Layer-specific residual stretch changes along the human aorta: Effects of age, gender, and circumferential quadrant

BackgroundResidual strains in the unloaded human aorta are fundamental for understanding the in vivo stress and strain distribution across the aortic wall, including the intima, media, and adventitia, which is crucial for aortic function.ObjectiveTo report the detailed pattern of axial variation in layer-specific residual stretches and its relationship to age, gender, and circumferential location.MethodsCircumferential and axial strips from the anterior and posterior quadrants of nine aortic levels from twenty-one autopsy subjects were photographed before and after dissection into layers to determine layer-specific zero-stress states. Image analysis was used to assess variations in opening angles, residual stretches, and thickness at each level and direction.ResultsAge-related changes included a significant decline in the axial opening angle of the intact wall, driven by the adventitia. Its axial external residual stretch declined strikingly with age in the descending thoracic and abdominal aorta, outweighing the smaller increase in intact wall external residual stretch. Similarly, the slight age-related increase in intact wall internal residual stretch was more than offset by the significant decrease in circumferential internal residual stretch of the intima in the arch and descending thoracic aorta. The posterior quadrant was thicker and experienced lower external residual strains than the anterior. Gender-related differences were minimal, aside from greater wall thickness in males.ConclusionsThe age-related differences identified, distinguished by direction and layer, are consistent with previous observations on the orientation and age-related depletion of elastin across aortic layers, reinforcing its role as the primary determinant of residual strains.