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 extent of irreversible deformation and breaking stress of the human thoracic aorta. Methods: From 14 human heart valve donors without aortic disease (mean age 35 years, range 8-59 years), 14 intact segments of the thoracic descending aorta were studied within 48 h after cardiac arrest. In an experimental setup, the segments were submitted to increasing hydrostatic pressure loads, both statically and dynamically, while radius and wall thickness were monitored echocardiographically. Pressure-radius curves were constructed. Radius and wall thickness were determined at a pressure of 100 mmHg. Radius at elastin resting length and collagen recruitment pressure (P-col, mmHg) were derived from the pressure-radius relationship and stress-strain curves were constructed to yield Young's moduli of elastin and collagen. Distensibility (D, mmHg(-1)) was determined while loading the segment with a sinusoidal pressure wave of 120/50 mmHg at both 0.5 and 1 Hz. Subsequently increasing static pressure loads of 400, 800, 1200 and 1600 mmHg were applied. After each pressure load, the increase in aortic radius at a pressure of 100 mmHg (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 survived a pressure load of 800 mmHg, in these vessels, the extent of irreversible dilation was positively correlated with age (r(2)=0.42) and negatively with D (r(2)=0.40) and P-col (r(2)=0.40). Conclusion: Permanent deformation and rupture of the human thoracic aorta following pressure overload are influenced by age, distensibility and collagen recruitment pressure. (C) 1999 Elsevier Science B.V. All rights reserved.