Increased Sympathetic Activation in Idiopathic Orthostatic Intolerance

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Abstract
Idiopathic orthostatic intolerance (OI) is characterized by adrenergic symptoms with standing. Changes in central sympathetic tone or in adrenoreceptor sensitivity could contribute to this syndrome. In OI patients and control subjects, we determined heart rate (HR) and systolic blood pressure (SBP) changes after incremental bolus doses of isoproterenol and phenylephrine before and during ganglionic blockade with trimethaphan. SBP decreased by 17±1.6 mm Hg in patients and 3.9±3.8 mm Hg in control subjects ( P 1 - and β-adrenoreceptors but rather originates in enhanced sympathetic activation.