Pathophysiology of Orthostatic Intolerance

Not Applicable

Active, not recruiting

• Conditions: Tachycardia; Postural Orthostatic Tachycardia Syndrome
• Interventions: Radiation: DAXOR; Procedure: QSweat; Drug: Intrinsic Heart Rate

• Registration Number: NCT00608725
• Lead Sponsor: Satish R. Raj

Brief Summary

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.

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 Timeline

• Study Start: 1996-12-01
• Study First Submitted: 2008-01-22
• Study First Submitted QC: 2008-02-05
• Study First Posted: 2008-02-06
• Status Verified: 2025-10
• Last Update Submitted: 2025-10-03
• Last Update Posted: 2025-10-08
• Primary Completion: 2029-12
• Study Completion: 2029-12-01

Recruitment & Eligibility

• Status: ACTIVE_NOT_RECRUITING
• Sex: All
• Target Recruitment: 260

Inclusion Criteria

• Orthostatic intolerance

Exclusion Criteria

• Inability or unwillingness to give informed consent

Study & Design

• Study Type: INTERVENTIONAL
• Study Design: PARALLEL

Arm && Interventions

Group	Intervention	Description
Patients	DAXOR	Patients with orthostatic intolerance
Patients	QSweat	Patients with orthostatic intolerance
Patients	Intrinsic Heart Rate	Patients with orthostatic intolerance
Healthy Control Subjects	DAXOR	Healthy subjects to determine "normal" response
Healthy Control Subjects	QSweat	Healthy subjects to determine "normal" response
Healthy Control Subjects	Intrinsic Heart Rate	Healthy subjects to determine "normal" response

Primary Outcome Measures

Name	Time	Method
Physiological abnormalities in orthostatic intolerance	1 day	varied metrics used here

Secondary Outcome Measures

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

Trial Locations

Locations (1)

Vanderbilt University; 🇺🇸 Nashville, Tennessee, United States