Anatomic Characterization of Intrapulmonary Bronchopulmonary Anastomoses in Healthy Rat Lungs

Many neonates with pulmonary hypertension die from right‐to‐left shunt and hypoxemia soon after birth. Intrapulmonary bronchopulmonary anastomotic pathways (IBAPs) have been observed in the lungs of these infants. We indirectly characterized right‐to‐left shunt recruitment by hypoxia (12% O 2 ) in healthy humans and animals that can be reversed by 100% O 2 . We hypothesized that IBAPs are a normal lung feature whose recruitment is induced by hypoxia. Anesthetized rats were ventilated with 21% or 12% O 2 for 20 minutes. Lungs were then immediately removed, airway fixed with 10% formalin, sectioned, and stained for the histological evaluation of IBAPs. The direction of blood flow through these pathways was evaluated by injecting red and green fluorescent microspheres into the right (RV) and left (LV) ventricles of rats ventilated with 12% or 100% O 2 and determining their abundance in the lung. Histological sections demonstrated abundant IBAPs in 12% O 2 ‐ventilated lungs, connecting the pulmonary and bronchial arterial trees, but not 21% O 2 ‐ventilated lungs. Consistent with right‐to‐left shunt through these pathways, microspheres injected into the right ventricle were found in the pleural and bronchial vascular beds, but LV‐injected spheres were not found in the pleura. In 100% O 2 ‐ventilated lungs, both RV‐ and LV‐injected microspheres were found coincidentally in pleural vessels, suggesting a possible left‐to‐right shunt. Future studies will aim to anatomically determine the vessel type containing co‐localized red and green microspheres and further characterize IBAPs, including describing their receptor expression. Support or Funding Information University of Iowa Start‐Up Fund