The physiological conundrum of hyperadrenergic orthostatic intolerance

Area of Science:

• Cardiology
• Neurology
• Endocrinology

Background:

• Orthostatic hypotension involves a significant blood pressure drop upon standing.
• Orthostatic intolerance presents with standing-induced symptoms but minimal blood pressure changes.
• A brisk tachycardia upon standing is common in orthostatic intolerance patients.

Purpose of the Study:

• To explore the mechanisms and clinical spectrum of orthostatic intolerance.
• To investigate the role of mild dysautonomia in orthostatic intolerance.
• To understand the hyperadrenergic subgroup of orthostatic intolerance.

Main Methods:

• Characterization of patients with orthostatic intolerance.
• Assessment of autonomic nervous system function.
• Measurement of plasma norepinephrine and epinephrine levels.
• Evaluation of plasma renin activity and aldosterone levels.
• Analysis of blood volume and norepinephrine clearance.

Main Results:

• Many orthostatic intolerance patients exhibit mild dysautonomia, potentially triggered by viral illness, rheumatologic disorders, or surgery.
• The hyperadrenergic subgroup shows a spectrum of findings: attenuated renin and aldosterone, reduced blood volume with dynamic hypovolemia.
• Elevated plasma norepinephrine and epinephrine, and impaired norepinephrine clearance are observed.
• Evidence of partial dysautonomia is documented in affected individuals.

Conclusions:

• Partial dysautonomia is emerging as a significant mechanism in orthostatic intolerance.
• Recognizing dysautonomia may substantially alter therapeutic strategies for orthostatic intolerance.
• Further research into dysautonomia can improve patient management and outcomes.