Impedance-pH Test

Combined multi-channel intraluminal impedance and pH (MII-pH) has become the new GOLD standard in esophageal testing. In many laboratories across the world this test has replaced traditional pH testing. The weakness of standard pH test is that it only detects reflux episodes during which the pH drops below 4.0. It therefore provides limited information on reflux episodes during which the pH doesn´t drop below 4.0 (i.e. nonacid reflux). This limitation has become even more important as doctors routinely prescribe proton pump inhibitors (PPI’s), leading to a change in pattern of GERD patients referred for consultation. Specialists with an interest in reflux disease (Gastro specialists but also ENT’s, Pulmonologists amongst other) are more regularly consulted regarding patients with persistent GERD symptoms on acid-suppressive therapy.

Reflux is detected by changes in intraluminal resistance determined by the presence of liquid or gas inside the esophagus, and pH data are used to classify reflux as acid or nonacid or weakly acid. Combined MII-pH is the preferred method of testing patients with persistent symptoms on acid suppressive therapy, as it can clarify whether symptoms are associated with acid or nonacid reflux or not associated with reflux at all.

Principles of MII-pH Testing

In1991 multichannel intra luminal impedance (MII) was a method of detecting intraesophageal bolus movement. This method is based on measuring the resistance to alternating current (i.e. impedance) of the content of the esophageal lumen. When a pair of electrodes, separated by an isolator (i.e., catheter), is placed inside the esophagus, the electrical circuit is closed by electrical charges (i.e., ions) present in the esophageal mucosa that surround the catheter. The conductivity of the empty esophageal lumen is relatively stable, with the electrical circuit registering values around 2000 to 4000 ohm. The appearance of a liquid bolus in the impedance-measuring segment is recognized as a rapid drop in impedance as the increased ionic content of the bolus improves the electrical conductivity between the two electrodes. The impedance will remain low as long as the bolus is present between the two electrodes and will start rising once the bolus is cleared from the segment by a contraction. The presence of gas in the impedance-measuring segment is recognized by a rise in impedance typically above 5000 ohm, as there are no electrical charges to close the circuit when the two electrodes are suspended in air. Impedance will return to the baseline values once the air bolus has passed and the electrodes are back in contact with the esophageal mucosa.

Advantages of MII-pH using the ZepHr Monitor

• one can now test ALL acid refulx (non-acid and weakly acids too)
• the test is completely mobile, as an LES locator is used
• one can test for symptom correlation and see whether it is a reflux induced symptom, or a symptom induced reflux
• The MII-pH test can be done while patient is on PPI.
• Greater diagnostic information

tags flagship1; impedance; ph, leenyx, zephr; reflux; esophageal, non-acidic,