Time-course of axial residual strain remodeling and layer-specific thickening during aging along the human aorta

Detailed estimation of axial residual strains in the human aorta is necessary when performing biomechanical analyses of physiologic functions and pathologic conditions. We recently published such data for autopsied aortas and the present aim was to measure axial residual stretches at different wall depths, along with layer thicknesses on images borrowed from that work. Residual stretches at the external surface and medial-adventitial interface increased along the aorta's ascending course, decreased along its descending course, and increased from the diaphragm toward the iliac arteries. Residual stretches at the intimal-medial interface and internal surface decreased down the distal one-third of the aorta. A continuous decrease in medial thickness was witnessed along the vessel, whereas intimal and adventitial thickness remained fairly stable. At some axial locations, smaller were the axial residual stretches of the outer than those of the other quadrants, with minor differences in layer-specific thicknesses among quadrants. Adventitial thickness did not vary with age, while the intima and media thickened considerably with different time-courses. The observed intimal thickening solely between young (≤40 yr) and middle-aged subjects (40-60 yr) is consistent with the increased circumferential residual stretches previously established by our group between those subject groups and the minimal further increase in old subjects (≥60 yr). The observed medial thickening between middle-aged and old subjects was accompanied by decreased axial residual stretches that were not seen between young and middle-aged subjects. These observations suggest distinct roles for the intima and media in determining circumferential and axial residual stretches that merit further attention.