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Sex-Dependent Differences In Rheological Properties And The Relation Of Blood Viscosity To Erythrocyte Aggregation Indices Among Morbidly Obese Patients

Measures of blood flow may be different between obese men and obese women, according to researchers at the Medical University of Silesia in Poland.  The group, Wiewiora et al. compared rheological parameters of 20 obese women to that of 18 obese men.  Additionally, they evaluated the relationship between measures of red blood cell (RBC) properties and measured native blood viscosity as well as hematocrit-standardized blood viscosity.  Describing the rationale for the study, the authors noted that blood flow alterations are typically found in those who are obese and that men and women typically present with different types of obesity (i.e. localization of fat distribution).  Specifically, fat localized in the abdomen (i.e. “apple-shaped” or android obesity) is typical in obese men while present fat localized in the thighs and buttocks (i.e. “pear-shaped” or gynoid obesity) is typical in obese women.  The link between blood flow and these differences was investigated.

Native blood viscosity was significantly higher in obese men than women at all measured shear rates (p < 0.05 at 150 s-1, 300 s-1, and 450 s-1).  After adjusting to hematocrit of 45, however, there were no significant gender differences in blood viscosity (p > 0.05 at 150 s-1, 300 s-1, and 450 s-1).  Therefore, hematocrit was an important contributor to the gender related viscosity differences in this population.  Additionally, plasma viscosity was not significantly different between obese males and females, despite higher fibrinogen concentrations in males.

Elongation index, a measure of RBC deformability, was lower in obese females; however, RBC aggregation was not significantly different between genders.  Amplitude, a measure of the extent of RBC aggregation, was correlated with blood viscosity at 150 s-1 in obese women.  Meanwhile, men demonstrated correlations between aggregation index, a measure that describes the rate and extent of RBC aggregation, and blood viscosity at all shear rates (150 s-1, 300 s-1, and 450 s-1).  Consequently, higher viscosity in men was correlated to a greater extent of RBC aggregation and a shorter time for aggregation to occur.  The authors stated, “The correlations between blood viscosity and aggregation are to be expected, but this relation at higher shear stress is surprising”.1 Additionally, the authors speculated that the higher native blood viscosity in men may be counterregulated by enhanced RBC deformability.  Overall, however, the clinical importance of these findings has not yet been established and correlation does not necessarily imply a causal relationship between the study variables. 


Wiewiora M, Sosada K, Slowinska L, et al. Sex-dependent differences in rheological properties and the relation of blood viscosity to erythrocyte aggregation indices among morbidly obese patients. Clin Hemorheol Microcirc. 2010;44(4):259-267.


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