Dynamic Strength of Porcine Arteries
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The failure behavior of collagenous soft tissues is important for clinical problems of plaque rupture and trauma. Cyclic tests require high frequencies that may affect the strength properties of the soft tissues. Experimental results of mechanical response of blood vessels to physiologic loads can be used to model and predict plaque rupture and direct medical therapy or surgical intervention. The goal of the study is to measure the mechanical failure properties of arteries to determine if they are strain rate and cycle dependant and to measure the progressive damage of arteries with time dependent loading. Ring specimens of porcine carotid arteries were preconditioned and then pulled to failure. In all cases, the intima broke first. Ultimate stress increased as a weak function of increasing strain rates. The ultimate stress at 100 mm/s was 4.54 MPa, greater than the 3.26 MPa at 0.1 mm/s. Strain rates between 1 and 100 mm/s correspond to a cyclic frequency of 0.5 Hz to 5 Hz for fatigue testing. In contrast, ultimate strain in arteries was independent of strain rate over the range tested. The creep tests showed a logarithmic relationship between stress magnitude and stress duration for this soft tissue. The creep testing indicates that damage is accumulating above certain threshold stress levels. The values of ultimate strength showed a 35% increase after 10,000 cycling loading. In contrast, the ultimate strain had a 13% decrease after cycling and the difference was statistically significant with p=0.018. The testing results showed that there were no significant differences on strength among fresh arteries and arteries stored at 5¡ã C for up to two weeks. The test results may be useful for developing a mathematical model to predict the behavior of arterial soft tissues and may be extended to estimate fracture and fatigue in the atherosclerotic plaque cap.