Maria J. Ferrua

Modeling the fluid dynamics in a human stomach to gain insight of food digestion.

During gastric digestion, food is disintegrated by a complex interaction of chemical and mechanical effects. Although the mechanisms of chemical digestion are usually characterized by using in vitro analysis, the difficulty in reproducing the stomach geometry and motility has prevented a good understanding of the local fluid dynamics of gastric contents. The goal of this study was to use computational fluid dynamics (CFD) to develop a 3-D model of the shape and motility pattern of the stomach wall during digestion, and use it to characterize the fluid dynamics of gastric contents of different viscosities. A geometrical model of an averaged-sized human stomach was created, and its motility was characterized by a series of antral-contraction waves of up to 80% relative occlusion. The flow field within the model (predicted using the software Fluent™) strongly depended on the viscosity of gastric contents. By increasing the viscosity, the formation of the 2 flow patterns commonly regarded as the main mechanisms driving digestion (i.e., the retropulsive jet-like motion and eddy structures) was significantly diminished, while a significant increase of the pressure field was predicted. These results were in good agreement with experimental data previously reported in the literature, and suggest that, contrary to the traditional idea of a rapid and complete homogenization of the meal, gastric contents associated with high viscous meals are poorly mixed. This study illustrates the capability of CFD to provide a unique insight into the fluid dynamics of the gastric contents, and points out its potential to develop a fundamental understanding and modeling of the mechanisms involved in the digestion process. Practical Application This study illustrates the capability of computational fluid dynamic techniques to provide a unique insight into the dynamics of the gastric contents, pointing out its potential to develop a fundamental understanding and modeling of the human digestion process.

On the kinematics and efficiency of advective mixing during gastric digestion – A numerical analysis

The mixing performance of gastric contents during digestion is expected to have a major role on the rate and final bioavailability of nutrients within the body. The aim of this study was to characterize the ability of the human stomach to advect gastric contents with different rheological properties. The flow behavior of two Newtonian fluids (10(-3)Pas, 1Pas) and a pseudoplastic solution (K=0.223Pas(0.59)) during gastric digestion were numerically characterized within a simplified 3D model of the stomach geometry and motility during the process (ANSYS-FLUENT). The advective performances of each of these gastric flows were determined by analyzing the spatial distribution and temporal history of their stretching abilities (Lagrangian analysis). Results illustrate the limited influence that large retropulsive and vortex structures have on the overall dynamics of gastric flows. Even within the distal region, more than 50% of the flow experienced velocity and shear values lower than 10% of their respective maximums. While chaotic, gastric advection was always relatively poor (with Lyapunov exponents an order of magnitude lower than those of a laminar stirred tank). Contrary to expectations, gastric rheology had only a minor role on the advective properties of the flow (particularly within the distal region). As viscosity increased above 1St, the role of fluid viscosity became largely negligible. By characterizing the fluid dynamic and mixing conditions that develop during digestion, this work will inform the design of novel in vitro systems of enhanced biomechanical performance and facilitate a more accurate diagnosis of gastric digestion processes.

Dynamics of Gastric Contents During Digestion—Computational and Rheological Considerations

Abstract Underpinned by the delivery of better human health and well-being through food innovation, a new generation of food products aimed at improving bioavailability through the controlled release of nutrients and bioactive compounds has become a leading trend for the global food sector. The efficient design of these novel functional foods requires a better understanding of the physicochemical conditions to which foods are exposed upon ingestion. While the experimental characterization of these conditions has proved difficult, recent advances in medical imaging technologies has facilitated a good improvement in in vivo characterization of the physiological responses of the gastrointestinal tract that trigger and modulate these conditions. This information, together with continuous developments in computational modeling tools, has opened new opportunities to numerically analyze the physicochemical processes underlying food digestion.

Human Gastric Simulator (Riddet Model)

An in vitro ‘dynamic’ model for food digestion diagnosis, the Human Gastric Simulator (HGS), has been designed to reproduce the fluid mechanical conditions driving the disintegration and mixing of gastric contents during digestion. The HGS simulates the stomach as a flexible compartment, and mimics its contractive motility by a series of rollers that continuously impinge and compress the compartment wall with increasing amplitude. Operated at 37 °C, the HGS facilitates a precise control of the mechanical forces to which foods are exposed during the process, as well as of the rate of simulated gastric secretions and emptying patterns.

Computational Modeling of Gastrointestinal Fluid Dynamics

Knowledge of the fluid dynamic behavior of gastrointestinal (GI) contents during digestion is essential to further understand and model the bioavailability of nutrients and pharmaceuticals in health and disease. The dynamics that develop within the GI tract are the result of a complex and self-regulated interplay between the physical properties of the intraluminal contents and the motor responses of the GI wall. Recent advances in the characterization of GI motility patterns have facilitated the use of engineering simulation tools to investigate the mechanisms driving different GI functions. In this chapter, current research aimed at using computational fluid dynamic (CFD) techniques to predict the flow and mixing behavior of gastric and small intestinal contents during digestion will be reviewed. The unique capability and potential applications of this new approach to advance research in the food and health sectors will be discussed.