The mechanistic relationships between hemorheological characteristics and cardiovascular disease

Abstract

Historically, the approach to atherogenesis research has been focused on factors that primarily include vessel wall histology, blood and vessel wall biochemistry, clotting factors and platelets. This approach can be referred to as the 'biochemical' approach. We now recognize that atherosclerosis is an ongoing sterile process that starts with functional impairment of the arterial endothelium. However, the cause of the endothelial injury that initiates this process has not yet been identified. This commentary article proposes that the vasculature is a dynamic organ in which the initiating event leading to atherosclerosis is a protective, adaptive response of the endothelium to a mechanical injury related to the work of the heart (WOH). Evidence is presented that this mechanical injury is readily explained by changes in blood rheology. This represents a paradigm shift from a strictly biochemical approach to our understanding of the atherogenic process to a biomechanical one. Elevated whole blood viscosity (WBV) has been independently correlated with increased carotid intima media thickness and major cardiovascular disease risk factors, including hypertension, smoking, diabetes, advanced age, elevated low density lipoprotein cholesterol, and decreased high density lipoprotein cholesterol. These associations have led several authors to propose increased WBV as a unifying factor linking major cardiovascular risk factors and atherosclerosis. Blood rheology has been more difficult to accurately study than other risk factors for cardiovascular disease, explaining why it may be an overlooked factor in our understanding of cardiovascular disease. The science of rheology is now entering a new phase of acceptance with the development of a new scanning capillary rheometer which, unlike conventional rheometers, easily and accurately determines whole blood viscosity as a function of shear rate.

Whole blood viscosity and arterial thrombotic events in patients with systemic lupus erythematosus

“…Damage index scores were not performed in the current study. Elevation in WBV among SLE patients with arterial events was most prominent at low shear rates, an environment in which erythrocyte aggregation and rouleaux formation are thought to be major determinants of WBV (16,20). Ernst et al (28) documented increased erythrocyte aggregates and normal erythrocyte deformability in patients with SLE relative to controls, which is consonant with our findings of elevated WBV at low shear rates in patients with SLE.…”

“…WBV is predominantly determined by hematocrit, plasma viscosity (primarily driven by acute-phase reactants such as fibrinogen), and red blood cell aggregation and deformability (16). In contrast to serum or plasma viscosity, measurement of WBV does not involve separation of the constituents of blood, and therefore most closely resembles the natural rheologic conditions in the bloodstream.…”

“…At high shear rates, normal erythrocytes deform and cell-cell aggregates are broken apart. Excessive rigidity of erythrocytes, such as seen in hypertension and diabetes (17)(18)(19), results in increased WBV at high shear rates, due to the failure of erythrocytes to deform in high velocity conditions (16,20). In contrast, at low shear rates, excessive erythrocyte rigidity may lower WBV due to impairment in the formation of erythrocyte aggregates.…”

Paradoxical hypotension following increased hematocrit and blood viscosity

“…The results of this study may be explained by experiments with blood flowing in capillary tubes, which show that the RBC column is surrounded by a plasma layer that shields the intima from extensive contact with RBCs (20). With the increase of Hct, the RBC column expands, which in turn decreases the size of the plasma layer, causing erythrocytes to more effectively interact with endothelial cells, leading to increased shear stress and thus stimulation of NO release.…”

Vitex Agnus-Castus L. Essential Oil Increases Human Erythrocyte Membrane Fluidity

“…One of these, Vac essential oil, has shown promising effects in the treatment of ageing symptoms in women (7). Cardiovascular conditions related to female ageing include hypertension and atherosclerosis, whose pathophysiology is linked to changes in erythrocyte membrane fluidity (11) and blood viscosity (27), while an increase of erythrocytes' elastic deformability is the therapeutic imperative.…”