Dimensions and Circumferential Stress-Strain Relation in the Porcine Esophagus in Vitro Determined by Combined Impedance Planimetry and High-Frequency Ultrasound

Abstract

The mechanical properties of the esophagus are important for its function because the esophagus is subjected to changes in wall stress and strains caused by the passage of boli and the action of peristalsis. Electrodes for impedance planimetry and an ultrasound transducer were placed on the probe inside a fluid-filled bag and used to study the circumferential stress and strain relation of the porcine esophagus in vitro. Impedance planimetry was used to determine the luminal cross-sectional area (CSA) and high-frequency ultrasound was used to determine the esophageal wall thickness during bag distension. Circumferential stress and strain were computed from steady-state values of pressure, CSA, and wall thickness. The incremental elastic modulus was obtained from the slope of the stress-strain curve and was plotted as a function of strain. The steady state pressure-CSA relation was nonlinear. At the lowest and highest luminal pressure load of 1 and 5 kPa, the steady state CSA was 159+/-20 and 338+/-25 mm(2), respectively. In the same pressure range, the wall thickness decreased from 1.93+/-0.08 to 1.44+/-0.08 mm. The slope of the stress-strain curve was 2.58+/-0.35 kPa. The circumferential stress and the incremental elastic modulus as function of the strain were exponential, that is, the tissue was soft at physiologic pressures and stiffer in the supraphysiologic pressure range. These biomechanical properties of the esophageal wall seem to prevent overstretch of the esophageal wall when luminal loading becomes supraphysiologic.

Simulation studies of the role of esophageal mucosa in bolus transport

“…That is probably because the in-vitro mechanical properties of esophageal mucosa, depending on the test procedure and tissue preparation, are quite different from in-vivo ones at normal physiological conditions. This might also explain why the reported in-vitro material properties vary substantially among studies (Yang et al 2006a; Zhao et al 2007; Natali et al 2009; Stavropoulou et al 2009). …”

“…The active and passive properties of the muscular layers have been relatively well studied (Nicosia and Brasseur 2002; Jung et al 2004; Ghosh et al 2005; Mittal et al 2006; Brasseur et al 2007; Zhao et al 2007; Kou et al 2015a). However, the submucosa and mucosa, here collectively called mucosa, has been the object of relatively little research relating to bolus transport.…”

“…Most studies of the mucosa relate to changes in its permeability as a defense mechanism against intraluminal acidity (Sarosiek and McCallum 2000; Orlando 2006), and biomechanical studies mainly focused on its geometry and material properties from in-vitro tests (Gregersen et al 2000; Yang et al 2006a,b, 2007; Zhao et al 2007; Natali et al 2009; Stavropoulou et al 2009; Li et al 2011a). The mucosa is generally modeled as an anisotropic elastic material, but presumably due to the complexity of biological tissues and of in-vitro testing, the reported material properties vary substantially among studies (Yang et al 2006a; Zhao et al 2007; Natali et al 2009; Stavropoulou et al 2009). Mucosal folding, which probably originates from residual stress in the esophageal wall, has also attracted substantial interest among researchers (Gregersen et al 2000; Yang et al 2007; Li et al 2011a,b).…”

Diabetes‐induced mechanophysiological changes in the esophagus

“…The biomechanical characteristics of the normal esophagus (esophageal body) can be summarized as follows: (1) the tension and stress of the esophageal wall increase exponentially as functions of the pressure, 28-34 and, consequently, the tissue is soft at physiologic pressures and stiffer in the supraphysiologic pressure range; (2) the tension and stress distributions are nonuniform along the esophagus 30,31 and across the esophageal wall; 33 (3) the esophageal wall is anisotropic, with different stiffness in the circumferential, longitudinal, and the circumferential-longitudinal shear directions; 35 (4) the stress distribution in the different layers is nonlinear and anisotropic; [36][37][38][39][40][41][42] (5) collagen and elastin are important for the passive biomechanical properties of the esophagus; 23 (6) the stress-strain relationship of the active muscle contraction is different during isovolumic and isobaric distensions, but the passive components are similar under these experimental conditions; 43,44 and (7) the stress softening in the rat esophagus is reversible after the activation of KCl-induced contractions. 45 The UES and the LES control passage between the pharynx and the esophagus and passage between the esophagus and the stomach.…”

The Esophagiome: concept, status, and future perspectives

“…A Newton's law force balance across the esophageal wall relates wall‐averaged stress to an appropriate esophageal wall strain measure. From the force balance, total wall stress can be estimated from concurrent measurement of intraluminal pressure, luminal cross‐sectional area, and wall thickness in vivo as well as in vitro . With estimated total stress and measured strain relationship from different patients and age groups, the stiffness of the esophageal wall can be estimated and compared between different groups .…”