Viscometric methods for assessing red cell deformability and fragmentation.

Erythrocyte deformability is an important determinant of red cell life span and depends on at least three key factors: shape, internal viscosity and membrane mechanical properties. In this paper we describe three viscometric methods for assessing red cell deformability and fragmentation: 1) Plasma and whole blood are sheared with a coneplate viscometer at high shear rates. A mathematical model for liquid behaviour is applied to the results from plasma and whole blood viscosity, and a rheological parameter called internal viscosity is obtained. 2) Shearing packed red cells (Haematocrit greater than or equal to 95%) at high shear rates, a mechanical fragmentation curve is obtained, and a new rheological parameter called rupture stress is determined. 3) Shearing whole blood at 230 Sec-1 and increasing continuously the temperature from 37 degrees C to 57 degrees C, a thermic curve is obtained. A viscosity increase is observed at about 48 degrees C and thermic curve changes are related to effects of heat on the red cell membrane. Internal viscosity, mechanical fragmentation curve and thermic curve assess red cell deformability and fragmentation and can be used as diagnostic tools in diseases with red cell abnormalities.