Mucosa-submucosa Layer Research Articles

Experimental investigations of the human oesophagus: anisotropic properties of the embalmed mucosa–submucosa layer under large deformation

Mechanical characterisation of the layer-specific, viscoelastic properties of the human oesophagus is crucial in furthering the development of devices emerging in the field, such as robotic endoscopic biopsy devices, as well as in enhancing the realism, and therefore effectiveness, of surgical simulations. In this study, the viscoelastic and stress-softening behaviour of the passive human oesophagus was investigated through ex vivo cyclic mechanical tests. Due to restrictions placed on the laboratory as a result of COVID-19, only oesophagi from cadavers fixed in formalin were allowed for testing. Three oesophagi in total were separated into their two main layers and the mucosa–submucosa layer was investigated. A series of uniaxial tensile tests were conducted in the form of increasing stretch level cyclic tests at two different strain rates: 1% s^{-1} and 10% s^{-1}. Rectangular samples in both the longitudinal and circumferential directions were tested to observe any anisotropy. Histological analysis was also performed through a variety of staining methods. Overall, the longitudinal direction was found to be much stiffer than the circumferential direction. Stress-softening was observed in both directions, as well as permanent set and hysteresis. Strain rate-dependent behaviour was also apparent in the two directions, with an increase in strain rate resulting in an increase in stiffness. This strain rate dependency was more pronounced in the longitudinal direction than the circumferential direction. Finally, the results were discussed in regard to the histological content of the layer, and the behaviour was modelled and validated using a visco-hyperelastic matrix-fibre model.

Rectal mucosal prolapse with an emphasis on endoscopic ultrasound appearance

AimThe diagnosis of mucosal prolapse syndrome (MPS) continues to be a challenge. Endoscopic ultrasound (EUS) is of clinical value in anorectal diseases. This study seeks to investigate the use of EUS in the diagnosis of MPS. MethodsA total of 39 patients diagnosed with MPS between June 2015 to December 2019 were included in this study. Their clinical histories, endoscopic images, EUS images, and pathological data were retrospectively collected, and the EUS images were reviewed to summarize the characteristics of MPS. ResultsIn total, 39 MPS patients were enrolled. The main presenting symptoms were bleeding (61.5%) and constipation (53.8%). Gross appearance of the rectal lesions was mainly classified into three types: 51.3% of the lesions were polypoidal/nodular, 33.3% were ulcerative and 15.4% were flat with erythematous mucosa only. A total of 10 patients underwent EUS operation. With regard to the EUS appearance of MPS, four patients with polypoidal/nodular lesions showed thickening of the mucosa on EUS. The diffuse thickening of the mucosa-submucosa layer and disappearance of the architectural structure was observed in four patients with ulcerative lesions. Finally, the thickening of the muscularis propria was observed in two flat lesions. The serosal layers were intact in all the MPS patients. Neither blood flow signals nor regional lymph nodes were observed on EUS. ConclusionThe EUS characteristics for MPS corresponding to different gross appearance can be classified into three types. These findings suggest that EUS is useful in the diagnosis of MPS.

Reversible stress softening in layered rat esophagus in vitro after potassium chloride activation.

Significant stress softening recovery after potassium chloride (KCl) administration was previously demonstrated in the intact rat esophageal wall. The aim of this study is to investigate the effect of KCl activation on stress softening recovery in the separated mucosa-submucosa layer and muscle layer of rat esophagus. Three series of loading-unloading distensions were carried out on 10 rat esophagi where the two separated layers were distended at luminal pressure levels 0.5, 1.0 and 2.0 kPa. Numerous distension cycles were done in [Formula: see text]-free Krebs solution before and after activation with KCl (110 mmol) for 3min in calcium-containing media. The diameter and luminal pressure were recorded for stress and strain calculation. During KCl activation, the muscle layer responded with a high-amplitude contraction, and the mucosa-submucosa layer responded with a longer-lasting low-amplitude contraction. The hysteresis loop areas from the muscle layer were significantly bigger than those from the mucosa-submucosa layer at distension pressures 1.0 and 2.0 kPa ([Formula: see text]). The calculated stiffness in the mucosa-submucosa layer was significantly higher than that in the muscle layer ([Formula: see text]). After activation with KCl, the stored energy and the stiffness after the stress and viscoelasticity softening increased in both layers, indicating that the reversible stress softening in esophagus after KCl activation is existed in both layers.

Sa1112 Three-Dimensional Myoarchitecture of Porcine Gastro-Esophageal Junction With Diffusion Tensor Imaging

Introduction: The anatomy and function of the gastro-esophageal junction (GEJ) is complex with mucosa-submucosa layers and smooth muscle layers organized into circular and longitudinal muscle layers. These layers continue from the esophagus into the GEJ and the stomach. Furthermore, the crura of the diaphragm and the lower esophageal sphincter are components of the GEJ. Little is known about the microstructure of the GEJ. Diffusion tensor imaging (DTI) allows mapping of the diffusion process of molecules, mainly water, in biological tissues. Water molecule diffusion patterns can therefore reveal microscopic details about tissue architecture. Its main clinical application has been in the study of neurological disorders such as acute stroke. Until now DTI has not be used much in esophagology. Aims: This study aims to reconstruct an anatomically realistic 3D model of the GEJ on the basis of DTI and more specifically to distinguish the muscle fiber transition between the esophagus, the stomach, and the diaphragmatic crura. Methods: Three 40-60kg pigs were used for obtaining the GEJ and adjacent parts of the esophagus, stomach and diaphragm. The pig was sacrificed during deep anesthesia before opening the abdominal and thoracic cavities. The intestines were removed whereas the liver and stomach was kept in place for maintaining the anatomical position of GEJ. The abdominal cavity and thoracic cavities were filled with formalin and closed. After 24h of tissue fixation, the pigs were reopened and the esophagus, upper part of stomach and intact diaphragm were dissected out and fixed with 4% formalin in an organ bath for further 2-3 days. A 7x7x7cm3 block including the entire GEJ region and lower part of the esophagus, upper part of the stomach, and the diaphragmatic crura was prepared for Magnetic Resonance (MR) scanning. Scanning was done in a Philips Intera, 1.5T MR scanner for obtaining anatomy imaging and DTI. The wall thickness at different layers of the GEJ as well as the helical angles of the longitudinal muscle fiber, the circular muscle fiber, the gastric sling fiber, gastric oblique fibers and diaphragm crura fiber along the central axis of the GEJ were calculated on the basis of the anatomic imaging and DTI. Results: It was possible to visualize the anatomical features of GEJ using DTI. The figure shows the total muscle fibers 3D distribution along the GEJ in a traced DT image. Differences in diffusion properties between the GEJ structures such as the sling fibers were easy to recognize and detailed layer data were obtained and used as input for an ongoing development of a realistic functional model of the GEJ. Conclusions and perspectives: This study clearly demonstrated that DTI may be useful in esophagology and moved a step further by establishing an anatomical-functional realistic computer model of the GEJ.

Tu1155 Stress Softening Behavior in the Mucosa-Submucosa and Muscle Layers in Normal and Diabetic Rat Esophagus

Tu1155 Stress Softening Behavior in the Mucosa-Submucosa and Muscle Layers in Normal and Diabetic Rat Esophagus

Mechanical characterization of stomach tissue under uniaxial tensile action

In this article, the tensile properties of gastric wall were investigated by using biomechanical test and theoretical analysis. The samples of porcine stomach strips from smaller and greater curvature of the stomach were cut in longitudinal and circumferential direction, respectively. The loading-unloading, stress relaxation, strain creep, tensile fracture tests were performed at mucosa-submucosa, serosa-muscle and intact layer, respectively. Results showed that the biomechanical properties of the porcine stomach depended on the layers, orientations and locations of the gastric wall and presented typical viscoelastic, nonlinear and anisotropic mechanical properties. During loading-unloading test, the stress of serosa-muscle layer in the longitudinal direction was 15–20% more than that in the circumferential direction at 12% stretch ratio, while it could reach about 40% for the intact layer and 50% for the mucosa-submucosa layer. The results of stress relaxation and strain creep showed that the variation degree was obviously faster in the circumferential direction than that in the longitudinal direction, and the ultimate residual values were also different for the different layers, orientations and locations. In the process of fracture test, the serosa-muscle layer fractured firstly followed by the mucosa-submucosa layer when the intact layer was tested, the longitudinal strips firstly began to fracture and the required stress value was about twice as much as that in the circumferential strips. The anisotropy and heterogeneity of mechanical characterization of the porcine stomach were related to its complicated geometry, structure and functions. The results would help us to understand the biomechanics of soft organ tissue.

Multiaxial mechanical response and constitutive modeling of esophageal tissues: Impact on esophageal tissue engineering

Congenital defects of the esophagus are relatively frequent, with 1 out of 2500 babies suffering from such a defect. A new method of treatment by implanting tissue engineered esophagi into newborns is currently being developed and tested using ovine esophagi. For the reconstruction of the biological function of native tissues with engineered esophagi, their cellular structure as well as their mechanical properties must be considered. Since very limited mechanical and structural data for the esophagus are available, the aim of this study was to investigate the multiaxial mechanical behavior of the ovine esophagus and the underlying microstructure. Therefore, uniaxial tensile, biaxial tensile and extension-inflation tests on esophagi were performed. The underlying microstructure was examined in stained histological sections through standard optical microscopy techniques. Moreover, the uniaxial ultimate tensile strength and residual deformations of the tissue were determined. Both the mucosa-submucosa and the muscle layers showed nonlinear and anisotropic mechanical behavior during uniaxial, biaxial and inflation testing. Cyclical inflation of the intact esophageal tube caused marked softening of the passive esophagi in the circumferential direction. The rupture strength of the mucosa-submucosa layer was much higher than that of the muscle layer. Overall, the ovine esophagus showed a heterogeneous and anisotropic behavior with different mechanical properties for the individual layers. The intact and layer-specific multiaxial properties were characterized using a well-known three-dimensional microstructurally based strain-energy function. This novel and complete set of data serves the basis for a better understanding of tissue remodeling in diseased esophagi and can be used to perform computer simulations of surgical interventions or medical-device applications.

Histomorphometrical study of the cervix during the oestrous cycle in adult Azarbaijan buffalo.

Summary In this study, genital tracts of 20 healthy non-pregnant buffaloes were collected from Urmia abattoir. These genital tracts were selected based on their ovaries conditions, half of them were in follicular phase and the other half were in luteal phase. The samples were taken from anterior, middle and posterior regions of the cervix and fixed in 10% buffer formalin. Then, histological sections of 5-7 µm thickness were prepared and stained with haematoxylin and eosin for histomorphometrical study and toluidine blue for study of mast cells. Histomorphometrical study was accomplished by graded and latticed objective lens device. The results revealed that the thickness of epithelium significantly (P<0.05) increased in the luteal phase. Mean thickness of mucosa-submucosa layers in the middle (290.4 ± 12.69 µm) and posterior (283.14 ± 16.49 µm) regions of the cervix in the follicular phase was significantly more than the luteal phase (P<0.05). Mean thickness of tunica muscularis increased significantly (P<0.05) during the follicular phase in the anterior region of the cervix (3325.28 ± 286.69 µm). This study also revealed that the mean distribution of mast cells in the luteal phase (0.53 ± 0.02) was significantly more than the follicular phase (P<0.001). Generally, this study showed that the histomorphometrical changes in the cervix of buffalo occur in the follicular and luteal phases of oestrous cycle. These changes may be related to the fluctuation of oestrogen and progesterone hormones and distribution of mast cells.

Stomach stress and strain depend on location, direction and the layered structure

The stomach is as other parts of the gastrointestinal tract functionally subjected to dimensional change. Hence, the biomechanical properties are of functional importance. Our group has previously demonstrated that the stress–strain properties of the rat and rabbit stomach wall were species-, location- and direction-dependent. We further wanted to study the anisotropic biomechanical properties of the stomach wall in pigs. Furthermore, we made an in-depth biomechanical test on the layered wall of the stomach in different regions. Two stomach strips were cut both in longitudinal direction (parallel with the greater curvature) and circumferential direction (perpendicular to the greater curvature) from the gastric fundus, corpus and antrum. One strip was used for the non-separated (intact) wall test and the other one was separated for the test on the mucosa–submucosa and muscle layers individually. The length, thickness and width of each strip were measured from digital images. The uni-axial stress and strain were computed from the force generation and the tissue strip deformation during stretching. The muscle layer was the thickest in the antrum whereas the mucosal–submucosal layer was the thickest in the corpus of the stomach ( P<0.01). The strips from the corpus were stiffest among the three regions in both longitudinal and circumferential directions ( P<0.001). The longitudinal strips was stiffer than the circumferential strips in all three regions ( P<0.001) and the mucosa–submucosa strips was stiffer than the intact wall and the muscle layer in both directions for the fundus and the corpus ( P<0.001). The constant a of the intact wall and mucosa–submucosa layer was in both directions linearly associated with the mucosa–submucosa thickness. In conclusion, the uni-axial stress–strain curves of pig stomach were location-, direction- and layer-dependent. The stiffer wall in the corpus is likely due to its thicker mucosa, i.e., the stiffness of the mucosa–submucosa layer seems can explain the intact wall stiffness. Since the structure and function of the pig stomach are similar to the human stomach, we believe that the data obtained from this study can be extended to humans. Detailed biomechanical mapping of the stomach will likely help us to understand physiological functions of the different parts of the human stomach, such as gastric accommodation and mechanosensation.

Determination of Homeostatic Elastic Moduli in Two Layers of the Esophagus

The function of the esophagus is mechanical. To understand the function, it is necessary to know how the stress and strain in the esophagus can be computed, and how to determine the stress-strain relationship of the wall materials. The present article is devoted to the issue of determining the incremental elastic moduli in the layers of the esophagus under homeostatic conditions. The esophagus is treated as a two-layered structure consisting of an inner collagen-rich submucosa layer and an outer muscle layer. We adopt a theory based on small perturbation experiments at homeostatic conditions for determination of incremental moduli in circumferential, axial, and cross directions in the two layers. The experiments are inflation, axial stretching, circumferential bending, and axial bending. The analysis takes advantage of knowing the esophageal zero-stress state (an open sector with an opening angle of 59.4 +/- 13.2 deg). The neutral axis was located 27% +/- 1.9%away from the mucosal surface. It is demonstrated that under homeostatic conditions, the incremental moduli are layer and direction dependent. The incremental modulus is the highest in the axial direction. Furthermore, the axial moduli for the two layers are similar, whereas in the circumferential direction, the incremental modulus is a factor of 6 higher in the mucosa-submucosa layer compared to the muscle layer. Hence, the esophagus has to be treated as a composite, anisotropic body. With this additional information, we can then look forward to a vision of truly understanding the mechanical events of the esophagus.

Opening angle and residual strain in a three-layered model of pig oesophagus

Studies of various biological tissues have shown that residual strains are important for tissue function. Since a force balance exists in whole wall thickness specimens cut radially, it is evident that layer separation is an important procedure in the understanding of the meaning of residual stresses and strains. The present study investigated the zero-stress state and residual strain distribution in a three-layer model of the pig oesophagus. The middle part of the oesophagus was obtained from six slaughterhouse pigs. Four 3-mm-wide rings were serially cut from each oesophagus. Two of them were used for separating the wall into mucosa–submucosa, inner and outer muscle layers. The remaining two rings were kept as intact rings. The inner and outer circumferences and wall thickness of different layers in intact and separated rings were measured from the digital images in the no-load state and zero-stress state. The opening angle was measured and the residual strain at the inner and outer surface of different layers and the intact wall were computed. Compared with intact sectors (62.8±9.8°), the opening angles were smaller in the inner muscle sectors (37.2±11.4°, P<0.01), whereas the opening angles of mucosa–submucosa (63.9±6.8°) and outer muscle sectors (63.9±6.8°) did not differ ( P>0.1). Referenced to the zero-stress state of the intact sectors, the inner and outer residual strains of the intact rings was −0.128±0.043 and outer residual strain was 0.308±0.032. Referenced to the “true” zero-stress state of separated three-layered sectors, the inner residual strain of intact rings were −0.223±0.021 ( P<0.01) and 0.071±0.022 ( P<0.01). Referenced to the “true” zero-stress state, the residual strain distribution of different layers in intact rings was shown that the inner surface residual strain was negative at mucosa–submucosa and inner muscle layers and was positive at outer muscle layer, whereas the outer surface residual strain was negative at the mucosa–submucosa layer and positive at the inner and outer muscle layers. For the separated different layered rings, the inner residual strain was negative and outer residual strain was positive; however, the absolute values did not differ ( P>0.1). In conclusion, it is possible to microsurgically separate the oesophagus into three layers, i.e., mucosa–submucosa, inner muscle and outer muscle layers, the residual strain differ between the layers, and the residual strain distribution was more uniform after the layers were separated.

Impaired contractility and remodeling of the upper gastrointestinal tract in diabetes mellitus type-1

To investigate that both the neuronal function of the contractile system and structural apparatus of the gastrointestinal tract are affected in patients with longstanding diabetes and auto mic neuropathy. The evoked esophageal and duodenal contractile activity to standardized bag distension was assessed using a specialized ultrasound-based probe. Twelve type-1 diabetic patients with autonomic neuropathy and severe gastrointestinal symptoms and 12 healthy controls were studied. The geometry and biomechanical parameters (strain, tension/stress, and stiffness) were assessed. The diabetic patients had increased frequency of distension-induced contractions (6.0 +/- 0.6 vs 3.3 +/- 0.5, P < 0.001). This increased reactivity was correlated with the duration of the disease (P = 0.009). Impaired coordination of the contractile activity in diabetic patients was demonstrated as imbalance between the time required to evoke the first contraction at the distension site and proximal to it (1.5 +/- 0.6 vs 0.5 +/- 0.1, P = 0.03). The esophageal wall and especially the mucosa-submucosa layer had increased thickness in the patients (P < 0.001), and the longitudinal and radial compressive stretch was less in diabetics (P < 0.001). The esophageal and duodenal wall stiffness and circumferential deformation induced by the distensions were not affected in the patients (all P > 0.14). The impaired contractile activity with an imbalance in the distension-induced contractions likely reflects neuronal abnormalities due to autonomic neuropathy. However, structural changes and remodeling of the gastrointestinal tract are also evident and may add to the neuronal changes. This may contribute to the pathophysiology of diabetic gut dysfunction and impact on future management of diabetic patients with gastrointestinal symptoms.

Biomechanical and histomorphometric esophageal remodeling in type 2 diabetic GK rats

Diabetes mellitus induces remodeling of the morphology and mechanical properties in the gastrointestinal tract. This study aimed to investigate the histomorphometric and biomechanical remodeling of esophagus in the diabetic type 2 model Goto-Kakizaki (GK) rats. Five male diabetic GK rats and five male nondiabetic Wistar rats were used in this study. The mechanical test was performed in vitro where the whole esophagus was stretched to its in situ length and distended with pressures up to 10 cm H 2O using a ramp distension protocol. The pressure and outer diameter were recorded. Circumferential stress (force per area) and strain (deformation) were computed from the diameter and pressure data using the zero-stress state as reference. The zero-stress state was obtained by cutting esophageal rings radially. This caused the rings to open up into a sector. The thickness, area, and the opening angle were measured from the digitized images. The layer circumference, thickness, and area were measured from histological slides. The collagen fraction was determined from histological slides with Van Gieson stain. Diabetes induced pronounced morphometric changes, e.g., the wall thickness and wall cross-sectional area significantly increased in the GK rats ( P<.01). Histologically, the circumference, thickness, and area of the muscle layer and the collagen fraction of mucosa–submucosa layer were significantly increased in the GK rats ( P<.01). The opening angle, outer residual strain, and residual strain difference to wall thickness ratio decreased significantly in the GK rats ( P<.05 and P<.01). Furthermore, the circumferential stiffness of the esophagus is significantly higher in the GK rats than in the normal rats ( P<.01). In conclusion, histomorphometric and biomechanical remodeling is a feature of the esophageal wall in GK rats.

The Effect of Digestion of Collagen and Elastin on Histomorphometry and the Zero-Stress State in Rat Esophagus

To understand the physiology and pathology of the esophagus, it is necessary to know the mechanical properties and their dependence on the structural components. The aim of this study was to investigate the effect of collagenase and elastase on the morphological and biomechanical properties in the no-load and zero-stress states in the rat esophagus. Twenty tissue rings from each esophagus of seven normal rats were sectioned in an organ bath containing calcium-free Krebs solution with dextran and EGTA. After the rings were photographed in the no-load state, 8 of the 20 rings were separated into mucosa-submucosa and muscle rings and the rings were transferred to four different solutions containing collagenase, elastase, or corresponding control solutions. The rings were cut radially to obtain the zero-stress state and photographed again. The thickness, area, and opening angle were measured from the digitized images. The collagen and elastin area fractions were determined from histological slides with Van Gieson and Weigert's elastic stain. The opening angles and residual strain did not differ in the nonseparated enzyme-treated rings and control rings. However, in the separated mucosa-submucosa ring the opening angle was significantly smaller after treatment than that in control rings (P < 0.01). Collagenase and elastase reduced collagen and elastin in the mucosa-submucosa layer about 40% in the nonseparated wall and 54% in the separated mucosa-submucosa layer (P < 0.01). Collagenase and elastase increased the thickness in the separated mucosa-submucosa layer compared to the control (P < 0.05). Disconnection between the epithelia and the lamina propria was histologically observed after elastase digestion. In conclusion, collagenase and elastase caused the opening angle and the residual strain in the separated mucosa-submucosa layer to decrease. The opening angle of the separated mucosa-submucosa layer depended to some extent on the fraction of collagen and elastin.

Biomechanical properties of the layered oesophagus and its remodelling in experimental type-1 diabetes

Passive biomechanical properties in term of the stress–strain relationship and the shear modulus were studied in separated muscle layer and mucosa–submucosa layer in the oesophagus of normal and STZ (streptozotocin)-induced diabetic rats. The mucosa–submucosa and muscle layers were separated using microsurgery and studied in vitro using a self-developed test machine. Stepwise elongation and inflation plus continuous twist were applied to the samples. A constitutive equation based on a strain energy function was used for the stress–strain analysis. Five material constants were obtained for both layers. The mucosa–submucosa layer was significantly stiffer than the muscle layer in longitudinal, circumferential and circumferential–longitudinal shear direction. The mechanical constants of the oesophagus show that the oesophageal wall was anisotropic, the stiffness in the longitudinal direction was higher than in the circumferential direction in the intact oesophagus ( P < 0.001 ) and in the muscle layer ( P < 0.05 ). Diabetes-induced pronounced increase in the outer perimeter, inner perimeter and lumen area in both the muscle and mucosa–submucosa layer. The growth of the mucosa–submucosa layer ( P < 0.001 ) was more pronounced than the muscle layer ( P < 0.05 ). Furthermore, the circumferential stiffness of the mucosa–submucosa layer increased 28 days after STZ treatment. In conclusion, the oesophagus is a non-homogeneous anisotropic tube. Thus, the mechanical properties differed between layers as well as in different directions. Morphological and biomechanical remodelling is prominent in the diabetic oesophagus.

A two-layered mechanical model of the rat esophagus. Experiment and theory

BackgroundThe function of esophagus is to move food by peristaltic motion which is the result of the interaction of the tissue forces in the esophageal wall and the hydrodynamic forces in the food bolus. The structure of the esophagus is layered. In this paper, the esophagus is treated as a two-layered structure consisting of an inner collagen-rich submucosa layer and an outer muscle layer. We developed a model and experimental setup for determination of elastic moduli in the two layers in circumferential direction and related the measured elastic modulus of the intact esophagus to the elastic modulus computed from the elastic moduli of the two layers.MethodsInflation experiments were done at in vivo length and pressure-diameters relations were recorded for the rat esophagus. Furthermore, the zero-stress state was taken into consideration.ResultsThe radius and the strain increased as function of pressure in the intact as well as in the individual layers of the esophagus. At pressures higher than 1.5 cmH2O the muscle layer had a larger radius and strain than the mucosa-submucosa layer. The strain for the intact esophagus and for the muscle layer was negative at low pressures indicating the presence of residual strains in the tissue. The stress-strain curve for the submucosa-mucosa layer was shifted to the left of the curves for the muscle layer and for the intact esophagus at strains higher than 0.3. The tangent modulus was highest in the submucosa-mucosa layer, indicating that the submucosa-mucosa has the highest stiffness. A good agreement was found between the measured elastic modulus of the intact esophagus and the elastic modulus computed from the elastic moduli of the two separated layers.

Two-layered quasi-3D finite element model of the oesophagus

Analysis of oesophageal mechanoreceptor-dependent responses requires knowledge about the distribution of stresses and strains in the layers of the organ. A two-layered and a one-layered quasi-3D finite element model of the rat oesophagus were used for simulation. An exponential pseudo-strain energy density function was used as the constitutive equation in each model. Stress and strain distributions at the distension pressures 0.25 and 1.0 kPa were studied. The stress and strain distributions depended on the wall geometry. In the one-layered model, the stress ranged from −0.24 to 0.38 kPa at a pressure of 0.25 kPa and from −0.67 to 2.57 kPa at a pressure of 1.0 kPa. The stress in the two-layered model at the pressure of 0.25 and 1.0 kPa varied from −0.52 to 0.64 kPa and from −1.38 to 3.84 kPa. In the two-layered model, the stress was discontinuous at the interface between the muscle layer and the mucosa–submucosa layer. The maximum stress jump was 1.67 kPa at the pressure of 1.0 kPa. The present study provides a numerical simulation tool for characterising the mechanical behaviour of a multi-layered, complex geometry organ.

Ex Vivo 1H MR Spectroscopy: Normal gastric and cancer tissue

Purpose: In this study, we attempted to ascertain the proton magnetic resonance spectroscopy ( MRS) peak characteristics of human gastric tissue layers and finally to use the metabolic peaks of MRS to distinguish between normal and abnormal gastric specimens. Materials and Methods: Ex-vivo MRS examinations of thirty-five gastric specimens were performed to distinguish abnormal gastric tissues invaded by carcinoma cells from normal stomach-wall tissues. High-resolution 400-MHz (9.4-T) nuclear magnetic resonance (NMR) spectra of two gastric layers, a proper muscle layer, and a composite mucosasubmucosa layer were compared with those of clinical 64- MHz (1.5-T) MR spectra. Three-dimensional spoiled gradient recalled (SPGR) images were used to determine the size and the position of a voxel for MRS data collection. Results: For normal gastric tissue layers, the metabolite peaks of 400-MHz MRS were primarily found to be as follows: lipids at 0.9 ppm and 1.3 ppm; alanine at 1.58 ppm; N-acetyl neuraminic acid (sialic acid) at 2.03 ppm; and glutathione at 2.25 ppm in common. The broad and featureless featureless spectral peaks of the 64-MHz MRS were bunched near 0.9, 1.3, and 2.0, and 2.2 ppm in human specimens without respect to layers. In a specimen (Borrmmann type III) with a tubular adenocarcinoma, the resonance peaks were measured at 1.26, 1.36 and 3.22 ppm. All the peak intensities of the spectrum of the normal gastric tissue were reduced, but for gastric tumor tissue layers, the lactate peak split into 1.26 and 1.39 ppm, and the peak intensity of choline at 3.21 ppm was increased. Conclusion: We found that decreasing lipids, an increasing lactate peak that split into two peaks, 1.26 ppm and 1.36 ppm, and an increasing choline peak at 3.22 ppm were markers of tumor invasion into the gastric tissue layers. This study implies that MR spectroscopy can be a useful diagnostic tool for gastric cancer.

Histomorphometry and strain distribution in pig duodenum with reference to zero-stress state.

The morphometry at no-load and zero-stress states and residual circumferential strains were determined along the pig duodenum in vitro in seven pigs. The no-load state was obtained by cutting eleven 2-mm-wide rings at 10% intervals along the duodenum. The zero-stress state was obtained by cutting the rings radially. The zero-stress state provides a standard morphological state to describe tissue since internal and external forces do not affect the tissue. The morphometric measures were obtained from digitized images, and the layer thicknesses were measured from histological sections. The mucosal and serosal circumferences, the wall thickness, and the wall thickness-to-mucosal radius ratio were largest in the proximal end of the duodenum (f > 1.9, P < 0.05). The thickness of the submucosal stratum compactum layer and the opening angle increased in distal direction (f = 2.3, P < 0.05 and = 6.5, P < 0.001). The residual strain at the mucosal surface was negative, indicating that the mucosa-submucosa layers of duodenum in no-load state are in compression. Distension experiments showed that the residual strain makes the stress distribution through the wall more uniform in the pressurized state. In conclusion, the large circumferential residual strains must be taken into account in the study of physiological problems, in which the stresses and strains are important, eg, the bolus transport function.

Radial heat and water transport across the airway wall

The thermal profiles in the airways of healthy human volunteers and patients with asthma differ after cessation of hyperpnea. The asthmatic patients rewarm their airways more rapidly. To identify thermal properties and processes that could account for the difference between these populations, we developed a model describing the radial transport of heat and water across the trachea. A distinctive feature of the model is a variable parameter describing blood supply to the mucosal and submucosal layers. Simulations performed with the model are initiated by a breath-hold maneuver and are propagative in time. Blood perfusion rates in the airway wall, the thickness of the layer of airway surface liquid, and the mucosa-submucosa thickness, all thought to be more pronounced in asthmatic patients, were varied by changing model parameters and initial conditions. Increasing the thickness of the liquid layer by more than an order of magnitude had little effect on the temperature or water content in the airway lumen. Doubling the blood flow to the mucosa-submucosa resulted in a slight increase in airway temperature. When this effect was coupled, however, with an increase in the thickness of the mucosa-submucosa layer, the increase in temperature was more pronounced. Because the bronchial circulation is the major source of heat to the airway, these results indicate that differences in airway wall thickness coupled with differences in the magnitude or responsiveness of the bronchial microcirculation could account for the differences in intra-airway temperature between the two populations.