The effects of paraoesophageal structures and vagotomy on the canine lower oesophageal sphincter function.

The effects of paraoesophageal structures and vagotomy on lower oesophageal sphincter (LOS) function were studied in the dog using modern oesophageal manometric technique. The isolation of the gastro-oesophageal junction from surrounding structures by a stiff-walled Silastic-tube led to a slight decrease in LOS pressure, but the difference was not statistically significant. LOS response to abdominal compression also decreased slightly, but the difference was without statistical significance. Bilateral transabdominal, transthoracic and cervical vagotomy did not produce any marked changes in resting LOS pressure, whereas a statistically significant decrease in LOS response to abdominal compression occurred after each type of vagotomy. The results suggest that the mechanism intrinsic to the gastro-oesophageal junction, the LOS, is mainly responsible for the maintenance of gastro-oesophageal competence, and the effect of extrinsic paraoesophageal structures is of minor importance. The vagus nerves apparently have no major role in the maintenance of resting LOS pressure. LOS response to increased intra-abdominal pressure seems to represent a genuine increase in LOS tone, to which extrinsic mechanical factors add only a small contribution. This response seems to be mediated by a vagal reflex arc, the afferent part of which has its origin below the diaphragm.