Abstract
The purpose of this study was to determine whether levator veli palatini muscle activity can be elicited by simultaneous changes in oral air pressure and nasal air flow rate when a speech appliance is in place. The previously operated on cleft palate patients were selected as subjects. The subjects were found to have normal articulation and resonance with a speech appliance in place but showed hypernasality without it. Speech appliances worn routinely by the subjects were modified by drilling a hole in the veritical center of the pharyngeal bulb. The air flow rate into the nasal cavity through the opening in the bulb was systematically altered by changing the circular areas of the opening in the bulb from the occluded condition to 4mm in diameter and then to 7mm in diameter. Electromyographic activity of the levator veli palatini muscle was measured with changes in the nasal air flow rate and oral air pressure that were induced by the alteration of the circular area of the opening at the bottom of the bulb. To evaluate the effect of the nasal air flow rate and oral air pressure on levator veli palatini muscle activity, multiple regression analysis, using levator veli palatini muscle activity as the criterion variable and the nasal air flow rate and oral air pressure as explanatory variables, was carried out after standardization of all the obtained data.
Multiple regression analysis revealed that the nasal air flow rate may affect levator veli palatini muscle activity more dominantly than oral air pressure. The results indicate that aerodynamic variables of nasal air flow and oral air pressure might be involved in he neural control of speech production in individuals wearing a speech appliance, even if they exhibit velopha ryngeal incompetence when a speech appliance is not used.
