Implications of Systemic Hematocrit on the Radial Distribution of Red Cells in Arterioles

Abstract

It is well‐established that the tube hemacocrit (HctT) in blood vessels and glass tubes with an internal diameter less than 200‐microns is significantly lower than feed or discharge Hct (the Fahraeus Effect). Microscopic imaging of the flow stream reveals a decrease in Hct in the vicinity of the wall (the plasma layer, PL) but the mechanism of the effect is unclear. To address this question, we recorded high speed videos (3000 fps) of blood flow in 35‐micron diameter arterioles of the rat cremaster muscle at systemic Hct (HctS) levels of 20% to 72%. We found that the PL is an annulus bordering the wall that occupies 12% to 50% of the flow stream cross section, and that it is inversely related to HctS. In addition, results indicate that the Hct in the core region of the flow stream is not significantly different from HctS. The position of the PL coincides with the region of maximal shear stress in the flow stream, which may strip away the red cell monolayer adjacent to the wall, creating the PL while the monolayer moves toward the faster‐flowing center of the flow stream. In conclusion, while volumetric flow is related to the cross section of the flow stream, the PL is related to the circumference, thus reducing HctT as radius decreases.Support or Funding InformationThis work was supported by the NIH Heart Lung and Blood Institute under Grants R01HL126945 and R01HL138116.