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

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