Hemodynamic changes during aging associated with cerebral blood flow and impaired cognitive function.

This study investigates the age associated changes in hemorheological properties and cerebral blood flow. Partial correlations indicate that part of the age-dependent decrease in flow velocities can be attributed to a hemorheological decrement resulting in part from enhanced oxidative stress in the aged. A possible link with Alzheimer's pathology is suggested by the augmented hemorheological impairment resulting from in vitro incubation of red cells with amyloids. These results suggest that in aging, oxidative stress as well as amyloids may influence the fluid properties of blood, resulting in a potential decrement in blood flow and oxygen delivery to the brain. Animal intervention studies further demonstrate that altered hemorheological properties of blood can actually influence cognitive function. The relationships shown to exist between hemorheology, blood flow, amyloids, oxidative stress, and cognitive function suggest that these factors may be one of the mechanisms operating in the complex etiology of Alzheimer's disease.

Hemorheological changes during human aging.

Various researchers have reported an association of hemorheological, hematological and metabolic changes with human aging. In this article an attempt has been made to review the present understanding of hemorheological changes and their probable role in the development of certain disorders/diseases during aging. The rise in fibrinogen, blood viscosity, plasma viscosity, red cell rigidity, fibrin degradation products and early activation of the coagulation system are some of the most prominent findings. It is generally agreed that a rise in blood viscosity factors leads to a state of hypoperfusion which results in impaired microcirculation. The cumulative effect of these changes appears in the form of a disturbed blood flow profile in older subjects leading to the development or aggravation of various circulatory disorders. Many studies indicate that hemorheological parameters that change in a number of diseases prevalent during aging include hypertension, stroke, diabetes. In addition correlations found between hemorheological parameters in the aged and decrements in certain cognitive functions and behavioral patterns suggest that hemorheological changes contribute to nonclinical aging changes.

Hypertension and hemorheology.

Hemorheological disturbances in hypertension are the outcome of changes in red cell characteristics, their interaction in the presence of fibrinogen, and the magnitude and distribution of flow forces. Hemorheological alteration coupled with changes in biochemical variables and vessel characteristics in hypertension may affect the hemodynamic profile, which could possibly contribute to the development of hemorrhagic disorders. The complex pathophysiology of hypertension also depends upon the life style, presence of other risk factors, emotional/psychological stress, age and the genetic constitution of an individual. This review article summarizes the hemorheological changes in hypertension and their probable role in the deterioration of blood flow.