Influence of feeding hematocrit and perfusion pressure on hematocrit reduction (Fåhraeus 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 Fåhraeus effect. We analyzed the influence of feeding Hct and perfusion pressure on the Fåhraeus effect in an AMVN.

Methods: RBC suspensions in plasma with Hcts between 20% and 70% were perfused at pressures of 5-60 cm H O through the AMVN. A microscope and high-speed camera were used to measure RBC velocity and Hct in microchannels of height of 5 μm and widths of 5-19 μm.

Results: Channel Hcts were reduced compared with Hct in 5 and 7 μm microchannels, but not in larger microchannels. The magnitude of Hct reduction increased with decreasing Hct and decreasing ΔP (flow velocity), showing an about sevenfold higher effect for 40% Hct and low pressure/flow velocity than for 60% Hct and high pressure/flow velocity.

Conclusions: The magnitude of the network Fåhraeus effect in an AMVN is inversely related to Hct and ΔP.