Validation of an ambulatory esophageal pH monitoring system.

The present study documents the accuracy of a commercially available ambulatory esophageal pH instrument. The distal esophagus of five subjects with daily heartburn was monitored for 24 h in the laboratory via an antimony pH electrode. The computer output from the ambulatory unit was compared to the on-line recording in terms of all events in which the pH dropped below four. A signal detection model was used, with an on-line pH tracing serving as the criterion response. The events noted as true positives (80%) were an accurate representation by the computer output of the events of pH less than four displayed by the on-line recording. The processing done by this particular ambulatory system tends to actually "ignore" transient pH drops (18% false negatives) and, may, in fact, provide more physiologically meaningful information than hardwired analog techniques for 24-h pH monitoring. The results confirm that ambulatory pH monitoring can produce meaningful and reliable physiological data concerning gastroesophageal reflux.