title: Energy loss, a novel biomechanical parameter, correlates with aortic aneurysm size and histopathologic findings.
abstract: OBJECTIVE
  Energy loss is a biomechanical parameter that represents the relative amount of energy absorbed by the aorta during the cardiac cycle. We aimed to correlate energy loss with ascending aortic aneurysm size and histopathologic findings to elucidate the pathophysiology of aneurysm complications.
  
  
  METHODS
  Aneurysmal ascending aortic specimens were obtained during surgery. Control specimens were obtained from autopsy and organ donors. Biaxial tensile tests were performed on the 4 quadrants of the aortic ring. Energy loss was calculated using the integral of the stress-strain curve during loading and unloading. It was compared with the size and the traditional biomechanical parameter, stiffness (apparent modulus of elasticity). Elastin, collagen, and mucopolysaccharide content were quantified using Movat pentachrome staining of histology slides.
  
  
  RESULTS
  A total of 41 aortas were collected (34 aneurysmal, 7 control). The aneurysms exhibited increased stiffness (P < .0001) and energy loss (P < .0001) compared with the controls. Energy loss correlated significantly with aortic size (P < .0001, r(2) = .60). A hinge point was noted at a diameter of 5.5 cm, after which energy loss increased rapidly. The relationship between energy loss and size became strongly linear once the size was indexed to the body surface area (P < .0001, r(2) = .78). Energy loss correlated with the histopathologic findings, especially the collagen/elastin ratio (P = .0002, r(2) = .49). High energy loss distinguished patients with pathologic histologic findings from others with similar diameters.
  
  
  CONCLUSIONS
  As ascending aortas dilate, they exhibit greater energy loss that rapidly increases after 5.5 cm. This mirrors the increase in complications at this size. Energy loss correlates with imbalances in elastin and collagen composition, suggesting a measurable link between the histopathologic features and mechanical function.
authors.affiliation: Divisions of Cardiac Surgery, McGill University, Montreal, Quebec, Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Chung
authors.affiliation: Divisions of Cardiac Surgery, McGill University, Montreal, Quebec, Canada.
authors.forename: Kevin
authors.initials: K
authors.lastname: Lachapelle
authors.affiliation: Department of Chemical Engineering, McGill University, Montreal, Quebec, Canada.
authors.forename: Evan
authors.initials: E
authors.lastname: Wener
authors.affiliation: Montreal Heart Institute, Montreal, Quebec, Canada.
authors.forename: Raymond
authors.initials: R
authors.lastname: Cartier
authors.affiliation: Divisions of Cardiac Surgery, McGill University, Montreal, Quebec, Canada.
authors.forename: Benoit
authors.initials: B
authors.lastname: De Varennes
authors.affiliation: Department of Pathology, McGill University, Montreal, Quebec, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Fraser
authors.affiliation: Department of Chemical Engineering, McGill University, Montreal, Quebec, Canada; Montreal Heart Institute, Montreal, Quebec, Canada. Electronic address: richard.leask@mcgill.ca.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Leask
mesh_terms: D000328:Adult; D000368:Aged; D001011:Aorta / Q000737:chemistry / Q000473:pathology* / Q000503:physiopathology; D001014:Aortic Aneurysm / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D003094:Collagen / Q000032:analysis; D004108:Dilatation, Pathologic; D055119:Elastic Modulus; D004549:Elastin / Q000032:analysis; D005260:Female; D006025:Glycosaminoglycans / Q000032:analysis; D006801:Humans; D008297:Male; D008875:Middle Aged; D013314:Stress, Mechanical; D013718:Tensile Strength
chemical_list: D006025:Glycosaminoglycans; D003094:Collagen; D004549:Elastin