Relation of blood viscosity to demographic and physiologic variables and to cardiovascular risk factors in apparently normal adults.

Although increased blood viscosity occurs in several cardiovascular diseases, little is known of factors influencing blood rheology in normal adults. Accordingly, we examined the relations of whole blood viscosity (WBV) to its rheologic determinants (hematocrit level, plasma viscosity, protein concentration, and red cell aggregability and rigidity), to demographic and laboratory variables, and to cardiovascular risk factors in 128 normotensive employed adults. Hematocrit levels accounted for 67-84% of variability of WBV at shear rates from 208 to 0.1 sec-1 with lesser contributions from plasma viscosity, red cell aggregability, and rigidity (multiple r = 0.95-0.97); WBV was predicted accurately from standard measurements of hematocrit and total plasma protein levels (multiple r = 0.78-0.92 in "learning" and "test" analysis). Male sex, obesity, dietary Na+ intake, and increasing age had additive effects on WBV (multiple r greater than or equal to 0.59, p less than 0.00001); the last three of these factors and black race independently predicted plasma viscosity (multiple r = 0.36, p less than 0.001). Among regulators of plasma volume, plasma renin activity and urinary Na+ excretion bore independent positive relations to WBV. Diastolic and mean blood pressures were independent predictors of WBV and hematocrit levels (all p less than 0.05). Conventional risk factors (e.g., triglycerides, obesity, and cholesterol levels) were positively related to WBV or plasma viscosity. Thus, in apparently normal adults, 1) WBV or plasma viscosity are increased by male sex, obesity, high sodium intake, aging, and black race, 2) WBV is positively related to plasma renin activity, 3) WBV or plasma viscosity are related to diastolic and mean blood pressures, triglycerides and cholesterol concentrations, and 4) WBV can be predicted from simple measurements of hematocrit and total plasma protein levels.