Hemodynamic Response of Neuropathic And Non-Neuropathic POTS Patients To Adrenoreceptor Agonist And Antagonist

The purpose of this study is to test the hypothesis that patients with non-neuropathic POTS will have different responsiveness than patients with neuropathic POTS to direct alpha-1 adrenoreceptor agonist therapy (droxidopa) and to non-selective beta-adrenoreceptor antagonist therapy (atenolol). The specific goal of this protocol is to investigate the effect of atenolol and droxidopa on cardiovascular autonomic functions such as cardiovagal control, sympathetic nerve activity, and sympathetic vascular transduction, systemic hemodynamic response to orthostatic stress and on the quality of life in neuropathic and non-neuropathic patients with postural tachycardia syndrome (POTS). Standardized tests are used to assess cardiovagal control function, sympathetic nerve activity, sympathetic vascular transduction, systemic hemodynamic response to head-up tilt test and standardized questionnaires to assess the quality of life in patients with POTS. The cardiovagal, sympathetic and hemodynamic measurements are performed after and during drug administration. To control the effect of medications placebo is used on separate testing visits. The order of drugs and placebo is randomized.