Biomechanical Study of Vascular Walls

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Abstract
The static mechanical properties of vascular walls were determined from the change in external radius due to distending pressure as a series of the biomechanical studies of the blood circulation system. Segments of abdominal aorta, carotid artery and femoral artery excised from mongrel dogs were used as the test specimens. The arrangement and interrelation of the structural components were also examined on the transverse and longitudinal sections of these walls fixed at various distending pressures. The results obtained are summarized as follows: (1) In the low pressure range below 100mmHg, the wall radius increases rapidly with increasing pressure. However, vascular walls become much stiffer as they are distended in the pressure range between 100mmHg and 150mmHg. And above 150mmHg they almost lose their distensibility. (2) Distensibility of vascular walls decreases in the following order: abdominal aorta, carotid artery and femoral artery. It corresponds to the order of their distance from heart or of the volumetric fraction of elastin component existing in their walls. (3) The distension ratio (λθ)0, which is the ratio of external radius at each pressure to that at 20mmHg, can be related to the distending pressure p by the following equation in and below the physiological pressure range; logp=a+b(λθ)0. The constants a and b in this equation can be used as parameters representing the mechanical properties of vascular walls. (4) The tangential stress induced in the wall of abdominal aorta, which is calculated by Lame's equation, can be related to the tangential strain by a logarithmic function in the low stress range below 10g/mm2 and by an exponential one in the higher range. (5) Waviness of the elastin lamellae and interlamellar distances decrease markedly with increasing pressure between 100mmHg and 150mmHg. At and adove 150mmHg elastin lamellae become almost straight and interlamellar distances become uniform. These microscopic observations correspond to the unique change in distensibility of vascular walls stated in (1).

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