Branching coefficient ("area ratio") of the human aortic bifurcation determined in distended specimens

Branching coefficient or "area ratio" is the ratio of the sum of the cross-sectional areas of the daughter vessels of a bifurcation to that of the parent stem. The value of area ratio is important for the assessment of flow patterns in the bifurcation and, consequently, of its functional load. In this series of cases, the area ratio was determined in aortic bifurcations of 19 young persons who died suddenly. The specimens were distended during fixation. The area ratio found in this study (1.18 +/- 0.6 SE) corresponded to the optimal value (1.15) predicted on a theoretical basis for an equibifurcation. Our ratio demonstrates an increase of 1.18 in size of the vascular bed of the human aortic bifurcation. We found a significant difference between the aortic circumference measured at the level of the divider compared with the circumference 2-2.5 cm above the bifurcation. The precise level of measurement is therefore critical for a correct determination of the area ratio of the aortic bifurcation and may explain varying values reported in the literature. Deviation from optimal value, e.g. with age, may be accompanied by increased mechanical stress and could favor the prominent involvement of aortic bifurcation by atherosclerotic lesions in man.