Heart rate variability in pheochromocytoma.

The results of our study show that parasympathetic tone was higher in patients with pheochromocytoma than in patients with primary hypertension. An unusual spectral form of vagal activity was seen during excessive beta-adrenergic stimulation, while persistent hypertension with an excessive alpha-adrenergic stimulation was responsible for low cardiac sympathetic tone, probably due to desensitization of beta-adrenergic receptors.