Computerized ambulatory esophageal pH monitoring in 50 asymptomatic volunteer subjects. Results and clinical implications.

Fifty asymptomatic volunteer subjects underwent prolonged computerized ambulatory distal esophageal pH monitoring to characterize acid reflux patterns. A bimodal distribution of data, which corresponded to the erect and supine positions, occurred in 45 subjects, and separate mean baseline pH values were noted for the erect and supine positions (pH 6.46 and pH 5.46, respectively, p less than 0.001). At esophageal pH 4, reflux episodes occurred more commonly in the erect position (44 percent) than in the supine position (20 percent). There were also significantly greater numbers of reflux events and longer durations when the pH was below 3 (p less than 0.02) and 4 (p less than 0.001) in the erect compared with the supine position, but prolonged events (more than 10 minutes) occurred in both positions. Postprandial reflux occurred in 78.7 percent of the subjects, with an average of 5.1 episodes. A slight but significant correlation between age and erect reflux was seen (p less than 0.04). In the pH 3 to 5 range, 18 percent of the subjects had acid exposure in excess of the group mean plus 2 standard deviations and 10 percent in excess of the mean plus 3 standard deviations. Overall, a nonnormal distribution of pH data was found with 28 subjects having less than 1.6 percent of their values below pH 4. This finding may represent either the true spectrum of normal acid reflux or a subclinical pathologic state that will become symptomatic over time.