Tongue, Palatal, and Pharyngeal Muscle Activity in Mastication and Respiration

Objectives: The oropharyngeal muscles play critical roles in chewing, swallowing, and respiration but the characteristics of their activity are not fully understood. Thus, this study aimed to analyze electromyographic activity (EMG) of oropharyngeal muscles during natural chewing and swallowing in relation to respiratory phases.
Methods: Eight 7-8-month-old Yucatan-minipigs were used. Eight pairs of EMG wire electrodes were implanted in following left muscles: genioglossus and styloglossus (GG and SG), pharyngeal middle constrictor and thyrohyoid (MC and TH), tensor and levator veli palatini muscles (TVP and LVP), and masseter and digastric (MA and DA). Natural pig chow was provided and signals of muscle activity and respiratory airflow via a nasal catheter were recorded simultaneously for 5-10 minutes. MA and MC were used as reference muscles for determining the chewing side and swallowing episodes respectively.
Results: The onsets of ipsilateral SG preceded 20-30% the MA activation (p≤0.05). Similarly, the LVP preceded 10-15% the MA onset. In contrast, the MC activated later than MA. The mean and integrated activity of MA and TVP/LVP were 35% higher than DA and twofold the amplitude of the MC (p≤0.05). No change in respiratory phases was seen during chewing. During swallowing, the activation of SG, TH and TVP/LVP preceded 10-20% the activation of the MC. The mean and integrated activity of TVP/LVP, TH, and SG were 40-50% higher than MA and DA (p≤0.05). A brief interruption of respiration was seen in both inspiratory/expiratory phases and there was a delay of 0.43-1.72s in the next inspiratory phase when swallowing occurred at the end of expiratory phase.
Conclusions: These results suggests that palatal and pharyngeal muscles are active in chewing and swallowing. Swallowing affects both inspiratory and expiratory phases and this occurs along with simultaneous activation of the tongue, palatal, and pharyngeal muscles. These findings pave the basis for later studies in swallowing disorders.