Passive mechanical properties and structure of the aorta: segmental analysis

Abstract

This study assessed segmental changes in the mechanical properties of the aorta at low, physiologic and high stresses, in relation with wall composition and morphometry. The aorta of 10 healthy pigs was divided into six thoracic and three abdominal segments. Aortic specimens were mechanically tested to failure, i.e. rupture, using a uniaxial tension device. Elastic modulus-stress curves were obtained for low (part I), physiologic (part II) and high (part III) stresses, and submitted to regression analysis; failure parameters were calculated. Histological evaluation was performed using an image-processing system, with quantification of morphometric parameters and composition of the entire vessel and its layers, i.e. media and adventitia. Significant differences were found in the regression parameters of parts I, II and III, and in failure parameters, suggesting that the proximal segments were stiffer at low stresses, whereas the distal were less extensible, stronger and stiffer at physiologic and high stresses. Image analysis demonstrated significant differences in morphometry and composition among the different layers and segments of the aorta, with higher elastin content proximally and collagen content distally. Good correlations were found between the regression parameters of parts I and II and elastin content, and between the failure and regression parameters of parts II and III and collagen content. Segmental changes exist in the structure and mechanical properties of the aorta, depending on the level of aortic pressure. This information is necessary for understanding aortic function at general non-physiologic stress states.