Inferior mesenteric artery back pressure and collateral circulation to the distal colon.

The contribution of the hypogastric and superior mesenteric arteries to inferior mesenteric artery collateral (back) pressure (r-IMA) was measured in eight patients who were free from arterial disease and were operated on for small sigmoid carcinoma. Peak and mean r-IMAs were measured after clamping both common iliac arteries and the middle colic artery together with the marginal artery of Drummond. Measurements were repeated after the injection of 50 mg papaverine into the inferior mesenteric artery. For comparison the r-IMA was normalized against the radial artery pressure to create the r-IMA:radial artery pressure ratio. At peak systolic pressure the r-IMA:radial artery pressure was approximately 0.6. This fell with crossclamping of the middle colic artery and marginal artery of Drummond; a slightly greater fall was observed when the common iliac arteries were clamped. The findings were similar when mean pressures were compared. The changes in pressure ratio observed after collateral clamping were slightly amplified by injection of papaverine. These data suggest that the hypogastric arteries make at least as great or a slightly greater contribution to r-IMA than do the middle colic artery plus marginal artery of Drummond. The data also indicate the presence of other substantial collaterals. These findings stress the importance of the hypogastric collateral supplying the sigmoid colon when the inferior mesenteric artery is acutely occluded as it is during aneurysm resection.