Dietary Salt in Postural Tachycardia Syndrome

Not Applicable

Completed

Conditions: Postural Orthostatic Tachycardia Syndrome

Interventions: Radiation: Blood Volume
Radiation: Total Blood Volume
Procedure: Exercise Capacity Test - Bicycle
Procedure: Posture Study

Registration Number: NCT01547117

Lead Sponsor: Vanderbilt University

Brief Summary: Patients with POTS may not adequately expand their plasma volume in response to a high-sodium (Na+) diet. Mechanisms involved in the regulation of plasma volume, such as the renin-angiotensin-aldosterone system and renal dopamine, may be impaired in POTS and may respond inappropriately to changes in dietary sodium.The purpose of this study is to determine (1) whether a high dietary sodium level appropriately expands plasma volume in POTS; (2) whether plasma renin activity and aldosterone are modified appropriately by changes in dietary sodium in POTS; and (3) whether patients with POTS have improvements in their orthostatic tachycardia and symptoms as a result of a high dietary sodium level.

Detailed Description: 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)

Recruitment & Eligibility

Status: COMPLETED

Sex: All

Target Recruitment: 38

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

Study & Design

Study Type: INTERVENTIONAL

Study Design: CROSSOVER

Arm && Interventions

Group	Intervention	Description
High Sodium Level	Posture Study	POTS and healthy controls will be randomly assigned the order of dietary sodium levels. All procedures are performed at both levels. The high sodium diet will provide 300 milliequivalents (mEq) sodium/day.
Low Sodium Dietary Level	Exercise Capacity Test - Bicycle	POTS and healthy controls will be randomly assigned the order of dietary sodium levels. All procedures are performed at both levels. The low sodium diet will provide 10 mEq sodium/day.
High Sodium Level	Exercise Capacity Test - Bicycle	POTS and healthy controls will be randomly assigned the order of dietary sodium levels. All procedures are performed at both levels. The high sodium diet will provide 300 milliequivalents (mEq) sodium/day.
High Sodium Level	Total Blood Volume	POTS and healthy controls will be randomly assigned the order of dietary sodium levels. All procedures are performed at both levels. The high sodium diet will provide 300 milliequivalents (mEq) sodium/day.
High Sodium Level	Blood Volume	POTS and healthy controls will be randomly assigned the order of dietary sodium levels. All procedures are performed at both levels. The high sodium diet will provide 300 milliequivalents (mEq) sodium/day.
Low Sodium Dietary Level	Blood Volume	POTS and healthy controls will be randomly assigned the order of dietary sodium levels. All procedures are performed at both levels. The low sodium diet will provide 10 mEq sodium/day.
Low Sodium Dietary Level	Posture Study	POTS and healthy controls will be randomly assigned the order of dietary sodium levels. All procedures are performed at both levels. The low sodium diet will provide 10 mEq sodium/day.
Low Sodium Dietary Level	Total Blood Volume	POTS and healthy controls will be randomly assigned the order of dietary sodium levels. All procedures are performed at both levels. The low sodium diet will provide 10 mEq sodium/day.

Primary Outcome Measures

Name	Time	Method
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 Outcome Measures

Name	Time	Method
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.