Tongue is essential to a lot of orofacial movements including chewing and swallowing. Although numerous previous studies were focused on the measurement of tongue pressure (TP) against the palate to evaluate the swallow related oral function, few studies have been focused on the physiological role of the pressure in swallowing. The aim of the present study was to clarify the physiological mechanism of tongue pressure and to investigate the relationship between the TP waves, the supra-hyoid muscle activity, and videofluorographic (VF) images during swallowing.
Methods:
Fifteen healthy subjects (mean 27.3 +/- 2.5 yrs) participated in this study. Tongue pressure, electromyographic (EMG) activity of supra-hyoid muscles and VF were recorded synchronously during 4-ml barium liquid swallowing. TP was measured by our original sensor sheet with five channels attached on hard palate directly. The temporal relationship between the events measured from the TP, muscle activity, and VF data were evaluated.
Results:
TP waveforms during liquid swallowing exhibited either mono- or bi-phasic patterns. TP at Chs 4 and 5 located on the posterio-lateral point of hard palate tended to have biphasic peaks. TP with monophasic pattern appeared during the same period as the second peak of biphasic pattern. The onset of TP was later than the start of hyoid movement and onset of supra-hyoid muscle activity, and the offset was observed between hyoid at Up-Fw position and hyoid reposition. The onset of Ch1 had relationship with the start of slight hyoid elevation. The bolus movement seemed to have relationship with onset of Ch3 at mid-posterior area. Offset of TP at Chs4 and 5 was strongly time-locked with the hyoid reaching at Up-Fw position.
Conclusions:
The present results suggest that tongue pressure was produced not only by tongue movement itself for bolus propulsion but also closely related with hyoid movement during swallowing.