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Studies performed in the last decades have highlighted the need to better understand the contribution of the endothelium, vascular function, oxidative stress, inflammation, coagulation, hemolysis and vascular adhesion mechanisms to the pathophysiology of acute vaso-occlusive like events and chronic organ damages in sickle cell disease (SCD). Although SCD is a hemorheological disease, a few works focused on the contribution of blood viscosity, plasma viscosity, red blood cell deformability and aggregation in the pathophysiology of SCD. After a brief description of basic hemorheology, the present review focuses on the role of the hemorheological abnormalities in the causation of several SCD complications, mainly in sickle cell anemia and hemoglobin (Hb) SC disease. Several genetic and cellular modulators of blood rheology in SCD are discussed, as well as unresolved questions and perspectives.

Background: Recent evidence suggests that red blood cell aggregation and the ratio of hematocrit to blood viscosity (HVR), an index of the oxygen transport potential of blood, might considerably modulate blood flow dynamics in the microcirculation. It thus seems likely that these factors could play a role in sickle cell disease., Design and Methods: We compared red blood cell aggregation characteristics, blood viscosity and HVR at different shear rates between sickle cell anemia and sickle cell hemoglobin C disease (SCC) patients, sickle cell trait carriers (AS) and control individuals (AA)., Results: Blood viscosity determined at high shear rate was lower in sickle cell anemia (n=21) than in AA (n=52), AS (n=33) or SCC (n=21), and was markedly increased in both SCC and AS. Despite differences in blood viscosity, both sickle cell anemia and SCC had similar low HVR values compared to both AA and AS. Sickle cell anemia (n=21) and SCC (n=19) subjects had a lower red blood cell aggregation index and longer time for red blood cell aggregates formation than AA (n=16) and AS (n=15), and a 2 to 3 fold greater shear rate required to disperse red blood cell aggregates., Conclusions: The low HVR levels found in sickle cell anemia and SCC indicates a comparable low oxygen transport potential of blood in both genotypes. Red blood cell aggregation properties are likely to be involved in the pathophysiology of sickle cell disease: the increased shear forces needed to disperse red blood cell aggregates may disturb blood flow, especially at the microcirculatory level, since red blood cell are only able to pass through narrow capillaries as single cells rather than as aggregates.

Recent basic science and large-scale clinical studies involving blood rheological factors have led to a similar conclusion: the mechanics of blood flow play an important role in the development and progression of various cardiovascular diseases (e.g., coronary artery disease, stroke). Several viscometer systems to measure whole blood viscosity have been developed, yet blood viscosity measurements are not routinely employed in clinical practice, primarily due to the complexity of currently available methods. Herein we provide a description of a new, computer-controlled capillary viscometer that offers a convenient approach to the measurement of blood viscosity over a wide range of shear rates. The new viscometer uses a disposable test section, requires small volumes of blood, provides viscosity data that compare well with those from other viscometers, and completes all testing and data analysis within five minutes.

Background: von Willebrand factor is a blood glycoprotein that is required for normal hemostasis. Its level can be increased by endothelial cell damage., Hypothesis: von Willebrand factor is a suitable marker of endothelial dysfunction., Methods: von Willebrand factor activity was determined by ELISA in patients with acute coronary syndromes, acute stroke and chronic vascular diseases, and was compared with the values of healthy controls., Results: von Willebrand factor activity of patients in each group was significantly higher (P<0.001) than that of the control group. The values of patients with acute coronary syndrome and acute stroke were significantly higher (P<0.05 and P<0.01, respectively) than those of patients with chronic vascular diseases. von Willebrand factor activity was significantly higher in patients with acute coronary syndrome and acute stroke (P<0.05 and P<0.01, respectively) on the sixth day than on admission., Conclusions: By measuring von Willebrand factor activity, a considerable, significant difference could be found between healthy people and chronic and acute vascular patients. The routine measurement of von Willebrand factor activity in vascular patients as an index of endothelial dysfunction may have clinical importance, because detection of this marker can be a noninvasive way of assisting diagnosis and indicating disease progression.