Investigating the relationships between peristaltic contraction and fluid transport in the human colon using Smoothed Particle Hydrodynamics

Abstract

The gastrointestinal tract comprises of several distinct organs in sequence, extending over 7 meters in the human abdomen. Controlled propulsion and mixing of content along the digestive tract is essential for a normal life. This is achieved by a rich assortment of motor patterns that ensure that movements and propulsion are appropriate for the breakdown of food, absorption of nutrients and excretion of waste. These movements (motility) are due to coordinated contractions and relaxations of circular and longitudinal smooth muscle layers. For oesophageal FGIDs the combined technical advances in recording abnormal contractility, via oesophageal manometry, and relating these abnormalities to impaired flow [2] has seen a dramatic improvement in our understanding of the problem and therefore our ability to treat the patient.However, this is not the case for FGIDs in regions below the stomach. The small and large intestines are relatively inaccessible and obtaining detailed manometric recordings and visualizing the movement of digesta is difficult. As a result our understanding of normal pressure/flow relationships is still relatively simplistic [3]. Therefore while abnormal contractility is implicated in , how these abnormalities relate to impaired flow remains largely unknown.Computational modeling of gastrointestinal systems has the potential to help understand these complex relationships. Many mathematical models of peristaltic pumping in flexible tubes have been developed over the last decades and the reader is referred to [7,8] for comprehensive reviews of 3/37 this research. The vast majority of these models do not take into account the solid wall mechanics of the flexible tube in predicting the transient wall deformation. Instead the wall shape is fully prescribed. Some exceptions to this include Carew and Pedley [9] who developed a model of peristaltic flow in the ureter with an active contracting wall coupled to the internal resistance from the intra-luminal pressures in an infinitely long tube. Such models are based on lubrication theory and are therefore limited to simple geometry systems with low inertial flows and long waves. They are well suited to studying the dynamics of the ureter. However, the development of intestinal flow models for studying the effect of single and multiple wave trains on transport requires an active wall model that can accommodate more realistic geometry and non-linear wall mechanics.More recently detailed computational models of oesophageal motility [10,11] have helped to define relationships between motility and flow. In addition CFD models have started to consider the effect of peristaltic motor patterns in the small intestine [12] and the stomach [13,14]. While these studies in the stomach and small bowel have sourced anatomically accurate wall geometries from MRI, they have not attempted a 2-way coupling of the motor activity in the wall with the fluid content.Instead motor patterns are prescribed as a sequence of fixed geometric changes to the boundary.Physiologically real...

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