The influence of aging and aortic stiffness on permanent dilation and breaking stress of the thoracic descending aorta

Objective: To assess the influence of aging and aortic stiffness on the ext ent of irreversible deformation and breaking stress of the human thoracic a orta. Methods: From 14 human heart valve donors without aortic disease (mea n age 35 years, range 8-59 years), 14 intact segments of the thoracic desce nding aorta were studied within 48 h after cardiac arrest. In an experiment al setup, the segments were submitted to increasing hydrostatic pressure lo ads, both statically and dynamically, while radius and wall thickness were monitored echocardiographically. Pressure-radius curves were constructed. R adius and wall thickness were determined at a pressure of 100 mmHg. Radius at elastin resting length and collagen recruitment pressure (P-col, mmHg) w ere derived from the pressure-radius relationship and stress-strain curves were constructed to yield Young's moduli of elastin and collagen. Distensib ility (D, mmHg(-1)) was determined while loading the segment with a sinusoi dal pressure wave of 120/50 mmHg at both 0.5 and 1 Hz. Subsequently increas ing static pressure loads of 400, 800, 1200 and 1600 mmHg were applied. Aft er each pressure load, the increase in aortic radius at a pressure of 100 m mHg (R-inc) was determined. The experiment continued until rupture occurred and breaking stress (sigma(break), N m(-2)) was calculated. donor age and aortic stiffness were correlated with R-inc and sigma(break) of the aortic segments. Results: Mean breaking stress of the 14 segments was 2.7 x 10(6) N m(-2). Breaking stress was negatively correlated with age (r(2)=0.66) and positively with D (r(2)=0.44) and with P-col (r(2)=0.18). Seven segments s urvived a pressure load of 800 mmHg, in these vessels, the extent of irreve rsible dilation was positively correlated with age (r(2)=0.42) and negative ly with D (r(2)=0.40) and P-col (r(2)=0.40). Conclusion: Permanent deformat ion and rupture of the human thoracic aorta following pressure overload are influenced by age, distensibility and collagen recruitment pressure. (C) 1 999 Elsevier Science B.V. All rights reserved.