Abstract
Speech appliances are available for correction of hypernasality or nasal emission that is caused by velopharyngeal incompetence following primary palatoplasty. When a speech appliance is in place, patients, who are accustomed to wearing a speech appliance, can exhibit adequate velopharyngeal function during production of pressure consonants or blowing. That is, it is likely that velopharyngeal function can be regulated in relation to changes in oral air pressure accompanied by production of obstruent sounds or blowing so as not to avoid nasal emission or hypernasal speech.
The purpose of this study was to clarify the physiologic basis underlying an effect of a speech ap pliance placed to improve velopharyngeal function. Six patients with repaired cleft palate were employed as subjects. The subjects were accustomed to wearing a speech appliance. Three out of six subjects routinely wore a bulb attached palatal lift prosthesis (Bulb-PLP) and the others a palatal lift prosthesis (PLP) for the correction of velopharyngeal incompetence. Electromyographic signals of the levator veli palatini muscle and peak oral air pressure were monitored during three levels of blowing pressure (soft, medium and hard blowing) when a speech appliance was in place and removed. For subjects routinely wearing a Bulb-PLP, levator activity was not correlated with changes in oral air pressure when a Bulb-PLP was removed. However, when a Bulb-PLP was in place, levator activity changed in relation to oral air pressure during blowing and the activity was identified to be smaller than that observed during soft and medium blowing in the condition that a Bulb-PLP was removed. For subjects routinely wearing a PLP, levator activity changed in relation to oral air pressure whether a PLP was in place or not. However, when a PLP was in place, levator activity was significantly smaller than that observed in the condition that a PLP was removed.
Standard deviation of levator activity was smaller in the condition of a speech appliance in place than that in the condition that a speech appliance was removed irrespective of a type of a speech appliance. The results possibly imply that differential activity of the levator muscle, which is generated by placement of a speech appliance, might be a reserve to enable velopharyngeal function to close adequately in relation to changes in oral air pressure with context so as not to allow air to escape into the nasal cavity, and smaller deviation of levator activity is possible to imply that levator muscle activity can be adequately regulated to respond to target tasks.
