Twenty-four-hour gastric luminal pH in normal subjects: influence of probe position, food, posture, and duodenogastric reflux.

Objectives: The aim of this study was to determine the gastric pH at different levels in the stomach under varying physiological circumstances.

Methods: Simultaneous 24-hour ambulatory gastric pH monitoring was performed with multiple electrodes in 24 normal subjects, divided into groups of six, to study the influence of food, the supine posture, and physiological duodenogastric reflux on gastric pH in different parts of the stomach. In 18 subjects, simultaneous recordings were made from two electrodes positioned 5 and/or 10 cm below the manometrically-defined lower border of the lower esophageal sphincter and, in six subjects, from three electrodes, one positioned 5 cm below the lower esophageal sphincter and two others positioned 5 and 8 cm proximal to the pylorus.

Results: During the daytime fasting period, pH was homogenous across the stomach with most time being spent between pH 1 and 2. Marked similarities in recorded pH were noted when two probes were placed in the stomach at the same level, indicating regional consistency in the pH of the chyme. This finding was observed when probes were free from each other or tethered together. Food increased pH most in the fundus, less in the midstomach, and least in the antrum. At night, when supine, alkaline shifts occurred in the distal stomach, most likely because of physiological duodenogastric reflux. These were commonly recorded in the antrum but only occasionally in the proximal stomach.

Conclusions: Measurement of the gastric pH environment requires standardization of the probe position, of feeding, and of posture, and global measurement of gastric pH requires simultaneous recording in both the proximal and distal stomach.