Finite strain elastodynamics of intracranial saccular aneurysms

Various investigators suggest that intracranial saccular aneurysms are dyna mically unstable, that they resonate in response to pulsatile blood flow. T his hypothesis is based on linearized analyses or experiments on rubber "mo dels", however. and there is a need for a more critical examination. Toward this end, we (a) derive a new nonlinear equation of motion for a pulsating spherical aneurysm that is surrounded by cerebral spinal fluid and whose b ehavior is described by a Fung-type pseudostrain-energy function that fits data on human lesions, and (b) use methods of nonlinear dynamics to examine the stability of such lesions against perturbations to both in vivo and in vitro conditions. The numerical results suggest that this sub-class of les ions is dynamically stable. Moreover, with the exception of transients asso ciated with initial perturbations, inertial effects appear to be insignific ant for fundamental forcing frequencies less than 10 Hz and hence for typic al physiologic and laboratory conditions. We submit, therefore, that furthe r study of the mechanics of saccular aneurysms should be focused on quasi-s tatic stress analyses that investigate the roles of lesion geometry and mat erial properties, including growth and remodeling. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.