Fåhraeus-Vejlens effect: margination of platelets and leukocytes in blood flow through branches

Evaluation of a new point-of-care diagnostic test measuring inflammation in emergency settings

Erythrocyte aggregation kinetics is accelerated in diseases with a strong inflammation component. This study aimed to evaluate whether, in an emergency setting, a new point-of-care test measuring erythrocyte aggregation kinetics (EAK) can identify patients with underlying inflammation. Patients visiting an emergency department and needing a blood exam were successively included. EAK was measured at the point-of-care in 20 s directly on the blood samples collected in regular tubes without any manipulation. The primary measure was EAK's half-life during the first 5 s (EAK5s). Each patient's inflammation status was assessed blind to the EAK test results. Receiver Operating Characteristic (ROC) curves for inflammation status were built. 268 patients had their EAK5s measured, and a clear inflammation status was determined for 214 patients (65 had inflammation). Mean EAK5s were 2.18 s and 1.75 s for no inflammation and inflammation groups respectively (p < 0.001). EAK5s appears to be a better inflammation marker than C-Reactive protein (CRP), with an area under the ROC curve of 0.845 compared to 0.806 for CRP (p < 0.0001). The Youden threshold for prediction of inflammation was 1.86 s with 84.6% (78.5-89.9%) specificity and 70.8% (60-81.5%) sensitivity. Point-of-care EAK is an easily measured, immediately available marker of inflammation with a better predictive power than CRP's.

Hemorheological Approach to Improve Perfusion of Red Blood Cells with Reduced Deformability Using Drag-Reducing Polymer (In Vitro Study)

Drag-reducing polymers (DRPs) are nontoxic water-soluble blood additives that have been shown to beneficially alter hemodynamics when delivered intravenously in nanomolar concentrations. This study examines the ability of DRPs to alter the traffic of mixtures of normal and less-deformable red blood cells (RBCs) through branched microchannels and is intended to support and expand upon previous experiments within straight capillary tubes to promote DRPs for future clinical use. Branched polydimethylsiloxane microchannels were perfused with a mixture of normal bovine RBCs also containing heat-treated less-deformable RBCs at a hematocrit of 30% with 10 ppm of the DRP poly(ethylene oxide) (MW 4M Da). Suspensions were driven by syringe pump, collected at outlets, and RBC dimensions measured while subject to shear stress to determine the proportion of healthy RBCs in each sample. DRPs eliminated evidence of the plasma skimming phenomena and significantly increased the pressure drop across microchannels. Further, DRPs were found to cause an increase in the proportion of healthy RBCs exiting the branch outlet from -8.5 ± 2.5% (control groups) to +12.1 ± 5.4% (n = 6, p = 0.02). These results suggest DRP additives may be used to improve the perfusion of less-deformable RBCs in vivo and indicates their potential for future clinical use.

Blood rheology as a mirror of endocrine and metabolic homeostasis in health and disease1

Rheological properties of plasma and blood cells are markedly influenced by the surrounding milieu: physicochemical factors, metabolism and hormones. Acid/base status, osmolality, lipid status, plasma protein pattern, oxidative stress induced by increased free radicals production, endothelium-derived factors such as nitric oxide (NO), achidonic acid derivatives modulate both red blood cell (RBC) and white cell mechanics. Therefore, regulatory axes involving liver, endothelium, kidney, pancreas, adrenal gland, endocrine heart, adipose tissue, pituitary gland, and surely other tissues play important roles in the regulation of blood fluidity. A comprehensive picture of all this complex network of regulatory loops is still unavailable but current progress of knowledge suggest that some attempts can currently be made.

Isolating the influences of fluid dynamics on selectin-mediated particle rolling at venular junctional regions

The objective of this study was to isolate the impact of hydrodynamics on selectin-mediated cell rolling in branched microvessels. Significant advancements have been made in furthering the understanding of complex interactions between biochemical and physical factors in the inflammatory cascade in simplified planar geometries. However, few studies have sought to quantify the effects of branched configurations and to isolate the effects of associated fluid forces. Experimental techniques were developed to perform in vitro adhesion experiments in Y-shaped micro-slides. The micro-slides were coated with P-selectin and microspheres coated with Sialyl-Lewis^x were observed as they rolled in the chambers at different wall shear stresses. Study results revealed that microsphere rolling velocities and rolling flux were lowest in regions closest to the apex of a junctional region and were dependent on both branch angle and wall shear stress. The regions closest to the junctional region were shown to have low bulk flow velocities and shear stresses using computational fluid dynamics (CFD) modeling. Collectively, the study demonstrates that despite the presence of a uniform coating of P-selectin, hydrodynamic factors associated with the chamber geometry yield non-uniform effects on particle behavior. These findings could explain why cells have been observed to preferentially adhere or transmigrate near junctional regions. Future characterization of inflammatory processes in microvascular network configurations is therefore crucial for furthering our fundamental understanding of inflammation.