ABSTRACT
Normal erythrocytes are highly deformable and this greatly facilitates blood flow in the narrow channels of the circulation, compensating for the effect of the much less deformable leukocyte. Deformability is therefore crucial for the normal circulation, and also survival, of the erythrocyte. Fortunately, the erythrocyte is tailor-made for deformability. The interrelationship between erythrocyte mean cell volume (MCV) and erythrocyte deformability has been underestimated in rheological studies. Electronic measurement of erythrocyte MCV is influenced by erythrocyte deformability and, conversely, measurement of erythrocyte deformability is influenced by erythrocyte MCV. Mean cell hemoglobin concentration is an important determinant of cytoplasmic viscosity which, as it rises, causes a loss of erythrocyte deformability. This is seen in congenital disorders such as hereditary xerocytosis and sickle cell disease. Loss of the biconcave, discocyte shape of the erythrocyte can compromise the advantageous surface area-to-volume geometry of the normal cell.
