Velopharyngeal closure pattern exerted by contraction of the pharyngeal constrictor muscle in dogs

Objective: This study was performed to investigate aspects of velopharyngea l closure demonstrated by movements of the parapharyngeal wall under variou s physiological conditions and especially the stimulation of several intrap neumonal receptors, Materials and Methods: Fifteen mongrel dogs were anesthetized and a nasopha ryngeal fiberscope was inserted from the oronasal fistula at the center of the hard palate, with the tip fixed around the choana, Mechanical and chemi cal stimulation was applied, and ongoing velopharyngeal movements were obse rved. In each case examined, the muscle nerve located under the bilateral l evator veli palatini (LVP) was severed, Results: Two different closure patterns were recognized between rebreathing and deglutition, Chemical stimulation of the pulmonary irritant receptor a nd type-J receptor induced a sphincteric tight closure of the velopharynx b ut only a weak inward movement of the lateral pharyngeal wall at lung infla tion. Conclusion: The movements of the parapharyngeal wall, mainly represented by the pharyngeal constrictor muscle's contraction, are facilitated as a sphi ncteric velopharyngeal closure under reflexive movements such as deglutitio n or gagging.