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.

Cold acclimation-induced increase of systolic blood pressure in rats is associated with volume expansion.

To investigate the mechanisms of cold-induced hypertension, the systolic blood pressure (SBP) and average daily water consumption were measured weekly in 6-month-old male Wistar rats; they were subsequently acclimated to thermoneutrality (26 degrees C for 7 weeks), to cold temperature (6 degrees C for 9 weeks), and then again reacclimated to 26 degrees C for 5 weeks. Circulating plasma volume and whole blood viscosity were measured in subgroups of rats at the end of acclimation to 26 degrees C after 2 days, after 1, 6, and 8 weeks of cold, and after 2 and 5 weeks of rewarming. The control values obtained at the end of thermoneutral period were: SBP = 130.8 +/- 18.6 mm Hg, plasma volume = 41.9 +/- 4.64 mL/kg, whole body viscosity at shear rate of 22.5 per sec = 6.7 +/- 0.48 cps, and daily water consumption = 42.25 +/- 16.81 mL. After 48 h of cold exposure there was almost a 50% increase in plasma volume that persisted to a lesser degree throughout the whole period of cold exposure (P < .05). After 2 weeks of cold exposure the daily water consumption increased and SBP began to increase. After 6 weeks of cold exposure the SBP was 30 mm Hg above that of the control level (P < .001) and was accompanied by a 25% increase in whole blood viscosity (P < .05). At the end of 8 weeks of cold exposure the plasma volume was 56.8 +/- 9.51 mL/ kg and the whole blood viscosity was 8.0 +/- 1.79 cps at the 22.5 per sec shear rate. During the 5 weeks of rewarming the elevation of SBP and increased whole blood viscosity persisted, whereas the increased daily water consumption and expanded plasma volume returned to normal. Therefore, the acclimation to cold is accompanied by the development of a volume-associated hypertension, which is sustained after rewarming without volume expansion.

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.

Risk factors evaluation in some cardiovascular diseases.

Cardiovascular risk factors are associated with limitations of blood fluidity. Rheological behaviour of blood in transient flow may result from the internal organization, which in turn depends upon many parameters, which may be considered as possible elements of a profiling algorithm for diagnostic and prognostic values in various pathophysiological states. This study was designed to investigate haemorheological parameters in patients being treated for hypertension, coronary heart disease and myocardial infarct. On the basis of plasma viscosity, whole blood viscosity, haematocrit, red cell aggregation and red cell deformation, the risk was evaluated. In cases of hypertension there was a significant rise in plasma viscosity, whole blood viscosity, red cell aggregation and a fall in red cell deformability. In cases of coronary disease, plasma viscosity and red cell aggregation was increased, while in patients with myocardial infarcts, where the degree of severity is greater it was found that there was a significant rise in both plasma and whole blood viscosity. Haematocrit values were unaffected in all three groups.