The current paradigm for swallowing based on liquid command swallows does not apply to subjects eating solid foods. In normal adults, solid foods are processed in the oral cavity but the bolus is formed in the oropharynx. The accumulating bolus is carried forwards and backwards on the cycling surface of the tongue. There is no posterior oral seal as classically described. A Process Model for feeding on solid foods is proposed (Hiiemae and Palmer, 1999). We plan three experiments to validate the model by testing the following four hypotheses: a) there is a volume/consistency threshold which differs between hard and soft foods, and above which bolus formation normatively occurs in the oropharynx; b) the 'swallow on command' instruction will disrupt normal bolus formation, suggesting a cortical override of the hindbrain pattern generators; c) respiration will become slower and less regular during feeding, and high frequency oscillations in nasal air pressure will occur in chewing when the fauces are open; d) the soft palate will exhibit some intrinsic rhythmicity, but not make regular contact with the tongue except in early chewing cycles. The following techniques will be used: (a) lateral videofluorography (VFG) with radiopaque food in graduated initial bite sizes and consistencies (2-12 g banana, 1-8 g cookie), and with liquid swallows from 10-25 cc to assess the effect of bite size and consistency on feeding. Half of these subjects will have a soft palate marker or sniff barium to highlight the palatal surface and the posterior pharyngeal wall; radiopaque markers will also be glued to the tongue in a subset; (b) VFG (lateral and P-A) with subjects serving as their own controls to test the effect of the """"""""command swallow"""""""" on sequence behavior. 8 VFG with simultaneous recording of respiratory rate (measured with a thoracic strain gauge and nasal pressure transducer), and masseter and suprahyoid EMG during feeding on natural bite sizes of banana (12 g) and cookie (6 g) to delineate the interactions between respiration, mastication, and swallowing in complete feeding sequences. Data will be analyzed visually, and by digitization and coordinate manipulation as appropriate. The linkages between events will be tested. The results will further delineate the circumstances in which oropharyngeal bolus formation occurs and have direct relevance to the evaluation of dysphagic patients, those with food processing problems and enhance our knowledge of CNS control of mastication and swallowing.
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