In vivo estimation of the contribution of elastin and collagen to the mechanical properties in the human abdominal aorta: effect of age and sex

The mechanical properties of the aorta affect cardiac function and are related to cardiovascular morbidity/mortality. This study was designed to evaluate the isotropic (mainly elastin, elastin(iso)) and anisotropic (mainly collagen, collagen(ani)) material parameters within the human aorta in vivo. Thirty healthy men and women in three different age categories (23-30, 41-54, and 67-72 yr) were included. A novel mechanical model was used to identify the mechanical properties and the strain field with aid of simultaneously recorded pressure and radius in the abdominal aorta. The magnitudes of the material parameters relating to both the stiffness of elastin(iso) and collagen(ani) were in agreement with earlier in vitro studies. The load-bearing fraction attributed to collagen(ani) oscillated from 10 to 30% between diastolic and systolic pressures during the cardiac cycle. With age, stiffness of elastin(iso) increased in men, despite the decrease in elastin content that has been found due to elastolysis. Furthermore, an increase in stiffness of collagen(ani) at high physiological pressure was found. This might be due to increased glycation, as well as changed isoforms of collagen in the aortic wall with age. A marked sex difference was observed, with a much less age-related effect, both on elastin(iso) and collagen(ani) stiffness in women. Possible factors of importance could be the effect of sex hormones, as well as differing collagen isoforms, between the sexes.