CONTRACTIONS MOVE CONTENTS BY CHANGING THE CONFIGURATION OF THE ISOLATED CAT STOMACH

To understand how contractions move gastric contents, we measured, in isolated cat stomachs, the effects of contractions on gastric length, diameters, pressures, and emptying. Movements of the stomach and of ga stric contents were monitored by video camera and ultrasound and were related to mechanical events. Based on pressures, we defined the follo wing four phases of contractions: 1) P-0, a steady pressure associated with tonic contraction of proximal stomach; 2) P', a pressure wave du ring which the contraction indents the gastric body; 3) a pressure nad ir while the contraction lifts the gastric sinus toward the incisura; and 4) a second pressure wave, P '', as the contraction advances throu gh the antrum. In open preparations, liquid output and shortening of t he greater curvature are large during P-0, stop during P', and resume with P ''. Contractions generate higher pressures when gastric volume is held steady. Contractions increase wall thickness and decrease gast ric diameters at sites they involve and have opposite effects at remot e sites. Contractions move the incisura and hence redraw the borders b etween gastric segments and shift volumes back and forth within the ga stric lumen. Contractions furthermore stir up, compress, and disperse particulate beans without moving them to the pylorus. We conclude that gastric contractions 1) reverse changes in gastric length that occur during gastric filling, 2) move gastric contents directly through loca l contact and indirectly by changing the configuration of the stomach, and 3) interact with structures such as the incisura in retaining and breaking up solid gastric contents.