Effect of Dietary Sodium Intake on Vascular Endothelium

Study Overview
=================
Brief Summary
-----------------
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.

Detailed Description
-----------------
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

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

Conditions
-----------------
Postural Tachycardia Syndrome (POTS)

Intervention / Treatment
-----------------
* Procedure: Pulsitile Arterial Tonometry (PAT) Protocol
* Device: Calf Blood Flow in Reactive Hyperemia (CBF-RH)
* Device: Evaluation of Forearm-Mediated Dilation


Participation Criteria
=================
Eligibility Criteria
-----------------
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.

Ages Eligible for Study
-----------------
Minimum Age: 18 Years
Maximum Age: 60 Years

Sexes Eligible for Study
-----------------
All

Accepts Healthy Volunteers
-----------------
Accepts Healthy Volunteers

Study Plan
=================
How is the study designed?
-----------------

Design Details

Primary Purpose: Basic Science
Allocation: Non-Randomized
Intervention Model: Crossover Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: High Sodium - POTS & Controls<br>Subjects will receive a high sodium diet for 4-5 days prior to study day. Procedures include: blood work, urine collection, Pulsitile Arterial Tonometry (PAT), PAT analysis, Calf Blood Flow in Reactive Hyperemia (CBF-RH), & evaluation of forearm-mediated dilation. | Procedure: Pulsitile Arterial Tonometry (PAT) Protocol<br>* A blood pressure cuff will be placed on one upper arm (study arm; non-dominant), while the contralateral arm will serve as a control (control arm). RH-PAT probes will be placed on one finger (finger II, III, or IV) of each hand (same finger on both hands). The fingers on either side of the one with the probe will be separated using soft sponge rings. Continuous recording of pulsatile blood volume responses from both hands will be initiated. After a 10-min equilibration period, the blood pressure cuff on the study arm will be inflated to 60 mm Hg above systolic pressure for 5 min. The cuff will then be deflated to induce reactive hyperemia, PAT recording will be stopped.<br>* Other names: EndoPat;Device: Calf Blood Flow in Reactive Hyperemia (CBF-RH)<br>* Calf blood flow (CBF) will be determined using venous occlusion plethysmography and calibrated mercury strain-gauges during reactive hyperemia after a 5 min of ischemia of the distal limb. Strain-gauges will be applied to the widest part of the non-dominant calf ( 10 cm below patella). Participants will remain quietly supine for 10 min with legs elevated on foam pads above the right atrium to achieve stable baseline measurements of CBF. The venous occlusion cuff is inflated for 4 seconds at 8 seconds intervals, while monitoring the change in resistance in the system, pressure inside the measuring cuff, and 5-10 determinations are performed<br>* Other names: Hokansan strain guage venous plethysmography;Device: Evaluation of Forearm-Mediated Dilation<br>* The arm will be kept extended and immobilized at heart level. Brachial artery diameter will be measured using a high resolution ultrasonography using a linear array probe with a 5 to 17 MHz frequency range. The brachial artery will be imaged in longitudinal sections, 5-10 cm proximal to placement of an occlusion cuff in the dominant forearm just below the antecubital fossa. The probe will be held with a stereotaxic holder with micrometer movement capabilities.<br>* Other names: Ultrasound;|
| Other: Low Sodium Diet (POTS & Controls)<br>Participants will consume a very low sodium diet (10 mEq/day) for 4-5 days prior to study day. Procedures include: blood work, urine collection, Pulsitile Arterial Tonometry (PAT), PAT analysis, Calf Blood Flow in Reactive Hyperemia (CBF-RH), & evaluation of forearm-mediated dilation. | Procedure: Pulsitile Arterial Tonometry (PAT) Protocol<br>* A blood pressure cuff will be placed on one upper arm (study arm; non-dominant), while the contralateral arm will serve as a control (control arm). RH-PAT probes will be placed on one finger (finger II, III, or IV) of each hand (same finger on both hands). The fingers on either side of the one with the probe will be separated using soft sponge rings. Continuous recording of pulsatile blood volume responses from both hands will be initiated. After a 10-min equilibration period, the blood pressure cuff on the study arm will be inflated to 60 mm Hg above systolic pressure for 5 min. The cuff will then be deflated to induce reactive hyperemia, PAT recording will be stopped.<br>* Other names: EndoPat;Device: Calf Blood Flow in Reactive Hyperemia (CBF-RH)<br>* Calf blood flow (CBF) will be determined using venous occlusion plethysmography and calibrated mercury strain-gauges during reactive hyperemia after a 5 min of ischemia of the distal limb. Strain-gauges will be applied to the widest part of the non-dominant calf ( 10 cm below patella). Participants will remain quietly supine for 10 min with legs elevated on foam pads above the right atrium to achieve stable baseline measurements of CBF. The venous occlusion cuff is inflated for 4 seconds at 8 seconds intervals, while monitoring the change in resistance in the system, pressure inside the measuring cuff, and 5-10 determinations are performed<br>* Other names: Hokansan strain guage venous plethysmography;Device: Evaluation of Forearm-Mediated Dilation<br>* The arm will be kept extended and immobilized at heart level. Brachial artery diameter will be measured using a high resolution ultrasonography using a linear array probe with a 5 to 17 MHz frequency range. The brachial artery will be imaged in longitudinal sections, 5-10 cm proximal to placement of an occlusion cuff in the dominant forearm just below the antecubital fossa. The probe will be held with a stereotaxic holder with micrometer movement capabilities.<br>* Other names: Ultrasound;|

What is the study measuring?
-----------------
Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| FMD (% Change) | The primary analysis will involve a non-parametric, paired, Signed Rank test of flow mediated dilation (FMD) between all subjects (POTS & control subjects) on the high sodium diet vs low sodium diet | FMD was assessed on the morning of day 7, after 6 days of being on either a high salt diet or a low salt diet. | 

 Terms related to the study
=================
Keywords Provided by Centre Hospitalier Valida
-----------------
POTS, endothelial function, high salt vs low salt diet, PAT protocol, Calf blood flow, forearm mediated dilation