NCT01563107

Dietary Sodium's Effect on Urinary Sodium and Dopamine Excretion in Patients With Postural Tachycardia Syndrome

• Status: Completed
• Phase: N/A
• Study type: Interventional
• Enrollment: 38 (actual)
• Sponsor: Vanderbilt University Medical Center · Academic / Other
• Sex: Female
• Age: 18 Years – 50 Years
• Healthy volunteers: Accepted

Summary

Patients with Postural Tachycardia Syndrome (POTS) may not adequately expand their plasma volume in response to a high sodium diet. Mechanisms involved in the regulation of plasma volume, such as the renin-angiotensin-aldosterone system and renal dopamine (DA), may be impaired in POTS and may respond inappropriately to changes in dietary sodium. The investigators propose that the changes in urinary sodium and dopamine excretion caused by consuming low-sodium and high-sodium diets will be different between patients with POTS and healthy volunteers. The purpose of this study is to determine (1) whether changes in dietary sodium level appropriately influence sodium excretion in POTS; (2) whether changes in dietary sodium level appropriately influence DA excretion in POTS; (3) whether a high dietary sodium level appropriately expands plasma volume in POTS; and (4) whether patients with POTS have improvements in their orthostatic tachycardia and symptoms as a result of a high dietary sodium level.

Detailed description

Study Day 1 * Start 150 mEq Na+/day diet (POTS patients as inpatients; healthy control subjects with Clinical Research Center(CRC)- provided outpatient diet); consume 1.5-2 liters of water per day * Start a 24hour (24hr) urine collection (for sodium (Na+), potassium (K+), creatinine (Cr), fractionated catecholamines) * Blood work Study Days 2-5 * Continue 24hr urine collection * Start STUDY DIET (10 mEq Na+/day or 300 mEq Na+/day in a random order) after 3 meals of 150 mEq Na+/day are complete; consume 1.5-2 liters of water per day * On Day 5, a 24 hr Holter combined ECG monitor and BP monitor will be placed on the subjects. Study Day 6 * Continue STUDY DIET; consume 1.5-2 liters of water per day * Remove 24hr Holter combined ECG monitor and BP monitor from subject * Continue 24hr urine collection (for Na+, K+, Cr, fractionated catecholamines) * Admit to CRC in afternoon (healthy control subjects only, as POTS patients will have already been admitted). Each subject will spend the night in the CRC and remain supine * Nothing by mouth (NPO) after midnight for study next day Study Day 7 * Awaken early (\~6am) to void (still collecting 24hr urine) * Patient returns to bed, IV catheter inserted * Posture Study (in morning; between 7-8am ideally) * Blood pressure and heart rate will be measured while supine and then while standing for up to 30 minutes * We will draw blood in each body position to measure electrolytes and hormones that regulate blood pressure and blood volume * Subjects will rate symptoms during supine period and at end of stand using Vanderbilt Orthostatic Symptoms Score (VOSS) * Total Blood Volume (DAXOR)- using injection of iodinated I-131 tagged human serum albumin nominally 25 micro-Ci of radiation blood samples drawn through IV catheter before injection and for \~30 minutes post-injection (total - 25 ml) * This will be done after supine assessment, but before standing the subject up * Exercise Capacity Test (in the afternoon) Will estimate maximal oxygen consumption (VO2 max). This test will be conducted on a stationary bicycle. Effort will be gradually increased while expired air is measured during exhaustive physical work. All procedures are repeated at least a month later with the 2nd level of dietary salt. (Randomized to high or low salt in the first phase, the second phase is the remaining level)

Conditions

• Postural Orthostatic Tachycardia Syndrome

Interventions

Type	Name	Description
RADIATION	Plasma Volume	Using injection of iodinated I-131 tagged human serum albumin nominally 25 micro-Ci of radiation, blood samples are drawn before and 30 minutes after injection.
PROCEDURE	Exercise Capacity Test - Bicycle	subjects breathe room air through a mouthpiece and exhale the air into a tube that connects to a machine (metabolic cart) that analyzes carbon dioxide and oxygen content, which allows the investigator to calculate the amount of oxygen they are using under resting and exercise conditions.
PROCEDURE	Posture Study	Blood pressure and heart rate will be measured while supine and then while standing for up to 30 minutes. Blood will be drawn in each position to measure hormones that regulate blood pressure and blood volume.

Timeline

• Start date: 2012-03-01
• Primary completion: 2020-12-01
• Completion: 2020-12-01
• First posted: 2012-03-26
• Last updated: 2022-01-25
• Results posted: 2022-01-25

Locations

1 site across 1 country: United States