Role of exchange vessels in the regulation of intestinal oxygenation.

The contribution of changes in capillary exchange capacity to local regulation of oxygen uptake was assessed in the cat small intestine. Oxygen extraction, oxygen uptake, and the capillary filtration coefficient (KF,C) were measured at blood flows ranging between 4 and 70 ml.min-1.100 g-1. Blood flow was altered via pump perfusion or partial arterial occlusion. Both oxygen extraction and capillary exchange capacity (KF,C) increased progressively as blood flow was reduced in a stepwise fashion. Oxygen uptake remained constant between blood flows of 30 and 70 ml.min-1.100 g-1, yet it decreased progressively as blood flow was reduced below 30 ml.min-1.100 g-1. These findings support the hypothesis that intrinsic modulation of intestinal oxygen extraction is mediated by vascular elements that govern capillary exchange capacity.