Abnormal Parasympathetic Vagal Function in Patients with Spasmodic Dysphonia

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Abstract
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 < 0.01). Cardiac vagal function was assessed in 11 patients by measuring heart rate during deep respiration and also during and after Valsalva maneuver. Patients with spasmoid dysphonia had a significanlty 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 < 0.005). The ratio of tachycardia during Valsalva manuever to bradycardia after Valsalva manuever was also lower in patients than in controls (P < 0.005). The auditory brainstem response was abnormal in 11 of 15 patients. Either a central brainstem abnormality or several cranial abnormalities exist in some patients with spasmodic dysphonia.