Abnormal parasympathetic vagal function in patients with spasmodic dysphonia.

Gastric vagal function was assessed in 15 patients with spasmodic dysphonia by measuring gastric acid output in response to sham feeding. Patients secreted significantly less acid than controls (p less than 0.001). Cardiac vagal function was assessed in 11 patients by measuring heart rate during deep respiration and also during and after Valsalva maneuver. Patients with spasmodic dysphonia had a significantly reduced fluctuation of heart rate during deep respiration (sinus arrhythmia). The expiratory to inspiratory R-R interval averaged 1.08 +/- 0.08 (mean +/- SD) in patients and 1.22 +/- 0.10 in controls (p less than 0.005). The ratio of tachycardia during Valsalva maneuver to bradycardia after Valsalva maneuver was also lower in patients than in controls (p less than 0.005). The auditory brainstem response was abnormal in 11 of 15 patients. Our results show either a central brainstem abnormality or several cranial nerve abnormalities in some patients with spasmodic dysphonia.