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Have conventional pH monitoring techniques substantially underestimated the duration of acid exposure for the most distal segment of the oesophagus?
For a simple organ like the oesophagus, which functions primarily as a conduit, it is hard to imagine a more unpleasant neighbour than the stomach, a reservoir of concentrated acid constrained by a leaky valve. Studies using pH monitoring techniques developed in the 1970s have shown that the distal oesophagus of normal ambulatory individuals can be exposed to refluxed gastric acid (with pH <4) for up to 5% of a 24 hour monitoring period.1 Conventionally, oesophageal pH monitoring has been performed with the pH sensor positioned at a level 5 cm above the lower oesophageal sphincter (LOS). In a study reported in this issue of Gut, Fletcher and colleagues2 in Glasgow have found that conventional pH monitoring techniques have substantially underestimated the duration of acid exposure for the most distal segment of the oesophagus [see page 168].
To study acid exposure in the most distal oesophagus, the investigators devised a novel endoscopic technique for positioning a modified pH catheter, with two pH electrodes located 5 cm apart. A short prolene loop was attached to the catheter 5 mm below the distal pH electrode and the catheter was passed through the nose into the oesophagus. An endoscopic examination was performed, the junction of squamous and columnar epithelia (the Z line) in the distal oesophagus was identified, and an endoscopic clip was used to fix the prolene loop to the Z line. In this way, the distal pH electrode was anchored in the distal oesophagus at a level 5 mm above the Z line whereas the proximal electrode …