Chapter 19 Physiology and electromyography of swallowing and its disorders

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The objective evaluation of the swallowing is clinically very important. For 80% of all individuals with dysphagia, neurological disorders are responsible. Swallowing is usually subdivided into four phases: an initial oral phase (including both oral preparatory and oral propulsive activity), a pharyngeal phase and an esophageal phase. The oral phase is mainly voluntary and highly variable in duration depending upon food consistency, taste, environment, hunger and motivation. The oral and pharyngeal phases are highly interrelated; the distinction between them is often unclear. When the pharyngeal phase begins, the following physiological events occur in rapid overlapping sequence so that they are nearly simultaneous. The approach to the diagnosis of impaired swallowing is two-fold, requiring both etiological and physiological considerations. The etiological approach depends on differential diagnosis while the physiological approach depends on analysis of the mechanism of swallowing. The EMG methods are derived from the known physiological events of oropharyngeal swallowing, which are amenable to clinical EMG techniques. The onset and duration of pharyngeal swallowing can be recorded from submental/suprahyoid muscles (SM-EMG). Standard needle EMG is sometimes performed for muscles innervated by the lower cranial muscles, such as tongue, larynx, and facial muscles. These studies are useful for differential diagnosis of neuromuscular disorders causing dysphagia and dysphonia but pharyngeal EMG is performed infrequently. Kinesiologic EMG also has a crucial role in the evaluation of the swallowing and its disorders.

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      Pharyngeal manometry is technically difficult, because the rapid motions of the pharynx and UES during swallowing make it difficult to know the precise physical location of the pressure sensor during the recording. Sometimes it is combined with VFS so the position of the sensor can be recorded during the swallow (Ertekin and Palmer, 2000). Methods other than the clinical, neurological and neurophysiological techniques may be useful for neurological patients with suspected dysphagia; however, these methods mentioned above are basically important for the studies of the end-organ or the peripheral apparatus of deglutition.

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