Effects of subglottal air pressure on velopharyngeal muscle activity in dogs

Objective: To analyze the effects of airflow in the larynx on activity of the levator veli palatini and pterygopharyngeal muscles. Design: Ten adult beagle dogs were anesthetized with sodium pentobarbital. In each dog, two tracheal tubes were inserted subsequent to tracheotomy, one in the direction of the vocal folds and the other toward the lungs for respiration. In the first of three experiments, the effect of artificial airflow on electromyographic activity of the levator and pterygopharyngeal muscles was studied. In the second experiment, the effect of air pressure beneath the vocal folds on the activity of these muscles was studied. For the third experiment, the larynx was isolated surgically without cutting the bilateral superior laryngeal nerves and the effect of airflow through it examined. Results and Conclusion: Both outward airflow and higher pressure enhanced expiratory activity of the levator and pterygopharyngeal muscles. Receptors in the subglottal area play major roles in this enhancement. Furthermore, an increase in air pressure during expiration enhances closure of the velopharynx.