Oesophageal pH has a power-law distribution in control and gastro-oesophageal reflux disease subjects

Abstract

Background: We are unaware of any solid theoretical or pathophysiological basis for selecting pH 4 or any other pH value to assess oesophageal acid exposure or to define oesophageal reflux episodes. Aim: To examine the frequency of different oesophageal pH values in control and GERD subjects. Methods: Oesophageal pH was measured for 24 h in 57 gastro-oesophageal reflux disease subjects and 26 control subjects. Histograms were constructed using the 21 600 values from each recording and bins of 0.25 pH units. Results: Compared with controls, gastro-oesophageal reflux disease subjects had significantly more low pH values and significantly fewer high pH values. In both gastro-oesophageal reflux disease and control subjects, the frequency of oesophageal pH values was characterized by a power-law distribution indicating that the same relationship that describes low pH values also describes high pH values, as well as all values in between. Conclusions: The distribution of oesophageal pH values indicates that a variety of different pH values can be used to assess oesophageal acid exposure, but raises important questions regarding how oesophageal reflux episodes are defined.