Depressed respiratory sinus arrhythmia: additional evidence for impairment of vagal activity in human hyperthyroidism.

The efferent activity of the parasympathetic component of the autonomic nervous system was evaluated by measuring the magnitude of the respiratory sinus arrhythmia in 3 female patients with hyperthyroidism (Basedow-Graves' disease) before and after treatment. The heart rate variations induced by the test increased in all patients after treatment of thyrotoxicosis (from 15 +/- 2.9 to 28.3 +/- 6.6 beats/min; mean +/- SEM) with propylthiouracil (600 mg/day). This result confirms our previous observations indicating an important and reversible impairment of the efferent vagal activity in human hyperthyroidism.