Pathophysiology of Orthostatic Intolerance

• blood volume [ Time Frame: 1 day ] [ Designated as safety issue: No ]
• intrinsic heart rate [ Time Frame: 1 hour ] [ Designated as safety issue: No ]
• quantitative sweat testing [ Time Frame: 2 hours ] [ Designated as safety issue: No ]
• residual sympathetic function after pharmacological autonomic blockade [ Time Frame: 3 hours ] [ Designated as safety issue: No ]
• norepinephrine spillover [ Time Frame: 3 hours ] [ Designated as safety issue: No ]

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.

• Tachycardia
• Postural Orthostatic Tachycardia Syndrome

• Radiation: DAXOR
  131-I-Human Serum Albumin Blood Volume Assessment Kit
  Other Name: 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

• Patients
  Patients with orthostatic intolerance
  Interventions:

  • Radiation: DAXOR
  • Procedure: QSweat
  • Drug: Intrinsic Heart Rate
• Healthy Control Subjects
  Healthy subjects to determine "normal" response
  Interventions:

  • Radiation: DAXOR
  • Procedure: QSweat
  • Drug: Intrinsic Heart Rate

Inclusion Criteria:

• Orthostatic intolerance

Exclusion Criteria:

• Inability or unwillingness to give informed consent