The Fahraeus Effect in Sheet Flows With a Gap Thickness of 4 to 36 μm

We measured the Fahraeus effect of blood flowing in a sheet flow model formed with two glass slides. The number of red blood cells in the sheet flow was counted to determine a sheet hematocrit H_s and the discharge hemotocrit H_d was measured from blood collection. For a H_d in the range of 3 to 30 percent, we find that H_s/H_d is about .83 for a gap of 4.1 μm. When the discharge hematocrit is 30 percent, the ratio decreases to .66 as the gap approaches 7 μm and then increases as the gap becomes thicker. The results indicate that the hematocrit ratio for a gap thicker than 4.1 μm is an increasing function of the discharge hematocrit. The value of H_s/H_d found for the sheet flow models and its dependence on H_d are comparable to those of circular tubes when their diameter equals the gap thickness.