The oesophageal zero-stress state and mucosal folding from a GIOME perspective

Abstract

The oesophagus is a cylindrical organ with a collapsed lumen and mucosal folds. The mucosal folding may serve to advance the function of the oesophagus, i.e. the folds have a major influence on the flow of air and bolus through the oesophagus. Experimental studies have demonstrated oesophageal mucosal folds in the no-load state. This indicates that mucosal buckling must be considered in the analysis of the mechanical reference state since the material stiffness drops dramatically after tissue collapse. Most previous work on the oesophageal zero-stress state and mucosal folding has been experimental. However, numerical analysis offers a promising alternative approach, with the additional ability to predict the mucosal buckling behaviour and to calculate the regional stress and strain in complex structures. A numerical model used for describing the mechanical behaviour of the mucosal-folded, three-layered, two-dimensional oesophageal model is reviewed. GIOME models can be used in the future to predict the tissue function physiologically and pathologically.

Figure 1

The configurations of the separated muscle (left) and the mucosal (right) layer at the zero-stress state (open sectors) and the no-load state (closed circular rings). The no-load state was obtained by forcing the opening sector to be closed using a pure bending deformation. The pure bending loads are indicted by arrows. The numerical model was conducted by using the ABAQUS software.

Figure 2

Circumferential experimental and curvefitted stress-strain curves for the muscle (A) and mucosal (B) layers. The curves were fitted by using the Ogden 2nd order strain energy function. The stress-strain curve of the epithelial layer was tested from the mucosal-submucosal layer while the stress strain curve of the MMS layer was assumed to have a similar pattern as the epithelial layer with the magnitude about one order softer than the epithelial layer. For the circumferential uni-axial test and the circumferential planar test the separated muscle and mucosal-submucosal rings were fixed in two L shape rods, one end of the L shape rod was connected to a cannula. The cannulas were connected to rods that could be moved at controlled velocities by a motor. One of the rods was attached to a force transducer. The distance between the rods was adjusted manually to the in vitro length of the strips (reference length). The force (F) was recorded online by a Labview program.

Math 3

Math(A3).

Math 4

Math(A4).

Figure 3

The circumferential strain (A) and stress (B) distribution throughout the muscle and mucosal (MMS + epithelial) layers after the separated muscle and mucosal layer sectors were closed. The strain and stress jump occurred at the interface between the epithelial and MMS layer.

Figure 4

Circumferential residual strain (A) and residual Mises stress (B) distribution in the muscle layer at the no-load state. Strain was positive throughout the muscle wall.

Figure 5

Residual stress of the mucosal layer in a three folds model (Top, left) and five folds model (Top, right). The morphological oesophageal images indicated that the folds numbers are between three (bottom, left) and five (bottom, right) at the no-load state.