title: Determination of biomechanical properties in guinea pig esophagus by means of high frequency ultrasound and impedance planimetry.
abstract: Impedance planimetry and high-frequency ultrasound were used to determine circumferential stress and strain from measurements of luminal cross-sectional area and wall thickness during balloon distension of the guinea pig esophagus in vitro (N = 30). The excised esophagus was mounted on two plastic tubes in an organ bath containing oxygenated calcium-free Krebs-Ringer solution with 10(-2) M MgCl2 to abolish smooth muscle contractile activity. One of the plastic tubes was movable in order to stretch the esophagus longitudinally by 15% (elongated state). The impedance planimetry probe was placed with the balloon inside the lumen of the esophagus. A 20-MHz ultrasound transducer was mounted above the esophagus and provided scans in the transverse and longitudinal directions. The luminal cross-sectional area at the highest applied pressure of 2.9 kPa was 13.3 +/- 0.3 mm2 in the resting state. In the elongated state the luminal cross-sectional area at the highest pressure was 12.5 +/- 0.1 mm2 (P < 0.02). The wall thickness decreased from 990 +/- 21 microm at 0 kPa to 640 +/- 9 microm at 2.9 kPa at in vitro length. In the elongated state, the values were 940 +/- 32 microm to 480 +/- 13 microm (P < 0.01). The stress-strain relation was exponential (sigma = alpha(ebetaepsilon - 1), r2 > 0.98, P < 0.01). The circumferential elastic modulus calculated at a Green strain of 0.95 was 44.5 +/- 10.5 kPa in the in vitro state and 81.7 +/- 13.1 kPa in the elongated state. The elastic modulus differed between the resting and elongated states (P < 0.02).
authors.affiliation: Institute of Experimental Clinical Research, Aarhus University Hospital, Section SKS, Denmark.
authors.forename: J E
authors.initials: JE
authors.lastname: Assentoft
authors.forename: H
authors.initials: H
authors.lastname: Gregersen
authors.forename: W D
authors.initials: WD
authors.lastname: O'Brien
mesh_terms: D000818:Animals; D017097:Electric Impedance; D004947:Esophagus / Q000000981:diagnostic imaging / Q000502:physiology*; D005260:Female; D006168:Guinea Pigs / Q000502:physiology*; D008954:Models, Biological; D013314:Stress, Mechanical; D013718:Tensile Strength; D014463:Ultrasonography