Renal Resistive Index Predicts Post–Bariatric Surgery Renal Outcome in Nondiabetic Individuals with Severe Obesity

Objective: Bariatric surgery may ameliorate renal function through vascular mechanisms. This study tested surgery's ability to improve measured glomerular filtration rate (mGFR) and identified clinical, renal, and systemic vascular predictors of such improvement. Methods: Twenty-five nondiabetic subjects with severe obesity were studied before and 1 year after Roux-en-Y gastric bypass, evaluating mGFR and renal plasma flow, basal renal resistive index (RI) and dynamic renal RI, renal visceral fat, and systemic vascular parameters, including flow-mediated dilation, aortic pulse wave velocity, and carotid intima media thickness and stiffness. Results: After Roux-en-Y gastric bypass, BMI decreased by 31%. At follow-up, body surface area (BSA)-adjusted mGFR increased (from 86.9 ± 15.2 to 109.0 ± 18.2 mL/min/1.73 m2, P < 0.001), whereas the absolute mGFR did not change. Renal plasma flow did not vary. RI decreased; flow-mediated dilation, pulse wave velocity, carotid intima media thickness, and carotid stiffness improved. mGFR changes after surgery (ΔmGFR/BSA) were associated with younger age and lower fasting glucose. Among vascular variables, an improved ΔmGFR/BSA was associated with smaller brachial artery diameter, lower intima media thickness, and lower RI; this latter association remained after adjusting for covariates. No measure of adiposity was associated with ΔmGFR. Conclusions: In subjects with obesity and normal renal function, bariatric surgery improves mGFR/BSA (although absolute mGFR is unchanged) and renal and systemic vascular function. Lower renal intravascular resistance can predict these improvements, maximizing them in relatively young individuals.