Dietary Salt in Postural Tachycardia Syndrome
Condition: Postural Orthostatic Tachycardia Syndrome
MeSH terms: Postural Orthostatic Tachycardia Syndrome; Tachycardia; Syndrome
Study type: Interventional

Summary: 
      Patients with POTS may not adequately expand their plasma volume in response to a high-sodium
      (Na+) diet. Mechanisms involved in the regulation of plasma volume, such as the
      renin-angiotensin-aldosterone system and renal dopamine, may be impaired in POTS and may
      respond inappropriately to changes in dietary sodium.The purpose of this study is to
      determine (1) whether a high dietary sodium level appropriately expands plasma volume in
      POTS; (2) whether plasma renin activity and aldosterone are modified appropriately by changes
      in dietary sodium in POTS; and (3) 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 milliequivalents (mEq) Na+/day diet (POTS patients as inpatients; healthy
           control subjects with clinical research center (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

        -  Nothing by mouth (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)
    

Intervention name(s): Blood Volume; Total Blood Volume; Exercise Capacity Test - Bicycle; Posture Study
Intervention type(s): Radiation; Radiation; Procedure; Procedure
Intervention description(s): we will measure the amount of hemoglobin and myoglobin in the body by a procedure called CO rebreathing. One teaspoon of blood is taken before and after a small amount of CO has been absorbed into the bloodstream.; Using injection of iodinated I-131 tagged human serum albumin nominally 25 microcuries of radiation, blood samples are drawn before and 30 minutes after injection.; subjects breath 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.; 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.
Other intervention name(s): carbon monoxide (CO)-red blood cell (RBC) Blood Volume; DAXOR; VO2 Max (maximal oxygen consumption); Standing Orthostatic Challenge
Intervention MeSH terms: Carbon Monoxide
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: Randomization tables will be used to determine whether the 10 mEq sodium/day or 300 mEq sodium/day diet will be consumed first. Both diets will be completed on each subject (randomized crossover study), so all of the study procedures (after screening) will be repeated.
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: POTS; Orthostatic Intolerance; Orthostatic Tachycardia