Effect of Dietary Sodium Intake on Vascular Endothelium

A Pilot Study of the Effect of Dietary Sodium Intake on Assessments of Vascular Endothelium

The investigators will test the hypothesis that markers of vascular endothelial dysfunction will be exaggerated acutely with an extreme high sodium diet compared to an extreme low-sodium diet. The investigators will compare patients with postural orthostatic tachycardia (POTS) to healthy control subjects.

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.