Use of an inert marker (phenol red) to improve accuracy in gastric secretion studies.

Gastric secretion from 24 subjects was collected by continuous nasogastric aspiration during the plateau of secretion evoked by intravenous histamine diphosphate, 0.01 mg/kg/hr. Simultaneously, phenol red was instilled at a constant rate into the proximal part of the stomach. Concentrations of phenol red in 15-minute aspirates were measured, and used to deduce pyloric losses and the reasons for random variation in the volumes aspirated. The average coefficient of variation in the volume was 26%, irrespective of the nature of the nasogastric tube. Correction by phenol red reduced this value to 21%. The coefficient of variation of volume diminished as secretion rate increased. Pyloric losses amounted to 7 ml/15 min, and were independent of the secretion rate. The quantitative effect of these errors upon the assessment of gastric secretion was minimal at high secretion rates but important at low rates.