Computerized identification of pathologic duodenogastric reflux using 24-hour gastric pH monitoring. Duodenogastric reflux is a naturally occurring sporadic event, the incidence, occurrence, and detrimental effects of which have been difficult to assess. The reliability of 24-hour gastric pH monitoring to detect duodenogastric reflux was studied. Central to the use of pH monitoring for this purpose is confidence in its ability to measure and display pH data in a way that reflects changes in the gastric pH environment with sufficient sensitivity. To test this the gastric pH of 10 dogs was measured in the fasting state, after feeding, and after pentagastrin stimulation. The antrum was more alkaline in the fasting state (p less than 0.01) and the display of data by frequency distribution graph was sensitive enough to reflect induced pH changes. To test the consistency of gastric pH at a given position, simultaneous 24-hour gastric monitoring was performed in 12 normal subjects with two probes placed at either 5 or 10 cm below the lower esophageal sphincter. Only at the 5-cm position did the two probes read within 1 pH unit of each other more than 90% of the time. Based on these principles, gastric pH monitoring was performed 5 cm below the lower esophageal sphincter in 30 normal subjects and 11 patients, fulfilling Ritchie's clinical criteria for pathologic duodenogastric reflux. The data obtained was arranged into 71 variables and subjected to discriminant analysis. Sixteen variables were identified, each with a corresponding coefficient to be used as a multiplier to derive a score. A score of more than +2.2 indicated a high probability of pathologic duodenogastric reflux. The test was applied to a validation population consisting of 10 additional normal subjects and 10 patients meeting Ritchie's criteria. All normal subjects had a normal score and all but one (90%) of the patients had an abnormal score. When compared to O-diisopropyl iminodiacetic acid (DISIDA) scintigraphy in another group of 22 normal subjects and 60 patients, 24-hour gastric pH monitoring was superior in the detection of pathologic duodenogastric reflux. The study shows how the application of computer technology can be used to diagnose pathologic duodenogastric reflux in patients with complex foregut complaints. 