Characterization and mechanisms of the pharyngeal swallow activated by stimulation of the esophagus

Abstract

Stimulation of the esophagus activates the pharyngeal swallow response (EPSR) in human infants and animals. The aims of this study were to characterize the stimulus and response of the EPSR and to determine the function and mechanisms generating the EPSR. Studies were conducted in 46 decerebrate cats in which pharyngeal, laryngeal, and esophageal motility was monitored using EMG, strain gauges, or manometry. The esophagus was stimulated by balloon distension or luminal fluid infusion. We found that esophageal distension increased the chance of occurrence of the EPSR, but the delay was variable. The chance of occurrence of the EPSR was related to the position, magnitude, and length of the stimulus in the esophagus. The most effective stimulus was long, strong, and situated in the cervical esophagus. Acidification of the esophagus activated pharyngeal swallows and sensitized the receptors that activate the EPSR. The EPSR was blocked by local anesthesia applied to the esophageal lumen, and electrical stimulation of the recurrent laryngeal nerve caudal to the cricoid cartilage (RLNc) activated the pharyngeal swallow response. We conclude that the EPSR is activated in a probabilistic manner. The receptors mediating the EPSR are probably mucosal slowly adapting tension receptors. The sensory neural pathway includes the RLNc and superior laryngeal nerve. We hypothesize that, because the EPSR is observed in human infants and animals, but not human adults, activation of EPSR is related to the elevated position of the larynx. In this situation, the EPSR occurs rather than secondary peristalsis to prevent supraesophageal reflux when the esophageal bolus is in the proximal esophagus.

Characterization and mechanisms of the supragastric belch in the cat

“…In addition, the cat SGB is a rapid complex event involving numerous different muscles, i.e., hyoid, pharynx, larynx, esophagus, and diaphragm, acting in concert with each other, and such organization would require control by preprogrammed neural circuitry. Swallowing (2,11,22) and the gastric belch (17,19) are also preprogrammed complex neural reflex processes of the brain stem involving striated muscles (2,13,19,22). Therefore we suggest that the cat SGB is a reflex response similar to swallowing and the gastric belch response.…”

“…2, 5, and 6 for definitions. animal studies we can activate the pharyngeal swallow by applying tension to the esophagus (11,22), whereas when the swallow is initiated voluntarily from the cortex, the pharyngeal swallow begins before the esophagus is activated by the swallowed contents (8,11). The sequence is different, but the reflex response portions of the events are identical.…”

“…The trachea was cannulated, Electromyographic (EMG) electrodes were placed on the geniohyoideus, thyrohyoideus, thyropharyngeus, cricopharyngeus (CP), and esophagus 2 and 4 cm from the CP. The CP is the primary muscle (7,22) of the upper esophageal sphincter (UES), and its actions are considered responses of the UES. The abdomen was then opened along the ventral midline, and a fistula of the proximal stomach was formed using a 3-ml plastic syringe that exited the abdominal cavity.…”

“…The previously characterized supraesophageal responses to mechanical stimulation of the esophagus include esophago-UES contractile reflex [EUCR (4,5,18,35)], belch response (11,19,35), and esophagus-stimulated pharyngeal swallow reflex [EPSR (5,22)] (Fig. 2).…”

Pathological classification of equine recurrent laryngeal neuropathy

“…The greater numbers of myelinated fibers in the right RLn might reflect the presence of afferent (sensory) fibers, however the presence of sensory axons within equine RLn has not been investigated. In humans, these sensory axons receive input from the mucosa in the region of the vocal folds, and in cats, the pharyngeal swallow reflex occurs in part, from esophageal pressure increases transmitted through the RLn . However, staining for afferent branches in the rat RLn did not show any sensory branches suggesting that there are species differences in RLn‐associated sensory pathways.…”