Dietary Salt in Postural Tachycardia Syndrome

Summary

Participation Requirements

Description

Study Day 1 Start 150 mEq Na+/day diet (POTS patients as inpatients; healthy control subjects with CRC provided outpatient diet) Start a 24h urine collection (for Na+, K+, Cr, fractionated catecholamines) Blood work Blood volume - carbon monoxide rebreathing Study Day 2 Complete 24h urine Start STUD...

Study Day 1 Start 150 mEq Na+/day diet (POTS patients as inpatients; healthy control subjects with CRC provided outpatient diet) Start a 24h urine collection (for Na+, K+, Cr, fractionated catecholamines) Blood work Blood volume - carbon monoxide rebreathing Study Day 2 Complete 24h urine 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; water ad lib Study Day 3 - 5 Continue STUDY DIET; water ad lib On Day 5, a 24 hr holter combined ECG monitor will be placed on the subjects. Study Day 6 Continue STUDY DIET; water ad lib Remove 24h Holter combined ECG monitor and BP monitor from subject Start a 24h urine collection (for Na+, K+, Cr, fractionated catecholamines) Complete questionnaires NPO after midnight for study next day Study Day 7 (BIG DAY) Awaken early (~6am) to void (still collecting 24h 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 3 tablespoons of blood in each body position to measure hormones that regulate blood pressure and blood volume Hormones to verify the subject's phase of menstrual cycle Serum/plasma aliquots for future analysis 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 Autonomic Function Test with Cardiac Output and Brief Tilt The subject will be tilted up to 60-75 degrees head-up tilt for up to 10 minutes to measure the changes in heart rate and blood pressure and symptoms with upright challenge. Blood volume - carbon monoxide rebreathing 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 increase 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 to the first phase, the second phase is the remaining level)

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