AJP - Heart and Circulatory Physiology, Vol 270, Issue 2 750-H759, Copyright © 1996 by American Physiological Society
Direct measurement of transverse residual strains in aorta
H. C. Han and Y. C. Fung
Department of Engineering Mechanics, Xi'an Jiaotong University, China. stchen@xjtu.edu.cn
Residual strains were measured in the porcine aorta. Segments were cut from
the aorta perpendicular to its longitudinal axis. Microdots of
water-insoluble 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 microns) 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 exists 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.
