MATHEMATICAL MORPHOLOGIC ANALYSIS OF THE AORTIC MEDIAL STRUCTURE - BIOMECHANICAL IMPLICATIONS

The architecture of the aortic tunica media was studied in 55 autopsy specimens (26 normotensive and 29 hypertensive patients). The purpose of the study was to elucidate whether, as commonly stated, homogeneous disposition of concentric lamellar units could be substantiated or wh ether an architectural gradient reflecting the decreasing biomechanica l gradient in the circumferential stress, concentrated towards the inn er wall, was present. The elastin lamellae thickness, interlamellar di stance, fibrosis index and fragmentation index were quantitated by mat hematical morphology methods. The results did not support classic hist ologic descriptions but showed that lamellar units were significantly thicker in the inner than in the outer zones of the media - i.e., a mo rphologic gradient was present. The differences between inner and oute r zones were more marked in hypertensive patients than in controls. Th e fibrosis index increased with age, especially in hypertensive patien ts. The fragmentation index in hypertensive patients was significantly higher than in controls and more marked in abdominal than in thoracic aorta. This weakening in the biomechanical resistance of elastin fibe rs could be one of the factors explaining the predominance of aneurysm s in the abdominal aorta.