Chain Mediation of the Aortic Path in the Relationship between Body Mass Index and Abdominal Aortic Diameter

Introduction: the aorta, sensitive to excess weight, can undergo changes associated with cardiovascular risk. Studying its segments will allow a better understanding of the relationship between BMI and distal structural alterations. Objective: to analyze the relationship between BMI and abdominal aortic diameter, considering the thoracoabdominal aortic segments as mediators. Materials and methods: a cross-sectional study based on secondary data from 801 adults evaluated by thoracoabdominal computed tomography. The independent variable was BMI. The dependent variable was abdominal aortic diameter at the origin of the celiac trunk. The potential mediating effect of aortic diameters was evaluated using a six-segment chain mediation model: aortic sinus of Valsalva, sinotubular junction, mid-ascending aorta, mid-aortic arch, mid-descending aorta, and aorta at the level of the diaphragm. A directed acyclic graph was developed to support the causal structure. Results: BMI was not directly associated with abdominal aortic diameter but was associated with the aortic sinus of Valsalva (B=14.159; p<0.001) and the sinotubular junction (B=0.4686; p=0.0036). There was no relationship with the middle ascending aorta (B=-0.0715; p=0.757). A positive effect was observed on the middle descending aorta (B=0.4837; p<0.001) and the aorta at the diaphragm (B=0.6110; p<0.001), both of which were directly associated with abdominal aortic diameter (B=0.1570 and B=0.6113, respectively; p<0.001). These findings suggest a structural sequence where distal thoracic diameters progressively influence abdominal aortic caliber. Three significant indirect pathways were identified: BMI → sinus of Valsalva→ mid-descending aorta → diaphragmatic aorta → abdominal aorta (effect = 0.1807; 95% CI [0.0878–0.2778]), BMI → mid-ascending aorta → mid-aortic arch → mid-descending aorta → abdominal aorta (effect = 0.0611), and BMI → mid-descending aorta → abdominal aorta (effect = 0.0759; 95% CI [0.0306–0.1343]). Conclusions: the findings suggest that BMI may indirectly influence abdominal aortic diameter through interconnected aortic segments. This structural pattern could have clinical implications for the early detection of vascular abnormalities associated with excess weight.