Mechanical behavior of calcified plaques: a summary of compression and stress-relaxation experiments

This paper summarizes the results from mechanical testing of atheroscleroti c plaques performed in the Cardiovascular Mechanics Laboratory and the Labo ratory for Implantable Materials at UMBC. The motivation for our work is th at balloon angioplasty, stenting, and roto-ablation are mechanical processe s that are designed to permanently alter the shape of an occluded arterial lumen. The mechanisms of permanent plaque deformation are not known. Theref ore, to study the mechanical behavior of plaques, we performed mechanical t ests on atherosclerotic lesions with different compositions and investigate d differences in the materials' mechanical responses. Atherosclerotic plaqu e specimens were subjected to two main types of loading: multiple cyclic co mpression and stress-relaxation. The multiple-cycle test protocol was two f ifteen-cycle loading phases that were separated by a 10-15 minute unloaded "rest" period. The compressive stress-relaxation test protocol was a series of three consecutive loadings (called phases I, II, and III). Each phase c onsisted of a 25 % compression that was achieved in less than 1 second, a 1 0 minute relaxation period, and a 10 minute unloaded "rest" period between loadings. In the multiple cycle compressive loading, plaques exhibited thre e distinct types of behavior, which corresponded to the plaque compositions . Calcified plaques showed behaviors distinct from other plaque types and h ealthy vessels. In contrast to the cyclic compression results, plaque types could not be distinguished solely on the basis of stress relaxation behavi or. Calcified and fibrous plaques had similar behavior, and therefore histo logy was used for definite identification. Calcified plaques have unique me chanical properties, and therefore interventions like angioplasty, roto-abl ation, and stenting may require protocols specific for calcified lesions. T he optimum protocols for calcified plaques may be quite different from plaq ues with other compositions. It is essential to learn more about the mechan ical behavior of all plaque types to increase the success rate of occlusive atherosclerosis treatments.