Mechanical characterization and constitutive modeling of the coronary artery

Coronary heart disease is the most frequently occurring cardiovascular disease in Europe. The components of the arterial wall are strongly related to the arterial mechanical behavior, and the composition may change because of remodeling processes that take place in the arterial wall, upon disease or intervention. Accordingly, much interest lies in modeling the mechanical behavior of the coronary arterial wall. The main objective of the research described in this thesis is therefore to mechanically characterize the coronary artery and describe its behavior with a constitutive model. An in-vitro experimental model has been developed that enables measurement of the mechanical behavior of an artery under physiological conditions, through dynamic simultaneous measurement of pressure, internal diameter, and axial force. By analysis of the properties of a mixture of xanthan gum and normal culture medium, a new culture medium has been developed, which has blood mimicking rheological properties to induce physiological wall shear stresses at physiological flow rates. This blood-analog culture medium does not influence cell and tissue biology otherwise. To apply physiological loading to the coronary artery in this set-up, we have investigated a way to assess the physiological axial pre-stretch of the coronary artery. It has been validated that at the in-vivo pre-stretch, the axial force is relatively insensitive to changes in pressure. For the purpose of predicting the mechanical behavior of a specific coronary artery, we have derived a generic constitutive model, by providing it with a generic set of material and geometric parameters. This generic constitutive model is able to predict the pressure-inner radius and pressure-axial force change relations of a passive porcine coronary artery, by just measuring its radius at physiological loads and the corresponding pressure. When, instead of a generic, an artery-specific description of the coronary artery is desired and only in-vivo pressure-radius data are available, more structural information of the artery is desired. In this thesis it has been shown, by the analysis of the fitted material parameters, that the preferred material model fiber orientation at physiological loading is (36.6 ± 0.4)¿ for human as well as porcine coronary arteries. This finding can be used as an optimization constraint in fitting a constitutive model to the mechanical data available. Finally, a new model to describe the extra stress generated by maximally constricted smooth muscle cells, has been proposed. This model is well able to describe the extra smooth muscle stress generated in an arterial ring test, also beyond the physiological range, and has successfully been added to the generic constitutive model of the coronary artery

Mechanical behavior of the porcine coronary artery

Knowledge of mechanical properties of living arteries is important to understand vascular function inarterial pathologies and different treatments. We have developed an ex vivo model in which a porcinecoronary artery can be kept at physiological circumstances, while enabling measurement of itsmechanical behavior. Arterial mechanical behavior was determined for segments of the porcine leftanterior descending coronary artery (LAD) during dynamic loading at different axial strains. Also, thephysiological axial strain of the LAD was determined, based on the hypothesis that the in vivo axialstrain of an artery is the strain at which the axial force is relatively insensitive to changes in pressur

A generic material model of the passive porcine coronary artery

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Mechanical characterization and constitutive modeling of the coronary artery

Coronary heart disease is the most frequently occurring cardiovascular disease in Europe. The components of the arterial wall are strongly related to the arterial mechanical behavior, and the composition may change because of remodeling processes that take place in the arterial wall, upon disease or intervention. Accordingly, much interest lies in modeling the mechanical behavior of the coronary arterial wall. The main objective of the research described in this thesis is therefore to mechanically characterize the coronary artery and describe its behavior with a constitutive model. An in-vitro experimental model has been developed that enables measurement of the mechanical behavior of an artery under physiological conditions, through dynamic simultaneous measurement of pressure, internal diameter, and axial force. By analysis of the properties of a mixture of xanthan gum and normal culture medium, a new culture medium has been developed, which has blood mimicking rheological properties to induce physiological wall shear stresses at physiological flow rates. This blood-analog culture medium does not influence cell and tissue biology otherwise. To apply physiological loading to the coronary artery in this set-up, we have investigated a way to assess the physiological axial pre-stretch of the coronary artery. It has been validated that at the in-vivo pre-stretch, the axial force is relatively insensitive to changes in pressure. For the purpose of predicting the mechanical behavior of a specific coronary artery, we have derived a generic constitutive model, by providing it with a generic set of material and geometric parameters. This generic constitutive model is able to predict the pressure-inner radius and pressure-axial force change relations of a passive porcine coronary artery, by just measuring its radius at physiological loads and the corresponding pressure. When, instead of a generic, an artery-specific description of the coronary artery is desired and only in-vivo pressure-radius data are available, more structural information of the artery is desired. In this thesis it has been shown, by the analysis of the fitted material parameters, that the preferred material model fiber orientation at physiological loading is (36.6 ± 0.4)¿ for human as well as porcine coronary arteries. This finding can be used as an optimization constraint in fitting a constitutive model to the mechanical data available. Finally, a new model to describe the extra stress generated by maximally constricted smooth muscle cells, has been proposed. This model is well able to describe the extra smooth muscle stress generated in an arterial ring test, also beyond the physiological range, and has successfully been added to the generic constitutive model of the coronary artery