Relative contributions of "pressure pump" and "peristaltic pump" to gastric emptying

The relative contributions to gastric emptying horn common cavity antroduod enal pressure difference ("pressure pump") vs. propagating high-pressure wa ves in the distal antrum ("peristaltic pump") were analyzed in humans by hi gh-resolution manometry concurrently with time-resolved three-dimensional m agnetic resonance imaging during intraduodenal nutrient infusion at 2 kcal/ min. Gastric volume, space-time pressure, and contraction wave histories in the antropyloroduodenal region were measured in seven healthy subjects. Th e subjects fell into two distinct groups with an order of magnitude differe nce in levels of antral pressure activity. However, there was no significan t difference in average rate of gastric emptying between the two groups. An tral pressure history was separated into "propagating high-pressure events" (HPE), "nonpropagating HPEs," and "quiescent periods." Quiescent periods d ominated, and average pressure during quiescent periods remained unchanged with decreasing gastric volume, suggesting that common cavity pressure leve ls were maintained by increasing wall muscle tone with decreasing volume. W hen propagating HPEs moved to within 2-3 cm of the pylorus, pyloric resista nce was found statistically to increase with decreasing distance between pe ristaltic waves and the pylorus, We conclude that transpyloric flow tends t o be blocked when antral contraction waves are within a "zone of influence" proximal to the pylorus, suggesting physiological coordination between pyl oric and antral contractile activity. We further conclude that gastric empt ying of nutrient liquids is primarily through the "pressure pump" mechanism controlled by pyloric opening during periods of relative quiescence in ant ral contractile wave activity.