Non-acid gastroesophageal reflux: documenting its relationship to symptoms using multichannel intraluminal impedance (MII).

Multichannel intraluminal impedance (MII) is a new technique for evaluating esophageal function and gastroesophageal reflux. This technique depends on changes in resistance to alternating current between two metal electrodes produced by the presence of liquid or gas bolus inside the esophageal lumen. Combined multichannel intraluminal impedance and manometry (MII-EM) provides simultaneous information on intraluminal pressure changes and bolus movement whereas combined multichannel intraluminal impedance and pH (MII-pH) allows detection of gastroesophageal reflux (GER) episodes irrespective of their pH values (i.e. acid and non-acid reflux). Combined MII-pH testing presents a new paradigm for reflux testing. In MII-pH studies reflux events are no longer primarily detected by pH. Refluxate presence, distribution and clearing is primarily detected by MII and simply characterized as acid or non-acid based on pH change and as liquid, gas or mixed based on MII. MII determines refluxate clearance time while pH measures acid clearance time. MII-pH shows promise to become an important clinical tool, particularly to assess GER in the postprandial period and in patients with persistent symptoms on acid suppression therapy.