Direct measurement of transverse residual strains in aorta.
Han, Hai Chao, and Yuan Cheng Fung.
Department of Engineering Mechanics, Xi'an Jiaotong University,
Xi'an 710049, P. R. China, Department of Bioengineering, University
of California, San Diego, La Jolla, CA 92093-0412. USA
APStracts 2:0273H, 1995.
Residual strains were measured in the porcine aorta. Segments were cut
from the aorta perpendicular to its longitudinal axis. Microdots of
water-insoluable black ink were sprinkled onto the transverse
sectional surface of the segments in the no-load state. The segments
were then cut radially and sectional zero-stress states were
approached. The coordinates of selected microdots (2-20 m) were
digitized from photographs taken in the no-load state and the zero
-stress state. Residual strains in the transverse section were
calculated from the displacement of the microdots. The
circumferential residual strains on the inner wall and outer wall
were calculated from the circumferential lengths in the no-load state
and the zero-stress state. Results show that the circumferential
residual strain is negative (compressive) in the inner layer of the
aortic wall and positive (tensile) in the outer layer, whereas the
radial residual strain is tensile in the inner layer and compressive
in the outer layer. This residual strain distribution reduces the
stress concentration in the aorta under physiological load. The
experimental results compared well with theoretical estimations of a
cylindrical model. Regional difference of the residual strain exist,
and is significant (p<0.01); e.g., the circumferential residual
strains on the inner wall of the ascending, descending thoracic, and
abdominal regions of the aorta are -0.133 0.019, -0.074 0.020, and
-0.046 0.017 (mean SD) respectively. More radial cuts of a segment
produced no significant additional strains. This means that an aortic
segment after one radial cut can be considered as the zero-stress
state.
Received 13 March 1995; accepted in final form 21 June 1995.
APS Manuscript Number H236-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.