Assessment of the swallowing function through High-Density surface EMG

Swallowing is one of the most important human functions in our daily life consisting in a coordinated sequence of events aimed at moving nutrients from the mouth to the stomach. Despite its relevance, it has been less investigated than other motor activities. This is likely due to the complexity of this sensorimotor task. Indeed, a single swallow involves the coordination of more than 30 muscles within 1 second, including voluntary and reflexive activities: manipulation of food, displacements of the hyoid bone, hyolaringeal elevation and tilting of the epiglottis. All these events are possible because of the contraction of specific muscles of the submental region and in the anterior portion of the neck, controlled by swallowing center of the brainstem. Any structural or neurological impairment along the swallowing pathway is referred to as dysphagia, a pathology with high impact on the quality of life. An objective evaluation of the swallowing disorders is potentially relevant to identify and classify the type of dysfunction and to evaluate the outcome of treatments. Nevertheless, the evaluation of disorders of swallowing has to be preceded by a correct understanding of the normal physiology of swallowing. Currently, several technologies can be used in order to assess different aspects (e.g. mechanical or electrophysiological) of the swallowing function: videofluoroscopy (VFSS), endoscopy (FEES), manometry, electromyography. In this study we designed an integrated measurement framework for non-invasive assessment of the swallowing function of healthy and dysphagic subjects. Specifically, the proposed experimental setup includes high-density surface electromyography (HD-sEMG) for a spatio-temporal evaluation of the electrical muscular activity and accelerometry for the temporal segmentation of swallowing phases based on hyolaringeal excursion. An experimental study was carried-out to: (i) assess the validity of this innovative setup by comparing the accelerometer-based task segmentation with that obtained with the clinical standard (FEES), (ii) study the spatiotemporal evolution of EMG activity to refine the indexes used to describe the activation of muscles involved in the swallowing (e.g. symmetry indexes). The study was conducted on a group of 10 healthy subjects performing 15 swallowing tasks with 5 types of bolus: saliva (dry swallow), 3 and 10 ml of water, 3 and 10 ml of gelled water. Results indicate: (i) a good intra-subject consistency between the accelerometer- and FEES-based identification of the swallowing onset. In fact, the accelerometer-based onset occurred, on average, 250 ms before that obtained with FEES, with an inter-subject variability of 300 ms (interquartile range), regardless to the type of bolus. Moreover, no significant differences were found in EMG symmetry indexes estimated considering the FEES-based and accelerometer-based segmentation. (ii) The sequence of muscle activation can be mapped with HD-sEMG that provides a spatiotemporal variation of EMG activity which is consistent among healthy subjects. In conclusion, the present study proposed a possible, alternative method for the evaluation of swallowing function with a non invasive, easy to use and innovative setup. The application of the proposed method on subjects with swallowing impairments is ongoing in order to assess its reliability for the assessment and the treatment of dysphagia itself.