Vagal Stimulation in POTS

Overview

The purpose of this study is to investigate how the electrical stimulation of a nerve in the skin of the earlobe (transcutaneous vagal nerve stimulation), alone or in combination with two medications (galantamine and pyridostigmine), affects the way the autonomic (involuntary) nervous system controls heart rhythm, symptoms on standing, and inflammatory markers in female patients with postural tachycardia syndrome (POTS). The study consists of 2 parts: a screening (1-2 study days), and 3 testing days. The study will take 5 days total and about 16 participants will be screened for the study. The investigators estimate 13 will be eligible to participate in all of the study days.

This study will test the hypothesis that impairment of the parasympathetic nervous system contributes to the symptoms of POTS and that stimulation of this part of the nervous system improves the excessive increase in heart rate, standing tolerance and inflammation in patients with POTS. For this purpose, the investigators will use electrical stimulation of a nerve in the skin of the earlobe (transcutaneous vagal nerve stimulation) and two medications that increase the levels of acetylcholine (a neurotransmitter) in the central or peripheral nervous system (galantamine and pyridostigmine, respectively) to increase the activity of the parasympathetic nervous system. Screening Procedures: Potential participants will be screened in the Vanderbilt Autonomic Dysfunction Center (ADC). Medications affecting heart rate, blood pressure, blood volume, inflammatory markers and the autonomic nervous system will be withdrawn for at least five half-lives before studies. Patients will undergo a complete history and physical examination, ECG, routine clinical laboratory analyses and a blood pregnancy test for women of childbearing potential. Autonomic testing including a posture study with plasma catecholamines is then performed to determine if they meet the inclusion/exclusion criteria. Eligible participants will be studied on three separate days in a randomized, double-blind, crossover fashion. On each testing day, patients will be given one dose of the study medication (either pyridostigmine, galantamine or placebo pill), and then will have two tilt table tests (a motorized table with a footboard that moves to an upright position): one with the vagal stimulation and one with sham electrical stimulation. Heart rhythm, blood pressure and the amount of fluid in the body (body impedance) will be monitored during studies. Blood samples (up to a total of 2 tablespoons per study day) will also be collected. The order of the study days and tilt tests will be decided at random, like the toss of a coin. Each study day will last about 5 hours.