LAUSR

BACKGROUND The perivascular adipose tissue has been studied as a critical element that could influence physiological and disease processes of the vessel covered by it. In terms of anatomy, during the abdominal aorta's dissection, it is possible to identify the periaortic adipose tissue and the periaortic parietal peritoneum lying over it, sealing the retroperitoneal space. They seem to be fragile layers, with apparently no biomechanical role in the abdomen. However, it is well known that most cases of ruptured abdominal aortic aneurysms that reach the emergency department still alive present retroperitoneal bleeding contained by the above-mentioned two-layer combination, eventually allowing time for surgical treatment. In previous studies about aortic wall stress, tension, and abdominal aortic aneurysm rupture prediction, only information concerning the vessel wall itself is highlighted. Therefore, the present work aims to study the biomechanical and histological properties of the periaortic tissue, comparing them to the same variables measured in aortic wall samples described in the medical literature. MATERIALS AND METHODS Samples of periaortic tissue were harvested from 27 individuals during necropsy. Smoking status and the presence of abdominal aortic aneurysm were observed. Biomechanical uniaxial destructive tests were performed up to samples rupture. Values of failure stress, tension, and strain were obtained. Samples were also harvested for histological analysis. RESULTS Periaortic tissue presented less amount of collagen in smokers than in non-smokers (p = 0.017). The periaortic tissue seems to be more elastic than aortic walls described in the literature (strain: 0.75 ± 0.37). Analyzing periaortic tissue failure stress (56.8 ± 101.26 N/cm2) and tension (7.65 ± 4.99 N/cm), it has at least 52% and 55%, respectively of the stress and tension described in the medical literature for abdominal aortic aneurysm walls. CONCLUSIONS The periaortic tissue presents less collagen fibers in smokers than in non-smokers. The periaortic tissue seemed very delicate during an autopsy, but the study of its biomechanical properties showed that it presents more than half of the resistance of an abdominal aortic aneurysm wall. This information suggests this tissue might have a mechanical protective role against massive bleeding when it comes to an aortic rupture. Therefore this tissue's biomechanical information should be included in computational models on enlargement and rupture prediction of abdominal aortic aneurysms.