title: Form and function of fetal and neonatal pulmonary arterial bifurcations.
abstract: 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, beta = (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 beta 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 beta = 0.890 (0.886-0.895 CI) and x = 1.75 (1.74-1.76 CI); and for the newborn were beta = 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 (beta > 1, x = 3) or the West-Brown-Enquist law (beta = 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.
authors.affiliation: Department of Pediatrics, Division of Neonatology, University of California Davis, Davis, California 95616, USA. shbennett@ucdavis.edu
authors.forename: S H
authors.initials: SH
authors.lastname: Bennett
authors.forename: M W
authors.initials: MW
authors.lastname: Eldridge
authors.forename: D
authors.initials: D
authors.lastname: Zaghi
authors.forename: S E
authors.initials: SE
authors.lastname: Zaghi
authors.forename: J M
authors.initials: JM
authors.lastname: Milstein
authors.forename: B W
authors.initials: BW
authors.lastname: Goetzman
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D005260:Female; D005333:Fetus / Q000033:anatomy & histology / Q000196:embryology / Q000502:physiology; D008955:Models, Cardiovascular; D011247:Pregnancy; D011651:Pulmonary Artery / Q000033:anatomy & histology / Q000196:embryology / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology*; D012756:Sheep; D013314:Stress, Mechanical