Main determinants of red blood cell deformability. Clinical and pharmacological applications

Abstract

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 deform ability). As far as the microrheological parameters are concerned, red blood cell deformability is quite definitely the most important parameter in any physiophathological study of capillary circulation and the resulting exchanges.

The main intrinsic parameters of R.B.C. deform ability are:

internal viscosity of the cell (concentration and physico-chemical properties of hemoglobin)

surface/volume ratio. The surface of the membrane is 50% greater than that of a sphere with the same volume as the erythrocyte (90µm³); deformations at constant volume are therefore possible,

membrane properties related to the lipid bi-layer (changes in composition or structure) or to the cytoskeleton.

Abnormal erythrocyte microrheology may result from alterations of anyone of these three parameters and would affect the ability of the cell to transit in capillaries. Disturbances of red blood cell deform ability are encountered in many clinical cases and mainly:

• during anomalies relating to hemoglobin structure or its oxygen affinity

• in constitutional deficiency of the memr.cane

• during degenerative cardiovascular diseases or diseases which are considered to be atherosclerosis risk factors.

The significance of the determinants of R. B.C. deformability in microcirculation and the clinical and pharmacological applications are discussed.