Current concepts of the antireflux barrier.

The lower esophageal sphincter, crural diaphragm, and phrenoesophageal ligament are the anatomic structures that constitute the antireflux barrier. The intraluminal pressure at the esophagogastric junction (EGJ) reflects the strength of the antireflux barrier. The end-expiratory pressure is a result of the tonic activity of the smooth muscles of the lower esophageal sphincter. The EGJ pressure increases during inspiration owing to the effect of the crural diaphragm. There is a reflex increase in the EGJ pressure during periods of increased intra-abdominal pressure, and the crural diaphragm contributes to this reflex contraction of the EGJ. Based on the contribution of the lower esophageal sphincter and crural diaphragm to the EGJ pressure, a two sphincter hypothesis of the antireflux barrier competence is suggested.