Rheological studies of Hb SS blood: influence of hematocrit, hypertonicity, separation of cells, deoxygenation, and mixture with normal cells.

Studies of the rheological properties of Hb SS blood indicate that the marked increase in viscosity with deoxygenation is primarily due to cell-cell interaction of cells which were not permanently deformed. The permanently deformed cells, the bottom fraction of cells separated by centrifugation, show only a fraction of the increase in viscosity compared to top cells, when each was deoxygenated. Top cells showed a greater degree of morphologic change with deoxygenation compared to bottom cells. The viscosity of deoxygenated Hb SS blood was disproportionately reduced by the addition of compatible deoxygenated Hb AA cells. A mixture of 1/4 Hb AA cells and 3/4 Hb SS cells reduced the viscosity of deoxygenated Hb SS blood 50 per cent. Studies of Hb SS cells in hypertonic media indicate that hypertonicity per se does not cause sickling. Normal and Hb SS erythrocytes both show identical changes in rheological properties when suspended in hypertonic serum. However, changes in oxygen saturation due to a decrease in intracellular pH with certain hypertonic media may lead to sickling when Hb SS blood is at intermediate PO2 levels. The addition of x-ray contrast material to blood results in the changes due to hypertonicity but does not cause sickling of Hb SS cells. The contrast material lowers the pH of the media and raises intracellular pH.