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Cardiovascular Hemodynamics

Cardiovascular disease is the number one cause of death in the industrialized world. Despite the fact that over the past twenty-five years significant advances have reduced the frequency of this killer, the etiology, or root cause, of cardiovascular disease remains elusive. It increasingly appears as though something may be missing in our understanding of the disease process.

At diastole, when arterial blood flow slows down or recirculates, rouleaux form, platelets aggregates, and other intermolecular reactions occur between cellular and plasma components that increase blood viscosity. Conversely, when blood flow accelerates with normal velocity and increasing shear rates during each cardiac cycle, these aggregates tend to disperse, resulting in a decrease in blood viscosity.

Blood viscosity holds certain similarities with blood pressure; it is a major determinant of the work of the heart and is also a major determinant of the perfusion of every cell of the body. Like blood pressure, the viscosity of blood changes during the course of each cardiac cycle and can be reported using two numerical quantities: systolic and diastolic viscosity. However, while blood pressure is parameter of the circulatory system, blood viscosity is a parameter of the fluid flowing through the system. Therefore, blood viscosity can be said to be more fundamental than blood pressure.

The number of studies of blood viscosity’s role in cardiovascular diseases has been rapidly accelerating in recent years. Blood viscosity has been found to play a role in the pathogenesis of atherosclerosis and is also independently associated with the major risk factors for cardiovascular disease including: hypertension1-3; hyperlipidema (positive correlation with total cholesterol, LDL-cholesterol and triglyceride; negative correlation with HDL-cholesterol)4-9; diabetes, insulin resistance syndrome and obesity9-13; tobacco smoking14-17; male gender 9,18,19; and aging9,17,20.

In the 1990s, the Edinburgh Artery Study observed 1,592 men between the ages of 45 and 59 years for five years and showed that 20% of the individuals with the highest viscosity had 55% of the major cardiovascular events; whereas, only 4% of those with low viscosity had any significant cardiovascular event. Over a period of 5 years, age and gender-adjusted mean rheological variables including blood viscosity, hematocrit, hematocrit-corrected blood viscosity, plasma viscosity, and fibrinogen were all significantly higher in patients who experienced cardiovascular events (ischemic heart disease and stroke) than in those who did not. The difference in mean whole blood viscosity between the two groups of patients was statistically very significant (p=0.0003), and the relationship of blood viscosity to the occurrence of cardiovascular events was at least as strong as for diastolic blood pressure and LDL cholesterol and stronger than that of smoking. These results suggest that blood viscosity is an important predictor of cardiovascular events in the adult population. It is noteworthy that blood viscosity levels were reported by the Edinburgh Artery Study to remain higher in subjects that experienced cardiovascular events than those who did not after adjustment for age and sex.21


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21. Lowe GD, Lee AJ, Rumley A, Price JF, Fowkes FG. Blood viscosity and risk of cardiovascular events: the Edinburgh Artery Study. Br J Haematol 1997;96:168-73.


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