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



Status:Active, not recruiting
Conditions:Cardiology
Therapuetic Areas:Cardiology / Vascular Diseases
Healthy:No
Age Range:18 - 50
Updated:4/6/2019
Start Date:March 2012
End Date:December 2019

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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.

Study Day 1

- Start 150 mEq Na+/day diet (POTS patients as inpatients; healthy control subjects with
CRC provided outpatient diet); consume 1.5-2 liters of water per day

- Start a 24h urine collection (for Na+, K+, Cr, fractionated catecholamines)

- Blood work

Study Days 2-5

- Continue 24h 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 24h Holter combined ECG monitor and BP monitor from subject

- Continue 24h 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

- NPO after midnight for study next day

Study Day 7

- 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 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
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 in the first phase, the second phase is the remaining level)

Inclusion Criteria:

- Premenopausal patients with POTS and healthy volunteers, 18-50 years old, who are
non-smokers and free of medications with the potential to influence blood pressure

- Patients diagnosed with postural tachycardia syndrome by the Vanderbilt Autonomic
Dysfunction Center

- Increase in heart rate ≥30 beats/min with position change from supine to standing (10
minutes)

- Chronic symptoms consistent with POTS that are worse when upright and get better with
recumbence

- Only female participants are eligible. Since 80-90% of POTS patients are female, and
there can be differences in measures with the menstrual cycle, including a small
number of males might introduce a significant amount of noise.

- Able and willing to provide informed consent

Exclusion Criteria:

- Smokers

- Overt cause for postural tachycardia, i.e., acute dehydration

- Significant cardiovascular, pulmonary, hepatic, or hematological disease by history or
screening results

- Positive pregnancy test or breastfeeding

- Hypertension defined as BP>145/95 off medications when supine or needing
antihypertensive medication

- Other factors which in the investigator's opinion would prevent the participant from
completing the protocol, including poor compliance during previous studies or an
unpredictable schedule

- Unable to give informed consent
We found this trial at
1
site
2201 West End Ave
Nashville, Tennessee 37232
(615) 322-7311
Principal Investigator: Emily M Garland, PhD
Phone: 615-322-2931
Vanderbilt University Vanderbilt offers undergraduate programs in the liberal arts and sciences, engineering, music, education...
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