Relationship of transient lower esophageal sphincter relaxation to postprandial gastroesophageal reflux and belching in dogs.

Methods have been developed for the recording of patterns of motor function associated with spontaneous gastroesophageal reflux and belching in trained, unsedated dogs. Pharyngeal, esophageal body, lower esophageal sphincter (LES), and gastric pressures were monitored in 3 dogs with a manometric assembly inserted through a cervical esophagostomy. Spontaneous changes in esophageal pH were recorded simultaneously with a glass electrode. Each dog was studied three times for 3 h starting directly after completion of a full-sized meal. Acid reflux was recorded on 40 occasions; on 35 of these occasions it was possible to analyze, in detail, motor events at the time of reflux. This analysis showed that the LES was completely relaxed at the time of reflux and that the relaxation occurred within the 15 s before the onset of esophageal acidification. In 77% of the reflux episodes LES relaxation occurred independently of swallowing or any other motor event. The remainder of the LES relaxations associated with reflux were secondary to a swallowing salvo or a single swallow that did not trigger an esophageal body peristaltic wave. Straining was associated with reflux during many episodes of LES relaxation, but did not induce reflux if there was measurable LES pressure. Belching was also related to complete LES relaxations with a pattern identical to that associated with acid reflux. In the dog, liquid and gas reflux occurred during transient LES relaxations that were very similar to those that allow reflux to occur in humans. The dog is a suitable model for investigation of the nature and control of reflux associated with transient LES relaxation.