1. 1. The effects of acute bowel distention on intestinal circulation were studied in dogs. 2. 2. Intraluminal pressures at or above 30 mm. Hg produced a consistent immediate fall in intestinal blood flow. Higher pressures produced correspondingly greater diminutions in flow until an irreducible 20 to 35 per cent of flow remained. 3. 3. As blood flow fell, there was an associated decrease in the arteriovenous oxygen difference indicating diminished oxygen extraction by the intestine. 4. 4. Injection studies performed in situ with increasing intraluminal pressures showed filling of only the submucosal and serosal vessels with pressures at or above 60 to 90 mm. Hg. 5. 5. Krypton 85 washout studies are compatible with a shift of blood flow away from the mucosa at intraluminal pressures above 60 mm. Hg. 6. 6. These findings indicate that above an intraluminal pressure of 30 mm. Hg, blood is shunted through functional or anatomic arteriovenous communications depriving the bowel mucosa. 7. 7. The roles of increased intraluminal pressure, intestinal ischemia, and hypoxia are discussed as accounting for the colitis seen proximal to colonic neoplasms.
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