COMPOSITION-DEPENDEN AND HISTORY-DEPENDENT RADIAL COMPRESSIVE BEHAVIOR OF HUMAN ATHEROSCLEROTIC PLAQUE

Invasive procedures to revascularize occluded blood vessels rely on th e mechanical response of the diseased tissue. Failure rates associated with such procedures show the need for improvement. to understand the associated mechanics, the material properties of atherosclerotic plaq ue should be known; yet data are scant. The purpose of this study was to investigate the different mechanical responses exhibited by plaques with different compositions, focusing specifically on radial compress ive behavior. A custom-built experimental system was developed that wa s fully computer controlled with a broad range of loading capabilities . A temperature-controlled, physiologic specimen bath allowed testing at 37 degrees C. Monotonically loaded specimens showed that plaque beh avior was nonlinear under finite deformations. A multiple cycle protoc ol, executed in two phases, distinguished three types of mechanical re sponse of different plaques. The differences in behavior were associat ed with histologic differences in plaque composition, and mechanically characterized by different ''repeatability'' (the stabilization of th e cyclic response) and ''recoverability'' (the second loading phase re tracing the first loading phase behavior). Type 1 behavior was categor ized by repeatability and recoverability . Type 2 behavior displayed r epeatability but only partial recovery during the second loading phase . Recovery was absent in type 3 behavior. The histologic observations demonstrated that calcified tissue was present only in specimens displ aying type 1 behavior. Fibrous tissue and part of a modified media (du e to disease) were present in specimens displaying type 2 behavior. An atheroma, along with a relatively thin modified media, was present in specimens displaying type 3 behavior. The differences in the maximum stretches attained at the end of phase I loading, the stretch offset f rom the first to the 15th cycle of phase I loading, and the hysteresis in the first and 15th cycles of phase I loading distinguished the spe cimen behaviors with statistical significance. These compression data showed that plaques exhibit composition- and history-dependent nonline ar and inelastic responses under finite deformations. (C) 1997 John Wi ley & Sons, Inc.