Additional causes include Respiratory distress syndrome Premature ductus arteriosus or foramen ovale closure (see Neonatal Endocrine Function), which increases fetal pulmonary blood flow and may be triggered by maternal nonsteroidal anti-inflammatory drug (NSAID) use (1) Pulmonary hypoplasia with associated pulmonary vasculature hypoplasia leading to PPHN (2) Congenital diaphragmatic hernia, in which one lung is severely hypoplastic, also leading to pulmonary vasculature hypoplasia and PPHN Neonatal sepsis or neonatal pneumonia presumably because vasoconstrictive prostaglandins are produced by activation of the cyclooxygenase pathway by bacterial phospholipids, and acidosis due to systemic hypoperfusion caused by the infection also contributes to PPHN in this scenario Etiology references 1.