title: 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.
  
  
  OBJECTIVE
  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.
authors.affiliation: Science for Organizations, Inc., Chatham, NJ 07928, USA. gardnerj@scifororg.com
authors.forename: J D
authors.initials: JD
authors.lastname: Gardner
authors.forename: S
authors.initials: S
authors.lastname: Sloan
authors.forename: M
authors.initials: M
authors.lastname: Robinson
authors.forename: P B
authors.initials: PB
authors.lastname: Miner
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002940:Circadian Rhythm; D004947:Esophagus / Q000737:chemistry*; D005260:Female; D005744:Gastric Acid / Q000502:physiology; D005764:Gastroesophageal Reflux / Q000175:diagnosis*; D006356:Heartburn / Q000209:etiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008875:Middle Aged; D012016:Reference Values