Comparison of the Bravo™ wireless and Digitrapper™ catheter-based pH monitoring systems for measuring esophageal acid exposure

INTRODUCTION: We compared esophageal acid exposure data obtained during simultaneous esophageal pH studies using the Bravo™ wireless and the Slimline™ catheter-Mark III Digitrapper™ pH systems. METHODS: Twenty-five asymptomatic subjects underwent endoscopy with endoclip placement at the squamocolumnar junction (SCJ) and manometry to localize the lower esophageal sphincter (LES). A Bravo™ capsule was placed 6 cm above the SCJ and a Slimline™ catheter 5 cm above the LES. Relative positions were checked fluoroscopically. Synchronized pH data were compared by manual extraction into Excel spreadsheets. An in vivo pH reference was established with swallows of orange juice (pH 3.88). RESULTS: Median acid exposure time was greater with the Slimline™ compared to the Bravo™ system (Slimline™, 3.4%; Bravo™, 1.76%, p < 0.05) but electrode positions were similar. The dominant source of discrepancy between systems was an offset in recorded pH values around pH 4 as evidenced by the recorded values of the swallowed orange juice. Bench-top testing suggested that this offset was mainly attributable to the software designed to compensate for the difference in electrode recording characteristics between room and body temperature. After adjusting the pH data sets to accurately reflect actual orange juice pH, acid exposure between systems was similar (Slimline™, 0.90%; Bravo™, 1.15%). CONCLUSION: The Slimline™ system on average over-recorded esophageal acid exposure compared to the Bravo™ system largely because of a flawed software scheme for electrode thermal calibration. Accuracy of pH data sets from both systems can be improved by scrutiny for artifacts and use of an in vivo pH reference.