The present study aimed to evaluate the patterns of antral contractility and pylorus opening and closure in relation to transpyloric flow of a nutrient liquid meal.
Ultrasound images of the antro-pyloro-duodenal tract were continuously tape-recorded in healthy volunteers for 1 h postprandially and were reviewed twice later by independent observers. Episodes and patterns of pylorus opening and closure, antral-wall contractions, and transpyloric flow were assessed separately and their time relations were identified.
Transpyloric flow (forward, 56%+/-13%; retrograde, 19%+/-11%; and to and fro, 25%+/-14%) occurred essentially during episodes of prolonged pylorus opening not associated with occlusive antral or duodenal proximal contraction, which represented the antro-pyloro-duodenal common chamber. The antro-pyloro-duodenal common chamber lasted on average 36+/-12 s and represented 41%+/-12% of the total observation period. Different patterns of antral contractions were identified according to whether they reached or occluded the terminal antrum and pylorus. Preterminal antral contractions (46%+/-12%) did not propagate beyond the proximal two thirds of the antrum. Terminal antral contractions (54%+/-12%) propagated along the entire antrum and could either occlude (20%+/-9%) or not occlude (42%+/-17%) the lumen. Pyloric opening independent of antral contractions and related to nonocclusive antral contractions could occur equally at the onset of the antro-pyloro-duodenal common chamber. Pyloric closure independent of antral contractions put an end to transpyloric flow in 73%+/-6% of the antro-pyloro-duodenal common chamber.
The final passage of contents from the stomach to the duodenum after the ingestion of a caloric liquid meal is the result of one or more episodes of uni- or bi-directional transpyloric flow, which are regulated by several motor events. The contractile states of the antrum and pylorus show specific features that variably interrelate to provide mixing and to regulate the transpyloric flow of ingesta. A crucial regulator of transpyloric flow appears to be the spatio-temporal relation between antral contractions and pyloric closure rather than the contractile events per se. An equal number of pyloric openings related, and unrelated, to antral contractions appears to determine the onset of the antro-pyloro-duodenal common chamber and, thus, of transpyloric flow. Pyloric closure unrelated to antral contractions appears to be the main mechanism that interrupts transpyloric flow. In conclusion, it appears that the antro-pyloro-duodenal tract acts as a functional unit in the digestion of a liquid caloric meal.