Influence of feeding hematocrit and perfusion pressure on hematocrit reduction (Fåhræus effect) in an artificial microvascular network

Objective Hct in narrow vessels is reduced due to concentration of fast?flowing RBCs in the center, and of slower flowing plasma along the wall of the vessel, which in combination with plasma skimming at bifurcations leads to the striking heterogeneity of local Hct in branching capillary networks known as the network Fåhræus effect. We analyzed the influence of feeding Hct and perfusion pressure on the Fåhræus effect in an AMVN. Methods RBC suspensions in plasma with Hcts between 20% and 70% were perfused at pressures of 5?60 cm H2O through the AMVN. A microscope and high?speed camera were used to measure RBC velocity and Hct in microchannels of height of 5 ?m and widths of 5?19 ?m.

Results Channel Hcts were reduced compared with Hctfeeding in 5 and 7 ?m microchannels, but not in larger microchannels. The magnitude of Hct reduction increased with decreasing Hctfeeding and decreasing ?P (flow velocity), showing an about sevenfold higher effect for 40% Hctfeeding and low pressure/flow velocity than for 60% Hctfeeding and high pressure/flow velocity. Conclusions The magnitude of the network Fåhræus effect in an AMVN is inversely related to Hctfeeding and ?P.