Red cell fluidity in hypertension.

Rheological findings in essential hypertension are increases in haematocrit, plasma fibrinogen, plasma and whole blood viscosity, and erythrocyte aggregability as well as impaired erythrocyte deformability. Are these abnormalities secondary effects of an increased blood pressure via an increased filtration pressure rendering haemoconcentration or is the initial pressure-increase the result of a deterioration of any of the rheologic variables? Since the diameter of the red cell is about 8.5 microm, and that of the smallest capillaries about 3 microm, the ability of the cell to deform is of vital importance for capillary flow, and a decreased erythrocyte deformability could cause an increased microvascular flow resistance. We found a negative correlation between erythrocyte deformability and fasting insulin and also a decreased erythrocyte deformability in hypertensive patients during a 2 h euglycaemic insulin clamp. Associations between increased intracellular Ca2+ and decreased erythrocyte deformability on one hand and between in vitro insulin and an accumulation of Ca2+ in red blood cells on the other have earlier been shown. Hence, a decreased insulin sensitivity might be one important factor in the development of hypertension acting via an impaired erythrocyte deformability and an increased flow resistance in the microcirculation.