Mechanism of heartburn and damage

One unresolved issue in GERD is the inconsistent relationships among acid reflux, heartburn, and damage to the lining of the esophagus (esophagitis and the complications). Why do only a few of the many episodes of acid reflux that occur in a patient with GERD cause heartburn? Why do some patients with mildly increased acid reflux develop heartburn, while other patients with the same amount of acid reflux do not? Why does heartburn usually occur in an esophagus that is not damaged? Why is it that some patients with more damage to the esophagus have less heartburn than patients with no damage? Clearly, we have much to learn about the relationship between acid reflux and esophageal damage, and about the processes (mechanisms) responsible for heartburn. This issue is of more than passing interest. Knowledge of the mechanisms that produce heartburn and esophageal damage raises the possibility of new treatments that would target processes other than acid reflux.

One of the more interesting theories that has been proposed to explain some of these questions involves the reason for pain when acid refluxes. It often is assumed that the pain is caused by irritating acid contacting an inflamed esophageal lining. But the esophageal lining usually is not inflamed. It is possible therefore, that the acid is stimulating the pain nerves within the esophageal wall just beneath the lining. Although this may be the case, a second explanation is supported by the work of one group of scientists. These scientists find that heartburn provoked by acid in the esophagus is associated with contraction of the muscle in the lower esophagus. Perhaps it is the contraction of the muscle that somehow leads to the pain. It also is possible, however, that the contraction is an epiphenomenon, that is, refluxed acid stimulates pain nerves and causes the muscle to contract, but it is not the contraction that causes the pain. More studies will be necessary before the exact mechanism(s) that causes heartburn is clear.

Understanding

In a normal digestive system

* The muscles that line your digestive system push food along in one direction.
* Special muscles called "sphincters" serve as valves that squeeze shut between one section of your digestive system and the next. Ordinarily, they allow food to pass only in one direction.
* Acid in the stomach helps digest food. The stomach lining resists the damaging effects of this acid.

When GERD strikes

* The sphincter between the stomach and the esophagus becomes loose or relaxes at the wrong time, allowing stomach acid to flow into the esophagus (acid reflux).
* Repeated acid reflux causes erosions or sores in the lining of the esophagus ("erosive esophagitis"), leading to pain or discomfort.
* GERD symptoms can be worse at night.

What are the symptoms of uncomplicated GERD?

The symptoms of uncomplicated GERD are primarily heartburn, regurgitation, and nausea. Other symptoms occur when there are complications of GERD and will be discussed with the complications.

Heartburn

When acid refluxes back into the esophagus in patients with GERD, nerve fibers in the esophagus are stimulated. This nerve stimulation results most commonly in heartburn, the pain that is characteristic of GERD. Heartburn usually is described as a burning pain in the middle of the chest. It may start high in the abdomen or may extend up into the neck. In some patients, however, the pain may be sharp or pressure-like, rather than burning. Such pain can mimic heart pain (angina). In other patients, the pain may extend to the back. Since acid reflux is more common after meals, heartburn is more common after meals. Heartburn is also more common when individuals lie down because without the effects of gravity, reflux occurs more easily, and acid is returned to the stomach more slowly.

Episodes of heartburn may occur infrequently or frequently, but episodes tend to happen periodically. This means that the episodes are more frequent or severe for a period of several weeks or months, and then they become less frequent or severe or even absent for several weeks or months. Nevertheless, heartburn is a life-long problem, and it almost always returns.

Regurgitation

Regurgitation is the appearance of refluxed liquid in the mouth. In GERD, usually only small quantities of liquid reach the esophagus, and the liquid remains in the lower esophagus. Occasionally, and particularly in some patients, larger quantities of liquid, sometimes containing food, are refluxed and reach the upper esophagus.

At the upper end of the esophagus is the upper esophageal sphincter (UES). The UES is a circular ring of muscle that is very similar in its actions to the LES. That is, the UES prevents esophageal contents from backing up into the throat. When small amounts of refluxed liquid and/or foods breach (get through) the UES and enter the throat, there may be an acid taste in the mouth. If larger quantities breach the UES, patients may suddenly find their mouths filled with the liquid or food. What's more, frequent or prolonged regurgitation can lead to acid-induced erosions of the teeth.

Nausea

Nausea is uncommon in GERD. In some patients, however, it may be frequent or severe and may result in vomiting. In fact, in patients with unexplained nausea and/or vomiting, GERD is one of the first conditions suspected. It is not clear why some patients with GERD develop mainly heartburn and others develop mainly nausea.