Modulation of the stretch reflex of jaw-closing muscles in different modesand phases of respiration

The objective of this study was to investigate whether and how changes in t he mode of respiration affect the electromyographic activity of human jaw-c losing muscles. Fifteen men were examined in this study. A pair of surface electrodes was attached bilaterally to the masseter and anterior and poster ior temporalis muscles for electromyographic recording. Respiratory movemen ts of the chest wall and nasal airflow were recorded simultaneously. Record ings were performed with subjects in the sitting position during quiet nasa l and oral respiration. The stretch reflex of jaw-closing muscles was elici ted by randomly tapping the chin with an impulse hammer. In 11 subjects, we measured nasal resistance with a rhinomanometer. The amplitude of electrom yographic activities of the masseter and anterior temporalis muscles during oral respiration was significantly less than that during nasal respiration , whereas that of the posterior temporalis muscle showed no significant dif ference between the different modes of respiration. Furthermore, the reduct ion in the amplitude of the electromyographic activity was more evident in the inspiratory phase during oral respiration. There was a significant posi tive correlation between the ratio of the reflex amplitude during inspirati on in the 2 respiratory modes and nasal resistance for the masseter muscle, but not for the anterior temporalis muscle. These results suggest that the reflexive electromyographic activity of some human jaw-closing muscles is modulated during oral respiration.