Fluid mechanical consequences of pendular activity, segmentation and pyloric outflow in the proximal duodenum of the rat and the guinea pig

Abstract

We conducted numerical experiments to study the influence of non-propagating longitudinal and circular contractions, i.e. pendular activity and segmentation, respectively, on flow and mixing in the proximal duodenum. A lattice-Boltzmann numerical method was developed to simulate the fluid mechanical consequences for each of 22 randomly selected sequences of high-definition video of real longitudinal and radial contractile activity in the isolated proximal duodenum of the rat and guinea pig. During pendular activity in the rat duodenum, the flow was characterized by regions of high shear rate. Mixing was so governed by shearing deformation of the fluid that increased the interface between adjacent domains and accelerated their interdiffusion (for diffusion coefficients approx. less than 10 28 m 2 s 21). When pendular activity was associated with a slow gastric outflow characteristic of post-prandial period, the dispersion was also improved, especially near the walls. Mixing was not promoted by isolated segmentative contractions in the guinea pig duodenum and not notably influenced by pylorus outflow. We concluded that pendular activity generates mixing of viscous fluids 'in situ' and accelerates the diffusive mass transfer, whereas segmentation may be more important in mixing particulate suspensions with high solid volume ratios.

Characterisation of Mixing in the Proximal Duodenum of the Rat during Longitudinal Contractions and Comparison with a Fluid Mechanical Model Based on Spatiotemporal Motility Data

“…The flow rate was chosen to mimic that of pyloric outflow during the post-prandial period in the rat [10], [28]. The syringe containing the perfusate was then switched to one containing normal saline coloured with 1.4 mg/mL Methylene Blue (BDH Laboratory Supplies, Poole, UK) to create a step increase in its concentration.…”

The imaging and modelling of the physical processes involved in digestion and absorption

“…, Lentle & Janssen , de Loubens et al . ). Concern for ‘unstirred intestinal layers’ motivated mechanical engineers to model the flow that would result from intestinal contractions.…”

The Enteric Nervous System

“…As the technique is relatively simple, most laboratories have developed their own hardware/software systems suitable to answer the questions they are most interested in. ST maps have also been useful, not only to map patterns of contraction in the gut, but also patterns of enteric neuron fi ring and ICC and smooth muscle activity (Smith/Hennig/ Sanders Labs (de Loubens et al 2013 )]. They are commonly used to diagnose esophageal motility using ST maps of pressure recorded using manometry catheters [see Brasseur /Dinning/Smout (De Schepper et al 2014 )].…”