Characterization of segmental collateral blood flow in the small intestine.

Collateral blood flow and the pressures and resistances determining that flow were measured between two adjacent segments of canine jejunum following acute occlusion of the arterial branch perfusing one of the segments (the "recipient" segment). Collateral flow was approximately 55% of control flow in the recipient segment. This flow was provided by an equal increment in arterial flow to the nonischemic ("donor") segment, such that pressures, resistances, and flows in the donor segment were not affected. Virtually all of the total collateral flow was derived from precapillary channels and was therefore available to the capillary bed of the recipient segment. Collateral flow was adequate to maintain the recipient segment in a nonischemic state, as indicated by the absence of a reactive hyperemia following release of the arterial occlusion. Selective occlusions of intramural or extramural collateral channels indicate that about two-thirds of the total collateral flow is derived from the extramural (marginal) vessels, while the remainder is supplied by intramural collaterals. For the most part collateral flow between adjacent segments is determined simply by the pressure gradient between connecting collateral channels.