The dynamics of swallowing. I. Normal pharyngeal mechanisms.

Swallowing is a complex mechanism in which the functions of the central and autonomic nervous systems are integrated to produce a smooth and speedy transference of the bolus from the mouth to the stomach. The pharyngeal phase of deglutition is the most rapid, being usually of less than a second's duration, and for this reason has been difficult to analyze fully. The forces involved in the propulsion of the bolus through the pharynx have been a source of controversy. Some have maintained that the bolus is advanced under positive pressure by the action of the muscles of the tongue and pharynx (1, 2); yet others have postulated negative intrapharyngeal pressures (3), in particular Barclay (4), who believed that, after preliminary elevation, the pharynx suddenly descended thereby sucking the bolus downward. Barclay's concepts have few adherents today, but transient negative pressures, uncertain as to origin and purpose, do appear during swallowing. Recently, for example, Fyke and Code (5) have recorded positive pressures from the upper pharynx and negative ones from the cricoid level on swallowing. It is generally assumed that the pharynx in the resting state is closed off from the esophagus, and although the existence of an anatomical sphincter in this region is controversial, the lower part of the inferior constrictor and perhaps the adjoining circular muscle of the esophagus are believed to perform this function (6, 7).1 A cricopharyngeal sphincter has been demonstrated radiographically by Templeton and Kredel (8) and its functioning has been illustrated by cinefluorography by Ramsey, Watson, Gramiak, and Weinberg (9). Whether the cricopharyngeus represents a true