title: Regional cycles of perfusion and non-perfusion in the lung of the term fetal rabbit.
abstract: The spatial distribution of pulmonary blood flow and its change over time was investigated in term fetal rabbits, using the plasma tracer fluorescein-isothiocyanate-labeled bovine serum albumin (FITC-BSA). A tracer bolus was injected intravenously and allowed to circulate in vivo for increasing periods of time (2-30 minutes) prior to arrest of the circulation and tissue preparation. Initially, fluorescence was present in the vasculature of 43% of lung parenchymal tissue, disposed as discrete regions or "lobules." Interspersed regions of lung tissue received no tracer inflow. With increasing tracer circulation times (10, 20, and 30 minutes), a greater percentage of lung cross-sectional area contained vessels exhibiting tracer fluorescence (64, 96, and 100%, respectively). In the fetal lung, a high pulmonary vascular resistance (PVR) is maintained. Our studies indicate that, at any given moment, fetal pulmonary blood flow is distributed only to a proportion of discrete lung "lobules," while interspersed "lobules" receive no flow at all. The "lobules" alternate between these "high" and "low" vascular resistance states with a periodicity of approximately 35 minutes, comprising 22 minutes of non-perfusion followed by 13 minutes of perfusion. This circulatory pattern permits both the maintenance of high PVR and uniform lung development. Further, by directing flow to only a portion of the vasculature, greater microvascular flow rates are achieved and hence the risk of blood sludging and stasis is reduced. Recruitment of these "non-perfused" regions at birth could thus produce a significant reduction in PVR.
authors.affiliation: Department of Anatomy and Histology, School of Medicine, Flinders University of South Australia.
authors.forename: J
authors.initials: J
authors.lastname: Lipsett
authors.forename: B
authors.initials: B
authors.lastname: Gannon
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D005260:Female; D008168:Lung / Q000098:blood supply*; D008856:Microscopy, Fluorescence; D011247:Pregnancy; D011817:Rabbits; D012039:Regional Blood Flow / Q000502:physiology