Abstract
＜Purpose＞ Velopharyngeal closure is observed not only in swallowing but also in pneumatic actions including speech and blowing．Clinically，velopharyngeal closure in pneumatic action is not distinguished from that in swallowing． However，pneumatic closure，which is acquired，prevents expiratory air from passing into the nasal cavity． While during swallowing，velopharyngeal closure is achieved innately；it keeps the bolus from regurgitating into the nasal cavity．This suggests that velopharyngeal closure during pneumatic action is operated by a different mechanism from that during swallowing． The purpose of this study is to clarify the differences in activity of the levator veli palatini muscle (LVP)，which is the primary muscle for velopharyngeal movement，during velopharyngeal closure for swallowing，speech and blowing，using power spectra analysis．＜Methods＞ Four normal adults were used as subjects in this study．Each subject was instructed to perform the three experimental tasks which were speech，blowing and swallowing．Electromyograms were recorded and analyzed for each task to calculate the mean power frequency (MPF)．＜Results＞ There was no significant difference in MPF between speech and blowing activities for all subjects．MPF was significantly greater during swallowing than during pneumatic action for all subjects．The MPF value reflects the composition of active motor units during muscle contraction．Therefore，it was clarified that the motor units which participated in contraction during swallowing were different from those used during respiration in LVP．＜Conclusion＞ The results of this study indicate that movement of the LVP in swallowing is operated by a different mechanism from that used in pneumatic action．
