Effect of Dietary Sodium Intake on Vascular Endothelium

The study will involve a crossover design in which each subject will be assessed (as below)
while on a very low-sodium (10 mEq/day) diet compared with a very high-sodium diet. These
acute dietary interventions will be part of the parent study ("Dietary Salt in Postural
Tachcyardia Syndrome" funded by R01 HL102387) 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.

Blood will be drawn and collected in a fasting state for future assay and analysis of the
following tests:

- Glucose, Insulin (glucose impairment, insulin resistance)

- Fasting lipid profile

- C-Reactive Protein (hsCRP) (inflammatory state)

- Inflammatory cytokines (inflammatory state)

- aliquots (future analysis)

Pulsitile Arterial Tonometry (PAT) Protocol Calf Blood Flow in Reactive Hyperemia (CBF-RH) -
venous occlusion plethysmography Evaluation of Forearm-Mediated Dilation

Inclusion Criteria:

- Subjects will be enrolled in the parent study "Dietary Salt in Postural Tachcyardia
Syndrome" funded by R01 HL102387 Postural Tachycardia Syndrome

- Diagnosed with postural tachycardia syndrome by the Vanderbilt Autonomic Dysfunction
Center

- Subjects will be enrolled in the parent study "Dietary Salt in Postural Tachcyardia
Syndrome" funded by R01 HL102387

- Postural Tachycardia Syndrome

- 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 Control Subjects

- Healthy, non-obese, non-smokers without orthostatic tachycardia

- Selected to match profiles of POTS patients (gender, age)

- Not using vasoactive medication

- Age between 18-60 years

- Male and female subjects are eligible.

- 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

- Pregnant

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