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 sympathovagal 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. Geliflimsel kekemeli¤i olan genç yetiflkinlerde otonom sinir sistemi düzensizli¤i Amaç: Otonom sinir sistemi, konuflman›n motor düzenlenmesinde anahtar rol oynar. Öte yandan, emosyonlarla iliflkili otonom sinir sisteminin aktivasyonuna ba¤l› fizyolojik de¤ifliklikler de konuflman›n düzenlenmesini etkiler. Bu nedenlerle, otonom sinir sistemi düzensizlikleri konuflman›n h›- z›n›, ritmini ve genel ak›c›l›¤›n› bozabilir veya konuflmadaki ak›c›l›k sorunlar›n› art›rabilir. Ancak, geliflimsel kekemeli¤i olan bireylerde otonomik tepkileri araflt›ran çal›flmalar oldukça s›n›rl›d›r. Bu çal›flmada sürekli geliflimsel kekemeli¤i olan genç yetiflkinlerde otonomik sinir sistemi düzensizli¤i varl›¤›n›n araflt›r›lmas› amaçlanm›flt›r. Yöntem: Çal›flmaya geliflimsel kekemeli¤i olan 26 hasta ve yafl aç›s›ndan benzer, normal konuflmas› olan 17 sa¤l›kl› kontrol al›nd›. Olgular›n tümü erkek ve 19-25 yafllar› aras›ndayd›. Kekeme olgular bir dil-konuflma terapisi uzman› taraf›ndan Kekemelik fiiddet Ölçe¤i ile derecelendirildi. Olgular›n tümüne Beck Depresyon ve Anksiyete Envanterleri uyguland›. Otonom sinir sistemi 24-saatlik Holter monitörizasyonu ile kalp at›m de¤iflkenli¤i ölçülerek de¤erlendirildi. Zaman düzleminde yap›lan kalp at›m de¤iflkenli¤i analizlerinde; aralar›nda 50 msn'den fazla fark bulunan ard›fl›k RR interval çiftinin yüzdesi (pNN50 %), komflu RR intervalleri aras›ndaki fark›n karelerinin ortalamas›n›n karekökü (RMSSD; msn) ve bütün NN (normal-normal) aral›klar›n›n ortalamalar›n›n standart sapmas› (SDNN; msn) de¤erlendirildi. Düflük frekans bölgelerinin gücünü (LF; 0.04-0.15 Hz), yüksek frekans bölgelerinin gücünü (HF; 0.15-0.40 Hz), LF/ HF oran›n›, normallefltirilmifl birimlerdeki LF ve HF güçleri ile bütün NN aral›klar›n›n varyans›n› (total güç; msn2) de¤erlendirmek için frekans düzlemi analizleri uyguland›. Bulgular: Kekeme olgularda, kekemelik bafllang›c› ortalama 7.9±3.7 yafllar›yd› (aral›k: 3 - 17 yafl) ve ortalama kekemelik süresi 13.0±4.2 y›ld› (aral›k: 2 - 20 y›l). Kekemelerin depresyon ve anksiyete puanlar› ak›c› konuflmas› olanlardan daha yüksekti. Kontrol grubuna göre, kekemelerde RMSDD yüksek, LF, LF/HF ve normalize LF de¤erleri düflük bulundu. Öznel anksiyete ve toplam anksiyete puanlar› ile LF ve total power aras›nda negatif iliflki saptand› Tart›flma: Düflük LF, normalize LF ve LF/HF kekeme hastalardaki sempatovagal düzensizli¤i göstermektedir. Kekemelerdeki yüksek RMSDD, bu dengesizli¤in parasempatik sistem bask›nl›¤›na do¤ru e¤ilim gösterdi¤ine iflaret etmektedir. Sonuçlar otonomik sinir sistemi düzensizli¤inin kiflileri konuflma ak›c›l›¤›nda bozulmaya duyarl› k›ld›¤›n› düflündürtmektedir. Bu sonuçlar teyit edilirse, geliflimsel kekemeli¤in patofizyolojisinin anlafl›lmas›na katk›da bulunacakt›r.