Acute Salt Handling in Orthostatic Intolerance

Acute Renal Salt Handling in Orthostatic Intolerance

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.

Inclusion Criteria:

• Diagnosed with orthostatic intolerance by Vanderbilt Autonomic Dysfunction Center (or healthy control subject)

Exclusion Criteria:

• Overt or acute cause for orthostatic tachycardia
• Hypertension (BP>145/95 or need for anti-hypertensive medications)
• QRS duration > 120 msec on EKG
• Pregnancy