Determination of a palatal lift prosthesis to decrease levator muscle fatigue.

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Purpose : This research was conducted to clarify crucial factors in construction procedure of a speech appliance to decrease muscle fatigue, which prevent speakers from performing continuous speech.Methods and Subjects : 1998 : Experimental speech appliances with variable portion of a palatal lift prosthesis were constructed. Electromyography of the levator veli palatini muscle during speech tasks was recorded when each type of experimental speech appliances was removed and inserted. Five normal speakers were selected as subject in the study of 1998. 1999 : Each subjects was instructed to perform 200 productions of/pu/when respective speech appliances were inserted and removed. In each experimental condition, levator EMG was recorded. Mean power frequency (MPF) were calculated on the basis of Fast Fourier Transfer (FFT) so as to examine 1) whether s speech appliance can decrease the muscle fatigue, 2) what type of a portion of a palatal lift prosthesis can decrease most effectively.Res … More ults : 1) Change in reserve capacity for velopharyngeal function for speech, which is defined as differential activity between levator activity during speech tasks and possible maximum activity, was greater in association with alteration of length and angle of a velum portion of an experimental palatal lift prosthesis than the condition of alteration of width of the appliances. That is, when the velum is elevated up to the level of the palatal plane, reserve capacity could become greater than any other vertical positions. 2) For normal speakers, the effect of a speech appliance to decrease levator muscle fatigue during 200 continuous productions of/pu/was not different between placement and removal conditions. On the other hand, in case of speakers with cleft palate with velopharyngeal incompetence, subjects, who showed greater increase in reserve capacity for speech in association with placement, exhibited greater decrease in muscle fatigue. Conclusion : The results obtained here can suggest that a palatal lift prosthesis which can elevate the velum up to the level of the palatal plane could decrease muscle fatigue most effectively, which might enable speakers to perform continuous speech production without collapse in velopharyngeal function. The effect might be more remarkable in speakers, for whom decrease in required levator muscle activity is marked in association with placement of the appliance. Less