Normal and abnormal proximal esophageal acid exposure: results of ambulatory dual-probe pH monitoring.

Ambulatory esophageal pH monitoring was performed in 26 normal volunteers, 20 patients with normal distal acid exposure, and 23 patients with abnormal distal acid exposure in an attempt to define normal values for proximal esophageal acid exposure using a standardized technique. We used a dual pH sensor with antimony electrodes spaced at 15 cm. The distal electrode was placed manometrically at 5 cm above the lower esophageal sphincter. Proximal electrode thus was located below the upper esophageal sphincter in the esophageal inlet. The patients underwent 24-h ambulatory pH monitoring and were told to pursue normal daily activities. The percentage of acid exposure time and number of episodes per 24 h at both pH < 4.0 and 5.0 were measured for the total, upright, and supine periods. Since the pH values were not normally distributed, the medians and 95th percentiles were used to define normal values. Minimal acid exposure occurred in the proximal esophagus (< 1% total; 0% supine) in volunteers and patients with normal distal reflux. Patients with abnormal distal acid exposure had significantly greater proximal reflux.