Duodenal acid clearance in humans: observations made with intraluminal impedance recording

Duodenal acid clearance appears to be involved not only in the pathogenesis of duodenal ulcer disease but also in functional dyspepsia. Duodenal contractile activity can help to maintain neutral pH in the duodenum by mixing acid with bicarbonate or by aborally transporting the acid load. Intraluminal impedance recording, allowing the detection of nonacid liquid boluses, can be carried out concomitantly with antroduodenal manometry and pH recording and may thus provide useful information about the mechanisms involved in duodenal clearance of endogenous acid and volume boluses. Eight H. pylori-negative healthy volunteers were studied with two catheters positioned across the pylorus, allowing the recording of five impedance signals (one antral, one pyloric, and three duodenal) simultaneously with six pressure signals (two antral, one pyloric, and three duodenal) as well as distal antral and proximal duodenal pH. During phase II of the migrating motor complex, which is known to be associated with the highest duodenal acid exposure, each duodenal acidification event (defined as a pH drop >2 pH units) was characterized by its maximal amplitude, duration, temporal relationship with antroduodenal manometric events, and relation to impedance variations. Acid was considered to have been cleared from the duodenum when the preacidification pH was restored (+/-0.2 unit). A total of 164 duodenal pH drops were recorded during the 323 min of phase II recordings. Eleven percent of the duodenal acidification events were short-lived (<10 sec). All of these events were temporally associated with a propagated antroduodenal contraction and a short-lived drop in impedance, suggesting rapid aboral passage of the acid bolus. The long-lived duodenal acidification events lasted a mean of 32 sec (range, 25-66 sec). In 90% of these events an antroduodenal propagated contraction was recorded at the time of onset. Repetitive duodenal contractions followed the onset of the long-lived acidification events in 34% of the cases. These remained present until complete clearance of the acid. In 81% of the long-lived acidification events, recovery of the associated impedance drop occurred simultaneously with the pH recovery, suggesting a complete clearance of the bolus. Less frequently (19%), the duodenal pH recovered while the impedance remained low, suggesting that the bolus was not cleared but neutralized. Interdigestive duodenal acidification events usually last about 30 sec. They evoke duodenal contractions in only one-third of cases. Combined pH and impedance recording makes it possible to distinguish between neutralization of acid boluses and their complete total clearance.