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Research
 

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. 

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