Babbs, Charles F., "Why Abdominal Aortic Aneurysms Rupture: Predicting Pressure and Diameter at Failure" (2021). Weldon School of Biomedical Engineering Faculty Working Papers. Paper 24.
Date of this Version
biomechanics, distensibility, elective repair, failure criteria, impending rupture, mechanics, noninvasive, pathogenesis, patient-specific, rupture risk, stiffness, wall stress
Objective: To perform a first-principles biomechanical analysis of the process of aortic aneurysm rupture, based upon the balance of expanding forces from blood pressure and reactive forces from wall elasticity, and to explore new methods for prediction of rupture risk. Methods: A mathematical model is created to describe the forces acting on a localized, weak patch of aneurysm wall during the cardiac cycle. A method to obtain patient-specific model parameters non-invasively, including incremental Young’s modulus, from cine ultrasonic or magnetic resonance images is proposed. Results: Pre-rupture integrity of an aneurysm is maintained by the balance between the expanding forces and the reactive elastic forces acting upon the aneurysm wall at its weakest point. Rupture happens when the diameter expands to a critical level, at which any further expansion causes expanding force to increase more than reactive force, producing a runaway increase in size. Using the prevailing systolic/diastolic blood pressure and the pulsatile expansion of the aneurysm, as observed by ultrasonic sector scanning, one can calculate the patient-specific force balance and the critical systolic blood pressure and diameter at failure, assuming a given upper limit of systolic blood pressure. Comparing these calculated values with the measured ones provides two indices of rupture risk. In general, greater than 10-percent pulsatile expansion during clinical testing signals a dangerously low margin of safety. Conclusions: The proposed method of noninvasive and low-cost risk stratification may be especially important when resources for elective surgery are limited, as in the current and future pandemics. Future clinical studies can be done with existing equipment and protocols, including cine ultrasonic sector scans and multi-institutional databases.