Effect of Dietary Sodium Intake on Vascular Endothelium
Condition: Postural Tachycardia Syndrome (POTS)
MeSH terms: Postural Orthostatic Tachycardia Syndrome; Tachycardia
Study type: Interventional

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
    

Intervention name(s): Pulsitile Arterial Tonometry (PAT) Protocol; Calf Blood Flow in Reactive Hyperemia (CBF-RH); Evaluation of Forearm-Mediated Dilation
Intervention type(s): Procedure; Device; Device
Intervention description(s): 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.; 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; 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.
Other intervention name(s): EndoPat; Hokansan strain guage venous plethysmography; Ultrasound
Allocation: Non-Randomized
Intervention model: Crossover Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: POTS; endothelial function; high salt vs low salt diet; PAT protocol; Calf blood flow; forearm mediated dilation