A swine model for studying intestinal circulation of the newborn

We describe a newborn swine model to study intestinal hemodynamics of developing mammals. The preparation is designed to allow measurement of perfusion pressure and blood flow in an isolated segment of ileum under controlled conditions. Piglets in this study had a mean blood pressure of 65 +/- 14 (SD) mm Hg and mean intestinal blood flow of 80 +/- 20 (SD) ml/100 g/min at an average age and weight of 6.1 +/- 3 (SD) days and 1,718 +/- 427 (SD) g (n = 21). Experiments were performed to evaluate the effects of common physiologic perturbations: (a) Increased venous pressure caused a decrease in blood flow proportional to the lower perfusion pressure, but the relative change in vascular resistance was greater than the blood flow change. This effect, suggestive of a myogenic response, was significantly greater at a venous pressure increase of 20 cm of water over baseline compared with an increase of 10 cm water. (b) Gradual decrease in mesenteric artery blood pressure by clamping resulted in proportional decreases in blood flow. The calculated peripheral vascular resistance remained constant at blood pressure greater than 50 mm Hg and then increased as blood pressure decreased. (c) Stimulation of periarterial, postganglionic nerves surrounding the mesenteric artery produced a characteristic initial vasoconstriction followed by "autoregulatory escape." Frequency response tests using trains of stimulation of 6 ms and 12 V demonstrated responses starting at 2 Hz and maximal at 16 Hz. We suggest that this model should be applicable to a number of physiologic studies including assessment of water and nutrient flux in the intestine concomitant to changes in the circulation.