The effects of weight loss surgery on blood rheology in severely obese patients.

Background: The effects of dieting on blood rheology in obese individuals suggest that improving the rheologic profiles depends on the amount of weight lost and its long-term maintenance. The aim of this study was to evaluate the effects of weight loss after surgery on blood rheology at 12-month follow-up.

Methods: We studied 38 obese patients who underwent laparoscopic weight loss surgery, 22 of whom had sleeve gastrectomy (SG) and 16 of whom had gastric banding (LAGB). We evaluated rheologic parameters such as blood viscosity, plasma viscosity, and erythrocyte deformability (as measured by elongation index [EI]) preoperatively and 12 months after surgery.

Results: Whole blood viscosity at 150 s(-1) shear rate (P<.01) and 300 s(-1) shear rate (P<.05), blood viscosity corrected to a standard hematocrit at both shear rates (P<.0005 and P<.005, respectively), and plasma viscosity (P<.005) were significantly reduced after surgery. EI evaluated at different shear stresses (18.49-60.03 Pa) decreased (P<.005) 12 months after surgery. There were significantly decreased EI and blood viscosity corrected to a standard hematocrit after SG (P<.005 and P<.05) and LAGB (P = .0621 and P<.05), but plasma viscosity significantly decreased only after SG (P<.005). Blood viscosity at both shear rates correlated with plasma viscosity (r = .51, P<.005 and r = .5, P<.005). Plasma viscosity correlated positively with body mass index (r = .57; P<.0005) and negatively with percentage of excess weight lost (r = -.56; P< .005).

Conclusions: This study found that weight loss after bariatric surgery induced improvement in blood rheology in obese patients at 12 months after surgery. The increased red blood cell rigidity after surgery requires further study because the physiologic importance of this change has not yet been established.