Reflux episodes identified by combined impedance-pH monitoring

Impedance-measuring segments are located 3, 5, 7, 9, 15, and 17 cm above the lower esophageal sphincter (LES), the esophageal pH sensor 5 cm above the LES (bottom channel). Reflux episodes are detected by the rapid decline in impedance starting in the distal esophagus and over time advancing proximally (ie, retrograde bolus movement). The example on the left (A) is an acid reflux episode as esophageal pH declines from above to below 4.0. Note that the esophageal pH remains below 4.0 longer than the refluxate presence in the esophagus and is later cleared by a swallow. The example on the right (B) is a non-acid reflux episode as the esophageal pH remains above 4.0. Note that this reflux episode would have been missed by conventional pH monitoring alone.