We investigated a miniature magnetically levitated centrifugal blood pump intended to deliver 0.3-1.5 l/min of support to neonates and infants. The back clearance gap between the housing and large volume of the rotor, where the suspension and motor bearings are located, forms a continuous leakage flow path. Within the gap, flow demonstrates a very complex three-dimensional structure: the fluid adjacent to the rotating disk tends to accelerate by centrifugal force to flow radially outwards toward the outlet of the impeller against an unfavorable pressure gradient, which in turn forces blood to return along the stationary housing surfaces. Consequently, one or multiple vortices may be generated in the gap to block blood flow and cause the formation of a retrograde and antegrade leakage flow phenomenon at the gap outlet using an optimization process including extensive computational fluid dynamics (CFD) analysis of impeller refinements, we found that secondary blades located along the back or extended to the side surfaces of the rotor have the capacity to reduce and eliminate the retrograde flow in the back clearance gap. Flow visualization confirmed the CFD-predicted flow patterns. This work demonstrates the utility of CFD-based design optimization to optimize the fluid path of a miniature centrifugal pump.

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The concept that the natural history of certain heart defects could be positively modified through in utero intervention has stimulated extensive research in fetal cardiac intervention and surgery since the early 1980s. Since the management of certain defects would require the use of cardiopulmonary support, extensive studies have been directed toward the application of a variety of perfusion circuits. The unique features of the fetal patient have directed the focus of many of these designs toward miniaturization of components and minimization of prime volume. Large extracorporeal surface contact areas and prime volumes have been identified as potential contributors to a frequently observed placental dysfunction following fetal cardiopulmonary bypass (CPB). We set out to develop means of CPB using a centrifugal micro-system that would not require supplemental prime volume. We describe the unique application of an adult right heart assist device, primarily used for 'off-pump' coronary revascularization for fetal cardiopulmonary support. Finally, while previous fetal experiments have used late-gestation mature fetuses, we studied more immature fetuses of mid-gestation, relevant to current clinical attempts in fetal therapy.

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