Reflex-mediated enhancement of airway protective mechanisms.

The upper esophageal sphincter (UES) and lower esophageal sphincter (LES) comprise the basal mechanisms against entry of gastric content into the aerodigestive tract and the airway. There are, however, other mechanisms referred to here as "response mechanisms" that become activated after certain stimulation, such as distention of the esophagus or tactile/pressure stimulation of the pharyngeal wall, and result either in fortification of the UES barriers--i.e., esophago-UES, pharyngo-UES, and laryngo-UES contractile reflexes--or closure of the glottis--i.e., esophagoglottal and pharyngoglottal closure reflexes. In addition, there are other reflexes included among the response mechanisms--such as pharyngeal swallow and secondary peristalsis induced by pharyngeal stimulation by liquid and esophageal distention by refluxate--that result in pharyngeal and esophageal volume clearance, thus reducing the chance for contact of refluxate with the tracheal, bronchial, and glottal structures.