Effects of age on the anisotropy of the descending human thoracic aorta determined by uniaxial tensile testing and digestion by NaOH under load

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Abstract
Strips of human thoracic aortic wall taken at autopsy from 23 individuals aged 15–81 years have been tested in two ways: in uniaxial loading and by digestion in 0.1 M NaOH at 75 °C under a load of 50 g. The circumferentially oriented strips were more extensible in loading and took a longer time to fail while being digested under load than the longitudinal strips from the same location. The stress versus strain curve was fitted to an exponential equation of the form, stress = A[exp(B strain)]. For circumferentially oriented strips from 19 subjects, parameter A was independent of age. Parameter B increased by a factor of 2.75 from 19 to 81 years. For longitudinally oriented strips for 14 subjects, A was also independent of age and B increased by 2.4 times from 25 to 81. With digestion under load for 11 matched pairs of strips aged from 32 to 75 the circumferential strips failed in 117 ± 23 min (standard error), while the longitudinal ones failed in 20.3 ± 3.2 min (standard error) (p < 0.003). The results have important implications for vessel attachments to the aorta in heart transplantation and in vascular surgery.Key words: aorta, aging, anisotropy, modulus of elasticity, connective tissue mechanics, elastin–collagen, stress–strain.

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