The quasistatic elastic properties of longitudinal strips of the canine aorta-iliac bifurcation.

Abstract

The quasistatic elastic properties of the abdominal aorta, external iliac artery, and their junctional area in 10 mongrel dogs were measured.Arterial strips were excised with a double-bladed cutter. The strips contained roughly equal lengths of abdominal aorta and external iliac artery, with a width which included half the circumference of the aorta and the whole of the iliac artery. Each tissue strip was divided into three regions, i.e., abdominal aortic region, bifurcation region, and external iliac region. An India ink grid was painted on each region for measurement of the elongation in each region during stretching. Uniaxial tensile stress at a strain rate of 0.08 min−1 was applied to each strip until it raptured, using an Instron machine. Pictures were taken before and during stretching. Test results were presented in the form of specimen loading versus time on the chart recorder. From these data, values of stress and strain were then calculated and plotted.The external iliac region was most extensible, especially at low tensile stress, the bifurcation was next, and then the abdominal aortic region. The initial modulus of the bifurcation (6.42 × 105 dyn/cm2 per 100% elongation; 1 dyn = 10 μN) was found to be lowest of any of the three arterial regions. Statistical analysis indicated that there was a significant difference between the initial modulus of the external iliac artery (9.58 × 105 dyn/cm2 per 100% elongation) while the difference was insignificant between abdominal aorta (7.49 × 105 dyn/cm2 per 100% elongation) and external iliac artery, even though histological studies showed that the abdominal aorta has a higher number of elastic lamellae per millimetre of wall thickness. This led to the speculation that the state and arrangement of the elastic lamellae in the bifurcation region make that area less able to resist distension, or that the elastic fibres have a weaker anchorage to the collagen in that region. There was, however, a progressive and significant decrease in the final modulus from the abdominal aorta (10.55 × 107 dyn/cm2 per 100% elongation) through the bifurcation (6.48 × 107 dyn/cm2 per 100% elongation) to the external iliac artery (4.77 × 107 dyn/cm2 per 100% elongation). This leads to the conclusion that the collagenous fibres were "strung" most closely in the abdominal aorta, least in the external iliac artery, and between in the bifurcation region.The torsional shearing strains which developed in the arterial strips under longitudinal loading varied from 0 to 0.048, and were much smaller than the corresponding longitudinal strains of 0 to 1.0. Therefore, the shearing strains which developed under loading were neglected. End effects due to the clamps were also found to play an insignificant role.