Characterization and mechanisms of the supragastric belch in the cat

Abstract

A response in which a belch occurs without gastric involvement, i.e., the supragastric belch (SGB), has been characterized in humans. The aims of this study were to determine whether animals have an SGB and, if so, to determine its mechanisms. Studies were conducted in decerebrate cats ( = 30) with electromyographic electrodes on hyoid, pharyngeal, esophageal, and diaphragm muscles. The effects of distending different regions of the esophagus in different manners using a balloon were quantified to determine the most appropriate stimulus for activating the cat SGB. The effects of esophageal perfusion of lidocaine ( = 3), vagus nerve transection ( = 3), or esophageal acidification ( = 5) on activation of the SGB were determined. Rapid large distensions of the thoracic esophagus best activated responses similar to the human SGB, i.e., rapid inhalation followed by a belch. The rapid inhalation was associated with activation of hiatal fibers and the belch with activation of dome fibers of the diaphragm. The rapid inhalation response was independent of the belch response. Lidocaine perfusion of the esophagus blocked the belch response without blocking the rapid inhalation, HCl perfusion sensitized the esophagus to activation of both the rapid inhalation and the belch response, and vagotomy blocked both responses. We conclude that the cat has an SGB that is composed of two independent reflex responses, i.e., rapid inhalation and belch, that are mediated by the vagus nerves and tension/mucosal receptors of the esophagus and sensitized by esophageal acid exposure. We hypothesize that the SGB is a learned voluntarily activated reflex response. Rapid strong distension of the thoracic esophagus activates rapid inhalation followed by a belch, which is the sequence of responses that compose the human supragastric belch (SGB). The rapid inhalation and belch phases of the cat SGB are activated by hiatal and dome fibers of the diaphragm, respectively, and are mediated by the vagus nerves and tension/mucosal receptors of the esophagus and sensitized by esophageal acid exposure. There are many similarities between the cat and human SGB.

Belching in Gastroesophageal Reflux Disease: Literature Review

“…In such cases, stressful life events might precipitate SBG. In animal experiments, Lang et al found that esophageal distension can trigger a reflex of inhaling air followed by belching via vagal nerves and esophageal tension/mucosal mechanoreceptors [ 15 ]. In light of this finding, a limited part of SGB might be a reflex rather than a behavior, especially when gas reflux causes the initial esophageal distension.…”

The Physiology of Esophageal Reflexes

“…The thoracic esophagus showed greater sensitivity to this reflex response than the cervical esophagus, and this response was sensitized by the exposure of the esophagus to acids [56]. All subreflexes of the SGB were blocked by vagotomy [56]. Local anesthesia of the esophageal mucosa blocked EURR, but could not trigger reflex activation of inhalation [56].…”

“…Initially, it was thought that this was a voluntary response [53][54][55], but recent studies [49] suggest that this may be a learned reflex response. It was observed in studies on decerebrate cats that rapid distention of the esophagus with a balloon could trigger an inhalation response that is immediately followed by activation of the EURR and release of air out of the esophagus and mouth [56]. The thoracic esophagus showed greater sensitivity to this reflex response than the cervical esophagus, and this response was sensitized by the exposure of the esophagus to acids [56].…”

“…All subreflexes of the SGB were blocked by vagotomy [56]. Local anesthesia of the esophageal mucosa blocked EURR, but could not trigger reflex activation of inhalation [56]. It is hypothesized that patients with a large number of GER that activate SGB over time learn to voluntarily initiate the SGB by rapid inhalation.…”

“…It is hypothesized that patients with a large number of GER that activate SGB over time learn to voluntarily initiate the SGB by rapid inhalation. Overall, belching can be learned [55], and swallowing is a digestive tract reflex response [54][55][56] that is activated voluntarily [57].…”