During the prenatal period a state of physiologic pulmonary hypertension exists due to the equalization of pressures by the patent ductus arteriosus, resulting in similar wall thickness of the ascending aorta (AA) and main pulmonary artery (MPA). After birth, as the ductus arteriosus closes and pulmonary arterial pressure decreases, attenuation of medial smooth muscle occurs such that the ratio of medial thickness to external diameter decreases from about 25% in fetuses to less than 10% in infants 3 to 6 months of age. After the first year of life, thickness of the MPA is normally less than half that of the adjacent ascending aorta, although the diameters of the two great arteries remain the same relative to one another [1]. During homeostatic conditions, the total pulmonary and systemic blood flows are essentially identical. In spite of their comparable blood flow rate and common embryologic origin, the anatomic characteristics of these two segments of the cardiovascular system differ substantially [2]. Futhremore, both these arteries are affected by many congenital abnormalities and also are subject to hypertension. Knowledge of the normal biomechanical properties of these great arteries is important for surgical treamtment, angioplasty, and tissue engineering. It can also provide insight into the disease processes and is a prerequisite to the study of mechanical behavior during disease conditions. In this study we characterized the biaxial mechanical behavior of both arteries as a function of location, which has not been previously performed in the pulmonary trunk.

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