Physiological approaches to establishing the evaluation of eating and swallowing disorders

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Afferent signals arising from the oral, pharyngeal and laryngeal structures may have important roles on the initiation of swallow. In this study, we sought the effects of taste and temperature on swallowing reflex in humans, in which swallowing behavior was recorded and swallow difficulty was evaluated. A thickening agent, that is stable in the physical properties, was employed as the test food. In case of the normal subject, both the parameters of taste and temperature were found to affect swallow difficulty, however, they did not affect the swallowing behavior, such as muscle activities and laryngeal movements. The result suggests that thickening agents prepared at higher temperature than oral temperature and with taste may make easier the initiation of swallowing reflex.Swallowing reflex may be initiated when food bolus is transferred from the oral cavity to pharynx. Although superior laryngeal nerve (SLN) stimulation does elicit swallowing in the anesthetized animal, mechanical stimulation around the pharynx may not elicit swallowing in healthy humans. Rather gag reflex is pedominant. In case of CP patients with difficulty in swallowing, cold stimulus to the pharynx is believed to make the swallow easier. Thereafter, we hypothesized that cortex may have an important role on the initiation of swallowing. We thus compared the threshold of SLN stimulation for swallowing during anesthesia and awake in the chronic preparation. A positive result was obtained in that the threshold decreased with lightening the depth of anesthesia, however it increased when the animal was in the awake and rest stage.