The missing negative effect of red cell aggregation upon blood flow in small capillaries at low shear forces

Abstract

Flow resistance of EDTA or defibrinized blood was measured in a vertical capillary viscometer. (Capillary I.D. = 0.3 mm, l = 475 mm, τ_W = 0.27 to 0.036 Pa). With decreasing shear forces the apparent viscosity increased from 12 to 16 mPa·s, i.e. by about 30%. There was no significant difference in flow resistance between red cells suspended in plasma or serum.

The apparent viscosity of the same blood sample increased from 14 to 45 mPa·s for RBC in plasma i.e. by about 320% if measured with a rotational viscometer. The attempt is made to explain this difference in flow resistance with the different effect of shear resistant RBC-aggregates upon a parabolic streaming profile in a capillary, or upon the quasi linear profile within the annular Gap of a rotational viscometer.