Influences of body posture on duration of oral swallowing in normal young adults.

The primary purpose of this study was to determine whether body posture altered the duration of oral swallowing. To answer this question, we recorded electromyograms (EMGs) from the anterior tongue and suprahyoid (SH) muscles as well as laryngeal movement associated with swallowing in nine normal young subjects. The subjects swallowed a test food after receiving a signal while in four randomly set postures: upright, two inclined (60 degrees and 30 degrees to the horizontal), and supine positions. We measured the durations from the start to the peak and from the peak to the end of the integrated tongue and SH EMGs. We assumed that the duration from the start to the peak of the integrated SH EMG would correspond to the duration of oral swallowing. The average duration from the start to the peak of the integrated SH EMG decreased after moving from the upright to the inclined and supine positions. The decrease in the duration was statistically significant and consistent for three experimental sessions. The duration from the start to the peak of the integrated tongue EMG during swallowing tended to decrease after lying down, but not significantly. The postural changes did not affect the remaining four durations. The decrease in the duration of oral swallowing induced by lying down suggests that the gravitational force placed on the test food facilitates the swallowing reflex. Large variation in the tongue activity during swallowing among the subjects can probably be attributed to the lack of a significant decrease in the duration of the tongue activity.