High Sodium Diet and External Abdominal Compression in POTS

The study will involve a crossover design in which each subject will be assessed (as below)
while on a very low-sodium (10 milliequivalent/day) diet compared with a very high-sodium
diet (300 milliequivalent/day). These acute dietary interventions will be part of the parent
study ("Dietary Salt in Postural Tachycardia Syndrome" IRB#111261) for 4-5 days at the time
of the study. Dietary success will be assessed using a 24h urine for sodium and creatinine
as a part of the parent study.

Study Day:

- Studies will be performed at the end of the low and high-sodium diet phases.

- Blood pressure recording will not begin until at least 2 hours after the last meal (to
avoid any confounding hypotension from the last meal).

- Subject will be asked to void prior to data collection.

- The subject will be seated in a chair, with their feet comfortably on the floor.

- The Dinamap electrocardiographic and blood pressure (brachial cuff) recorder will be
attached to the patient and set up for measurements every 10 minutes throughout the
study with digital download into the Autonomic Dysfunction Center BP database.

- After a 20-minute seated baseline, the subject will stand for up to10 minutes. Heart
rate and blood pressure (HR/BP) will be measured at 1, 3, 5, and 10 minutes of
standing. At the end of the baseline stand period, subjects will be asked to rate their
symptoms using the provided orthostatic intolerance Symptoms questionnaire.

- The subject will then be seated and the abdominal binder will be applied without
compression.

- The Dinamap electrocardiographic and blood pressure (brachial cuff) recorder will be
attached to the patient and set up for measurements every 10 minutes throughout the
study with digital download into the Autonomic Dysfunction Center BP database.

- At 1 and 2 hours post intervention, the subject will be asked to stand for up to 10
minutes while applying external automated abdominal binder compression (up to 40 mmHg).
HR/BP will be measured at 1, 3, 5, and 10 minutes of standing.

o If nursing staffing shortages make q1h standing difficult, then the subject should be
asked to stand at least at 2 hours post intervention.

- Study termination for that day.

Inclusion Criteria:

- Postural Tachycardia Syndrome: Diagnosed with POTS 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

- Participation in the parent study "Dietary Salt in Postural Tachycardia Syndrome"
(IRB#111261)

- Age between 18-60 years

- Male and females

- Able and willing to provide informed consent

Exclusion Criteria:

- Overt cause for postural tachycardia (such as acute dehydration)

- Inability to give, or withdrawal of, informed consent

- Pregnancy

- Other factors which in the investigator's opinion would prevent the subject from
completing the protocol.