Fig. 1.

Normal and abormal transition at birth and role of oxidative stress in persistent pulmonary hypertension of the newborn (PPHN). The fetus lives in a state of hypoxemia with low arterial (PaO₂) and alveolar oxygen (PAO₂) tension. Normal transition at birth results in room air ventilation and a modest increase in PaO2 and PAO2 leading to pulmonary vasodilation and establishment of lungs as the site of gas exchange. When transition is abnormal, pulmonary vasodilation does not occur resulting in persistence of high pulmonary arterial pressures and right-to-left extrapulmonary shunts leading to systemic hypoxemia despite alveolar hyperoxia. Alveolar hyperoxia leads to oxidative stress and release of reactive oxygen species. See text for details. Copyright Satyan Lakshminrusimha.