The Fahraeus effect in sheet flows with a gap thickness of 4 to 36 microns

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 Hs and the discharge hematocrit Hd was measured from blood collection. For a Hd in the range of 3 to 30 percent, we find that Hs/Hd is about .83 for a gap of 4.1 microns. When the discharge hematocrit is 30 percent, the ratio decreases to .66 as the gap approaches 7 microns and then increases as the gap becomes thicker. The results indicate that the hematocrit ratio for a gap thicker than 4.1 microns is an increasing function of the discharge hematocrit. The value of Hs/Hd found for the sheet flow models and its dependence on Hd are comparable to those of circular tubes when their diameter equals the gap thickness.