Autonomic Nervous System Imbalance in Young Adults with Developmental Stuttering

Autonomic nervous system imbalance in young adults with developmental stuttering Objective: Autonomic nervous system plays a key role on motor speech and its regulation. On the other hand, physiological changes associated with activation of branches of autonomic nervous system in relation to emotions may also affect speech regulation. Thus, autonomic nervous system dysregulation may impair rate, rhythm, and general flow of speech or may exacerbate speech disfluency. However, the studies of autonomic reactions in persons with developmental stuttering are very limited. The purpose of the study is to evaluate whether autonomic nervous system dysregulation is responsible for persistent developmental stuttering in young adults. Method: We studied 26 patients with persistent development stuttering and 17 normal speakers similar for age as healthy controls. The study comprised men who were between the ages of 19 and 25 years. Patients were examined by the speech pathologist using the Stuttering Severity Instrument (SSI-3). Beck Anxiety and Depression Inventories were performed to all subjects. Autonomic nervous system function was assessed by the 24-hour Holter monitorization for heart rate variability. Time-domain analyses were performed to evaluate the percentage of successive normal sinus RR intervals >50 ms (pNN50 %), the squares root of the mean of the sum the squares of differences between adjacent NN intervals (RMSSD; ms), and mean of the standard deviations of all NN (normal-normal) intervals of the entire recording (SDNN; ms). Frequency-domain analyses were performed to evaluate low-frequency power (LF; 0.04-0.15 Hz), high-frequency power (HF; 0.15-0.40 Hz), the ratio of LF to HF (LF/HF), HF and LF in normalized units, and variance of all NN intervals (total power ms2). Results: In the stutterers, the mean onset of stuttering was 7.9±3.7 years (range: 3 - 17 years) and the mean duration of stuttering was 13.0±4.2 years (range: 2 - 20 years). Depression and anxiety scores were significantly higher in the stutterers than in those of the normal speakers. The stutterers had higher RMSDD and, lower LF, LF/HF and normalized LF values than the normal speakers. Subjective anxiety and total anxiety scores were negatively correlated with LF and total power. Conclusions: Lower LF, the normalized LF and LF/HF suggest sympatho- vagal imbalance in persons who stutter. Higher RMSDD in the stutterers may indicate a shift of sympatho-vagal balance towards parasympathetic predominance. The results suggest that general autonomic nervous system imbalance might render the person prone to speech disfluencies. If these results are replicated in larger samples, they might provide some contribution in explaining the underlying pathophysiology of developmental stuttering.