Impedance testing is a type of test that uses a probe that inflates a balloon inside the esophagus and measures how much pressure it takes to expand it a certain amount. An esophagus that is stiffer or looser than normal may indicate a disorder is present.
Before the test, people do not eat or drink anything for 4 hours.
In this test, doctors pass a thin plastic tube (catheter) through the person's nose down into the esophagus (the hollow tube that leads from the throat to the stomach). The tube is covered with a balloon filled with salt water (saline solution). The balloon is used to measure the area across the inside of a part of the digestive tract, such as the esophagus, as well as the pressure inside that part. As the balloon is inflated, sensors along the balloon measure the pressure and diameter of the esophagus. Wires from the sensors transmit findings to a data recorder worn by the person. The pressure measurements and data help doctors further evaluate people who are having problems with their digestive tract, such as trouble swallowing. Impedance testing can also be done to detect any liquid that comes into the esophagus from the stomach, regardless of acidity, so doctors are able to measure both acid (using pH monitors) and non-acid reflux into the esophagus.
Sometimes impedance testing is combined with manometry, another test that measures pressure.
Impedance testing is used to diagnose a variety of gastrointestinal disorders, particularly in the esophagus. For example, this test can be used to evaluate problems with the nerves that control the rhythmic contractions of the esophagus (achalasia), evaluate an inflammatory disorder in which the wall of the esophagus becomes filled with large numbers of white blood cells (eosinophilic esophagitis), and possibly evaluate the backward flow of stomach contents into the esophagus (gastroesophageal reflux disease [GERD]). It can provide doctors with useful diagnostic information if no diagnosis can be made by using manometry or if people cannot tolerate manometry.
Additionally, impedance testing is sometimes done during and after people receive treatment for a digestive disorder. For example, people who are undergoing treatment for achalasia (such as surgery) have the test again because it can determine whether the treatment is working and can help doctors decide what further treatment is needed. The test may also be done in people who have had bariatric surgery or surgery for reflux (fundoplication).
Complications of impedance testing are uncommon and include injury to the nose, throat, or the esophagus.
