Everybody experiences gastro-oesophageal reflux on occasion. In health, reflux of air (“belching”) occurs most commonly during “transient lower oesophageal sphincter relaxations” (TLOSRs) triggered by gastric distension. Acid secretions and semi-digested food may also pass into the oesophagus during such events. Gastro-oesophageal reflux disease (GORD) is present when this reflux of gastric contents causes symptoms or mucosal damage.1 GORD patients do not necessarily have more TLOSRs than healthy controls.2 Rather, structural degradation and instability of the gastro-oesophageal junction increase the likelihood of reflux during TLOSRs and at other times (e.g. on straining).3 4 It is likely that the same changes allow greater volumes of gastric contents to pass the reflux barrier and to extend further into the oesophagus.5 6 Once reflux has occurred, ineffective motility and clearance are also important because prolonged exposure to acid and other noxious substances in refluxate (e.g. bile salts, pepsin) increase the risk of erosive reflux disease (ERD), Barrett’s columnar lined oesophagus (CLO) and other complications.7 8 Whether reflux triggers patient symptoms depends on a dynamic interaction between several factors, including patient age and sex, dietary factors, the volume, composition and distribution of the refluxate, mucosal disease, visceral sensitivity, and central factors including stress and patient vigilance (see box).5^–20

Oesophageal pH testing was popularised by Johnson and …