Hc. Han et Yc. Fung, DIRECT MEASUREMENT OF TRANSVERSE RESIDUAL STRAINS IN AORTA, American journal of physiology. Heart and circulatory physiology, 39(2), 1996, pp. 750-759
Residual strains were measured in the porcine aorta. Segments were cut
from the aorta perpendicular to its longitudinal axis. Microdots of w
ater-insoluble black ink were sprinkled onto the transverse sectional
surface of the segments in the no-load state. The segments were then c
ut radially, and sectional zero-stress states were approached. The coo
rdinates of selected microdots (2-20 mu m) were digitized from photogr
aphs taken in the no-load state and the zero-stress state. Residual st
rains in the transverse section were calculated from the displacement
of the microdots. The circumferential residual strains on the inner wa
ll and outer wall were calculated from the circumferential lengths in
the no-load state and the zero-stress state. Results show that the cir
cumferential residual strain is negative (compressive) in the inner la
yer of the aortic wall and positive (tensile) in the outer layer, wher
eas the radial residual strain is tensile in the inner layer and compr
essive in the outer layer. This residual strain distribution reduces t
he stress concentration in the aorta under physiological load. The exp
erimental results compared well with theoretical estimations of a cyli
ndrical model. Regional difference of the residual strain exists and i
s significant (P < 0.01), e.g., the circumferential residual strains o
n the inner wall of the ascending, descending thoracic, and abdominal
regions of the aorta are -0.133 +/- 0.019, -0.074 +/- 0.020, and -0.04
6 +/- 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 sta
te.