Vessel Reactivity and Blood Flow in Rats Exposed to Neonatal Supplemental Oxygen

Premature babies make up 12.8% of live births per year. Because their lungs are poorly developed, supplemental oxygen is a necessary treatment. Recent studies in our laboratory, in a rat model of prematurity, show that aortic pulse wave velocities were higher in rats exposed to neonatal supplemental oxygen. This is an indicator of significant aortic stiffening. This study aims to determine if supplemental oxygen also affects the downstream vasculature reactivity. We hypothesized that exposure to supplemental oxygen during the neonatal period will decrease vessel reactivity and we will observe smaller changes in blood flow with hypoxic and carbon dioxide challenges. Twelve month old rats exposed to 80% and 21% oxygen for eight days during the neonatal period were ventilated with hypoxic (12% O₂), hypercapnic (5% CO₂), and room air conditions. Each exposure lasted 10 minutes and followed with different 10 µm neutron-activated BioPAL microspheres injections into the left ventricle. The microspheres were allowed to circulate for 300-400 cardiac cycles. Microspheres lodged in the tissues were used to quantify changes in visceral blood flow. 80% O₂ exposed rats showed a decreased baseline cardiac output to tissues compared to controls. In hypoxic and carbon dioxide conditions, 80% O₂ exposed rats showed decreased changes in blood flow to tissues compared to controls, but results were not significant. Some tissues showed decreased blood flows when the rats were exposed to hypoxia and carbon dioxide challenges suggesting some vasoconstrictive effects had also occurred.