A persistent challenge facing the quantitative design of turbodynamic blood pumps is the great disparity of spatial scales between the primary and auxiliary flow paths. Fluid passages within journals and adjacent to the blade tips are often on the scale of several blood cells, confounding the application of macroscopic continuum models. Yet, precisely in these regions there exists the highest shear stress, which is most likely to cause cellular trauma. This disparity has motivated these microscopic studies to visualize the kinematics of the blood cells within the small clearances of a miniature turbodynamic blood pump. A transparent model of a miniature centrifugal pump having an adjustable tip clearance (50-200 microm) was prepared for direct optical visualization of the region between the impeller blade tip and the stationary housing. Synchronized images of the blood cells were obtained by a microscopic visualization system, consisting of an inverted microscope fitted with long-working-distance objective lens (40x), mercury lamp, and high-resolution charge-coupled device camera electronically triggered by the rotation of the impeller. Experiments with 7 microm fluorescent particles revealed the influence of the gap dimension on the trajectory across the blade thickness. The lateral component of velocity (perpendicular to the blade) was dramatically enhanced in the 50 microm gap compared with the 200 microm gap, thereby reducing the exposure time. Studies with diluted bovine blood (Ht = 0.5 per cent) showed that the concentration of cells traversing the gap is also reduced dramatically (30 per cent) as the blade tip clearance is reduced from 200 microm to 50 microm. These results motivate further investigation into the microfluidic phenomena responsible for cellular trauma within turbodynamic blood pumps.
BackgroundLong-term use of extracorporeal membrane oxygenation (ECMO) remains limited because of poor biocompatibility, which often leads to clot formation and device failure. Despite this common pathway to failure, there are no published studies on the rate of clot formation and resulting performance deficits in current oxygenators.MethodsECMO cases with either Maquet’s CardioHelp (CH, n=28) or Quadrox (Qx, n=14) oxygenators were evaluated over a three-month period. Data was collected prospectively and included patient characteristics and hematological data. The inlet-outlet oxygen content difference (ΔCO2) and blood flow resistance were calculated as measures of device function, and device failure due to clot formation was defined as a resistance increase greater than 1 mmHg/(L/min)/day for more than one day.ResultsThere were no statistically significant differences in patient age, total days on ECMO, platelet count (PLT) prior to ECMO, activated partial thromboplastin time during ECMO, initial resistance, and device blood flow rate. During ECMO, the Qx group had a significantly greater change in PLT (Qx: - 34±10%; CH: 7±15%), rapidity to failure due to clot formation, and a greater decline in ΔCO2 (all p<0.05). Clot burden was focused at the center of the CH oxygenator, farthest from all inlets, whereas Qx devices developed a more diffuse clot pattern.ConclusionsQx oxygenators clot earlier than CH oxygenators with a correlated drop in ΔCO2 and greater PLT reduction. These differences are likely due to the distributed, four-inlet CH design vs. the single inlet Qx design and differences in pump-induced platelet activation.
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