Matern Health Neonatol Perinatol 3: 6, 2017. doi: 10.1186 / s40748 - 017 - 0045 - 1 Pathophysiology Whatever the cause, elevated resistance in the pulmonary arteries causes abnormal smooth muscle development and hypertrophy in the walls of the small pulmonary arteries and arterioles and right-to-left shunting via the ductus arteriosus or a foramen ovale, resulting in intractable systemic hypoxemia.