Shear stress and flow dynamics of the femoral vein among obese patients who qualify for bariatric surgery

Abstract

The aim of this study was to evaluate the effects of obesity on wall shear stress and its relationship to erythrocyte aggregation. We studied 35 morbidly obese patients who were qualified for bariatric surgery. The control group consisted of 20 non-obese people. Blood rheological measurements were performed using the Laser-assisted Optical Rotational Cell Analyzer (Mechatronics, the Netherlands) and a cone-plate viscometer (Brookfield DV-II). The venous flow dynamics were assessed using a duplex ultrasound. The shear rate was estimated from the measured blood flow velocity and the diameter of the femoral vein. Venous wall shear stress was calculated from the whole blood viscosity and the shear rate. The shear rate (P < 0.005) and the venous wall shear stress (P < 0.05) were significantly lower in obese patients compared with the controls. The aggregation index (P < 0.001), syllectogram amplitude – AMP (P < 0.05) and T_slow (P < 0.001) were significantly higher in the obese patients; the aggregation half-time (P < 0.001) and T_fast (P < 0.001) were decreased compared with the control group. Multivariate regression analyses found waist circumference (β −0.31, P < 0.05), thigh circumference (β 0.33, P < 0.05) and T_slow (β −0.47, P < 0.005) to be variables that independently influenced the shear rate. Nevertheless, the AMP (β 0.34, P < 0.05) and T_slow (β −0.47, P < 0.01) were independent predictors that influenced the wall shear stress. This study indicates that there is a relationship between wall shear stress in the femoral vein and the rheological impairment of the RBC among obese patients, but further studies are necessary to confirm this suggestion.