Physiological Pharmaceutics

122 Physiological PharmaceuticsFigure 6.6 Laminar mixing produced by repetitive longitudinal contractionsScintigraphy often demonstrates accumulation or bunching of material at theileocaecal junction, followed by spreading of material through the ascending colon 14 . Nondisintegratingmatrices may remain at this location for some hours 15 .SMALL INTESTINAL TRANSIT TIMESMethods for measuring small intestinal transitThere are several methods available for the measurement of small intestinal transit. Thehydrogen breath test relies on metabolism of certain carbohydrates, e.g. lactulose, bymicrobial flora within the large bowel. The carbohydrate must be one which is not absorbedfrom the small intestine. The gas generated is detected in the expired air. Using thistechnique, it is possible to estimate the sum of gastric emptying and small intestinal transittimes. This test assumes that the unabsorbed carbohydrate encounters fermentative bacteriaonly in the colon, however bacterial overgrowth into the small intestine will giveerroneously short transit times.Two-dimensional gamma scintigraphy can be used to measure stomach to caecumtransit times, but cannot be used to measure the distance travelled by a unit throughsegments of the small intestine since it is highly coiled. Transit time through segments of thesmall intestine has been measured using a perspex capsule containing technetium-99mlabelled ‘Amberlite’ resin 16 . External markers were placed on the front, back and sides ofvolunteers who were then imaged from the front, back and side. This enabled the threedimensionalmovement of the capsule through the small intestine to be reconstructed andan estimate to be made of the velocity of the unit. After transit through the duodenum,which was too fast to be accurately measured, the capsule moved through the small intestineat between 4.2 and 5.6 cm per minute. There was no difference in transit times for twocapsules with different specific gravities (1.0 and 1.6). The transit rate is in close agreementwith the velocity of the migrating myoelectric potential down the small intestine (4.7 cm.min -1 ) 17 and that of 1 to 4 cm per minute for chyme 2 .Many older textbooks quote small intestinal transit times based on barium X-raycontrast measurements, but barium is not a good model of the intestinal contents.