Late phase III of the interdigestive state is characterized by a retroperistaltic sequence in the descending duodenum followed by increases of antral pH. In this thesis the spatial organization of duodenal propagating pressure waves was further studied in the interdigestive state and postprandially. Furthermore, the relationship between interdigestive duodenal motility and luminal transport of duodenal contents and the potential effects of benzodiazepines (midazolam) on small bowel motility were studied. Antroduodenal manometry with a high temporospatial resolution technique was performed in healthy subjects. The intraluminal transport of a duodenal marker and a bile marker was studied by scintigraphy. In the most juxtapyloric duodenum the pressure waves were mainly retrograde in both early and late phase III (medians, 66 and 83%, respectively) and postprandially (40-50%). The duodenal propagating pressure waves of phase III were divergent along the entire duodenum with a proximal retrograde and a distal antegrade propagation direction from the start site of the pressure waves. The start site of the contractions moved gradually distal in the duodenum. There were no pyloric contractions during the retroperistaltic sequence of late duodenal phase III. The retroperistaltic activity fronts were always (100%) followed by retropulsion of duodenal marker to the stomach. A clear-cut reflux of bile marker was seen in only 17% of the activity fronts. Instead, the bile marker contents increased abruptly in the gallbladder during phase III. The incidence rate of duodenogastric reflux was highest in phase III compared with phase II (p<0.008). Midazolam affected only five out of 28 small bowel motility variables, e. g., shortening of MMC-duration, but duodenal phase III retroperistalsis was preserved.Conclusions: The duodenal contractions of phase III are divergent with retropropagation in the proximal part. The retroperistalsis is selectively propelling alkaline refluxate of duodenal origin to the stomach in late duodenal phase III. This physiologic duodenogastric reflux is aided by a non-contracting pylorus. Divergent contractions are also common postprandially in the juxtapyloric duodenum, tentatively contributing to gastric emptying regulation. Benzodiazepines, as studied by midazolam, have few motility effects and do not affect the phase III-related retroperistalsis
