Reliability of esophageal studies depends on experience
Tests for esophageal motor dysfunction and acid exposure have improved significantly in the last decade. High-resolution manometry (HRM) has replaced conventional manometry as the gold standard for assessing esophageal motility; impedance pH monitoring is an improvement over earlier pH tests; and the wireless Bravo system provides an option for patients who can't tolerate catheter-based pH studies or need longer monitoring. All three tests are used at Mayo Clinic's multidisciplinary esophageal clinic in Rochester, Minn.
High-resolution manometry with impedance monitoring
Manometry assesses motor function in the esophagus by measuring pressures generated by the esophageal muscles and sphincters. Conventional and high-resolution manometry differ mainly in the number of pressure sensors on the esophageal catheters. Conventional manometry uses catheters with four to eight sensors. HRM catheters, on the other hand, have 20 to 36 sensors spaced .4-inch (1 centimeter) apart, leading to greatly improved accuracy in the diagnosis of motility disorders.
HRM also allows more versatility in data analysis and is better tolerated by patients. The tube is more flexible and easily placed, and the actual test time — 10 to 20 minutes — is considerably shorter. Combined with intraluminal impedance monitoring, which measures the flow of liquids and gas in the esophagus, HRM can provide a far more complete study than previous tests.
But David A. Katzka, M.D., of Mayo Clinic in Minnesota, says that optimal use of HRM and impedance monitoring requires a thorough understanding of how the systems work and a high skill level in performing and interpreting the tests.
"These state-of-the art tests are really exciting," he says. "But it's important that they are performed and read by providers who do hundreds of them a year. With manometry, a computer generates an interpretation that is frequently wrong, and physicians who don't do many of these tests tend to rely on the computer-generated diagnosis. In low-volume centers, the diagnosis can be wrong 25 percent of the time."
Impedance testing also has a steep learning curve, but the test can be extremely accurate when performed in centers with high volumes.
Ambulatory impedance pH monitoring
Like HRM, esophageal impedance pH monitoring is a great advance over older methods. Impedance tests measure resistance to electrical currents generated by different substances. Air, for instance, has very low conductivity and therefore high impedance, whereas the conductivity of gastric juices is high, resulting in decreased impedance.
Alternating patterns of impedance throughout the esophagus can help assess the composition and duration of all types of reflux, from acidic to mildly alkaline, and the emerging data on nonacid reflux is likely to lead to novel reflux treatments.
But once again, experience in interpreting the test is essential. Dr. Katzka says, "You really need to look at hundreds of these tests on a regular basis to learn pattern recognition. Otherwise, it's easy to over- or undercall."
Bravo probe study
Consisting of a small pH capsule that attaches to the distal esophagus and a data receiver worn on the patient's waist, the wireless Bravo system is an alternative to 24-hour ambulatory pH testing. Intended mainly for people unable to tolerate catheter-based tests, it is used in about 10 percent of patients at Mayo Clinic. Although it does not measure nonacid reflux, the Bravo system does measure all episodes of acid reflux over a 96-hour period and so may prove increasingly useful for evaluating patients with mild, intermittent symptoms.
Ultimately, Dr. Katzka says, all technologically advanced tests are only as good as the people performing them. "We perform around 1,200 high-resolution manometries a year and have seen the difference experience makes," he says.