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ABSTRACT: Barrett's esophagus (BE) is characterized by intestinal metaplasia with the differentiated epithelium replaced by another type of epithelium morphologically similar to normal intestinal epithelium. The metaplasia is preceded by bile and acid reflux into the esophagus. BE is a premalignant condition associated with increased risk of esophageal cancer, especially esophageal adenocarcinoma. The Caudal-related homeodomain transcription factors Caudal-related homeodomain transcription factor CDX1 and CDX2 are expressed exclusively in the small and large intestine, playing important roles in proliferation and differentiation of intestinal epithelial cells. Ectopic expression of CDX1 and CDX2 occurs in BE. The apical sodium-dependent bile acid transporter (ASBT) is expressed primarily in terminal ileum where it is a key factor for intestinal reabsorption of bile salts. In addition to upregulation of CDX1 and CDX2, ASBT expression is up-regulated in BE. Furthermore, both CDX1/CDX2 and ASBT expressions are down-regulated in high-grade esophageal dysplasia. The alteration of the above-mentioned factors calls for attention: what is the relationship between CDXs and ASBT aberrant expression in BE? In this commentary, we discuss this issue on basis of the recent study done by Ma et al.
World Journal of Gastroenterology 05/2013; 19(18):2736-2739. · 2.47 Impact Factor
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ABSTRACT: Little is known about the mechanisms for the biomechanical remodeling in diabetes. The histomorphology, passive biomechanical properties and expression of advanced glycation end product (N epsilon-(carboxymethyl) lysine, AGE) and its receptor (RAGE) were studied in jejunal segments from 8 GK diabetic rats (GK group) and 10 age-matched normal rats (Normal group). The mechanical test was done by using a ramp distension of fluid into the jejunal segments in vitro. Circumferential stress and strain were computed from the length, diameter and pressure data and from the zero-stress state geometry. AGE and RAGE were detected by immunohistochemistry staining. Linear regression analysis was done to study association between the glucose level and AGE/RAGE expression with the histomorphometric and biomechanical parameters. The blood glucose level, the jejunal weight per length, wall thickness, wall area and layer thickness significantly increased in the GK group compared with the Normal group (P<0.05, P<0.01 and P<0.001). The opening angle and absolute values of residual strain decreased whereas the circumferential stiffness of the jejunal wall increased in the GK group (P<0.05 and P<0.01). Furthermore, stronger AGE expression in the villi and crypt and RAGE expression in the villi were found in the GK group (P<0.05 and P<0.01). Most histomorphometric and biomechanical changes were associated with blood glucose level and AGE/RAGE expression. In conclusion, histomorphometric and biomechanical remodeling occurred in type 2diabetic GK rats. The increasing blood glucose level and the increased AGE/RAGE expression were associated with the remodeling, indicating a causal relationship.
Journal of biomechanics 02/2013; · 2.66 Impact Factor
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ABSTRACT: OBJECTIVE
In patients with long-standing diabetes mellitus (DM), there is increasing evidence for abnormal processing of gastrointestinal sensations in the central nervous system. Using magnetic resonance diffusion tensor imaging, we characterized brain microstructure in areas involved in visceral sensory processing and correlated these findings to clinical parameters.RESEARCH DESIGN AND METHODS
Twenty-six patients with DM and gastrointestinal symptoms and 23 healthy control subjects were studied in a 3T scanner. The apparent diffusion coefficient (i.e., diffusivity of water) and fractional anisotropy (FA) (i.e., organization of fibers) were assessed in the "sensory matrix" (cingulate cortex, insula, prefrontal and secondary sensory cortex, amygdala, and corona radiata) and in corpus callosum.RESULTSPatients had decreased FA values compared with control subjects: 1) all areas (P = 0.025); 2) anterior (P < 0.001), mid- (P = 0.001), and posterior (P < 0.001) cingulate cortex; 3) prefrontal cortex gray matter (P < 0.001); 4) corona radiata (P < 0.001); 5) secondary sensory cortex (P = 0.008); 6) anterior white matter (P = 0.045); and anterior gray matter (P = 0.002) and posterior gray matter (P = 0.002) insula. No difference was found in corpus callosum (P > 0.05). The microstructural changes were for some areas correlated to clinical parameters such as bloating (anterior insula), mental well-being (anterior insula, prefrontal cortex, and mid-cingulated and corona radiata), autonomic function based on electrocardiographic results (posterior insula and anterior cingulate), and presence of gastroparesis (anterior insula).CONCLUSIONS
The findings of this explorative study indicate that microstructural changes of brain areas involved in visceral sensory processing are associated with autonomic dysfunction and therefore may be involved in the pathogenesis of gastrointestinal symptoms in DM patients.
Diabetes care 11/2012; · 8.09 Impact Factor
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ABSTRACT: Sensory nerve endings are widely distributed throughout the body. Neither the nature of the mechanosensitive channels nor the principal mechanical stimulus for these receptors is known. Afferents supplying the gastrointestinal tract respond to distension and contraction are responsible for coordinated reflex control, feeding behaviour and sensations including pain. Different populations of intestinal afferent fibres follow different pathways to the central nerve system (CNS), have different terminal fields, and possess different thresholds for activation that may reflect the extent to which mechanical forces are distributed and dissipated by non-neural structures in the bowel wall. In this study we have characterised the stimulus-response function of afferent fibres innervating the rat jejunum, correlating luminal distensions in the bowel wall with the firing frequency of mesenteric afferent nerve bundles. Combining video imaging with intraluminal pressure recordings and utilizing a strain softening protocol we have determined whether mechanoreceptors respond primarily to stress or strain. Multiunit afferent recordings were separated using spike discrimination software into low-threshold (LT) and high-threshold (HT) single units. For multifibre afferent recordings and both LT and HT single units we observed a linear relationship between circumferential stress and mesenteric afferent discharge that was independent of distension-induced tissue softening with correlation coefficients > 0.9. A 5 fold change in the rate of applied distension did not significantly alter the magnitude of the afferent response and the linearity of the stress-dependent mechanotransduction in both multifibre and the LT, HT afferent fibres (P>0.2). Thus, the firing characteristics of intestinal mechanoreceptors are linearly associated with the input in terms of mechanical stress.
Experimental physiology 07/2012; · 3.17 Impact Factor
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ABSTRACT: The stomach has the ability to change its geometry and volume during digestion. Thus, the stomach shape changes dynamically due to changes in contents and due to pressure from adjacent organs. Full-field strain analysis is therefore important for accurate estimation of the true deformation in this highly non-homogeneous, anisotropic organ. The aim of this study is to introduce a modified non-rigid image registration based 3D shape context method combined with a full-field strain analysis method to describe a distension-induced 3D gastric deformation. The geometry of a normal rat stomach at distension pressures from 0.05 kPa to 0.8 kPa were obtained by ultrasonic scanning. The full-field strain distribution of the 3D gastric model between the reference state and the distended state were computed on the basis of the improved 3D shape context method and full-field strain analysis method. The registered surface showed a good agreement with the real deformed surface for all distension states. However, the errors increased with the distension pressure due to increasing dissimilarity between the deformed and the reference surface. The strain distributions on the stomach surface were non-uniform with the largest deformation in the non-glandular part and the greater and lesser curvature when the pressure was higher than 0.2 kPa. The wall stiffness of the non-glandular part was softer than that of the glandular part. The modelling analysis method which is closely allied with the non-rigid image registration and strain analysis provides a kinematically possible deformation mode of the gastric wall. This method can be potentially used for clinical data estimating the kinematical properties of the human visceral organs in health and disease.
Journal of biomechanics 04/2012; 45(9):1566-73. · 2.66 Impact Factor
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ABSTRACT: BackgroundThis study aimed to investigate wound geometry and tissue damage caused by several different trocar types using a quantitative
functional luminal imaging probe (FLIP) geometric profile and histomorphologic analysis.
MethodsFour pigs were used in this study. After general anesthesia, six different trocars were randomly inserted at preselected locations
in the porcine abdominal wall. The hydration status of the animals was monitored and maintained. A bag mounted on a FLIP was
used to profile the geometry of the trocar holes during distension. After the FLIP study, the abdominal wall surrounding the
trocar holes was harvested. The tissue was fixed in neutral 10% buffered formalin solution for more than 24h. The samples
contained control tissue (undamaged) and test tissue (damaged) through the entire rectangular tissue block. Approximately
four to seven slides were cut parallel to the surface from each sample. Each slide was photographed, and the morphometry of
the hole and damaged areas were measured and displayed three-dimensionally. The histologic sections were analyzed with regard
to acute damage, bleeding, and acute inflammation of the skin, muscle, and fascia.
ResultsThe FLIP study demonstrated differences between the six trocars. These were mainly due to differences between the Versaport
Plus V2 bladed trocar with the smooth cannula, the Applied Medical Separator nonbladed access system with threaded cannula,
and the VersaStep Plus trocar. The morphometry data showed the smallest hole and damage areas for the Versaport Plus V2 bladed
trocar with the smooth cannula. The damaged area divided by the trocar hole area was smallest for the VersaStep plus trocar
and the Ethicon Endopath bladed trocar with a stability cannula (p<0.05). The histologic analysis showed that the VersaStep Plus trocar and the Ethicon Endopath bladed trocar with a stability
cannula gave the least bleeding and inflammation (p<0.05).
ConclusionAn agreement was found between the geometric data obtained by FLIP, the morphometric analysis, and the histology.
Surgical Endoscopy 04/2012; 23(5):1004-1012. · 4.01 Impact Factor
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ABSTRACT: To be able to characterize intestinal mechano-electrical transduction, i.e. the mechanoreceptor behaviour, quantitative nerve studies with controlled and quantified stimulus are needed. This study aimed to determine the relationship between mechanical stress relaxation and afferent discharge adaptation evoked by fast isovolumetric bag distensions in the rat jejunum.
Multiunit afferent activity was recorded in vivo from jejunum afferents from five male Wistar rats. The jejunum was distended via a bag at a distension speed of 0.5 ml/s to volumes of 0.2, 0.25, 0.3 and 0.4 ml, respectively. The distension was stopped and the volume was kept constant for 2 min to induce stress relaxation. The pressure in the bag, the afferent discharge (spike rate) and the diameter of the segment during the relaxation time were recorded simultaneously.
The afferent discharge responses to distension showed a pattern with a peak during the sudden loading followed by decreasing activity with time. At distension volumes of 0.2, 0.25, 0.3 and 0.4 ml, the afferent discharge declined faster and to a greater extent (94%, 91%,96% and 87%) than the stress decreased (55%, 45%, 59% and 56%) during stress relaxation (p<0.001). Both the stress and the afferent discharge during the constant volume distension were independent of the distension volumes (p>0.5). The stress and the afferent discharge during the distension can be described mathematically on the basis of the quasi-linear theory of viscoelasticity. The association between the stress and the afferent discharge during the constant volume distension is linear with the same slope under various distension volumes.
Intestinal mechanoreceptors were sensitive to the stress stimulus and a linear association between the stress relaxation and afferent discharge adaptation was found. The quasi-linear theory of visco-elasticity can be transferred to analysis of mechanical stimulus evoked afferent discharge.
Journal of biomechanics 04/2012; 45(9):1574-9. · 2.66 Impact Factor
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ABSTRACT: This study aimed to characterize the effect of mechanical stimuli on mesenteric afferent nerve signaling in the isolated rat jejunum in vitro. This was done to determine the effect of mechanical stresses and strains relative to nonmechanical parameters (neurogenic adaptation). Mechanical stimulations were applied to a segment of jejunum from 15 rats using ramp distension with water at three rates of distension, a relaxation test (volume maintained constant from initial pressure of 20 or 40 mmHg), and a creep test (pressure maintained constant). Circumferential stress and strain and the spike rate increase ratio were calculated for evaluation of afferent nerve activity during the mechanical stimulations. Ramp distension evoked two distinct phases of afferent nerve signaling as a function of circumferential stress or strain. Changing the volume distension rate did not change the stress-strain relationship, but faster distension rate increased the afferent firing rate (P < 0.05). In the stress relaxation test, the spike rate declined faster and to a greater extent than the stress. In the creep test, the spike rate declined, despite a small increase in the strain. Three classes of mechanosensitive single-afferent units (low, wide dynamic range, and high threshold units) showed different response profiles against stress and strain. Low-threshold units exhibited a near linear relationship against the strain (R(2) = 0.8095), whereas high-threshold units exhibited a linear profile against the stress (R(2) = 0.9642). The afferent response is sensitive to the distension speed and to the stress and strain level during distension. However, the afferent nerve response is not a simple function of either stress or strain. Nonmechanical time-dependent adaptive responses other than those related to viscoelasticity also play a role.
AJP Gastrointestinal and Liver Physiology 02/2012; 302(9):G1025-34. · 3.43 Impact Factor
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ABSTRACT: Previous numerical simulations on low-density lipoprotein (LDL) concentration polarization in the arterial system indicated that LDL concentration polarization might play an important role in the genesis and development of atherosclerosis. To date, no in vivo experiments have examined this question directly, and the molecular mechanisms are unknown. In this study, ten rabbits were treated with gel-silica loop to develop a defined local stenosis in the straight segment of the left carotid artery. Both numerical simulation and experiment measurements showed that the concentration of LDL was about 35% higher at the blood/arterial wall interface than in the lumen on the distal side of the stenosis. Atherosclerotic lesions with abundant lipid deposits were observed and stromal derived factor-1 (SDF-1) was detected at the distal end of the stenosis, while the straight segment was plaque-free. In vitro studies demonstrated that LDL-induced SDF-1 expression in endothelial cells and increased monocyte adhesion to endothelial cells in a dose-dependent manner. The adhesion was suppressed when endothelial cells were pretreated with SDF-1 antibody. These results suggested LDL concentration polarization contributed to the localization of atherosclerosis and to the expression of SDF-1. In turn, SDF-1 facilitated plaque formation.
Annals of biomedical engineering 01/2012; 40(5):1018-27. · 2.41 Impact Factor
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ABSTRACT: Background. Stapling devices for creating anastomosis in internal organs are commonly used during surgery. Despite the obvious advantages of shortened procedure duration and fewer complications to manual suturing, staple-line leakage during intestinal anastomosis likely relates to the interaction between the staples and the tissue and to the tissue mechanical properties. The authors studied the deformation pattern close to the anastomosis to learn more about the mechanism involved in leakage. Methods. End-to-end anastomosis in pig small intestine was done using 21-mm circular staplers. Distension with pressure up to 100 cm H(2)O was done on the anastomosed segment. Surface markers were tracked using a microscope and a CCD camera. Circumferential and longitudinal strains were computed. Results. The staples restricted the deformation both in circumferential and longitudinal directions and induced a heterogeneous strain distribution. Circumferential strains were bigger between the staples (range 0.5-1) than inside the staples (range 0-0.3). The longitudinal strain ranged from 0 to slightly negative between the staples, indicating longitudinal compression. The negative strains turned into positive strains with increasing distance from the anastomosis. Further away from the anastomosis the longitudinal strain was in the range 0.3 to 0.5. Conclusion. The surface strain field was heterogeneously close to the stapled anastomosis. The longitudinal compression between staples in the longitudinal direction during inflation may have a beneficial effect preventing leakage, a phenomenon that needs further studies. The method may be useful in the design and validation of new staplers.
Surgical Innovation 11/2011; 19(3):281-7. · 2.13 Impact Factor
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ABSTRACT: Gastrointestinal disorders and symptoms are common in diabetic patients. Advanced glycation end-products (AGEs) and their receptor (RAGE) have been proposed as an important pathological mechanism underlying diabetic complications, such as diabetic cardiopathy, retinopathy, nephropathy, etc. The aims were to study the distribution of AGE and RAGE in the normal and diabetic small intestine and colon in rats and the possible relationship between AGEs/RAGE and diabetes-induced intestinal structural remodeling.
Diabetic and age-matched normal rats survived for 56 days. The body weight and blood glucose were measured regularly until day 56. Jejunal, ileal, and colonic segments were excised. The wet weight per unit length and the layer thickness were measured. AGE and RAGE were detected by immunohistochemical staining.
The wet weight per unit length in the three segments and the layer thickness in jejunum and ileum increased in the diabetic rats. The staining density of AGE in diabetic rats was higher in the villi of jejunum and ileum, and in the crypt and circumferential muscle layer of ileum compared to normal rats. The staining intensity of RAGE increased in ganglia, crypt, and brush border of diabetic jejunum and ileum as well as in ganglia of diabetic colon. Positive association was found between the accumulation of AGE and RAGE and the thickness of the different layers.
The expression of AGE and RAGE is up-regulated in the small intestine and colon of diabetic rats. The increased AGE and RAGE levels may contribute to diabetic GI dysfunction.
Digestive Diseases and Sciences 11/2011; 57(1):48-57. · 2.12 Impact Factor
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ABSTRACT: The following on mechanism-based evaluation and treatment of esophageal disordered contains commentaries on multimodal stimulation to study esophageal function, the neurophysiological and autonomous assessment of sensory abnormalities, and the clinical value of the novel diagnostic combinations to propose a mechanically targeted treatment.
Annals of the New York Academy of Sciences 09/2011; 1232(1):341 - 348. · 3.15 Impact Factor
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ABSTRACT: The pathogenesis of symptoms in urolithiasis is poorly understood. Traditionally increased endoluminal pressure is considered the main mechanism causing pain in the upper urinary tract but clinical data are sparse. The aim of the present study was to develop a new model related to mechanosensation in order to describe the geometric and mechanical properties of the renal pelvis in patients with kidney stone disease. Pressure measurement in the renal pelvis was done during CT-pyelography in 15 patients who underwent percutaneus nephrolithotomy. The sensory intensity was recorded at the thresholds for first sensation and for pain. 3D deformation and strain were calculated in five patients. The deformation of pelvis during distension was not uniform due to the complex geometry. The pelvis deformed to 113 ± 6% and 115 ± 11% in the longitudinal and circumferential directions, respectively. Endoluminal pressure in the renal pelvis corresponded positively to the sensory ratings but the referred pain area was diffuse located and varied in size. The present study provides a method for describing the mechanosensory properties and 3D deformation of the complex renal pelvis geometry. Although there was a relation between pressure and pain score, the non-homogenous spatial strain distribution suggests that the 3D biomechanical properties of the renal pelvis are not reflected by simple estimates of tension based on pressure and volume.
Urological Research 09/2011; 40(4):305-16. · 1.23 Impact Factor
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ABSTRACT: The following contains commentaries on distensibility testing using the functional lumen imaging probe (FLIP); the use of the distention test of the esophageal body in the clinic diagnosis of noncardiac chest pain; the functional lumen imaging in gastroesophageal reflux disease-impaired esophagogastric junction; a multimodal pain model for the esophagus; the rationale for distensibility testing; and further developments in standardized distension protocols.
Annals of the New York Academy of Sciences 09/2011; 1232:331-40. · 3.15 Impact Factor
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ABSTRACT: Systemic sclerosis (SS) patients with severe esophageal affection have impaired peristalsis. However, motor function evaluated in vivo by manometry and fluoroscopy does not provide detailed information about the individual contraction cycles.
To apply, for the first time in gastrointestinal (GI) patients, a method and principles modified from cardiac research to study esophageal muscle behavior in SS patients.
Muscle contraction cycles were analyzed using pressure-cross-sectional area (P-CSA) loops during distension pressure up to 5 kPa. The probe with bag and electrodes for CSA measurements was positioned 7 and 15 cm above the lower esophageal sphincter (LES) in eleven healthy volunteers and eleven SS patients. The P-CSA, the wall tension, Δtension (afterload tension - preload tension), contraction velocity, work output (area of the tension-CSA loops), and power output (preload tension × CSA rate) were analyzed.
The P-CSA loops consisted of phases with relaxation and contraction behavior. The tension-stretch ratio loops in patients were shifted to the left at both distension sites, indicative of a stiffer wall in patients. Lower contraction amplitudes and smaller P-CSA loops were observed for the SS patients. The work output, power output, Δtension, and contraction velocity were lower in patients (P < 0.001). Association was found between disease duration and the work output, Δtension, and velocity at pressure steps higher than 3 kPa (P < 0.05).
Distension-evoked esophageal contraction can be studied in vivo and analyzed with advanced methods. Increased esophageal stiffness and impaired muscle function that depended on disease duration were observed for SS patients. The analysis may be useful for characterization of other diseases affecting GI function.
Digestive Diseases and Sciences 06/2011; 56(12):3559-68. · 2.12 Impact Factor
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ABSTRACT: Previous studies have demonstrated morphological and biomechanical remodeling in the intestine proximal to an obstruction. The present study aimed to obtain stress and strain thresholds to initiate contraction and the maximal contraction stress and strain in partially obstructed guinea pig jejunal segments. Partial obstruction and sham operations were surgically created in mid-jejunum of male guinea pigs. The animals survived 2, 4, 7 and 14 days. Animals not being operated on served as normal controls. The segments were used for no-load state, zero-stress state and distension analyses. The segment was inflated to 10 cmH(2)O pressure in an organ bath containing 37°C Krebs solution and the outer diameter change was monitored. The stress and strain at the contraction threshold and at maximum contraction were computed from the diameter, pressure and the zero-stress state data. Young's modulus was determined at the contraction threshold. The muscle layer thickness in obstructed intestinal segments increased up to 300%. Compared with sham-obstructed and normal groups, the contraction stress threshold, the maximum contraction stress and the Young's modulus at the contraction threshold increased whereas the strain threshold and maximum contraction strain decreased after 7 days obstruction (P<0.05 and 0.01). In conclusion, in the partially obstructed intestinal segments, a larger distension force was needed to evoke contraction likely due to tissue remodeling. Higher contraction stresses were produced and the contraction deformation (strain) became smaller.
Journal of biomechanics 05/2011; 44(11):2077-82. · 2.66 Impact Factor
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ABSTRACT: To investigate sensations to multimodal pain stimulation in the metaplastic and normal parts of the esophagus in patients with Barrett's esophagus (BE).
Fifteen patients with BE and 15 age-matched healthy volunteers were subjected to mechanical, thermal and electrical pain stimuli of the esophagus. Both the metaplastic part and the normal part (4 and 14 cm, respectively, above the esophago-gastric junction) were examined. At sensory thresholds the stimulation intensity, referred pain areas, and evoked brain potentials were recorded.
Patients were hyposensitive to heat stimulation both in the metaplastic part [median stimulation time to reach the pain detection threshold: 15 (12-34) s vs 14 (6-23) s in controls; F = 4.5, P = 0.04] and the normal part of the esophagus [median 17 (6-32) s vs 13 (8-20) s in controls; F = 6.2, P = 0.02]. Furthermore, patients were hyposensitive in the metaplastic part of the esophagus to mechanical distension [median volume at moderate pain: 50 (20-50) mL vs 33 (13-50) mL in controls; F = 5.7, P = 0.02]. No indication of central nervous system abnormalities was present, as responses were comparable between groups to electrical pain stimuli in the metaplastic part [median current evoking moderate pain: 13 (6-26) mA vs 12 (9-24) mA in controls; F = 0.1, P = 0.7], and in the normal part of the esophagus [median current evoking moderate pain: 9 (6-16) mA, vs 11 (5-11) mA in controls; F = 3.4, P = 0.07]. Furthermore, no differences were seen for the referred pain areas (P-values all > 0.3) or latencies and amplitudes for the evoked brain potentials (P-values all > 0.1).
Patients with BE are hyposensitive both in the metaplastic and normal part of esophagus likely as a result of abnormalities affecting peripheral nerve pathways.
World Journal of Gastroenterology 01/2011; 17(4):514-21. · 2.47 Impact Factor
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ABSTRACT: Introduction. Electrical stimulation is used in experimental human pain models. The aim was to develop a model that visualizes the distribution of electrical field in the esophagus close to ring and patch electrodes mounted on an esophageal catheter and to explain the obtained sensory responses. Methods. Electrical field distribution in esophageal layers (mucosa, muscle layers, and surrounding tissue) was computed using a finite element model based on a 3D model. Each layer was assigned different electrical properties. An electrical field exceeding 20 V/m was considered to activate the esophageal afferents. Results. The model output showed homogeneous and symmetrical field surrounding ring electrodes compared to a saddle-shaped field around patch electrodes. Increasing interelectrode distance enlarged the electrical field in muscle layer. Conclusion. Ring electrodes with 10 mm interelectrode distance seem optimal for future catheter designs. Though the model needs further validation, the results seem useful for electrode designs and understanding of electrical stimulation patterns.
Gastroenterology Research and Practice 01/2011; 2011:562592. · 0.98 Impact Factor
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ABSTRACT: This study was to generate phasic and tonic stress-strain curves for evaluation of smooth muscle function in the obstructed guinea pig jejunum. Partial and sham obstruction of the jejunum in guinea pigs was created surgically, with guinea pigs not being operated on served as normal controls. The animals survived 2, 4, 7, and 14 days, respectively. The jejunal segment was distended to 10 cm H(2)O. The pressure and outer diameter changes were recorded. Passive conditions were obtained by using papaverine. Total phasic, tonic, and passive circumferential stress and strain were computed from the diameter and pressure data with reference to the zero-stress-state geometry. The active phasic and tonic stresses were defined as the total phasic and tonic stress minus the passive stress. The thickness of intestinal muscle layers increased in a time-dependent manner after obstruction. The amplitude of passive, total phasic, total tonic, active phasic, and active tonic circumferential stresses increased as function of strain 7 days after obstruction. However, when normalized to muscle layer thickness, the amplitude of active stresses did not differ among the groups. In conclusion, the long-term-obstructed intestine exhibits increased total smooth muscle contraction force. However, the contraction force per smooth muscle unit did not increase.
Journal of Biomedicine and Biotechnology 01/2011; 2011:489720. · 2.44 Impact Factor
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ABSTRACT: Partial obstruction of the small intestine results in severe hypertrophy of smooth muscle cells, dilatation and functional denervation. Hypertrophy of the small intestine is associated with alteration of the wall structure and the mechanical properties. The aims of this study were to determine three dimensional material properties of the obstructed small intestine in guinea pigs and to obtain the 3D stress-strain distributions in the small intestinal wall.
Partial obstruction of mid-jejunum was created surgically in five guinea pigs that were euthanized 2 weeks after the surgery. Ten-cm-long segments proximal to the obstruction site were used for the stretch-inflation mechanical test using a tri-axial test machine. The outer diameter, longitudinal force and the luminal pressure during the test were recorded simultaneously. An anisotropic exponential pseudo-strain energy density function was used as the constitutive equation to fit the experimental loading curve and for computation of the stress-strain distribution.
The wall thickness and the wall area increased significantly in the obstructed jejunum (P<0.001). The pressure-outer radius curves in the obstructed segments were translated to the left of the normal segments, indicating wall stiffening after the obstruction. The circumferential stress and the longitudinal stress through the wall were higher in the obstructed segments (P<0.02). This was independent of whether the zero-stress state or the no-load states were used as the reference state.
The mechanical behaviour of the obstructed small intestine can be described using a 3D constitutive model. The obstruction-induced biomechanical properties change was characterized by higher circumferential and longitudinal stresses in the wall and altered material constants in the 3D constitutive model.
Journal of biomechanics 04/2010; 43(11):2079-86. · 2.66 Impact Factor
