The investigators will test the hypothesis that patients with chronic orthostatic
intolerance or postural orthostatic tachycardia syndrome (OI or POTS) will be unable to
conserve urinary sodium as compared to healthy control subjects.
Patients with chronic OI appear to be hypovolemic with abnormalities in hormones that
regulate salt & water handling. Increases in dietary salt have salutary effects on
orthostatic tolerance in a physiological laboratory. The infusion of intravenous saline
acutely decreased heart rate in this patient population. Preliminary data from Vanderbilt
suggests abnormal salt handling in patients with chronic OI in a few patients. These data
need to be confirmed and a better understanding of sodium handling in response to acute salt
loads is required in these patients.
- Diagnosed with orthostatic intolerance by Vanderbilt Autonomic Dysfunction Center (or
healthy control subject)
- Overt or acute cause for orthostatic tachycardia
- Hypertension (BP>145/95 or need for anti-hypertensive medications)
- QRS duration > 120 msec on EKG