Pathophysiology of Orthostatic Intolerance

October 3, 2025 updated by: Satish R. Raj
The purpose of this study is to describe the mechanism of orthostatic intolerance, relying on cardiovascular physiological studies. The syndrome is of undetermined etiology, but the syndrome causes impairment of a number of young adults, females more than males, with symptoms of tachycardia, fatigue, lightheadedness, palpitations, blurred vision, chest discomfort, difficulty concentrating, and dizziness with the upright posture. It is believed that many different pathophysiological processes can give rise to this disorder.

Study Overview

Status

Active, not recruiting

Conditions

Intervention / Treatment

Detailed Description

The purpose of this study is to describe the mechanism of orthostatic intolerance, relying on cardiovascular physiological studies. The syndrome is of undetermined etiology, but the syndrome causes impairment of a number of young adults, females more than males, with symptoms of tachycardia, fatigue, lightheadedness, palpitations, blurred vision, chest discomfort, difficulty concentrating, and dizziness with the upright posture. It is believed that many different pathophysiological processes can give rise to this disorder.

This is not a clinical trial in the classical sense, but an omnibus protocol to allow for disntinct and personalized pathophysiological testing.

Study Type

Interventional

Enrollment (Actual)

260

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • United States
    • Tennessee
      • Nashville, Tennessee, United States, 37232
        • Vanderbilt University

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years to 80 years (Adult, Older Adult)

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Orthostatic intolerance

Exclusion Criteria:

  • Inability or unwillingness to give informed consent

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Diagnostic
  • Allocation: Non-Randomized
  • Interventional Model: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Other: Patients
Patients with orthostatic intolerance
Radiation: DAXOR
131-I-Human Serum Albumin Blood Volume Assessment Kit
Other Names:
  • Volumex
Procedure: QSweat
Quantitative Sweat Testing
Other Names:
  • QSART
  • Quantitative Axonal Sudomotor Reflex Testing
Drug: Intrinsic Heart Rate
Atropine 0.04 mg/kg IV in divided doses Propranolol 0.2 mg/kg IV in divided doses
Other Names:
  • Inderal
  • IHR
Other: Healthy Control Subjects
Healthy subjects to determine "normal" response
Radiation: DAXOR
131-I-Human Serum Albumin Blood Volume Assessment Kit
Other Names:
  • Volumex
Procedure: QSweat
Quantitative Sweat Testing
Other Names:
  • QSART
  • Quantitative Axonal Sudomotor Reflex Testing
Drug: Intrinsic Heart Rate
Atropine 0.04 mg/kg IV in divided doses Propranolol 0.2 mg/kg IV in divided doses
Other Names:
  • Inderal
  • IHR

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Physiological abnormalities in orthostatic intolerance
Time Frame: 1 day
varied metrics used here
1 day

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
blood volume
Time Frame: 1 day
Blood volume as measured by DAXOR technique
1 day
intrinsic heart rate
Time Frame: 1 hour
Heart rate after IV propranolol and IV atropine
1 hour
quantitative sweat testing
Time Frame: 2 hours
sweat volumes after a QSweat test
2 hours
residual sympathetic function after pharmacological autonomic blockade
Time Frame: 3 hours
changes in BP after trimethaphan infusions
3 hours
norepinephrine spillover
Time Frame: 3 hours
tritiated norepunephrine spillover data
3 hours

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Satish R. Raj

Collaborators

National Institutes of Health (NIH)

Investigators

  • Principal Investigator: David Robertson, MD, Vanderbilt University

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Helpful Links

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start

December 1, 1996

Primary Completion (Estimated)

December 1, 2029

Study Completion (Estimated)

December 1, 2029

Study Registration Dates

First Submitted

January 22, 2008

First Submitted That Met QC Criteria

February 5, 2008

First Posted (Estimated)

February 6, 2008

Study Record Updates

Last Update Posted (Estimated)

October 8, 2025

Last Update Submitted That Met QC Criteria

October 3, 2025

Last Verified

October 1, 2025

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 8398
  • NIH HL56693

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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