Gastric Mixing and Acid Diffusion in a Human Stomach Simulated Using Smoothed Particle Hydrodynamics

This study develops a computational stomach model using the smoothed particle hydrodynamics (SPH) approach to investigate the effects of fluid viscosity, gastric motility, and acid diffusion rate on gastric mixing and acid distribution. The model incorporates antral contraction waves (ACW) and acid diffusion from the stomach wall. Our findings reveal that the mixing pattern generated by ACWs is strongly anisotropic. When the ACWs travel along the wall, highly effective tangential flow moves alongside and drives the circulatory flow and mixing. Conversely, the weak radial advection orthogonal to the wall provides minimal enhancement to the predominantly radial diffusion. Fluid viscosity influences the mixing dynamics within the stomach significantly, with higher viscosity fluids exhibiting slower and less efficient mixing. Gastric motility, characterized by ACW speed and occlusion, has a substantial impact on enhancing gastric mixing. Increased ACW speed and greater occlusion effectively promote more rapid mixing of the stomach contents. The diffusion coefficient emerges as the dominant factor in acid distribution, overtaking the impact of physical mixing induced by ACWs. This indicates that while mechanical mixing is crucial for overall fluid dynamics, acid diffusion has a greater impact on the distribution of acid and changes in pH within the stomach. These insights emphasize the complex interaction between mechanical and chemical processes in the stomach, highlighting the importance of considering both factors in developing accurate models for gastric digestion and nutrient absorption.