Swallowing Function in Patients With Head and Neck Cancers

The process of swallowing includes the conscious effort to ingest food and a subconscious or reflex effort of bolus preparation. The preparation of the bolus is referred to as the preparatory phase, the transport of the bolus from the oral cavity and pharynx to the oesophagus as the transport phase and through the oesophagus as the oesophageal transport phase. The rhythm and pattern of the swallowing mechanism is controlled by a central pattern generator located in the medulla. The tongue plays an important role in the preparatory phase by mixing the food and moving it towards the occlusal surface of the teeth. Sensory innervation across the oral mucosa and the tone of the facial muscles help in keeping the bolus within the oral cavity and in its manipulation. The soft palate approximates to the tongue to create a glossopalatal seal which prevents premature spillage in to the pharynx, while various movements of the mandible are imperative for the adequate grinding of the bolus. The tongue then contracts from anterior to posterior pushing the bolus back into the pharynx, the whole process taking about one second. This phase involves the Vth, VIIth and XIIth cranial nerves. The pharyngeal phase is involuntary, with sensations travelling through the IXth and Xth cranial nerves and usually lasting one second. In this phase, the soft palate closes the nasopharynx, the larynx is elevated and closed, the pharyngeal constrictors contract and the cricopharynx relaxes. The true cords, the false cords, the epiglottis and the aryepiglottic folds constrict to form a barrier of several layers preventing aspiration. The mechanism varies and there is no gold standard test that can accurately measure this dysfunction. Most patients are investigated only when it impairs the feeding and nasal feeding tubes are required. It is not know as to how much the function preserving conservative surgeries actually preserve the function and hence, the importance of this study.