Long-term recording and computer analysis of simultaneous gastric and duodenal pH under normal conditions in man

A technique has been developed to make simultaneous digital recordings of gastric and duodenal pH. An intraluminal miniature glass electrode assembly has been maintained in a stable position in the duodenal bulb and stomach in 34 out of 41 studies. The pH data can be logged by a transportable system at up to one second intervals for periods of 24 hours. The subject leads a nearly normal life whilst the effect of meals, drinks, smoking and medications are studied. The digital format of the data is suitable for computer analysis and allows calibration and drift correction factors to be applied. Computer program options provide a graphical representation of the corrected pH data as well as the arithmetic mean pH, mean hydrogen ion activity, log mean hydrogen ion activity and the percentage of total readings above and below any chosen pH level, for any selected block of data. An analogue technique has been used to study the response characteristics of the recording system and the spectrum of frequencies of duodenal pH readings. Although rapid changes in duodenal pH often occur, frequencies were nearly always less than 1.5-2.0 Hz.