Biomechanical Remodeling of the Chronically Obstructed Guinea Pig Small Intestine

Abstract

Small intestinal obstruction is a frequently encountered clinical problem. To understand the mechanisms behind obstruction and the clinical consequences, data are needed on the relation between the morphologic and biomechanical remodeling that takes place in the intestinal wall during chronic obstruction. We sought to determine the effect of partial obstruction on mechanical and morphologic properties of the guinea pig small intestine. Partial obstruction was created surgically in 2 groups of animals living for 2 and 4 weeks. Controls were sham operated and lived for 4 weeks. A combined impedance planimetry-high-frequency ultrasound system was designed to measure the luminal cross-sectional area and wall thickness. These measures were used to compute the circumferential stress and strain of the excised intestinal segments. The incremental elastic modulus was obtained by using nonlinear fitting of the stress-strain curve. Histologic analysis and the measurements of total wall collagen were also performed. The luminal cross-sectional area, wall thickness, and elastic modulus in circumferential direction increased in a time-dependent manner proximal to the obstruction site (P < 0.01), whereas no differences in these parameters were found distal to the obstruction site (P > 0.25). The circumferential stress-strain curves of the proximal segments in 2- and 4-week groups shifted to the left, indicating the intestinal wall became stiffer. Histologic examination revealed a massive increase in the thickness of the muscle layer especially the circular smooth muscle layer (P < 0.05). The collagen content proximal to the obstruction site was significantly larger in the partially obstructed animals compared to controls (P < 0.05). No difference was found distal to the obstruction site. Strong correlation was found between the collagen content and the elastic modulus at stress levels of 70 kPa stress (P < 0.01) and 10 kPa (P < 0.05) proximal to the obstruction site suggesting that the alteration of collagen has great impact on the mechanical remodeling. The morphologic and biomechanical remodeling likely influence the function of the intestine affected by partial obstructed intestine.

Phasic and Tonic Stress–Strain Data Obtained in Intact Intestinal Segment In Vitro

“…Longitudinal stretch decreased the circumferential muscle contractility. Such information may be relevant because lengthening can be caused by shear stresses induced by chyme flow [10,23], longitudinal muscle relaxation [24], and distension due to obstructive diseases [25,26]. The 20% elongation used in this study is probably in the same range as such physiological length changes whereas the deformation used in muscle strips studies often are much larger.…”

Intestinal remodelling in mink fed with reduced protein content

“…Therefore, the zero-stress state must be taken into account when studying the biomechanical remodelling of the GI tract in mink fed with reduced protein diet. Several studies have been conducted on biomechanical remodelling in different disease models (Gregersen et al, 2001;Dou et al, 2002;Zhao et al, 2003;Storkholm et al, 2007). We previously demonstrated that fasting induced pronounced biomechanical and structural remodelling in the rat small intestine (Dou et al, 2002).…”

“…After 1 h of equilibration, the specimens were photographed again for zero-stress state analysis and then immersed into 10% phosphate-buffered formalin solution for histological analysis. The selected time period was based on previous studies (Dou et al, 2002;Zhao et al, 2003;Storkholm et al, 2007).…”

3d Mechanical properties of the partially obstructed guinea pig small intestine

“…The body weight loss of the obstructed guinea pigs was likely caused by the surgery (Zhao et al, 2010). The guinea pigs had access to water but did not eat food overnight before operations and experiments (Storkholm et al, 2007). Since we have experience with this kind of operation, the mortality rate was kept below 20% and the number of animals in each group is the final numbers.…”

“…Recent biomechanical studies on the partially obstructed small intestine have shown that the intestinal hypertrophy is associated with a stiffer wall, more collagen and impaired motility of the small intestine (Storkholm et al, 2007(Storkholm et al, , 2008. Previous biomechanical studies on the obstructed small intestine only evaluated the mechanical properties on the basis of the isotropic assumption (Storkholm et al, 2007) or a two dimensional analysis by using a thin-walled model (Zhao et al, 2010). However, the small intestinal wall is anisotropic (Yamada Hiroshi, 1970) and the thin-walled mechanical model ignores the mechanical properties throughout the wall (Fung, 1993).…”