Dimensions and circumferential stress-strain relation in the porcine esophagus in vitro determined by combined impedance planimetry and high-frequency ultrasound.

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.