Duodenal bulb pH in normal subjects.

Four pH electrodes strapped together at 1 X 5 cm intervals were positioned in the pyloric region. Electrodes situated in the stomach record steady acid pH while electrodes distal to the pylorus show fluctuating pH, thereby enabling the electrodes to be localized from the pH pattern. Digital pH values were sampled and stored at a rate of 2/s from each electrode. For each 10-min period, the mean hydrogen ion activity, the percentage of time that the pH was at less than 3.0 and number of pH spikes were computed. Fourteen healthy subjects were studied in the fasting state and for 3 h after 300 ml chocolate milk. Log mean hydrogen ion activity in the proximal part of the duodenal bulb was (median and interquartile range): fasting pH 2.40 (2.23-3.00); 0-60 min after meal: pH 5.7 (4.92-5.95); 60-120 min: pH 2.31 (1.95-3.20) 120-180 min: pH 2.20 (1.99-2.44). Repeated studies in twelve subjects showed a linear correlation between 1st and 2nd study, r = 0.87. A significant linear correlation was found between peak acid output to pentagastrin and postprandial bulb acidity.