Differences in Swallow Mechanics in Infants

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DESCRIPTION (provided by applicant): Swallowing requires the coordination of a large number of muscles; this complexity arises partly from the need for airway protection. In the previous funding period, we added to the understanding of muscle activity and oropharyngeal kinematics in infant deglutition. However, the role of the majority of muscles during emptying of the valleculae and in the transport of the bolus past the laryngeal opening or the natural stimuli that initiate the emptying of the valleculae over maturation is not well understood. Our preliminary data suggest that two distinct pathways of bolus movement exist, either around the epiglottis/laryngeal opening (in the newborn) or over it (by the age of weaning). However the timing of the transition, from one path to the other and the associated changes in the kinematics or motor patterns, are unknown. The decerebrate pig is an excellent model for studying vallecular emptying because this phase of the swallow can be isolated experimentally. We propose to apply our existing techniques both to this model and to intact animals, in order to answer the following questions. What natural stimuli initiate vallecular emptying, and do they change during maturation? What is the pattern of muscle activity during vallecular emptying in terms of the order and amplitude of muscle activation? Does change in the consistency of the bolus alter the motor pattern during vallecular emptying, and does this change over developmental time? Does epiglottal movement result from: (i) direct muscle contraction; (ii) indirect movement of the rest of the larynx, (iii) the mechanical action of food on the epiglottis, or a combination of all three? Current studies of human dysphagia and rehabilitation rely heavily on several older studies of oral function in adult man and animal; these studies did not have the means to examine the ontogeny of vallecular function in detail. The proposed study of the maturation of motor patterns will provide an important baseline for treatment strategies aimed at human infant dysphagia.