Mechanisms of airway protection and upper esophageal sphincter opening during belching.

The mechanisms of airway protection, upper esophageal sphincter (UES) opening, and their coordination during belching were studied with a concurrent videoendoscopic, videofluoroscopic, and manometric technique. Analysis of videoendoscopic recordings revealed that glottal function during gastric and esophageal belching was similar and consisted of vocal cord adduction resulting in closure of intoitus to trachea, followed by anterior-caudad movement of the glottis, followed by slitlike or triangular UES opening. When a belch episode was associated with an intragastric pressure increase, in addition to the above features, there was approximation of arytenoids to the base of the epiglottis before the UES opened. Duration of vocal cord closure during belches induced by 40 ml intraesophageal air injection was significantly longer than belches induced by 20 ml (P less than 0.01). Vocal cord closure preceded the UES opening invariably. Analysis of videofluoroscopic recordings showed that hyoid bone movement during belching had a distinctive pattern different from its movement during swallowing. UES opening started generally when the hyoid bone was pulled anteriorly. Anterior hyoid excursion of 0.78 +/- 0.1 cm during belching was significantly shorter than its excursion of 1.8 +/- 0.09 cm during swallowing (P less than 0.01). We conclude that glottal closure is an integral component of both esophageal and gastric belch reflexes that prevents aspiration of regurgitated material into the airway. Glottal closure mechanism during belching has two tiers of closure: 1) vocal cord closure and 2) aryepiglottic approximation. Glottal and UES functions are closely coordinated during belching, and finally, during belching, UES is pulled open after its relaxation.