DOES CHOLESTEROL DEPLETION HAVE ADVERSE-EFFECTS ON BLOOD RHEOLOGY

Blood viscosity (eta(B)) at shear rates 10 and 100s-1, plasma viscosit y (eta(P)), hematocrit (Hct), and whole blood cholesterol (Chol) were measured in 50 patients with a history of myocardial infarction or uns table angina pectoris. Erythrocyte morphology was also studied by scan ning electron microscopy to determine the proportion of nondiscocytic erythrocytes (NDE). There was a significant positive correlation betwe en Chol and eta(P) (r = 0.41, P < 0.004) and a highly significant nega tive correlation (r = -0.69, P < 0.001) between Chol and Tk, a viscome tric index of erythrocyte rigidity based on relative blood viscosity a t high shear (eta(B)/eta(P)) corrected for Hct. This latter result ind icates Chol reduction in this population may increase erythrocyte rigi dity. Twenty-five patients with Chol values in the range 4.0-8.0 mmol/ L were commenced on a standard lipid-lowering diet and after eight wee ks half were also given pravastatin (40 mg daily). After thirty-two we eks Chol had fallen significantly more in the pravastatin group (28%) than in the diet only group (11%, P = 0.005). There was no change in e ta(P) for either group but a significant increase in Tk for the pravas tatin group only (P = 0.011). The change in total cholesterol (DELTACh ol) for each patient over thirty-two weeks was negatively correlated w ith both the change in the index of erythrocyte rigidity (DELTATk) (r = -0.40, P = 0.044) and the change in the proportion of nondiscocytic erythrocytes (DELTANDE) (r = -0.47, P = 0.026). These data suggest tha t cholesterol reduction within the normolipemic range may be associate d with unfavorable changes in blood rheology.