header image 2
header image 2

Biomechanics of the Ascending Aorta

The ascending aorta (AA) distributes blood from the heart to the rest of the body.  It is not a passive conduit, but rather a dynamic vessel vital to our health.  The AA is uniquely constructed to withstand the large fluid and tissue stresses created by the left ventricle.  The mechanical properties (viscoelastic) of this blood vessel allow it to absorb and redistribute blood flow energy throughout the cardiac cycle.  With age and disease, the AA can stiffen and dilate forming an aneurysm.  AA aneurysms affect systemic and coronary circulation and are associated with congestive heart failure, stroke and high mortality rates.  

We are testing the hypothesis that dilation of the AA in aortic valve patients is the result of a hemodynamic induced local tissue remodeling. This hypothesis cannot be directly tested in humans. Instead we will test a series of hypotheses based on AA tissue composition, structure and biomechanics of surgically removed AA tissue with preoperative hemodynamic parameters collected with cardiac magnetic resonance imaging .  We use bi-axial tensile testing to evaluate the local mechanical properties of the tissue at four locations around the circumference of the dilated section. Multiphoton microscopy is used to evaluate the morphology of elastin and collagen at each location.  The local content of matrix proteins, matrix metalloproteinases (MMPs), tissue inhibitors of matrix metalloproteinases (TIMPs) and smooth muscle cell phenotype markers are assessed from frozen and fixed samples. Numerical modeling is being used to test the role of aortic complience on vascular dynamics. Together, the data collected will be used to identify if a link between aneurysmal remodeling of the AA and AA hemodynamics exists. 

1 Nobari S, Mongrain R, Leask R, Cartier R. The effect of aortic wall and aortic leaflet stiffening on coronary hemodynamic: a fluid-structure interaction study. Med Biol Eng Comput 2013.
2 Nobari S, Mongrain R, Gaillard E, Leask R, Cartier R. Therapeutic vascular compliance change may cause significant variation in coronary perfusion: a numerical study. Comput Math Methods Med 2012;2012:791686.
3 Rouleau L, Tremblay D, Cartier R, Mongrain R, Leask RL. Regional variations in canine descending aortic tissue mechanical properties change with formalin fixation. Cardiovasc Pathol. 2012 Sep-Oct;21(5):390-
4 Tremblay D, Cartier R, Mongrain R, Leask RL. Regional dependency of the vascular smooth muscle cell contribution to the mechanical properties of the pig ascending aortic tissue. J Biomech 2010;43:2448-2451.
5 Tremblay D, Zigras T, Cartier R et al. A comparison of mechanical properties of materials used in aortic arch reconstruction. Ann Thorac Surg 2009;88:1484-1491.
6 Belisle J, Zigras T, Costantino S et al. Second harmonic generation microscopy to investigate collagen configuration: a pericarditis case study. Cardiovasc Pathol 2010;19:e125-e128.
7 Choudhury N, Bouchot O, Rouleau L, Tremblay D, Cartier R, Butany J, Mongrain R, Leask RL., Local mechanical and structural properties of healthy and diseased human ascending aorta tissue. Cardiovasc Pathol. 2009 Mar-Apr;18(2):83-91.

8 Fedak PW, Verma S, David TE, Leask RL, Weisel RD, Butany J. Clinical and pathophysiological implications of a bicuspid aortic valve. Circulation 2002;106:900-904.
9 Slack G, Cohen J, Lenkei-Kerwin SS, David T, Leask R, Butany J. Images in Cardiology. Postaortotomy false aneurysm of the ascending aorta. Can J Cardiol 2002;18:312-314.