Blood viscosity and aging

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Abstract

The objective of this study was to evaluate the relationship of whole blood viscosity and its major determinants (plasma fibrinogen level, hematocrit, hemoglobin and blood cell count) to advancing age. A total of 249 subjects (mean age 49.9±21.5; range 19–102 years) were included in the study. They were divided into three groups, (A) <30 years of age, n, 58; (B) 30–60 years, n, 107; (C) >60 years, n, 84. Whole blood viscosity at two different rates of shear (450 and 45 s−1) was evaluated using a cone-plate digital viscosimeter. The hematological parameters (hematocrit, hemoglobin and blood cell count) were evaluated using an automatic Coulter Counter. Plasma fibrinogen concentration was measured by a clotting method. When both sexes are considered together, whole blood viscosity shows no significant difference among age groups. Plasma fibrinogen concentration significantly increases with age (P<0.001); hemoglobin, red blood cell count and platelet count, on contrary, are significantly lower in aged group. In the male sex, blood viscosity at higher shear rate (450 s−1) negatively correlates with advancing age (P<0.005). The age-related decrease of hematocrit value in the male sex accounts for this occurrence.

Introduction

Since 1993, results of a meta-analysis of six prospective epidemiological studies, including 14 988 persons for a total of 92 147 person-years investigated, showed that plasma fibrinogen is a powerful independent predictor of myocardial infarction and stroke (Ernst and Resch, 1993). Afterwards, several prospective trials confirmed that increased whole blood viscosity, primarily dependent upon hematocrit value and fibrinogen concentration, is a major risk factor for ischemic heart disease and stroke (Heinrich and Balleisen, 1994, Suárez et al., 1996, Lowe et al., 1997).

The relationships of these rheological variables to cardiovascular events are at least as strong as those of conventional risk factors (smoking habit, diastolic blood pressure, and low-density lipoprotein cholesterol (Lowe et al., 1997).

At the same time, many investigations found that plasma fibrinogen concentration rises with advancing age (Weisert and Jeremic, 1974, Laharrague et al., 1993, Hager et al., 1994). The Italian multicenter Study on Centenarians (1995) confirmed this result in a representative population group of very elderly.

A few studies explored the relationship between rising age and whole blood viscosity. Nevertheless, some reports, based on the results of investigations carried out on very small population samples, tend to state that elderly healthy subjects display increased whole blood viscosity (Perego et al., 1981, Freyburger et al., 1987, Ciuffetti et al., 1989).

The aim of this study was to evaluate the relationship of whole blood viscosity and its major determinants to rising age in both sexes, considering the role of hemorheological abnormalities in the prevalence of ischemic heart disease and stroke, which are the major causes of death in an elderly population.

Section snippets

Patients and methods

Blood samples were obtained from 249 healthy volunteers (103 males and 146 females). Their age ranged between 19 and 102 years.

Informed consent was expressed after a clear explanation of the purpose and the potential hazards involved in this study.

Subjects aged 19–60 years (64 males and 100 females, mean age 37.2±12.7) were randomly selected among medical students and hospital employees. They were free from clinically detectable illness and their biochemical routine parameters were normal. They

Results

In total population sample (Table 1) whole blood viscosity, both at 450 and at 45 s−1 rate of shear, the mean values of hematocrit, hemoglobin, red and white blood cell count are significantly higher in men than in women (P<0.002). Plasma fibrinogen concentration and platelet count did not show any gender difference.

In Table 2, the mean values of parameters were categorized according to sex and age groups (group A, <30; group B, 30–60; group C, >60 years age).

Independently of gender, whole

Discussion

Although increased blood viscosity occurs in several cardiovascular diseases (Ernst and Resch, 1993, Heinrich and Balleisen, 1994, Suárez et al., 1996, Lowe et al., 1997) indicating that blood viscosity may be a major cardiovascular risk factor, little is known on the relationship between normal aging and whole blood viscosity.

Our study confirms that fibrinogen concentration, the main determinant of plasma viscosity, rises with aging in apparently normal subjects. Nevertheless, our data rule

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