Impact of reduced gravity on food mixing and emptying in human stomach: A numerical simulation study

Gravitational conditions in space diverge significantly from those experienced on Earth, and these alterations may have significant effects on gastric digestion, ultimately affecting the health of astronauts. To understand these effects, the behavior of mixing and emptying in the human stomach under both reduced and normal gravity is investigated numerically. The solver utilized in this study is developed based on the open-source toolbox OpenFOAM. The gastric contents consist of water and a soluble food bolus characterized by a density of 1100 kg m−3, viscosity of 10−5 m2 s−1, and diffusivity of 3.09 × 10−9 m2 s−1. The effects of gravity magnitude, initial food bolus location, and terminal antral contractions (TACs) are studied. The numerical results demonstrate that the food retention rate can be increased by up to ∼20% in the initial 6 min as normal gravity is reduced to zero gravity. The numerical results support that gravity favors the emptying of the food through the pylorus. The distributions of food concentrations and pH are also significantly influenced by the gravity condition. Under zero gravity conditions, food in the distal stomach is quickly emptied due to the strong flow dynamics in the antrum. A delay of approximately 6 min is observed when the food bolus is initially located in the proximal stomach. TACs efficiently enhance the emptying and mixing of the food in the distal stomach, while their effects on the proximal stomach are marginal.