High Pressure Zone (HPZ) Created By the Antireflux Barrier

Ever wonder how your stomach contents defy gravity and don’t leak out when you hang upside down?

Understanding the complexity of how the high pressure zone forms the antireflux barrier helps explain this phenomenon and leads to a better understanding of why heartburn happens.

In Part I, we discussed all the physical structures. In Part 2, we get into the details of how they all work together.

The antireflux barrier (ARB) is composed of well-defined structures that work synergistically to keep stomach contents out of the esophagus. The components of the ARB are:

  • the gastroesophageal valve (GEV)
  • the lower esophageal sphincter (LES)
  • the crura of the diaphragm, which “pinch” the distal esophagus aiding in closing the esophagus,
  • the intraabdominal esophagus which is exposed to positive intraabdominal pressure
  • esophageal peristalsis, motility and clearance

The anatomy of the esophagogastric junction has been known for a long time. What has changed is the understanding of how it works. In 1985, Boyle started to understand the role of the diaphragm compression on the structures in the region in a study made in cats.[1-2] Since then, more and more studies have helped clarify the functions of the EGJ.

The HPZ at the LES is created by a series of structures and physiological events:

  • The LES, although small, provides a sphincter-like function by a higher and maintained contraction tonus
  • The crura of the diaphragm add to this pressure, the HPZ is higher on the left side because of the anatomy of the region, causing the left crus of the respiratory diaphragm to exert a higher pressure on the left side of the esophagus
  • The intraabdominal pressure is higher on the abdominal region than in the thoracic region, helping close the abdominal esophagus

It is important to understand that the failure of any of these structures to perform its function can be the cause of GERD, as the higher intraabdominal pressure will force the gastric content towards the thoracic esophagus.

GERD is a progressive disease with symptoms that start with occasional episodes of heartburn. As the anatomical structures and HPZ break down, the frequency and intensity of reflux symptoms increase.


[1] Boyle JT, et. Al, Gastroenterology.1985 Mar;88(3):723-30.

[2] Boyle JT, et. Al, Am J Physiol.1987 Sep;253(3 Pt 1):G315-22.