Erythrocyte deformability and blood apparent viscosity in narrow capillaries

Abstract

The apparent viscosity of red blood cell (RBC) suspensions in saline was measured as a function of shear stress (from 20 to 180 dyne/cm²) and hae-matocrit (5–60%) in glass tube capillaries ranging from 30 to 400 μm in diameter. The erythrocyte deformability was altered by heating the suspension at 50°C for 1 min with continuous stirring or by glutaraldehyde fixation. An index of deformability was provided by the ‘packing factor’, ratio of apparent haematocrits read by centrifugation before and after the hardening process. This packing factor decreases from 1 for normal cells to 0.88 for heated RBC and 0.62 for fixed cells. The apparent viscosity, higher for hardened cell suspensions, correlates well with the packing factor. At 40% haematocrit the ratio of heated and normal RBC viscosities increases from 1.23 in a 200μm diameter tube to 1.53 for a 30μm tube. Results for heated RBC fall halfway between those for normal and fixed RBC. The Farhaeus-Lindqvist effect is less important for hardened RBC and presents a reversal as tube diameter falls below 80μm.

Key Words:

• Apparent blood viscosity
• erythrocyte deformability
• Fahraeus-Lindqvist effect