GRAVITATIONAL AND SHEAR-ASSOCIATED PRESSURE-GRADIENTS IN THE ABDOMEN

The abdomen has been variously characterized as a hydrostatic system, in which pressures exhibit a gravitational gradient and pressure fluct uations are spatially uniform, and as a compartment, in which pressure gradients are not simply gravitational and pressure fluctuations diff er markedly from place to place. To characterize the pressures acting on the ventral abdominal wall, we used saline-filled catheters and air -filled balloons in anesthetized dogs in various body positions during spontaneous breathing and mechanical ventilation. Pressures were meas ured in the stomach and at multiple sites next to the abdominal wall. Under most circumstances, measurements next to the abdominal wall exhi bited a hydrostatic gravitational gradient of similar to 0.89 cmH(2)O/ cm height and pressure fluctuations were spatially homogeneous. Deviat ions from this hydrostatic behavior were seen when abdominal pressures were compared with gastric pressures, when measurements were made wit h a balloon catheter, and when the lower abdomen was constricted with a binder. Analysis of these and previously published data suggests tha t the abdomen does, at times, behave like a hydraulic system but can d eviate from simple hydrostatic behavior to the extent that shape-stabl e abdominal viscera are deformed.