Differential transit of liquids and solid residue through the human ileum

We determined transit of liquids and the solid residue of a mixed meal through the ileocecal region of six healthy men. A multilumen polyvinyl tube was passed from above into a 20-cm segment of terminal ileum, and flow of liquid was assessed by indicator dilution techniques. Three test meals were eaten in random order at 5-hourly intervals. Meal A contained baked beans and polyethylene glycol (PEG 4000). Recovery of PEG 4000 from the ileum served to mark transit of the liquid phase, whereas arrival of solid residue (beans) in the cecum was heralded by a signal of H2 in the breath. PEG 4000 appeared promptly in ileal aspirates, peaking at 1-1.75 h postprandially. Breath H2 excretion was first detected at 1.5-2.5 h after meal A and always peaked later than PEG 4000. When meals shown to be unassociated with generation of breath hydrogen (meals B and C) followed meal A, an augmentation of hydrogen excretion was noted in the early postprandial period. The total volume calculated to pass from ileum to cecum over 24 h was 1,790 +/- 234 ml (range, 1,180-2,515 ml). Ileal flow increased promptly and significantly after each meal (P less than 0.005) and remained high for 3 h or more. These results confirm that, in healthy humans, about 2 liters of chyme pass from ileum to colon each 24 h and ileal flow increases postprandially. They also suggest that the liquid and solid phases of a mixed meal are separate in the ileocecal region.