Systems analysis of intestinal hemodynamics and oxygenation.

A systems analysis of intrinsic regulation of intestinal blood flow and oxygenation is presented. The model is based on current concepts of metabolic control of tissue oxygen delivery and incorporates recent data from the literature regarding the influence of oxygen availability-to-demand ratio on intestinal vascular resistance and perfused capillary density. The model was used to evaluate the relative importance of resistance and exchange vessels in preventing cellular hypoxia during reductions in oxygen delivery or increments in oxygen demand. The model predicted that capillary recruitment is of greater quantitative significance than blood flow autoregulation in preventing cellular hypoxia when intestinal perfusion pressure is reduced. However, the combination of capillary recruitment and blood flow autoregulation provides a large margin of safety against tissue hypoxia in the intestine. Simulation results also predict that oxygen extraction plays a greater role than blood flow in providing additional oxygen to the hypermetabolic intestine irrespective of which control system (resistance or exchange vessel) is operating.