More than 78 million adults in the U.S. are obese. Bariatric surgery is the only modality
that results in sustained weight loss along with reversal of diabetes mellitus, and a
decrease in cardiovascular events. Obesity is associated with increased sympathetic nervous
system (SNS) activity that contributes to blood pressure regulation; sympathetic
vasoconstrictor activity is maximally activated upon standing and is fundamental for the
maintenance of orthostatic tolerance. After bariatric surgery, there is a significant and
sustained reduction in SNS activity at three and six months after the procedure, which is
related to weight loss. Recently, multiple retrospective studies have reported an orthostatic
intolerance (OI) syndrome after bariatric surgery characterized by chronic pre-syncopal
symptoms, syncope and orthostatic hypotension. In the Vanderbilt University Medical Center
bariatric surgical center, 741 post-bariatric surgery patients reported OI symptoms, 98
(13.2%) of these patients, progressed to chronic OI and in17 cases, the OI was so disabling
that patients initiated treatment with pressor agents. More than 50% of OI cases in the
cohort developed the condition during a weight-stable period. Hence, investigators propose
the novel hypothesis that after bariatric surgery, the persistent reduction in SNS activity
contributes to impaired orthostatic tolerance, which is independent of weight loss.