Cardiovascular disease is responsible for about one third of all deaths globally, and coronary artery disease accounts for 42% of cardiovascular disease-related deaths. Mechanical properties of coronary arteries affect vascular health and disease. The normal coronary artery consists of two mechanically distinct layers: intima-media and adventitia. The objective of this study is to, for the first time, establish a two-layer three-dimensional (3-D) stress-strain relationship of porcine coronary arteries. Stretch-inflation tests were conducted on artery specimens. Deformations and external loadings were recorded. Material parameters in the Fung-type exponential constitutive equation were determined by curve fitting the experimental data. The exponential model was used to study the effects of opening angle (OA) on the stress distribution in vessel wall. It was found that a larger OA always shifts the circumferential stress from the intima-media to the adventitia layer. The circumferential stress at adventitia may exceed that at intima at physiological loading due to large OA in normal porcine coronary artery based on measured data. Increase of OA following acute hypertension was found to offload the stress from intima to adventitia. Finally, a new constitutive model with reduced number of nonlinear parameters proposed by our group has also been validated. Material parameters in the new model are easier to be determined and more capable to detect systematic changes in the blood vessel as compared to the exponential model.
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