Dietary Salt in Postural Tachycardia Syndrome

Study Day 1

* Start 150 milliequivalents (mEq) Na+/day diet (POTS patients as inpatients; healthy control subjects with clinical research center (CRC)- provided outpatient diet)
* Start a 24h urine collection (for Na+, K+, Cr, fractionated catecholamines)
* Blood work
* Blood volume - carbon monoxide rebreathing

Study Day 2

* Complete 24h urine
* Start STUDY DIET (10 mEq Na+/day or 300 mEq Na+/day in a random order) after 3 meals of 150 mEq Na+/day are complete; water ad lib

Study Day 3 - 5

* Continue STUDY DIET; water ad lib
* On Day 5, a 24 hr holter combined ECG monitor will be placed on the subjects.

Study Day 6

* Continue STUDY DIET; water ad lib
* Remove 24h Holter combined ECG monitor and BP monitor from subject
* Start a 24h urine collection (for Na+, K+, Cr, fractionated catecholamines)
* Complete questionnaires
* Nothing by mouth (NPO) after midnight for study next day

Study Day 7 (BIG DAY)

* Awaken early (\~6am) to void (still collecting 24h urine)
* Patient returns to bed, IV catheter inserted
* Posture Study (in morning; between 7-8am ideally)
* Blood pressure and heart rate will be measured while supine and then while standing for up to 30 minutes
* We will draw 3 tablespoons of blood in each body position to measure hormones that regulate blood pressure and blood volume
* Hormones to verify the subject's phase of menstrual cycle
* Serum/plasma aliquots for future analysis
* Subjects will rate symptoms during supine period and at end of stand using Vanderbilt Orthostatic Symptoms Score (VOSS)
* Total Blood Volume (DAXOR)- using injection of iodinated I-131 tagged human serum albumin nominally 25 micro-Ci of radiation blood samples drawn through IV catheter before injection and for \~30 minutes post-injection (total - 25 ml)
* This will be done after supine assessment, but before standing the subject up
* Autonomic Function Test with Cardiac Output and Brief Tilt
* The subject will be tilted up to 60-75 degrees head-up tilt for up to 10 minutes to measure the changes in heart rate and blood pressure and symptoms with upright challenge.
* Blood volume - carbon monoxide rebreathing
* Exercise Capacity Test (in the afternoon) Will estimate maximal oxygen consumption (VO2 max) This test will be conducted on a stationary bicycle. Effort will be gradually increase while expired air is measured during exhaustive physical work.

All procedures are repeated at least a month later with the 2nd level of dietary salt. (Randomized to high or low salt to the first phase, the second phase is the remaining level)

• Blood Volume (Radiation), also known as carbon monoxide (CO)-red blood cell (RBC) Blood Volume: we will measure the amount of hemoglobin and myoglobin in the body by a procedure called CO rebreathing. One teaspoon of blood is taken before and after a small amount of CO has been absorbed into the bloodstream.
• Total Blood Volume (Radiation), also known as DAXOR: Using injection of iodinated I-131 tagged human serum albumin nominally 25 microcuries of radiation, blood samples are drawn before and 30 minutes after injection.
• Exercise Capacity Test - Bicycle (Procedure), also known as VO2 Max (maximal oxygen consumption): subjects breath room air through a mouthpiece and exhale the air into a tube that connects to a machine (metabolic cart) that analyzes carbon dioxide and oxygen content, which allows the investigator to calculate the amount of oxygen they are using under resting and exercise conditions.
• Posture Study (Procedure), also known as Standing Orthostatic Challenge: Blood pressure and heart rate will be measured while supine and then while standing for up to 30 minutes. Blood will be drawn in each position to measure hormones that regulate blood pressure and blood volume.

Primary outcomes

• Plasma Volume [after 7 days of each dietary sodium level]: Plasma volume (PV) was determined by the indicator tracer-dilution technique, using the DAXOR Blood Volume Analyzer (BVA)-100 system (DAXOR Corporation), on Day 7 of the low sodium and high sodium dietary interventions. Outcome data are the absolute values for PV on Day 7 for each diet.

Secondary outcomes

• Magnitude of Suppression of Plasma Renin Activity (From Low Sodium to High Sodium Diets) [Upright blood samples were collected after up to 30 minutes of standing on the 7th day of each dietary sodium intervention]: Whether upright plasma renin activity was modified appropriately by changes in dietary sodium in POTS \& healthy controls. Outcome data are the absolute values for upright plasma renin activity on Day 7 of each diet.

Other outcomes

• Magnitude of Suppression of Serum Aldosterone (From Low Sodium to High Sodium Diets) [Upright blood samples were collected after up to 30 minutes of standing on the 7th day of each dietary sodium intervention]: Whether upright serum aldosterone was modified appropriately by changes in dietary sodium in POTS patients \& healthy controls. Outcome data are the absolute values for upright serum aldosterone on Day 7 of each diet.
• Magnitude of Orthostatic Tachycardia [Supine and upright heart rates were measured on Day 7 of High Sodium and Low Sodium diet.]: Whether the magnitude of the heart rate increase that occurs in patients with POTS when moving from a supine to an upright position is attenuated by a High Sodium diet relative to a Low Sodium diet. Heart rate was assessed after overnight rest and fasting after midnight, following at least 60 minutes of lying quietly. Heart rate was then measured at intervals after subjects had been standing for up to 30 minutes (as tolerated). Orthostatic tachycardia was calculated as the difference between standing and lying heart rates. Data are presented for 5 minutes standing (or maximal stand if <5 minutes) since several patients were unable to stand for 10 minutes. Data in POTS patients were compared to that of Healthy Controls.
• Upright Symptom Score [Upright symptoms were assessed on the 7th day of diet.]: Whether upright symptoms were improved in patients with POTS on a High Sodium diet relative to a Low Sodium diet. Patients were asked to report their standing symptom burden at the end of the Stand portion of the posture study, using the Vanderbilt Orthostatic Symptoms Scale (VOSS). They rated the severity of nine symptoms (palpitations, lightheadedness, mental confusion, blurred vision, shortness of breath, tremulousness, chest discomfort, headache, and nausea) on a scale from a minimum of 0 (reflecting an absence of symptoms) to a maximum of 10. The sum of the scores for the 9 symptoms was used to measure orthostatic symptom burden. Higher scores represent worse symptoms.

Sex: All, ages: 18 Years to 50 Years, accepts healthy volunteers

Inclusion Criteria:

* 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
* Age between 18-50 years old
* Non-smokers
* Premenopausal patients with POTS and healthy volunteers
* Only female participants are eligible.
* Since 80-90% of POTS patients are female, and there can be differences in measures with the menstrual cycle, including a small number of males might introduce a significant amount of noise.
* Able and willing to provide informed consent

Exclusion Criteria:

* Smokers
* Overt cause for postural tachycardia, i.e., acute dehydration
* Significant cardiovascular, pulmonary, hepatic, or hematological disease by history or screening results
* Pregnant (positive pregnancy test) or breastfeeding
* Hypertension defined as supine resting BP>145/95 mmHg off medications or needing antihypertensive medication
* Other factors which in the investigator's opinion would prevent the participant from completing the protocol, including poor compliance during previous studies or an unpredictable schedule
* Unable to give informed consent

Participant flow

Outcome results

• Plasma Volume (Primary), Median, mL: Healthy Participants Who Consumed Low Sodium Diet as Intervention A or Intervention B 2805 (2445 to 2949); Healthy Participants Who Consumed High Sodium Diet as Intervention A or Intervention B 3032 (2620 to 3482); Postural Tachycardia Syndrome (POTS) Participants Who Consumed Low Sodium Diet. 2362 (2161 to 2715); Postural Tachycardia Syndrome (POTS) Participants Who Consumed High Sodium Diet. 2633 (2468 to 2961)
• Magnitude of Suppression of Plasma Renin Activity (From Low Sodium to High Sodium Diets) (Secondary), Median, ng/mL/hr: Healthy Participants Who Consumed Low Sodium Diet as Intervention A or Intervention B 7.8 (3.3 to 13.9); Healthy Participants Who Consumed High Sodium Diet as Intervention A or Intervention B 1.0 (.8 to 1.9); Postural Tachycardia Syndrome (POTS) Participants Who Consumed Low Sodium Diet. 24.4 (10.1 to 26.7); Postural Tachycardia Syndrome (POTS) Participants Who Consumed High Sodium Diet. 2.7 (.7 to 4.8)
• Magnitude of Suppression of Serum Aldosterone (From Low Sodium to High Sodium Diets) (Other pre specified), Median, ng/dL: Healthy Participants Who Consumed Low Sodium Diet as Intervention A or Intervention B 444 (277 to 515); Healthy Participants Who Consumed High Sodium Diet as Intervention A or Intervention B 74 (52 to 129); Postural Tachycardia Syndrome (POTS) Participants Who Consumed Low Sodium Diet. 455 (359 to 650); Postural Tachycardia Syndrome (POTS) Participants Who Consumed High Sodium Diet. 64 (52 to 91)
• Magnitude of Orthostatic Tachycardia (Other pre specified), Median, beats per minute: Healthy Participants Who Consumed Low Sodium Diet as Intervention A or Intervention B 23 (19 to 36); Healthy Participants Who Consumed High Sodium Diet as Intervention A or Intervention B 19 (11 to 32); Postural Tachycardia Syndrome (POTS) Participants Who Consumed Low Sodium Diet. 60 (55 to 64); Postural Tachycardia Syndrome (POTS) Participants Who Consumed High Sodium Diet. 46 (32 to 55)
• Upright Symptom Score (Other pre specified), Median, score on a scale: Healthy Participants Who Consumed Low Sodium Diet as Intervention A or Intervention B 1 (0 to 4); Healthy Participants Who Consumed High Sodium Diet as Intervention A or Intervention B 0 (0 to 3); Postural Tachycardia Syndrome (POTS) Participants Who Consumed Low Sodium Diet. 30 (18 to 39); Postural Tachycardia Syndrome (POTS) Participants Who Consumed High Sodium Diet. 19 (10 to 26)

Adverse events

Time frame: Adverse event data were collected through discharge on the last day of phase 2 of the study. This would have been Day 8 if Low Sodium diet or Day 7 if High Sodium diet.

Other adverse events by term

• Results publication: Laurin JKH, Oyewunmi OA, Garland EM, Gamboa A, Nwazue VC, Paranjape SY, Black BK, Okamoto LE, Shibao CA, Biaggioni I, Robertson D, Diedrich A, Dupont WD, Sheldon RS, Raj SR. Adrenal gland response to adrenocorticotropic hormone is intact in patients with postural orthostatic tachycardia syndrome. Auton Neurosci. 2023 Sep;248:103105. doi: 10.1016/j.autneu.2023.103105. Epub 2023 Jun 24. PMID 37393658
• Results publication: Garland EM, Gamboa A, Nwazue VC, Celedonio JE, Paranjape SY, Black BK, Okamoto LE, Shibao CA, Biaggioni I, Robertson D, Diedrich A, Dupont WD, Raj SR. Effect of High Dietary Sodium Intake in Patients With Postural Tachycardia Syndrome. J Am Coll Cardiol. 2021 May 4;77(17):2174-2184. doi: 10.1016/j.jacc.2021.03.005. PMID 33926653

• Study Protocol and Statistical Analysis Plan (PDF, 2014-07-17)

• Alfredo J Gamboa, MD, Principal investigator, Vanderbilt University

NIH grants: R01HL102387