Interpreting manometric signals for propulsion in the gut

Propulsion of intestinal contents involves coordinated contractions and relaxations of the muscle controlled by polarised enteric neural reflex pathways. Due to the inaccessibility of the small and large bowel, obtaining detailed manometric measurements in the gut or visualizing the movement of digesta is difficult in vivo. Computational modelling that incorporates the complex interactions between gut content and wall contractility has the potential to explain the mechanisms behind propulsive motor patterns and aid the interpretation of manometric measurements. We present here a biomechanical computational model of coupled wall flexure and flow dynamics in a virtual segment of intestine. The model uses the smoothed particle hydrodynamics method which permits coupling of the fluid/solid motion and wall deformation in a natural way. Peristaltic waves of contraction and relaxation, similar to those observed in physiological experiments, were applied to the gut wall of the model. A catheter containing manometric sensors was also incorporated into the model to derive representative pressure readings. The sensitivity of the model to input parameters including wall stiffness, viscosity of content and degree of muscular contraction is also presented. The results show that there is a rapid rise in pressure of fluid content trapped between the catheter and the contracting wall. The peristaltic wave travels along the length of the virtual segment of intestine passing over each sensor. The bolus, formed by the peristaltic contraction, grows in size and longitudinal extent until the bolus size reaches steady state. The wall force and the peak fluid pressure both scale proportionally with the change in muscle length, indicating that manometric data provide a reliable means for measuring the strength of contractions. Changes in stiffness of the wall and viscosity of contents result in predictable changes in the parameters of peristalsis. The model can be thus applied to manometry measurements in real experimental conditions.