Abdominal Aortic Wall Cross-coupled Stiffness Could Potentially Contribute to Aortic Length Remodeling

Background: Wall stiffness of the abdominal aorta is an important factor in the cardiovascular risk assessment. We investigated abdominal aortic wall stiffness divided in direct and cross‑coupled stiffness components with respect to sex and age.Methods: Thirty healthy adult males (n = 15) and females were recruited and divided into three age groups: young, middle aged and elderly. Pulsatile diameter changes were determined noninvasively by an echo‑tracking system, and intra‑aortic pressure was measured simultaneously. A mechanical model was used to compute stress and stiffness in circumferential and longitudinal directions.Results: Circumferential stretch had a higher impact on longitudinal wall stress than longitudinal stretch had on circumferential wall stress. Furthermore, there were an age‑related and sex‑independent increase in circumferential and longitudinal direct and cross‑coupled stiffnesses and a decrease in circumferential and longitudinal stretch of the abdominal aortic wall. For the young group, females had a stiffer wall compared to males, while the male aortic wall grew stiffer with age at a higher rate, reaching a similar level to that of the females in the elderly group.Conclusion: Temporal changes in aortic stiffness suggest an age‑related change in wall constituents that is expressed in terms of circumferential remodeling impacting longitudinal stress. These mechanisms may be active in the development of aortic tortuosity. We observed an age‑dependent increase in circumferential and longitudinal stiffnesses as well as decrease in stretch. A possible mechanism related to the observed changes could act via chemi‑cal alterations of wall constituents and changes in the physical distribution of fibers. Furthermore, modeling of force distribution in the wall of the human abdominal aorta may contribute to a better understanding of elastin–collagen interactions during remodeling of the aortic wall.
Funding: Linkoping University; Region Ostergotland; Medical Faculty Linkoping University; Swedish Research Council [12661]; Swedish Heart-Lung Foundation