Our goals in this study were to evaluate the mechanisms operative in swallow-associated opening of the upper esophageal sphincter (UES) and to determine the dynamics of fluid flow across the sphincter. For this purpose, we obtained concurrent videofluorographic and manometric studies of 2- to 30-ml barium swallows in 15 normal subjects. We found that the resting UES high-pressure zone corresponded closely with the location of the cricopharyngeus. The findings indicated that manometric UES relaxation and anterior hyoid traction on the larynx invariably preceded UES opening. With graded increases in bolus volume, progressive increases occurred in UES diameter, cross-sectional area, flow duration, and transsphincteric flow rate. Intrabolus pressure upstream to the UES and within the UES at its opening during transsphincteric flow of barium remained within a narrow physiological range of less than 10 mmHg up to a bolus volume of 10 ml. With increases in bolus volume, anterior hyoid movement, UES relaxation, and UES opening occurred sooner in the swallow sequence to accommodate the early entry of large boluses into the pharynx. We conclude that during swallowing 1) normal UES opening involves sphincter relaxation, anterior laryngeal traction, and intrabolus pressure, 2) volume-dependent adaptive changes in UES dimension accommodate large bolus volumes and flow rates with minimal requirement for increases in upstream, or intrasphincteric, intrabolus pressure or UES opening duration, and 3) volume-dependent changes in UES dimensions as well as timing of UES relaxation and opening indicate a sensory feedback mechanism that modulates some components of the swallow response generated by the brain stem swallow centers.

In this investigation, we studied the effects of bolus volume and viscosity on the quantitative features of the oral and pharyngeal phases of swallowing. Concurrent videofluoroscopic and manometric studies were done in 10 healthy volunteers who were imaged in lateral projection. Videofluorography was done at 30 frames/s while concurrent manometry was done with 5 intraluminal transducers that straddled the pharynx and upper esophageal sphincter (UES). Submental electromyography was recorded also. Swallows of 2-20 ml were recorded for low-viscosity liquid barium and high-viscosity paste barium. Analysis indicated that the major effect of increases in bolus volume was an earlier onset of anterior tongue base movement, superior palatal movement, anterior laryngeal movement, and UES opening. These events provide receptive adaptation for receiving a swallowed bolus. Earlier UES opening was associated with an increase in the duration of sphincter opening and sphincter diameter. The major effects of high bolus viscosity, unrelated to bolus volume, were to delay oral and pharyngeal bolus transit, increase the duration of pharyngeal peristaltic waves, and prolong and increase UES opening. Thus the specific effect of bolus viscosity per se differs substantially from that of bolus volume. We conclude that 1) specific variables of swallowing are affected significantly by the variables of the swallowed bolus, such as volume and viscosity; 2) overall, bolus volume and viscosity affect swallowing in a different manner; and 3) the study findings have implications about the neural control mechanisms that govern swallowing as well as about the diagnosis and treatment of patients with abnormal oral-pharyngeal swallowing.

We investigated the mechanisms of esophageal distension-induced reflexes in decerebrate cats. Slow air esophageal distension activated esophago-upper esophageal sphincter (UES) contractile reflex (EUCR) and secondary peristalsis (2P). Rapid air distension activated esophago-UES relaxation reflex (EURR), esophago-glottal closure reflex (EGCR), esophago-hyoid distraction reflex (EHDR), and esophago-esophagus contraction reflex (EECR). Longitudinal esophageal stretch did not activate these reflexes. Magnitude and timing of EUCR were related to 2P but not injected air volume. Cervical esophagus transection did not affect the threshold of any reflex. Bolus diversion prevented swallow-related esophageal peristalsis. Lidocaine or capsaicin esophageal perfusion, esophageal mucosal layer removal, or intravenous baclofen blocked or inhibited EURR, EGCR, EHDR, and EECR but not EUCR or 2P. Thoracic vagotomy blocked all reflexes. These six reflexes can be activated by esophageal distension, and they occur in two sets depending on inflation rate rather than volume. EUCR was independent of 2P, but 2P activated EUCR; therefore, EUCR may help prevent reflux during peristalsis. All esophageal peristalsis may be secondary to esophageal stimulation in the cat. EURR, EHDR, EGCR, and EECR may contribute to belching and are probably mediated by capsaicin-sensitive, rapidly adapting mucosal mechanoreceptors. GABA-B receptors also inhibit these reflexes. EUCR and 2P are probably mediated by slowly adapting muscular mechanoreceptors. All six reflexes are mediated by vagal afferent fibers.

The phases of swallowing are controlled by central pattern-generating circuitry of the brain stem and peripheral reflexes. The oral, pharyngeal, and esophageal phases of swallowing are independent of each other. Although central pattern generators of the brain stem control the timing of these phases, the peripheral manifestation of these phases depends on sensory feedback through reflexes of the pharynx and esophagus. The dependence of the esophageal phase of swallowing on peripheral feedback explains its absence during failed swallows. Reflexes that initiate the pharyngeal phase of swallowing also inhibit the esophageal phase which ensures the appropriate timing of its occurrence to provide efficient bolus transport and which prevents the occurrence of multiple esophageal peristaltic events. These inhibitory reflexes are probably partly responsible for deglutitive inhibition. Three separate sets of brain stem nuclei mediate the oral, pharyngeal, and esophageal phases of swallowing. The trigeminal nucleus and reticular formation probably contain the oral phase pattern-generating neural circuitry. The nucleus tractus solitarius (NTS) probably contains the second-order sensory neurons as well as the pattern-generating circuitry of both the pharyngeal and esophageal phases of swallowing, whereas the nucleus ambiguus and dorsal motor nucleus contain the motor neurons of the pharyngeal and esophageal phases of swallowing. The ventromedial nucleus of the NTS may govern the coupling of the pharyngeal phase to the esophageal phase of swallowing.

No abstract