Study of Air Stream in Voice Production

Persons with abductor spasmodic dysphonia (ABSD) have difficulties with phonation onset after voiceless consonants resulting in breathy breaks. Previously, ABSD was thought to involve heightened activity of the laryngeal abductor muscle, the posterior cricoarytenoid. Botulinum toxin injection of the posterior cricoarytenoid muscle in this disorder, however, only provides a partial benefit in about 50% of persons with ABSD. An electromyographic study of the laryngeal muscles in ABSD found asymmetries in the adductor muscle (the thyroarytenoid muscle) in ABSD. Thyroarytenoid (TA) activation levels differed between the two sides in persons with ABSD. An electromyographic study of the laryngeal muscles in ABSD found asymmetries in the adductor muscle (the thyroarytenoid muscle) in ABSD. Thyroarytenoid (TA) activation levels differed between the two sides in persons with ABSD in comparison with controls; the right TA showed greater activity than the left. This suggested that ABSD might involve increased tone on one side of the larynx, and that treatment should address any such asymmetry in muscle tone. We hypothesize that if TA muscle activity was greater on one side in ABSD, then A) phonation threshold pressures should be greater than normal in persons with ABSD, and B) that treatment with botulinum toxin in those with phonation threshold pressures greater than normal should show symptom reduction following injection of the TA muscles on one side. Both normal volunteers and persons with ABSD will be studied. Phonation Threshold Pressure (PTP) will be measured using the brief interruption of supraglottal airflow with a valve during phonation into a tube. The electroglottographic signals will be used to determine when vocal fold vibration ceases after the valve closes. The PTP will be measured as the difference between an estimate of the subglottal pressure achieved after phonation offset following valve closure, and the minimum subglottal vocal tract pressure at the point just before vocal fold vibration ceases following the interruption of airflow. Persons with ABSD who have higher phonation threshold pressures than normal will then receive an injection with botulinum toxin injection into the thyroarytenoid muscle on one side based on movement asymmetries observed on fiberoptic nasolaryngoscopy. Blinded measures of symptom frequency made before and after treatment will determine if symptoms are improved.