Pulmonary hypertension in childhood.

In the presence of pulmonary hypertension, the pulmonary vasculature fails to remodel after birth. Secondary changes then develop, and do so more rapidly than in the adult lung because the cells are exposed to the insult whilst still relatively undifferentiated. The commonest causes of pulmonary hypertension in newborn and young infants are alveolar hypoxia, and congenital heart disease causing a left-to-right shunt and increased pulmonary blood flow. The initial response of an increase in pulmonary arterial muscularity is common to both, but intimal proliferation can develop rapidly in those with complex congenital heart disease. The structural abnormalities are accompanied by abnormalities in the control of pulmonary vascular reactivity, a problem which is the focus of much current research activity.