Priority of blood flow to splanchnic organs in humans during pre- and post-meal exercise

Cardiac output and superior mesenteric arterial flow in five healthy young men were followed using Doppler ultrasound techniques at rest and during 4 min bouts of bicycle exercise in both a pre- and a post-meal situation. The meal given was mixed and heavy, with an energy content (related to body size) of about 1400-1600 kcal (5.9-6.9 MJ). Two levels of exercise, 50-65 W and 150-200 W (about 75% of VO2max), were tested, with the subjects cycling in a reclining position. Superior mesenteric arterial flow increased threefold, to about 1.1 l min-1, after the meal. During exercise in the fasting situation there were only modest changes in splanchnic vascular conductance, and moderate increases in superior mesenteric arterial flow were actually recorded. Exercise in the post-prandial state caused appreciable reductions in splanchnic vascular conductance, and a 38% reduction was observed during the most heavy exercise. However, not even such a decrease in conductance resulted in any definite reduction in superior mesenteric arterial blood flow, which was maintained at the pre-exercise level. Cardiac output increased by about 1.3 l min-1 after the meal. The exercise-induced increases in cardiac output were of the same order in the fasting and in the post-prandial state. Variance analyses showed the high cardiac output levels reached during post-prandial exercise to be no different from levels that would be reached by pure summation of the changes caused by eating alone and by exercise alone. It is concluded that blood flow to the splanchnic organs in reclining man retains its high pre- and post-prandial priority during short exercise bouts of up to 75% of VO2max.