Perinatal pulmonary arterial architecture: A distinctive design

Branching architecture influences the distribution of blood flow and shear stress, the latter being a hemodynamic signal for the endothelium to remodel vessel diameter. We wondered if the perinatal pattern of architecture was similar to the adult. Plastic casts of the lamb pulmonary arterial circulation were made in a 140 day fetus and a 1 day old newborn. Diameters of bifurcations were measured with a video micrometer. Architecture was evaluated from the network area ratio, AR, defined as the regression slope of the relationship between summed daughter areas and parent areas of bifurcations, with AR ≥ 1 being similar to the adult pattern. AR was evaluated in three ranges of parent diameter (D in mm): 1-(0.08≤D≤0.50);2-(0.50<D≤2.00); 3-(D>2) N=#bifurcations. 1 2 3 Fetus 0.818±0.008 (1330) 0.925±0.005(1445) 0.958±0.018 (60) Newborn 0.968±0.017( 186) 0.979±0.006 (533) 1.050±0.009 (90) These results suggest that the perinatal circulation exhibits a regional branching hierarchy of decreasing cross-sectional area (AR < 1), distinctly different from the adult pattern of AR ≥ 1. This pattern predisposes peripheral arterial vessels to an increase in blood flow velocity and shear stress. The persistence of this architecture after birth, despite increased diameters with blood flow, may explain why some neonates exhibit endothelial dysfunction and pulmonary hypertension.