Multimodal Structural Analysis of the Human Aorta: From Valve to Bifurcation

The aims of the present study were to assess the relative proportion of collagen and elastin in the arterial wall and to evaluate the collagen microstructure from the aortic root to the external iliac artery.Arterial wall tissue samples sampled during post-mortem examination from 16 sites in 14 individuals without aneurysm disease were fixed and stained for collagen and elastin. Stained sections were imaged and analysed to calculate collagen and elastin content as a percentage of overall tissue area. Scanning electron microscopy was used to quantify the collagen microstructure at six specific arterial regions.From the aortic root to the level of the suprarenal aorta, the percentages (area fractions) of collagen (ascending, descending, and suprarenal aorta respectively with 95% confidence interval [CI] 37.5%, 31.7 - 43.2; 38.9%, 33.1 - 44.7; 44.8%, 37.4 - 52.1) and elastin (43.0%, 37.3 - 48.8; 40.3%, 34.8 - 46.1; 32.4%, 25.2 - 39.6) in the aortic wall were similar. From the suprarenal aorta to the internal iliac arteries, the percentage of collagen increased (abdominal aorta, common and internal iliac arteries and external iliac artery respectively with 95% CI 50.6%, 42.7 - 58.7; 51.2%, 45.5 - 56.9; 49.2%, 42.0 - 56.4) reaching a double percentage for elastin (23.6%, 15.7 - 31.6; 20.8%, 15.1 - 26.5; 22.2%, 14.9 - 29.5). Mean collagen fibre diameter (MFD) and average segment length (ASL) were significantly larger in the external iliac artery (MFD 6.03, 95% CI 5.95 - 6.11; ASL 22.21, 95% CI 20.80 - 23.61) than in the ascending aorta (MFD 5.81, 5.72 - 5.89; ASL 19.47, 18.07 - 20.88) and the abdominal aorta (MFD 5.92, 5.84 - 6.00; ASL 21.10, 19.69 - 22.50).In subjects lacking aneurysmal disease, the aorta and iliac arteries are not structurally uniform along their length. There is an increase in collagen percentage and decrease in elastin percentage progressing distally along the aorta. Mean collagen fibre diameter and average segment length are larger in the external iliac artery, compared with the ascending and the abdominal aorta.