much of these complications arise from damage to blood components due to the supraphysiologic shear stresses within a rotary blood pump. This work aims to explore a method of controlling red blood cell flow in a rotary blood pump by means of a spiral groove bearing, a hydrodynamic bearing that generates lift by pumping fluid along a set of grooves. The application of these bearings to rotary blood pump design will be explored in two contexts; first, as a means of generating washout flow in a miniature axial left ventricular assist device, and second, as a tool to reduce red blood cell shear stress exposure in a centrifugal blood pump. The salient findings of this work include i) the applicability of an analytical model to predict spiral groove bearing flow in an axial pump; ii) the induction of cell exclusion in a spiral groove bearing gap, allowing manipulation of red blood cell flow in rotary blood pumps to limit shear exposure; iii) the ability to track red blood cell flow in a complex pump geometry using erythrocyte ghosts as a blood analog solution, and iv) the implications of cell exclusion on red blood cell and von Willebrand Factor damage. Spiral groove bearings cab be utilized to reduce both the magnitude and duration of red blood cell exposure to supraphysiologic shear stress, thereby providing an additional tool to improve rotary blood pump hemocompatibility and patient outcomes.
Heart failure; hemocompatibility; rotary blood pump; ventricular assist device; spiral groove bearing