Multichannel intraluminal impedance: New insights into GERD and esophageal function testing
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Corresponding author Michael F Vaezi, MD, PhD, MSc(Epi) Division of Gastroenterology and Hepatology, Vanderbilt University Medical Center, 1660 TVC, 1301 22nd Avenue South, Nashville, TN 37232-5280, USA. E-mail: [email protected] Current GERD Reports 2007, 1:28 –38 Current Medicine Group LLC ISSN 1934-967X Copyright © 2007 by Current Medicine Group LLC
Multichannel intraluminal impedance (MII) is an evolving technique for the evaluation of gastroesophageal reflux disease (GERD) and of nonacid reflux in patients with persistent typical or atypical GERD symptoms refractory to acid suppression therapy. Similar to barium swallow, it can assess esophageal bolus transit, but without the hazards of radiation exposure. MII is frequently used in combination with pH monitoring to detect esophageal exposure to gastroduodenal content. This combination detects all types of reflux, the pH of the reflux, and the proximal extent of a reflux event. MII can be used in combination with esophageal manometry to allow concurrent assessment of esophageal function (bolus transit) and motility. Thus, it provides a more complete esophageal function test than esophageal manometry alone. The few limitations of impedance monitoring include the complexity of the interpretation of the tracings and the paucity of data in diseased populations. However, recent developments over the past 2 years have overcome these limitations, improving the detection of GERD and the evaluation of various esophageal function abnormalities.
Introduction Traditionally, gastroesophageal reflux (GERD) has been evaluated by ambulatory pH monitoring and esophageal function testing by manometry. The introduction of multichannel intraluminal impedance (MII) as a new technique to evaluate esophageal function promises to enhance the detection of esophageal abnormalities. This test uses inherent conductive or resistive properties of
the intraluminal bolus (liquid, gas, or mixed) to examine the presence and transit of the bolus in the esophageal lumen. Two variations of MII have been introduced for clinical use: combined MII and pH monitoring (MII-pH), and combined MII and manometry (MII-EM). MII-pH permits differentiation of the refluxate as either acid or nonacid and is useful for the evaluation of GERD. MIIEM allows concurrent measurement of the esophageal contraction and corresponding bolus movement and can be used for esophageal function testing. This article reviews the principles of impedance testing, the clinical utilities of MII-pH and MII-EM, and their limitations.
MII: Basic Principles Impedance is a measure of total resistance to the alternating current flow. In MII testing, impedance is measured between two electrodes spaced 2 cm apart (impedancemeasuring segment). The electrodes are connected to an impedance voltage transducer outside the body via thin wires that run the length of the catheter. The voltage generated by the transducer is limited to produce at most 8 μA of current, which is 1000-fold below the threshold for cardiac stimulation [1]. The act
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