Normal people without symptoms of reflux do in fact reflux small quantities of acid into the oesophagus when either standing or sitting, but do not reflux acid when they are sleeping lying flat. This ;physiological' incompetence in the upright position is not of great importance in that the oesophagus is able to, and consistently does, deal with small concentrations of refluxed acid material. The oesophageal measurements of pH have a limited use as a diagnostic measure and may indicate acid reflux in the relaxed person not demonstrated by radiology.