THE PH PCO2 METHOD FOR CONTINUOUS DETERMINATION OF HUMAN GASTRIC-ACIDAND BICARBONATE SECRETION - A VALIDATION-STUDY/

Background: The present paper describes and evaluates a methodologic a pproach for registration of the fast, interdigestive, motility-related changes in gastric acid and bicarbonate outputs seen in man. Methods: The technique is based on continuous gastric luminal perfusion and me asurements of pH and PCO2 in gastric effluent and concomitant intragas tric/duodenal manometry. Fourteen healthy volunteers participated. Res ults: Direct acid secretory estimations from pH recordings, corrected for hydrogen ion activity, correlated closely with values obtained by conventional titration. After intragastric infusion of bicarbonate, 96 +/- 5% of the newly measured steady-state value was registered virtua lly instantaneously provided that corrections for the PCO2 electrode t ime constant and the perfusion/aspiration time were made. In the neutr al pH range (pH 5-7), practically full quantitative recovery of intrag astrically infused bicarbonate was obtained. In the acid pH interval ( pH 2-5) the recovery was significantly lower (53 +/- 6%; p < 0.01). Wi th an aspirate without air admixture and during high perfusion rates ( 31 and 46 ml/min), full recovery of bicarbonate was obtained also at a n acid pH, whereas a reduced perfusion rate (16 ml/min) significantly (p < 0.05) reduced the recovery rate. Conclusions: With the pH/PCO2 te chnique both acid and bicarbonate assessments have a close to on-line time resolution. Acid output is measured accurately, but the method po tentially underestimates actual bicarbonate levels in the acid pH rang e, a combined effect of diffusion of CO2 into air bubbles in the aspir ate and into the gastric mucosa from the lumen. A high gastric perfusi on rate minimizes this source of error. The pH/PCO2 technique is well suited for studies of the interaction between secretion and motility i n the human stomach.