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.
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