Intramural blood flow distribution in the small intestine of the cat studied by carbon monoxide uptake and 85krypton elimination

Carbon monoxide (CO) uptake from the feline small intestine was measured to investigate if it could be used to determine blood flow in the superficial parts of the intestinal mucosa. Several observations were made that substantiated this proposal: 1) Lowering P_CO in the intestinal lumen from 100 to 70 kPa did not influence the rate of CO absorption during “resting” blood flow conditions, while the same reduction of lumen P_CO resulted in a decreased rate of CO uptake during isoprenaline induced vasodilatation. These observations suggest that CO uptake was flow limited during “rest” and diffusion limited during vasodilation. 2) Lowering perfusion pressure or totally occluding the intestinal vascular supply markedly reduced the rate of CO uptake. 3) The diffusion distance for CO into the tissue was calculated to be 75–225 μm, i. e. CO mainly diffused into the villous tissue. 4) The flow values calculated from the CO measurements were of the same order of magnitude as earlier reported with other techniques (microspheres, indicator dilution method). It was concluded that CO absorption mainly reflected villous blood flow during “resting” and low intestinal blood flow. Total blood flow (venous drop recorder) and muscle layer blood flow (⁸⁵Kr elimination) were measured simultaneously to CO uptake. From these determinations “resting” blood flow distribution in the small intestine was calculated.