The Spacing of Red Cells in the Microcirculation during Acute Anemia.

Abstract : When rats are made acutely anemic by replacing blood with solutions of albumin and salts, detectable gaps between red cells in capillaries increase in size from 4.44 + or - .63 micrometers at a hematocrit of 0.4, to 11.3 + or - 3.7 micrometers at a hematocrit of 0.1. At low hematocrits, cells appear to occupy a smaller fraction of the capillary cross section (.222 + or - .022 at a hematocrit of 0.1) than at higher hematocrits (.442 + or - .014 at a hematocrit of 0.4). The size of plasma gaps is not uniform, but so variable that cell-free plasma spaces as large as 12 micrometers are relatively common even at a hematocrit of 0.4. Gaps of this size could give rise to plasma P02 tensions 20 micrometers Hg lower than red cell P02. Such gradients are large enough to be detected by optical methods and suggest to us the possibility that plasma gaps may play a role in the regulation of blood flow.