Oxygen exchange in the mesenteric microcirculation of the dog

The relationships of O2 tension in mesenteric lymph (PmlO2) and mesenteric venous blood (PmvO2) to intestinal O2 delivery/O2 consumption (DO2/VO2) were examined after graded hemorrhage (10 dogs), stepwise increments in FIO2 (4 dogs), and regional infusion of papaverine (2 mg/min or IV glucagon (25 microgram/kg) (4 dogs). Measurements included superior mesenteric arterial flow (SMA-Q), PaO2, PmlO2, and arterial and mesenteric venous blood O2 content (CaO2, CmvO2). Intestinal DO2 was calculated as the product of SMA-Q and CaO2, and VO2 was calculated from the Fick equation [SMA-Q X (CaO2 - CmvO2)]. Graded hemorrhage lowered SMA-Q, DO2 and DO2/VO2 and increased splanchnic O2 extraction (CaO2 - CmvO2). Elevation of FIO2 increased PaO2, PmvO2, and PmlO2. Both PmlO2 and PmvO2 varied directly with DO2/VO2 and PaO2, but PmlO2 showed greater sensitivity to PaO2. Papaverine and glucagon both increased SMA-Q, DO2, CmvO2, and PmvO2, BUT PmlO2 rose after papaverine, indicating greater capillary perfusion, and fell after glucagon, suggesting diversion of mesenteric blood flow through arteriovenous shunts. Thus, either PmvO2 or PmlO2 is ordinarily an accurate measure of intestinal tissue oxygenation, but the disparate response after glucagon suggests that PmlO2 is a more reliable indicator.