Fig. 1. (A) Scheme of a bronchial junction showing the variables measured and the method to compute geometrical (d_G) and physical (d_P) distances. The bifurcation angle is , d₀ and l₀ are diameter and length of the parent bronchi, respectively, and l₁, l₂, d₁ and d₂ are the length and diameters of the daughter branches. The sub-index `1' always indicates the lowest value. (B,C) From the measurements in A the length and diameter scaling ratios ( and _d, respectively) and the length L_r and diameter D_r symmetry ratios were computed: =[(l₁+l₂)/2]/l₀); _d=[(d₁+d₂)/2)/d₀]; L_r=l₁/l₂; D_r=d₁/d₂. (A,B) From these measurements one point in the physical domain and one point in the geometrical domain were obtained (open circles in B and C, respectively). Geometrical and physical Euclidean distances are represented by the lines between the open circle and the optimum points (solid circle) in each domain.