Quantifying the Role of Duodenal Shape in Flow and Mixing: A Computational Fluid Dynamics Study on Anatomically Diverse Models.

Objective: Enzymatic digestion of food and absorption of nutrients in the duodenum are affected by flow and mixing driven by peristaltic contractions. Our understanding of how the duodenum shape varies among individuals and how these anatomical differences affect the transport dynamics is limited.

Methods: A landmark-free approach was used to perform statistical shape analysis of the duodenum, then computational fluid dynamics (CFD) simulations with anatomically realistic peristaltic contractions were used to characterize the effect of anatomical variations on flow and mixing. Leveraging the inherent tubular 'C' shape of the duodenum, centerlines and cross-sectional areas were computed for CT data from 34 subjects. The average radius and duodenal orientation in the form of the components of the tangent vectors to the centerline at 60 equally spaced (normalised by the centerline length) locations were used as inputs to a principal component analysis (PCA).

Results: CFD simulations revealed similar flow features across all geometries including the location of stagnation points and the presence of reversed flow, and swirling patterns. The most extreme geometry, experiencing the largest magnitude of radial contractions, achieved a mixing state approximately twice that of the mean geometry within a 60 s period.

Conclusion: This work provides new insights into duodenal shape variation and its impacts on intestinal fluid dynamics.

Significance: The methods and datasets developed here have broader implications for understanding gastrointestinal function, digestion, and drug delivery by establishing quantitative links between anatomical variation and digestive processes.