Usefulness of blood and plasma viscosity measurements in the evaluation of arteriopathic patients

Blood viscosity represents the internal friction of the blood, in other terms, its resistance to be deformed and to flow under a tangential force. This function is conditioned by the intrinsic characteristics of blood and the geometry of the system in which flow occurs. Thus, any in vitro (or ex vivo) system of measurement of blood viscosity represents a relatively approximate evaluation of the ratio between intertial forces and viscous resistance. However, the possibility of measuring blood viscosity in a reproducible way provided the opportunity of identifying some clinical conditions associated with a worsening in rheologic parameters. Thus, "primary" and "secondary" hyperviscosity syndromes have been defined, on the basis of the pathogenetic responsibility of rheologic or hemodynamic factors, respectively. The possibility of performing in vitro measurement of blood viscosity provided the opportunity of planning several clinical pharmacology studies with theoretically active drugs. On such a basis, the rationale has arisen for a "rheologic therapy" of circulatory disturbances. Moreover, the evaluation of rheologic parameters is extremely useful since epidemiological studies have shown that viscosity may represent a marker and a prognostic factor for the progression of ischemic diseases as well as an independent risk factor, thus suggesting the opportunity of performing controlled clinical studies to evaluate the impact of hemorheological changes in the prevention of cardiovascular events.