Quantitative assessment of the two-component model of intestinal circulation

Recently a two-component model of the intestinal circulation was proposed to explain the effects of vasodilators on intestinal oxygenation. This model assumes that the intestine is composed of two regions: one region in which oxygen uptake is blood flow independent (well perfused and normoxic) and a second region in which oxygen uptake is blood flow dependent (under-perfused and hypoxic). The model predicts that total intestinal oxygen uptake is increased by a vasodilator only if the blood flow-dependent region is affected. We used a systems analysis approach to predict the various boundary conditions that must be imposed on the two-component model for it to simulate experimental observations. The mathematical model was based on current concepts and available data regarding intestinal hemodynamics and oxygen exchange. The model simulations predict that 30-70% of the intestine must be hypoxic (regions where oxygen uptake is blood flow dependent) for the two-component hypothesis to adequately explain published observations. Since the existence of such an extensive hypoxic region seems unlikely for the normal intestine, the predictive value of the two-component hypothesis may be of limited value for describing the effects of vasodilators on oxygen uptake in the normal intestine. However, the two-component model may be useful in predicting the effects of vasodilators on intestinal oxygen uptake in the ischemic intestine.