Comparative rheology of nucleated and non-nucleated red blood cells. II. Rheological properties of avian red cells suspensions in narrow capillaries.

: The flow properties of nucleated avian (duck) red cell suspensions were determined in narrow glass capillaries (internal diameter 5- 11 micrometer) perfused at constant pressure. Measurements were carried out of cellular and suspending fluid flow velocity of dynamic (tube) hematocrit. Comparison with previous measurements on human erythrocyte suspensions showed that the dynamic hematocrit reduction (Fahraeus effect) of avian cell suspensions was significantly more sensitive to changes of hematocrit than observed on the human cells. It was in addition found that the Fahraeus effect is the dominating phenomenon determining the viscosity of the nucleated cell suspensions, in contrast to suspensions of non-nucleated human red cells. Furthermore, the apparent viscosity of the nucleated cell suspensions is significantly higher than that of human blood at equal capillary diameter and tube hematocrit. In the living capillary bed of birds, the unfavourable rheological properties of the nucleated red cells could be compensated for by a low capillary hematocrit and/or a higher capillary density compared to mammalian species.