Red blood cell microrheology (clinical and pharmacological applications)

In order to understand blood circulation, knowledge of the rheological properties of blood is required. However, the characteristic parameters which must be considered differ according to the circulatory region investigated. A distinction must therefore be made between the macrorheological parameters (viscosity, viscoelasticity) and the microrheological parameters (aggregation, cell deformability). As far as the microrheological parameters are concerned, red blood cell deformability is quite definitely the most important parameter in any physiopathological study of capillary circulation and the resulting exchanges. The main intrinsic parameters of red blood cell deformability are: inner viscosity of the cell, surface/volume ratio and membrane properties related to the lipid bilayer or to the cytoskeleton. Abnormal erythrocyte microrheology may result form alterations any one of these three parameters and would affect the ability of the cell to transit in the capillaries. Disturbances of red blood cell deformability are encountered in many clinical cases, mainly during anomalies relating to hemoglobin structure or its oxygen affinity, in constitutional deficiency of the membrane and during degenerative cardiovascular diseases or diseases which are considered to be atherosclerosis risk factors.