OBJECTIVE DETERMINATION OF PH THRESHOLDS IN THE ANALYSIS OF 24 H AMBULATORY ESOPHAGEAL PH MONITORING

In 24 h oesophageal pH monitoring, pH 4 is widely but arbitrarily used as the threshold between reflux and non-reflux pH values. The aim of the study was to define pH thresholds objectively, based on Gaussian c urve fitting of pH frequency distributions. Single-channel 24 h oesoph ageal pH monitoring was performed in 26 healthy volunteers and 26 pati ents with pathological gastro-oesophageal reflux, and five-channel pH; metry was performed in 14 healthy volunteers and 14 patients. The calc ulated pH thresholds varied between healthy volunteers from 5.0 to 6.4 in the upright position and from 4.5 to 5.7 in the supine position, b ut were constant between different oesophageal recording sites. In 15 and nine patients (single-channel and five-channel pH-metry respective ly), pH thresholds could not be determined at the distal oesophageal s ites. However, the calculated pH thresholds in the proximal oesophagus were in the same range as in the control subjects. The authors conclu de that the use of the conventional threshold of pH 4 leads to underes timation of the extent of gastro-oesophageal reflux, but are reluctant to advocate the use of higher thresholds in clinical practice.