The role of excessive esophageal acid exposure in patients with gastroesophageal reflux disease.

Gastroesophageal reflux disease (GERD), especially reflux esophagitis (RE), is characterized by excessive esophageal acid exposure. Transient lower esophageal sphincter (LES) relaxation is the major mechanism of acid reflux episodes in both healthy subjects (HS) and patients with GERD. In the sitting position, where acid reflux episodes often occur, there is no difference in the frequency of transient LES relaxations between these two groups; however, in patients with GERD, at 5 cm above the LES, the proportion of acid reflux episodes during transient LES relaxations is significantly greater than in the HS group. This difference is considered to be one of the causes of excessive esophageal acid exposure in patients with GERD, but its cause is still unclear. A recent study, which investigated the proportion of acid reflux episodes during transient LES relaxations at 2 and 7 cm above the LES, showed that there was no difference at 2 cm above the LES between HS and patients with RE, but at 7 cm they were significantly greater in patients with RE than in HS. Evaluation of acid reflux at 2 cm above the LES is difficult to measure, but the proximal extent of refluxate could be one of the important factors of excessive acid esophageal exposure in patients with RE. Ineffective esophageal motility, found in patients with moderate to severe RE, impairs esophageal bolus clearance of acid, therefore both the proximal extent of refluxate and the delay of esophageal bolus clearance of acid could be major causes of excessive esophageal acid exposure. Hiatus hernia also causes acid reflux, due to its association with hypotensive LES, and also impairs esophageal bolus clearance of acid.