Heterogeneous tube model for the study of small intestinal transit flow

Purpose. A Monte-Carlo computer simulation technique was employed to study the details of the small intestinal transit flow in the gastrointestinal (G I) tract. Methods. A heterogeneous tube model was constructed using a numerical compu ter simulation technique. The model was built from first principles and inc luded several heterogeneous characteristics of the GI tract structure. We u sed a random, dendritic-type internal structure representing the villi of t he GI tract. The small intestinal transit flow was simulated using two diff usion models, namely, the blind ant and the myopic ant models, which are di fferent models to account the elapse of time, and which are both based on s tatistical properties of random walks. For each one of the models we utiliz e two types of biased random walk, placing different emphasis in the motion towards the output of the tube. We monitored the flow of the drug in terms of Monte-Carlo time steps (MCS) through the tube walls and dendritic villi present. Results. The frequency of the transit times was dependent on the structure of the dendritic villi and on the type of biased random walk. The small int estinal flow profile of literature data for a large number of drugs was wel l characterized by the heterogeneous model using, as parameters, a certain number of villi per unit length of the tube and specific characteristics fo r both types of the biased random walk. A correspondence between the MCS an d real time units was achieved. Conclusions. The transit process of the oral dosage forms in the GI tract c an be reproduced with the heterogeneous model developed. This model can be used to study GI absorption phenomena.