The Morphomechanical Remodeling Research Of The Obstruction Rat Small Intestine

Small intestinal obstruction is a severe clinical condition.Partial or complete obstruction of the small intestine may occur if the the lumen is blocked by foreign bodies inside the lumen,by irreversible pathophysiological deformation such as volvulus,incarcerated hermia and intussusception,or by compression from tomors in the intestinal wall or in adjacent organs.Obstruction of the small intestine disrupts the absorption and barrier function,causes fluid and electrolyte loss as well as increases intraluminal pressure,which could impairs intestinal flow.Intestinal obstruction is a severe gastrointestinal condition with high mortality.Clinically,mechanical obstruction in the small intestine is the most common with complex pathogenesis and development.Hence,delay of treatment will severely affect recovery of intestinal structure and function,if reversible at all,and will result in 5-10% mortality,even 10% to 20% withstrangulation.One characteristic event following intestinal obstruction is morphomechanical remodeling.Animal studies have confirmed luminal dilation and intestinal wall hypertrophy proximal to the obstruction site due to the increased volume and pressure in the intestine.The wall compensates for the increased load by muscle hypertrophy and thickening of the wall to decrease the increased stress levels,which will prevent further stretch.Futhermore,changes in residual strains mainly depends on the thickness of the muscle layer,whereas stiffening to a large degree depends on thickening of the submucosa layer.The increased stiffness,i.e.resistance to distending forces mainly depends on increased collagen production.These protection mechanisms are time-dependent and location-dependent.Studies of the stress-strain properties of the tissue can provide important information on the mechanical function during the pathophysiological remodeling,which would help to understand the impaired food transport and smooth muscle function.A better understanding of the pathological changes following intestine obstrcution would also help develop strategies or devices for diagnosis and treatment.Recently,most previously studies on the partially obstructed in testinal focused on morphomechinal remodeling of longitudinal and circumferential direction in medium and long term.Few researches were done on complete obstruction and shear direction of partially obstruction.Hence,they cannot explain the morphometric and mechanical properties in small intestinal obstruction completely.In this study,a small loop was created to constrict the middle part of jejunum/distal ileum to obtain acute complete/partial small intestinal obstruction in a Spraque-Dawley rat model.In the acute complete of distal ileum model,five 6 cm-long intestinal segments proximal to the obstruction site were used for histological,morphometric and mechanical analysis at the designated times(6,12,24,36 and 48 hrs after complete intestinal obstruction).In partial obstruction of middle jejunum model,three 6-cm intestinal segments,obtained distal,proximal and further proximal to the site of obstruction or suturing site,were used for histological and un-load analysis.A independent development TRIAX mechine was used for mechanical testing.Moreover a numerical model was used for describing material characteristics of the tissue.The methods and main results were as follows:(1)Morphomechanical changes were huge but only subtle changes were observed between the five segments during the obstruction period.Due to dilation,the serosal length and mucosal length increased continuously from 6-48hrs(p<0.001).The wall area increased at 24 hrs and beyond(p<0.001),demonstrating tissue growth.The opening and bending angle decreased to minimum values at 24 hrs whereafter the opening angle increased and the bending angle returned to pre-obstruction levels.For the residual stretch ratios and the position of the neutral axis,the turning point occurred at 24 hrs.Histologically,the thickness and area of most wall layers were quite stable for the first 12 hrs but with an increase at the 24 hrs time point that continued to 48 hrs.The most pronounced change was found for the circumferential muscle layer(p<0.05).Analysis of picrosirius red stained slides showed that submucosal type 3 collagen fraction increased significantly(p<0.001)whereas the type ? collagen fraction decreased(p<0.001).Correlation analysis found that the circumferential residual stretch ratio of the mucosa was significantly positively correlated with the area of submucosa,circuferential longitudinal muscle,and moderate negative correlated with the type ? collagen.The longitudinal stretch ratio of the mucosa was positively correlated with the thickness of the submucosa.(2)The lumen size,wall thickness,wall cross-sectional area,and muscle layer thickness increased in S2 and S3 of the obstructed rats(P<0.001)with the most pronounced changes in S2.The opening angle decreased in S2 in the obstructed group(P<0.05).The tissue stiffness increased in circumferential and longitudinal direction whereas it was softer in shear direction,especially in S2(P<0.01).The ?1 of the Noe-Hooken model can represent the shear modulus of the small intestine.In conclusion,pronounced time-dependent morphomechanical remodeling was found in acute complete intestinal obstruction.The obstructed intestine went from dilation remodeling to growth remodeling during the 12-24 hrs interval after creating the obstruction.The material propoerties of partial obstructed segments were altered due to morphomechanical remodeling.The changes were biggest close to the site of obstruction.This study provides theoretical support for understanding the relationship between tissue remodeling and intestinal obstruction.It can form the rationale for improved diagnosis and treatment.