title: On the kinematics and efficiency of advective mixing during gastric digestion - A numerical analysis.
abstract: 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.
authors.affiliation: Riddet Institute, Massey University, PB 11 222, Palmerston North 4442, New Zealand. Electronic address: m.j.ferrua@massey.ac.nz.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Ferrua
authors.affiliation: Department of Biological and Agricultural Engineering, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Zhengjun
authors.initials: Z
authors.lastname: Xue
authors.affiliation: Riddet Institute, Massey University, PB 11 222, Palmerston North 4442, New Zealand; Department of Biological and Agricultural Engineering, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: R Paul
authors.initials: RP
authors.lastname: Singh
mesh_terms: D001696:Biomechanical Phenomena; D006801:Humans; D008954:Models, Biological; D012212:Rheology; D013270:Stomach / Q000502:physiology*; D014783:Viscosity
keywords: Advective mixing; Computational fluid dynamics.; Fluid rheology; Gastric digestion; Stretching