![]() Blood viscosity is a parameter which is technically difficult to measure: however it is a direct and strong function of Hct, which is relatively easy to determine, therefore we also analyzed the association between blood viscosity and Hct, to relate our findings to studies that investigated the blood pressure/Hct association. The present study was undertaken to test the hypothesis that blood pressure is independent of blood viscosity and Hct in a population presumed healthy according to medical history, anthropometric measurements, and blood parameters. The variability in Hct arises from genetic factors, gender, diet, environmental conditions, exercise, season, time of the year, and age and leads to corresponding variability in blood viscosity, as reported by Kameneva et al, 6 who also measured the dependence of blood viscosity on Hct for a population at sea level. The relationship between blood pressure and blood viscosity can be explored by performing transversal population studies in healthy subjects, taking advantage of the naturally occurring variability in Hct and therefore blood viscosity. Thus increased blood viscosity can cause vasodilation, which has a large non-linear effect in lowering peripheral vascular resistance that counteracts the increase due to viscosity. 4 Although it is commonly accepted that sustained hyperviscosity can decrease perfusion and increase blood pressure, it should be noted that increased blood viscosity has two effects in the cardiovascular system: it may act to increase shear stress on the endothelium and increase NO release, promoting vasodilation as well as an increase in the viscous component of vascular resistance. 3 In these studies, small increases in Hct lower blood pressure and vice versa due to the effect of blood viscosity and shear stress on the management of nitric oxide (NO) production by the endothelium. 2 However, it is possible that in these studies the cardiovascular system presents some form of regulatory impairment, due to either age or incipient disease, which hinders its blood pressure regulatory ability vis-a-vis changes in blood viscosity.Īlthough it is not entirely satisfactory to compare animal and human physiology, normal healthy awake hamsters respond paradoxically to acute changes in hematocrit (Hct) and therefore blood viscosity. ![]() 1 This same conclusion emerges from studies on the relationship between hypertension and blood rheological changes. The perception that blood pressure is universally positively correlated with blood viscosity is embodied in the statement: “In conclusion, our study provides good evidence of a strong association between blood viscosity and arterial pressure, independently of many possible confounding factors,” summarizing the findings of the Edinburgh Artery Study, which evaluated the blood pressure/viscosity association in 1592 men and women aged 55–74 years. The present results suggest that studies that show a positive correlation between MAP and blood viscosity (and Hct) do not differentiate data according to gender, or involve populations that do not compensate for increased blood viscosity and potentially increased shear stress. MAP and blood viscosity (and Hct) were not statistically associated when men and women were analyzed separately and were weakly positively correlated ( r 2 = 0.08, P < 0.02) when treated as a group. Separating the data by gender yielded positive, linear correlations ( r 2 = 0.18 and 0.10, respectively) with identical slopes, however blood viscosity for men was 1.2 cP greater than in women ( P = 0.02). The correlation between blood viscosity and Hct was linear and positive ( r 2 = 0.48) and identical to that of previous studies reported in the literature when men and women are taken as a single group. ![]() The relationship between blood viscosity, hematocrit (Hct), and mean arterial blood pressure (MAP) was studied in a healthy population of 91 men and 66 women with an average age of 30.6 ± 8.0 years, from the city of Victoria de Durango (1800 m elevation). ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |