Donghua Liao

A new technique for evaluating sphincter function in visceral organs: application of the functional lumen imaging probe (FLIP) for the evaluation of the oesophago–gastric junction

No quantitative method has been implemented routinely in clinical practice to assess the oesophago-gastric junction (OGJ). Using impedance planimetry a functional lumen imaging probe (FLIP) was constructed to measure eight cross-sectional areas (CSA) at 4 mm intervals inside a saline-filled bag. To validate the FLIP technique for profiling the OGJ, polymethylmethacrylate (Perspex) cylinders with different CSAs were measured ten times by the FLIP to assess reproducibility and accuracy. A geometric sphincter phantom was constructed and its geometry was measured with a 360 degrees radial ultrasound (US) mini-probe pulled through it at a rate of 1 mm s(-1). The measurements were compared with FLIP measurements. Safety and technique reproducibility were tested on a volunteer. Reproducibility and accuracy between the ten samples were good. The probe performed well with and without a balloon mounted on it except for the smallest CSA (38.5 mm(2)) where there was a difference of 22% from the actual value at one CSA measurement point. The FLIP imaged the phantom geometry as well as the radial scanning US mini-probe. Pilot studies on a volunteer showed that the probe could be placed in the OGJ and the balloon distensions revealed the geometry of the sphincter at various levels of distension. The technique may be useful in accessing the role of the OGJ in diseases such as gastroesophageal reflux disease (GORD) and achalasia and their treatments with surgical and endoscopic therapies.

Biomechanical regulation of vascular smooth muscle cell functions: from in vitro to in vivo understanding

Vascular smooth muscle cells (VSMCs) have critical functions in vascular diseases. Haemodynamic factors are important regulators of VSMC functions in vascular pathophysiology. VSMCs are physiologically active in the three-dimensional matrix and interact with the shear stress sensor of endothelial cells (ECs). The purpose of this review is to illustrate how haemodynamic factors regulate VSMC functions under two-dimensional conditions in vitro or three-dimensional co-culture conditions in vivo. Recent advances show that high shear stress induces VSMC apoptosis through endothelial-released nitric oxide and low shear stress upregulates VSMC proliferation and migration through platelet-derived growth factor released by ECs. This differential regulation emphasizes the need to construct more actual environments for future research on vascular diseases (such as atherosclerosis and hypertension) and cardiovascular tissue engineering.

Stress distribution in the layered wall of the rat oesophagus

The topic of this study is to obtain the constitutive equations for two layers in the oesophagus from inflation experiment of each layer in the in vivo state and to calculate the corresponding stress distribution referenced to a new stress-free state for multi-layered tissue. The oesophagus is treated as a two-layered structure consisting of an inner submucosa layer and an outer muscle layer. An anisotropic exponential pseudo-strain energy density function is used as the constitutive equation to fit the experimental loading curve and for the calculation of the stress distribution in each layer. Significant differences in the constitutive parameters and zero-stress parameter were found between the submucosa layer and the muscle layer. The stress in the submucosa layer was higher than that in the muscle layer and intact (non-separated) wall under the same loading conditions. The submucosa layer was stiffer than the muscle layer and the intact wall. The zero-stress state of the intact oesophagus and the zero-stress state after separation were used as a reference to compare the stress-strain distributions. The residual strain was discontinuous when using the zero-stress state after separation as a reference. Furthermore, the circumferential stress when using the zero-stress state of the intact wall as a reference was about 100 times higher than that referenced to the zero-stress state after separation. Hence, it is important to use the zero-stress state obtained after the layer separation as the stress-free state in the study of multi-layered tissue.

Analysis of surface geometry of the human stomach using real-time 3-D ultrasonography in vivo.

Abstract  The objective of this study was to develop an analytical method to describe the three‐dimensional (3‐D) geometry of the gastric antrum, gastric fundus and the whole stomach. The Fourier series method was used to simulate the organ surface geometry obtained from a 3‐D ultrasound system. Data generated from eight antrums and three whole stomachs, at pressures of approximately 7 cmH2O, were used for lumen curvature calculations. The principal curvatures spatial distributions were non‐homogeneous in the gastric antrum, gastric fundus and the stomach due to their complex geometry. The maximum longitudinal principal curvature in the antrum, fundus and total stomach were, respectively, 0.460 ± 0.066, 0.583 ± 0.087 and 1.123 ± 0.328, whereas the maximum circumferential curvature were 1.192 ± 0.090, 3.649 ± 1.574 and 8.444 ± 3.424, respectively. The present study provides an analytical tool for characterizing the complex 3‐D geometry of an organ‐like the human stomach reconstructed by clinical imaging modalities. Providing an average tension for the stomach does not reflect the large variation in tension throughout the stomach wall.

Three-dimensional biomechanical properties of the human rectum evaluated with magnetic resonance imaging.

Abstract  A method to evaluate the three‐dimensional (3‐D) geometry of the human gastrointestinal wall may be valuable for understanding tissue biomechanics, mechano‐sensation and function. In this paper we present a magnetic resonance imaging (MRI) based method to determine rectal geometry and validation of data obtained in three volunteers. A specially designed rectal bag was filled in a stepwise manner while MRI and bag pressure were recorded. 3‐D models of curvatures, radii of curvature, tension and stress were generated and the circumferential and longitudinal strains were calculated. The computed bag volumes corresponded to the infused volumes. A pronounced bag elongation and decrease in wall thickness was observed during the bag filling. The spatial distributions of the biomechanical parameters were distinctly different between individuals and non‐homogeneous throughout the rectal wall due to its complex geometry. The average tension and stress increased as a function of infused volume and circumferential strain. The present study provides a method for characterizing the complex in vivo 3‐D geometry of the human rectum. The non‐homogenous spatial curvature distribution suggests that simple estimates of tension based on pressure and volume do not reflect the true 3‐D biomechanical properties of the rectum.

Distensibility of the anal canal in patients with idiopathic fecal incontinence: A study with the Functional Lumen Imaging Probe

Anatomical structures and their distensibility vary along the length of the anal canal. The anal sphincter muscles have dynamic properties that are not well‐reflected by standard manometry. Abnormal distensibility of the anal canal may be of importance in idiopathic fecal incontinence (IFI). The functional lumen imaging probe (FLIP) allows detailed studies of the distensibility and axial variation of sphincters. We aimed at comparing segmental distensibility of the anal canal in patients with IFI and healthy subjects.

Shear modulus of elasticity of the esophagus

Experimental and diagnostic procedures like distension of a balloon catheter, bougie, and esophagogastroduodenoscopy can induce shear deformation in the esophageal wall. However, the shear modulus of the esophagus is yet unknown. The aim of this study was to determine the esophageal shear modulus and its dependence on the circumferential and longitudinal stresses and strains in the rat. The constitutive equation including the shear deformation based on a pseudo-strain-energy function was generated. Results were obtained using a new triaxial instrument to perform simultaneous torsion, inflation, and longitudinal stretching tests. The shear modulus varied with the inflation pressure and the longitudinal stretch ratio. The shear modulus at the longitudinal stretch ratio of 1.5 and between inflation pressures of 0 and 2.0 kPa ranged from 5.43 to 185.01 kPa. The mechanical constant of the esophagus showed that the esophageal wall was anisotropic with different stiffness in the circumferential, longitudinal, and the shear directions. The stiffness in the longitudinal direction was higher than in the circumferential direction (P < 0.001). This test can be extended for further mechanical remodeling experiments and for other tubular organs such as the small intestine or blood vessels.

Tension and stress in the rat and rabbit stomach are location- and direction-dependent.

Abstract  Distension studies in the stomach are very common. It is assumed in pressure–volume (barostat) studies of tone and tension in the gastric fundus that the fundus is a sphere, i.e. that the tension in all directions is identical. However, the complex geometry of the stomach indicates a more complex mechanical behaviour. The aim of this study was to determine uniaxial stress–strain properties of gastric strips obtained from rats (n = 12) and rabbits (n = 10). Furthermore, we aimed to study the gastric zero‐stress state since the stomach is one of the remaining parts of the gastrointestinal tract where residual strain studies have not been conducted. Longitudinal strips (in parallel with the lesser curvature) and circumferential strips (perpendicular to the lesser curvature) were cut from the gastric fundus (glandular part) and forestomach (non‐glandular part). The residual stress was evaluated as bending angles (unit: degree per unit length and negative when bending outwards). The residual strain was computed from the change in length between the zero‐stress state and no‐load state. The stress–strain test was performed using a tensile test machine. The thickness and width of each strip were measured from digital images. The strips data were compared with data obtained in the intact stomach in vitro. Most residual stresses and strains were bigger in the glandular part than in the forestomach, and in general the rat stomach had higher values than the rabbit stomach. The glandular strips were stiffer than the forestomach strips and the longitudinal glandular strips were stiffer than the circumferential glandular strips (P < 0.05). The gastric strips were stiffer in rats than in rabbits (P < 0.01). The data obtained in the intact rat stomach confirmed the strips data and indicated that those were obtained in the physiological range. In conclusion, the biomechanical properties of the gastric strips from the rat and rabbit are location‐dependent, direction‐dependent and species‐dependent. The assumption in physiological pressure–volume studies that the stomach is a sphere with uniform tension is not valid. Three‐dimensional geometric data obtained using imaging technology and mechanical data are needed for evaluation of the stomach function.

Viscoelastic behavior of small intestine in streptozotocin-induced diabetic rats.

Diabetes is associated with remodeling of the morphology and elastic properties of the small intestine. This study aims to study remodeling of the viscoelastic (time-dependent) properties of the small intestine during experimental diabetes. Stress relaxation tests were performed on the duodenum, jejunum, and ileum in 10 nondiabetic and 28 streptozotocin (STZ) -induced diabetic rats. The rats were made diabetic by a single intraperitoneal injection of 50 mg/kg STZ. The diabetic rats were allocated into groups living four days or one, two, or four weeks after the induction of diabetes (N = 7 in each group). The mechanical test was performed using a machine that rapidly stretched the intestinal tube to 40% more than the resting length. The intestinal diameter and wall area were obtained from digitized images of the intestinal segments at no-load and zero-stress states. The stress (force per area) was computed and a reduced-stress relaxation function was applied. The log decay parameter C and the slow and fast time constants τ1 and τ2 were computed. STZ-induced diabetes was associated with a progressive increase in the wall thickness and wall cross-sectional area (P < 0.05). τ1 and τ2 increased and C decreased. The slope α became consistently less negative (P < 0.05), and the stress after 600-sec relaxation gradually increased during diabetes (P < 0.01). In conclusion, the viscoelastic behavior of the intestinal wall changed during the development of diabetes.

Functional lumen imaging of the gastrointestinal tract.

This nonsystematic review aims to describe recent developments in the use of functional lumen imaging in the gastrointestinal tract stimulated by the introduction of the functional lumen imaging probe. When ingested food in liquid and solid form is transported along the gastrointestinal tract, sphincters provide an important role in the flow and control of these contents. Inadequate function of sphincters is the basis of many gastrointestinal diseases. Despite this, traditional methods of sphincter diagnosis and measurement such as fluoroscopy, manometry, and the barostat are limited in what they can tell us. It has long been thought that measurement of sphincter function through resistance to distension is a better approach, now more commonly known as distensibility testing. The functional lumen imaging probe is the first medical measurement device that purports in a practical way to provide geometric profiling and measurement of distensibility in sphincters. With use of impedance planimetry, an axial series of cross-sectional areas and pressure in a catheter-mounted allantoid bag are used for the calculation of distensibility parameters. The technique has been trialed in many valvular areas of the gastrointestinal tract, including the upper esophageal sphincter, the esophagogastric junction, and the anorectal region. It has shown potential in the biomechanical assessment of sphincter function and characterization of swallowing disorders, gastroesophageal reflux disease, eosinophilic esophagitis, achalasia, and fecal incontinence. From this early work, the functional lumen imaging technique has the potential to contribute to a better and more physiological understanding of narrowing regions in the gastrointestinal tract in general and sphincters in particular.