Mechanical Properties of Aneurysms of the Descending Human Aorta
Methods: Using an epi-aortic ultrasound probe intra-operatively, we measured aortic wall thickness during systole and diastole, circumference during systole and diastole, and blood pressure on 12 patients undergoing elective resection of their descending aortic aneurysms. From these measurements, we calculated the distensibility, wall stress, elastic modulus (Einc), and pulse wave velocity (PWV) for the neck (narrow portion) and belly (widest portion) of fusiform aneurysms. We compared these mechanical properties between the neck and belly of descending aortic aneurysms with a paired t-test, as well as between ascending and descending aortic aneurysms with an unpaired t-test.
Results: The average aneurysm belly was 4.1 cm in diameter compared to 2.7 cm in the neck (p = 0.0002). Distensibility was higher in the neck than the belly (p = 0.02), the wall stress was higher in the belly (p = 0.01), and Einc was non-significantly higher in the belly (p = 0.08). There was no significant difference in PWV (p = 0.33). There were no significant differences in any of the mechanical properties between descending and ascending aortic aneurysms.
Conclusion: Larger aneurysms are at increased risk of rupture because 1) they experience greater circumferential wall stress tending to expand the lumen, and 2) they are less distensible with a higher elastic modulus which indicates they have less reserve stretch capacity. We also showed that different sections of the same aneurysm behave differently but that the ascending and descending aortic aneurysms behave similarly. These findings have implications on the validity of using mechanical parameters to predict the natural course of aortic aneurysms. Finally, we demonstrated that there may be better ways to predict aortic rupture or dissection than current standards using diameter or growth rate alone.
School Location:USA - Connecticut
Source Type:Master's Thesis
Keywords:aortic aneurysm human decision making risk assessment elasticity rupture
Date of Publication:03/04/2008