Determination in vivo of regional circulatory dynamics in intact intestine

¹ Donner Laboratory, Donner Pavilion, and Lawrence Radiation Laboratory, University of California, Berkeley, California, and Department of Physiology, University of Minnesota Medical School, Minneapolis, Minnesota

A radioisotope technique employing a specially designed and critically shielded detector positioned in the gut lumen is utilized to monitor in vivo beta particle radioactivity in the circulation. The short range of the P³² beta in tissue (0.8 mm half thickness) is suited for this procedure because, with appropriate shielding, detected activity is limited to that contained in the blood perfusing the intestine surrounding the counter, with adjacent loops excluded. Regional blood volume is calculated from the regional counting rate of circulating P³²-labeled red blood cells; regional blood flow is estimated from the local blood dilution curve. The effects of a variety of experimental maneuvers on circulatory dynamics are presented. Acetylcholine decreases regional blood flow but increases regional blood volume while cardiac output is increased. In contrast, l-norepinephrine appears to decrease both regional blood flow and regional blood volume with cardiac output relatively unchanged. This technique can be used in human subjects to evaluate the relation of regional intestinal circulation to regional function and pathology.