RESIDUAL STRAIN AND LOCAL STRAIN DISTRIBUTIONS IN THE RABBIT ATHEROSCLEROTIC AORTA

Effect of atherosclerosis on the residual strain in the arterial wail was studied in the rabbit thoracic aorta. Atherosclerosis was induced by feeding a cholesterol diet or by combining denudation of aortic end othelial cells with the diet feeding. Diameter of each aorta in the ph ysiological state was determined from a static pressure-diameter test. A ring specimen was obtained from the position where the diameter was measured. After the measurement of its no-load diameters, the ring wa s cut radially to measure the opening angle. Histological section was then obtained from the opened-up ring specimen. The section was divide d into 32 subsections and local dimensions were measured for each subs ection. Residual and in vivo strains referring to the opened-up config uration were calculated from the local dimensions and the diameters in the unloaded and physiological states. The opening angle significantl y correlated with the area fraction of intimal hyperplasia until sever e calcification occurred, while it had a negative correlation with the area fraction of calcified region. Histological observation of opened -up ring specimens indicated that the media adjacent to hyperplastic i ntima remained stretched, while that away from the intima relaxed. Ana lysis of local strains showed that, in the atherosclerotic aorta witho ut calcification, higher residual strain (compressive), i.e., lower in vivo strain (tensile), appears in the thicker intima. These results s uggest that: (a) intimal hyperplasia increases residual strain and thu s reduces the in vivo strain exerted in the intima and (b) calcified t issue restrains the deformation of adjacent tissues. The intimal hyper plasia and the calcification may complicate strain fields in the ather osclerotic aorta.