Anatomically realistic computational model of flow and mixing in the human duodenum

Abstract

The small intestine is the primary site of enzymatic digestion and nutrient absorption in humans. Intestinal contractions facilitate digesta transport, mixing and contact with the absorptive surfaces. Previous computational models have been limited to idealised contraction patterns and/or simplified geometries to study digesta transport. This study develops a physiologically realistic model of flow and mixing in the first segment of the small intestine (duodenum) based upon a geometry obtained from the Visible Human Project dataset and contraction patterns derived from electrophysiological simulations of slow wave propagation. Features seen in previous simpler models such as reversed flow underneath the contracting region were also present in this model for water, Newtonian liquid digesta and non-Newtonian (power law) whole digesta. Increases in contraction amplitude from 10% to 50% resulted in faster transport with mean speeds over a cycle increasing from 1.7 mm/s to 8.7 mm/s. Glucose transport was advection dominated with Peclet numbers greater than 104. A metric of glucose mixing was computed with 0 representing no mixing and 1 perfect mixing. For antegrade contractions at a 50% amplitude, the metric after 60 s was 0.99 for water, 0.6 for liquid digesta and 0.19 for whole digesta. Retrograde contractions had a negligible impact on the flow and mixing. Colliding wavefronts resulted in swirling flows and increased the mixing metric by up to 2.6 times relative to antegrade slow wave patterns. The computational framework developed in this study provide new tools for understanding the mixing and nutrient absorption patterns under normal and diseased conditions.

A Systematic Review of Computational Fluid Dynamics Models in the Stomach and Small Intestine

“…All studies used a simplified geometry, while Trusov et al [65] used an idealized 3D geometry with aspects of realistic anatomy, which consisted of a 'C' shaped cylinder to represent the duodenum. Palmada et al [67] was the first study to incorporate an anatomically realistic geometry of the duodenum derived from the VHP (Figure 5).…”

“…Peristalsis is responsible for the propulsion of digesta along the intestine, and these contractions were studied by 10/15 studies. The majority of these studies only simulate a single peristaltic contraction moving in an antegrade direction, while Oyama et al [63] modeled the effect of multiple contractions and [61,67] also investigated the fluid mechanics of colliding peristaltic waves. Segmentation contractions involve localized contractions and relaxations with no overall propulsion along the intestine, and their role in mixing of digesta with surrounding fluids (enzymes and chemicals secreted into the intestinal lumen) has been studied by [56,57,59,62].…”

“…These motility patterns are prescribed into the CFD model as boundary deformations, which range from sinusoidal waves [63][64][65], Gaussian distribution function [60], fluid-structure interactions [33], and more realistic deformation patterns obtained from experimental recordings of ex-vivo intestinal samples [56,58,61,62]. A model of slow wave propagation was utilized by Palmada et al [67] to obtain anatomically realistic boundary deformations to be applied in the model of duodenum motility (Figure 5a).…”

“…These differences are likely due to the specific ex-vivo recordings of longitudinal motion used to define the contraction patterns. Colliding peristaltic waves resulted in swirling flow regions [67] and high-velocity fluid jets exiting the colliding region [61]. Several studies have investigated the effect of fluid viscosity on the flow behavior within the intestine.…”

Computational Insights into Colonic Motility: Mechanical Role of Mucus in Homeostasis and Inflammation

“…To date, computational models of intestinal processes have been used to characterize and model the fluid mechanics that drive digestion and nutrient absorption. Among various numerical techniques, mesh-based and particle-based methods such as discrete multiphysics (34) are frequently used to model intestinal flow (35,36), mixing (37), and absorption (38) in humans. However, the mucus layer is often overlooked, and its contribution to these processes is crucial, as dysregulation often leads to serious conditions.…”