Coordination in oro-pharyngeal biomechanics during human swallowing

In swallowing, the tongue contacts against the hard palate to generate pressure for propelling a bolus from the oral cavity into the pharynx. Meanwhile, the hyoid and larynx move upward and forward to facilitate the bolus from the pharynx into the esophagus. It has been well known that sequential coordination between those actions is critical for safety accomplishment of swallowing. However, the absence of noninvasive assessment for it limits the detection to the physiological symptom of dysphagia. We applied a sensor sheet on the hard palate to measure tongue contact pressure and a bend sensor on the frontal neck to monitor the laryngeal movement, which was synchronized with hyoid motion for assessing the coordination between both actions in 14 healthy male subjects when swallowing 5 ml of water. The sequential order of tongue pressure and hyoid movement was successfully displayed. Tongue pressure was produced after slight movement of the hyoid and closely to the hyoid elevation, then reached a maximum when the hyoid stabilized in the most anterior-superior position, and ceased concurrently with the onset of hyoid descent. Additionally, the synchronized data from both sensors showed positive correlations between identified time points on the laryngeal signal waveform and onset, peak and offset of tongue pressure. Our sensing system successfully showed the coordination between tongue pressure production and hyoid motion, and could be a simple and noninvasive method for clinicians to evaluate the oral and pharyngeal stages of swallowing.