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Anorectal physiology in health: A randomized trial to determine the optimum catheter for the balloon expulsion test

We read with interest the original article by Mazor et al1 Evacuation of fecal surrogates of different size and consistency in defecation disorders is an important issue, and any effort to deal with it is welcomed. The balloon expulsion test (BET) has been recommended because it predicts biofeedback treatment outcomes, but it remains poorly standardized and is limited to referral centers.2,3 We reported a simple Foley catheter BET that we showed was a reliable method for identifying patients with dyssynergic defecation with 2 minutes as the optimal upper limit of normal. In addition, findings from the BET have a high level of agreement with those from anorectal manometry and pelvic floor electromyography on straining.4 The Mazor study was carefully done, but some of the findings are a challenge to our study: Foley balloons took significantly longer to evacuate than party balloons or commercially available catheters, and outcomes were more variable in ways the Mazor team could not explain. They reported that the Foley catheter could not be evacuated by 25% of 44 healthy controls (mean age: 56 years) within 3 minutes. Moreover, a fair percentage of subjects displaying < 45 mm Hg rectal pushing effort could not evacuate the Foley catheter while easily passing different devices. In contrast to this, in our study, all 40 of our young healthy subjects (mean age: 38 years) evacuated the balloon in 2 minutes (37 of 40 passed it in <60 seconds). More importantly, we tested evacuation times twice, and they were highly reproducible. The Foley BET significantly separated the constipated patients from the healthy controls. A measurement technique that is reproducible and that separates healthy subjects from controls is unlikely to be an artifact. Mazor's finding that Foley balloons are more difficult to pass than other balloons surprised us as we had not compared them directly. This might turn out to be important. However, there are other factors that may influence balloon evacuation times such as the instructions to patients, test environment, balloon consistency, and costs that are more difficult to identify. These findings should be replicated, and an informed decision made on which catheter to use for diagnostic testing. The Mazor et al study is a major milestone, although perhaps not the final one. Clinical utility and ease of standardization will be important considerations.