Does Bariatric Surgery Reverse Obesity-associated Sympathoexcitation?

Abstract

Obesity is associated with an increase in resting levels of muscle sympathetic neural activity (MSNA) and a decrease in reflex sympathetic neural and cardiovagal responsiveness. Exercise and diet induced weight loss reverse these changes, however the potential effects of bariatric surgery induced weight loss are unknown. PURPOSE: We hypothesize that bariatric surgery will decrease baseline levels of MSNA and increase baroreflex sensitivity. METHODS: We measured MSNA (peroneal microneurography), R-R interval (ECG) and arterial pressure (arterial catheter) in three groups of subjects: (1) subjects > 12 months post bariatric surgery (N = 2) (2) obese subjects BMI > 35 kg/m2 (N = 7) (3) lean control subjects BMI < 25 kg/m2 (N = 5). MSNA, ECG and arterial blood pressure were measured continuously during intravenous vasodilator (sodium nitroprusside) and pressor (phenylephrine) boluses. Baroreflex control of sympathetic outflow and of the heart were determined by the relationships of arterial pressure with MSNA and R-R interval, respectively, during blood pressure fluctuations (modified Oxford technique). RESULTS: Our preliminary results indicate that chronic resting levels of MSNA were lower in post bariatric subjects [19 +/- 4 (SE) bursts/min vs 28 +/- 4 bursts/min in obese subjects] with values no different from non-obese control individuals (21 +/- 3 bursts/min). Bariatric surgery also appeared to increase the responsiveness of baroreflex control of the heart [14.23 msec/mmHg (RRI) vs 8.50 msec/mmHg for obese subjects (p <0.004)]. CONCLUSION: Preliminary results indicate bariatric surgery may reverse both obesity associated increases in chronic resting levels of MSNA and improve sensitivity of the baroreflex. Supported by NIH UL1 RR024150 (to the Mayo Clinic).