Ambulatory oesophageal pH-impedance monitoring is a widely used test to evaluate patients with reflux symptoms. Several types of pH electrodes are available: antimony, ion sensitive field effect transistor (ISFET), and glass electrodes. These pH electrodes have not been compared directly, and it is uncertain whether these different types of pH electrodes result in similar outcome.
In an in-vitro model the response time, sensitivity, and drift of an antimony, ISFET, and glass pH electrode were assessed simultaneously after calibration at 22 °C and at 37 °C. All measurements were performed at 37 °C and repeated five times with new catheters of each type. Fifteen patients with reflux symptoms underwent 24-h pH monitoring off PPI therapy using antimony, ISFET, and glass pH electrodes simultaneously.
After calibration at 22 °C, pH electrodes had similar response times, sensitivity and drift. In contrast to glass electrodes, antimony electrodes performed less accurately after calibration at 37 °C than after calibration at 22 °C. Calibration temperature did not affect ISFET electrodes significantly. During in-vivo experiments, significant differences were found in acid exposure times derived from antimony (4.0±0.8%), ISFET (5.7±1.1%), and glass pH electrodes (9.0±1.7%).
In vitro, antimony and glass pH electrodes are affected by different buffer components and temperature, respectively. In vivo, significant higher acid exposure times are obtained with glass electrodes compared with antimony and ISFET pH electrodes. ISFET electrodes produce stable in-vitro measurements and result in the most accurate in-vivo measurements of acid exposure time.
aDepartment of Gastroenterology, Sint Antonius Hospital, Nieuwegein
bGastrointestinal Research Center, University Medical Center, Utrecht, The Netherlands
Correspondence to Dr Gerrit J.M. Hemmink, MD, Department of Gastroenterology, Sint Antonius Hospital, PO Box 2500, 3430 EM Nieuwegein, The Netherlands
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Received 21 June 2009 Accepted 16 September 2009