In order to clarify the effects of aerodynamical variables such as oral air pressure and nasal air flow rate on the Levator Veli Palatini (LVP) Muscle activity during the production of Japanese plosive /pu/ electromyographically, three cleft palate patients routinely wearing Bulb-PLP for the velopharyngeal incompetence were selected as the subjects. The Bulb-PLPs were modified by removing the center of the bulb in the vertical plane so as to leave a 2 mm thick wall. Parameters were monitored in three conditions: Condition I; the opening in the bulb was occluded to simulate the unmodified Bulb PLP, Condition II; the modified Bulb-PLP was used so as to permit a flow of air into the nasal cavity, and Condition III; the Bulb-PLP was not used. Data collection included oral air pressure, nasal air flow rate, and simultaneously smoothed LVP-EMG in each experimental condition.
The results obtained were as follows;
1. LVP muscle activitits were revealed significantly greater in Condition III than in Condition II, which were significantly greater than Condition I in all subjects.
2. There were no significant Spearman correlation coefficient between LVP muscle activitied and nasal air flow, and between those activities and oral air pressure across Conditions I and II.
3. Multiple regression analyses based on LVP muscle activities as criterion variable, oral air pressure and nasal air flow rate, as the two explanatory variables of Conditions I and II, revealed that multiple correlation coefficients in all subjects ranged from 0.694 to 0.815. The analyses of variance proved that all the F values were statistically significant in all subjects.
The interpretation for these findings is that the LVP muscle activity, in patients wearing well adapted speech appliance, may be stimulated by the simultaneous increase and decrease in nasal air flow and oral air pressure respectively.
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