GASTROENTEROLOGY 1993;105:755-763 Duodenal pH Dips as an Index of Transpyloric Do@ CHARLES H. MALBERT and YVES RUCKEBUSCH-f Depattment of Physlology, National Veterinary School, Toulouse, France Flow in Conscious Background: To determine if duodenal pH fluctuations might be used as a valuable index of the occurrence of gastric chyme ejection, the transpyloric flow and pH in the duodenal bulb were monitored simultaneously in six dogs. Methods: Transpyloric flow, monitored by a chronically implanted electromagnetic flowmeter, was represented by individual pulses of flow. Relations be- tween the volume of these flow pulses and changes in duodenal pH were assessed both postprandially and during the increased gastric outflow that followed gas- tric loading of buffered saline solutions at pH 2 and 4. Results: During fasting and gastric loading with buff- ered saline at pH 2, no consistent relationship between flow pulses and duodenal pH fluctuations was evident. After instillation of buffer solution at pH 4 and post- prandially, the magnitude of duodenal pH fluctuations became proportional to the stroke volume of the flow pulses. The removal of bile from the proximal duode- num decreased the relationship. Conclusions: It is con- cluded that duodenal pH measured at 2 cm from the pylorus might be used postprandially as an index of the transpyloric flow rate of chyme. R elationships between gastroduodenal motor events, gastric outflow of acidic chyme, and re- flux of alkaline duodenal contents have been investi- gated in dogs’ and humans. In conscious sheep, in- creases in duodenal pH that occurred during both quiescent and regular spiking activity phases of the migrating motor complex (MMC) were related to epi- sodes of decreased transpyloric flo~.~*~ In humans, Houghton et al. (1988) suggested that the duodenal pH dip, which followed antro-pyloro-duodenal contrac- tions, may be caused by the arrival of acidic chyme through the pylorus.5 The possibility that the duodenal pH value repre- sents a useful index of the passage of acidic chyme through the pylorus has been considered.5 However, the interpretation of any relationship between gastric outflow and duodenal acidification is complicated by possible effects of both gastri@ and duodenal’ motility. Thus, a lower duodenal pH could result simply from the sequestration or stagnation of acidic chyme within the duodenal bulb. That duodenal acidifìcation may represent quantitatively the volume of transpyloric outflow has not yet been tested in conscious animals. The aim of the present study was to investigate rela- tionships between the magnitude of duodenal pH changes and the volume of chyme entering the duode- num in conscious dogs. The volume of chyme flowing through the pylorussy” was continuously quantified by means of an electromagnetic probe,” and the corre- sponding pH changes were monitored on a pulse to pulse basis. Materials and Methods Experimental Surgery Halothane vapor anesthesia (4%, vol/vol) was first obtained for 3-4 minutes via a face mask and then main- tained at 1%2% (vol/vol) via an endotracheal tube using a semiclosed technique. Under aseptic conditions, four large male mongrel dogs, weighing 25-30 kg, were fitted with a flowmeter probe built as formerly described.” Briefly, the core of the probe was two curved toroid C-shaped magnets glued to each other to form a ring. The magnetic field was generated by a copper-coated wire turned around a C- shaped iron fold 100 times. After insulation of the magnet, two carbon electrodes, glued exactly in the middle of each C, recorded the induced current that was proportional to flow and magnetic field. The proximal edge of each probe was placed as close as possible (<2 mm) to the duodenal side of the pylorus. One week after this initial surgery, under identical anes- thesia, a gastric silicone cannula was fixed on the fundic part of the stomach. The arm of the cannula (ID 1 cm, OD 1.3 cm) was exteriorized on the left side of the dog, caudal to the last rib. The duodenum was also cannulated, at 8 cm from the pylorus, with a Y-type silicone cannula, which allowed an access to the duodenal bulb without altering the pyloric function, for pH measurements as in sheep.” The arm of this smaller-bore cannula (ID 0.4 cm, OD 0.7 cm) was ex- teriorized on the right side of the dog, behind the last rib. In two dogs, besides the probe and gastric and duodenal 1 Deceased. 0 1993 by the American Gastroenterological Association 0016-5065/93/$3.00