Comparative plasma viscosity measurements in healthy subjects

The aim of the present investigation is to evaluate the measurement of plasma viscosity, carried out by tube capillary viscometer and to compare the results with those of the dynamic apparent viscosity, determined by standardized rotational viscometer. The study was carried out in 28 clinically healthy volunteers. Gravity force capillary viscometers of Ubbelohde type were worked out in the laboratory for the purpose of the study. Simultaneous measurement of plasma viscosity was performed with the rheometer LS 30 Contraves with diameters of cylinders φ₁ = 11 mm, φ₂ = 12 mm, h = 8 mm, and the shear rates varying from 0.017 to 128.5 s⁻¹. All rheological measurements were carried out at 37°C. Certain nonlinearity at the low shear rate range is displayed when the plasma dynamic viscosity is measured by rotational viscometer. The mean plasma viscosity values vary between 3.15 mPa.s at 0.0237 s⁻¹ to 1.34 mPa.s at 128.5 s⁻¹. The mean values of the dynamic plasma viscosity, estimated by capillary viscometer are 1.34 ± 0.05 mPa.s. The viscosity values obtained with the capillary viscometer are slightly lower than those obtained with the Couette viscometer. This phenomenon is probably due to surface adsorbed proteins resulting in spuriously high torque.