Form and function of fetal and neonatal pulmonary arterial bifurcations

• Published in: American journal of physiology. Heart and circulatory physiology 2000-12, Vol.279 (6), p.H3047-H3057
• Main Authors: Bennett, Stephen H, Eldridge, Marlowe W, Zaghi, Daniel, Zaghi, Shaaron E, Milstein, Jay M, Goetzman, Boyd W
• Format: Article
• Language: English
• Subjects: Animals; Animals, Newborn; Female; Fetus - anatomy & histology; Fetus - embryology; Fetus - physiology; Models, Cardiovascular; Pregnancy; Pulmonary Artery - anatomy & histology; Pulmonary Artery - embryology; Pulmonary Artery - physiology; Pulmonary Circulation - physiology; Sheep; Stress, Mechanical
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.2000.279.6.h3047

1  Department of Pediatrics, Division of Neonatology, University of California Davis, Davis, California 95616; and 2  Department of Pediatrics, University of Wisconsin School of Medicine, Madison, Wisconsin 53792-4108 Bifurcation is a basic form of vascular connection. It is composed of a parent vessel of diameter d 0 , and two daughter vessels, d 1 and d 2 , where d 0  >  d 1     d 2 . Optimal values for the bifurcation area ratio,  = ( d 1 2 +  d 2 2 )/ d 0 2 , and the junction exponent, x , in d 0 x  =  d 1 x  +  d 2 x , are postulated to be universal in nature. However, we have hypothesized that the perinatal pulmonary arterial circulation is an exception. Arterial diameters were measured in pulmonary vascular casts of a fetal lamb (140 days gestation/145 days term) and a neonatal lamb (1 day old). The values for  and x were evaluated in 10,970   fetal and 846 neonatal bifurcations sampled from the proximal and intermediate arterial regions. Mean values and confidence intervals (CI) for the fetus were  = 0.890 (0.886-0.895 CI) and x  = 1.75 (1.74-1.76 CI); and for the newborn were  = 0.913 (0.90-0.93 CI) and x  = 1.79 (1.75-1.82 CI). These values are significantly different from Murray's law (  > 1,  x  = 3) or the West-Brown-Enquist law (  = 1,  x  = 2). Therefore, perinatal pulmonary bifurcation design appears to be distinctive and exceptional. The decreasing cross-sectional area with branching leads to the hemodynamic consequence of shear stress amplification. This structural organization may be important for facilitating vascular development at low flow rates; however, it may be the origin of unstable reactivity if elevated blood flow and pressure occurs. pulmonary arterial morphometry; branching complexity; heterogeneity