Does cholesterol depletion have adverse effects on blood rheology?

Blood viscosity (eta B) at shear rates 10 and 100s-1, plasma viscosity (eta P), hematocrit (Hct), and whole blood cholesterol (Chol) were measured in 50 patients with a history of myocardial infarction or unstable angina pectoris. Erythrocyte morphology was also studied by scanning electron microscopy to determine the proportion of nondiscocytic erythrocytes (NDE). There was a significant positive correlation between Chol and eta P (r = 0.41, P < 0.004) and a highly significant negative correlation (r = -0.69, P < 0.001) between Chol and Tk, a viscometric index of erythrocyte rigidity based on relative blood viscosity at high shear (eta B/eta P) corrected for Hct. This latter result indicates Chol reduction in this population may increase erythrocyte rigidity. 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 weeks half were also given pravastatin (40 mg daily). After thirty-two weeks 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 eta P for either group but a significant increase in Tk for the pravastatin group only (P = 0.011). The change in total cholesterol (delta Chol) for each patient over thirty-two weeks was negatively correlated with both the change in the index of erythrocyte rigidity (delta Tk) (r = -0.40, P = 0.044) and the change in the proportion of nondiscocytic erythrocytes (delta NDE) (r = -0.47, P = 0.026). These data suggest that cholesterol reduction within the normolipemic range may be associated with unfavorable changes in blood rheology.