Blood viscosity and aging.

The objective of this study was to evaluate the relationship of whole blood viscosity and its major determinants (plasma fibrinogen level, hematocrit, hemoglobin and blood cell count) to advancing age. A total of 249 subjects (mean age 49.9+/-21.5; range 19-102 years) were included in the study. They were divided into three groups, (A) <30 years of age, n, 58; (B) 30-60 years, n, 107; (C) >60 years, n, 84. Whole blood viscosity at two different rates of shear (450 and 45 s(-1)) was evaluated using a cone-plate digital viscosimeter. The hematological parameters (hematocrit, hemoglobin and blood cell count) were evaluated using an automatic Coulter Counter. Plasma fibrinogen concentration was measured by a clotting method. When both sexes are considered together, whole blood viscosity shows no significant difference among age groups. Plasma fibrinogen concentration significantly increases with age (P<0.001); hemoglobin, red blood cell count and platelet count, on contrary, are significantly lower in aged group. In the male sex, blood viscosity at higher shear rate (450 s(-1)) negatively correlates with advancing age (P<0.005). The age-related decrease of hematocrit value in the male sex accounts for this occurrence.