ANALYSIS AND INTERPRETATION OF EMG SIGNALS DURING SWALLOWING

Swallowing is the most complex movement made by humans. It is based on a neuromuscular mechanism that undergoes a physiological maturation, represented by the passage from infantile to adult swallowing. It consists in the coordination of about 30 muscles and several joints, to ensure the bolus progression from the mouth to the stomach in about 1 second. It is made by the combination of multiple sequential behaviors like : (1) mouth closure, (2) oral food transport, (3) soft palate elevation, (4) hyoid elevation and forward displacement, (5) laryngeal closure, (6) UES opening, and it is influenced by the sensory and cortical inputs that arrive from the central pattern generator (CPG) for human swallowing. This complex mechanism has received less scientific attention than other motor activities, may be due to the fact that it involves a large number of muscles and cranial nerves (CN) in a very small anatomical area, which renders neurophysiological studies difficult in experimental humans. One of the most important events during swallowing is the airway protection from the influx of bolus material, that occurs during the involuntary pharyngeal phase. This happens through the elevation of the larynx accomplished by the elevation of the hyoid bone. This study was undertaken to determine the activation and coordination pattern of the suprahyoid muscles, which control the anterosuperior movement of the hyoid bone. Electromyography is the best tool to determine which muscles are activated to generate movement. Specifically, the signals were recorded by high-density surface electromyography (HD-sEMG), that allows for a space-time evaluation of muscle activity. The study was conducted on signals already acquired from 10 healthy subjects, who do not have anatomical and physiological alterations in swallowing. The aim of this work is to identify a possible description of healthy swallowing to be used as a standard for the recognition of non-physiological and consequently pathological swallowing. In fact, this could be useful to identify rehabilitation protocols and treatments for dysphagic patients. In the preliminary phase, the different muscular activities with bolus of different viscosity will be analyzed and described. Then, a possible temporal and spatial sequence of activation of the suprahyoid muscles will be identified, separating their activities in space and time. Through the implementation of appropriate filtering and visualization techniques, it will be possible to spatially separate the muscular contributions coming from the three major suprahyoid muscles: geniohyoid (GH), mylohyoid (MH) and anterior belly of the digastric (ABD). In fact, these muscles are responsible for the anterior and superior displacement of the hyoid bone. On the other hand, it will be impossible to distinguish the temporal activity of the muscles mentioned above, as their activity can be considered generally synchronous. Furthermore, the analysis shows the presence of a considerable variability between the subjects, due to the fact that swallowing is a mainly involuntary mechanism and so, not directly controllable. In conclusion, the present work proposes a description and visualization of the muscle activity of the hyoid complex, during the displacement of the hyoid bone through HD-sEMG. The possibility to obtain an objective description of healthy swallowing through a non-invasive setup is of great interest.