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Local Vasoconstriction in Postural Tachycardia Syndrome

The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government. Read our disclaimer for details. Identifier: NCT01210430
Recruitment Status : Completed
First Posted : September 28, 2010
Last Update Posted : June 10, 2021
Information provided by (Responsible Party):
Julian Stewart, New York Medical College

Brief Summary:
The investigators study will determine how often blood flow regulation abnormalities and abnormalities of sympathetic regulation produced by nitric oxide, angiotensin-II, and oxidative stress occur in POTS and the mechanism(s) of POTS in individual patients. Specific causes for POTS may vary from patient to patient. Patients will be compared to healthy control subjects. There is a treatment arm with a medication (losartan) that reduces the binding of angiotensin and increases NO. If the investigators know the specific biochemical mechanism the investigators may be able to offer further specific treatments to specific patients.

Condition or disease Intervention/treatment Phase
Postural Tachycardia Syndrome Drug: Losartan Drug: Ascorbic Acid (Vitamin C) Drug: Normal Saline Early Phase 1

Detailed Description:

Chronic orthostatic intolerance due to the postural tachycardia syndrome (POTS) severely impairs daily life in over a million Americans, mostly young women. POTS is defined by symptoms of orthostatic intolerance associated with excessive upright heart rate. While there is general agreement that abnormalities in vascular regulation and autonomic activity account for the tachycardia and symptoms of POTS, its pathophysiology is heterogeneous and only partially characterized.

The key feature of POTS is symptoms which are most prominent when standing. However, in some, findings are present supine (lying down) but worsened standing. Symptoms of POTS include dizziness in all patients, exercise provoked symptoms and thus exercise intolerance, excessive fatigue, nausea and abdominal pain, headache, shortness of breath and deep breathing, weakness, shakiness and postural anxiety, pallor, and neurocognitive loss (difficulty thinking). These occur on a day-to-day basis. The symptoms overlap with the case definition of chronic fatigue syndrome (CFS) and POTS is often found in CFS in the young. Fainting is relatively uncommon during daily life.

A major subset of POTS has increased peripheral resistance and low blood flow(LFP) related to increased angiotensin-II (Ang-II), and decreased nitric oxide (NO). NO deficits are reversed by Ang-II type-1 receptor (AT1R) blockade, ascorbic acid (AA) and tetrahydrobiopterin in skin suggesting the importance of oxidative stress. Preliminary data also suggest that the coupling of sympathetic nerve activity to blood vessel contraction is enhanced via ↑Ang-II and ↓NO. We hypothesize that this is due to activation of reactive oxygen species (ROS) including superoxide, which scavenges NO to generate peroxynitrite, and hydrogen peroxide. Combined measurements in the skin and the systemic circulation will be combined with local measurement of ROS production and sympathetic nerve activity will enable us to determine precisely how the autonomic nervous system is affected by the illness. Methods include cutaneous microdialysis to measure ROS, skin biopsy and blood tests to measure gene expression of nitric oxide synthase and Ang-II receptors, and peroneal microneurography to measure muscle sympathetic nerve activity (MSNA). Combined with ultrasonic femoral artery blood flow this will yield assessment of the interactions of nerves with the blood vessels that they control.

If we discover specific biochemical mechanisms of POTS in patients, then we may be able to specifically treat the defect.

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Study Type : Interventional  (Clinical Trial)
Actual Enrollment : 74 participants
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Double (Participant, Investigator)
Primary Purpose: Diagnostic
Official Title: Local Vasoconstriction in Postural Tachycardia Syndrome
Study Start Date : July 2010
Actual Primary Completion Date : June 2015
Actual Study Completion Date : June 2015

Resource links provided by the National Library of Medicine

MedlinePlus related topics: Vitamin C

Arm Intervention/treatment
Active Comparator: Losartan Drug: Losartan
Subjects will receive placebo or losartan for 4 weeks. Days 1-7, subjects will receive 12.5mg of Losartan or placebo. Days 7-14, subjects will receive 25mg of Losartan or placebo. Days 14-28, subjects will receive 50mg of Losartan or placebo.

Active Comparator: Ascorbic Acid (VItamin C) Drug: Ascorbic Acid (Vitamin C)
Subjects will receive 60mg/kg of Ascorbic Acid over 20 minutes followed by a maintenance infusion of 20mg/kg.
Other Name: Vitamin C

Placebo Comparator: Normal Saline Drug: Normal Saline
Subjects will receive 60mg/kg of normal saline over 20 minutes followed by a maintenance infusion of 20mg/kg of normal saline.

Primary Outcome Measures :
  1. Orthostatic tolerance measured by the heart rate and blood pressure response to upright tilt [ Time Frame: 2 months ]

Secondary Outcome Measures :
  1. Sympathetic activation and blood flow measured by sympathetic nerve recordings and Doppler blood flow in the leg [ Time Frame: 2 months ]

Information from the National Library of Medicine

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Ages Eligible for Study:   14 Years to 29 Years   (Child, Adult)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   Yes

Inclusion Criteria:

  • Cases will be between the ages of 14 and 29 years old referred for evaluation of orthostatic intolerance with 3 or more of the following symptoms for at least 3 months:

    • dizziness
    • nausea and vomiting
    • palpitations
    • fatigue
    • headache
    • exercise intolerance
    • blurred vision
    • abnormal sweating heat.
  • Cases will have the diagnosis of symptomatic postural tachycardia made during a screening tilt table test.
  • Cases will have normal physical examination, and normal electrocardiographic and echocardiographic evaluations.
  • Only those free from heart disease, and from systemic illness will be eligible to participate.
  • This excludes patients with illnesses and disease states known to be associated with endothelial cell dysfunction such as diabetes, renal disease, congestive heart failure, systemic hypertension, acute and chronic inflammatory diseases, neoplasm, immune mediated disease, trauma, morbid obesity and peripheral vascular disease.
  • At the time of testing all patients and control subjects must refrain from vasoactive drugs for two weeks. Please check with us about any medication that you are taking.

Exclusion Criteria:

  • Criteria for initial exclusion will include a condition known to be associated with endothelial dysfunction
  • An active medical condition that may explain the diagnosis
  • A previous medical condition with undocumented resolution that may explain the diagnosis
  • Past or present major psychiatric disorder
  • Substance abuse within 2 years before onset of symptoms.

Information from the National Library of Medicine

To learn more about this study, you or your doctor may contact the study research staff using the contact information provided by the sponsor.

Please refer to this study by its identifier (NCT number): NCT01210430

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United States, New York
New York Medical College/Bradhurst building
Hawthorne, New York, United States, 10532
Sponsors and Collaborators
New York Medical College
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Principal Investigator: Julian M Stewart, MD, PhD New York Medical College
Additional Information:
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Responsible Party: Julian Stewart, Professor of Pediatrics, New York Medical College Identifier: NCT01210430    
Other Study ID Numbers: 2R01HL074873-06A2 ( U.S. NIH Grant/Contract )
First Posted: September 28, 2010    Key Record Dates
Last Update Posted: June 10, 2021
Last Verified: June 2021
Keywords provided by Julian Stewart, New York Medical College:
Postural Tachycardia Syndrome
Orthostatic Intolerance
Reactive Oxygen Species
Oxidative Stress
Angiotensin II
Nitric Oxide
Blood Flow
Ascorbic Acid
Vitamin C
Additional relevant MeSH terms:
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Postural Orthostatic Tachycardia Syndrome
Pathologic Processes
Arrhythmias, Cardiac
Heart Diseases
Cardiovascular Diseases
Cardiac Conduction System Disease
Orthostatic Intolerance
Primary Dysautonomias
Autonomic Nervous System Diseases
Nervous System Diseases
Ascorbic Acid
Growth Substances
Physiological Effects of Drugs
Anti-Arrhythmia Agents
Antihypertensive Agents
Angiotensin II Type 1 Receptor Blockers
Angiotensin Receptor Antagonists
Molecular Mechanisms of Pharmacological Action
Protective Agents