CELLULAR DEFORMABILITY OF NORMOXIC AND HYPOXIC MAMMALIAN RED-BLOOD-CELLS

The deformability of red blood cells is important in the microcirculat ion where capillary diameters are often smaller than those of the red blood cells. In the present study, ektacytometry was used to examine t he effect of hypoxia on the deformability of red blood cells from five mammalian species: Human, cat, rat, rabbit, and dog. Deformability wa s characterized in both normoxic (PO2 = 129 +/- 6 mm Hg) and hypoxic ( PO2 = 47 +/- 6 mm Hg) conditions in two different ways. First, we used the Elongation Index (EI) which quantitates the extent of elongation of red blood cells in response to increasing fluid shear stress; secon d, we used the Elongation Constant (EC), which quantitates the exponen tial dependence of the fraction of maximal elongation on the varying s hear stress. The EI was measured at high shear stresses (150-250 dyn/c m(2)), as well as at lower shear stresses (15, 32 and 64 dyn/cm(2)) th at occur in the microcirculation. In response to hypoxia at high shear stresses, the EI of the rat red blood cells decreased by 9.3% (P < 0. 05), but was not altered in the other four species studied. Moreover, in all five species, the EC and EI at the lower shear stresses were un altered in response to hypoxia. These ektacytometry experiments indica te that (1) the elongation constant is a new and useful parameter for characterizing the deformability of red blood cells and (2), the defor mability of human, cat, dog, and rabbit red blood cells is unaltered b y hypoxia. results constrain the possible mechanisms that could accoun t for observation that hypoxia decreases the filterability of certain species of red blood cells, which was reported previously.