Esophageal acid clearance.

Esophageal acid clearance is an important defense against the development of reflux esophagitis. Acid clearance normally occurs in two sequential steps. One or two peristaltic sequences empty virtually all acid volume from the esophagus, leaving a minimal residual that sustains a low pH, and then the residual acid is neutralized by swallowed saliva. The ability of saliva to neutralize acid is primarily due to bicarbonate. Saliva flow normally increases concurrent with the onset of heartburn. Hypersalivation with heartburn, commonly referred to as waterbrash, may be a protective response to gastroesophageal reflux. Gastroesophageal reflux and esophageal acid clearance normally do not occur during sleep. Acid clearance may be delayed markedly in the event that a subject falls asleep before clearance of acid from the esophagus is complete. Esophageal acid clearance may be prolonged by abnormal esophageal emptying or impaired salivation in patients with gastroesophageal reflux disease.