The pulmonary circulation in congenital heart disease. II. Pulmonary hypertension.

In young children with congenital heart disease the pulmonary circulation is exposed to abnormal haemodynamic conditions before it is fully developed. In the newborn infant the persistence or development of pulmonary hypertension rapidly leads to structural change. The speed with which an increase in muscularity can develop has hitherto been underestimated. In most children dying in early infancy with congenital heart disease and pulmonary hypertension the presence of thick walled small arteries is due not to persistence of the high wall thickness of foetal life, but to a rapid postnatal response of the pulmonary circulation to pulmonary hypertension. In older patients with a ventricular septal defect, aged between 3 months and 4 years, the presence of pulmonary hypertension has been shown to interfere with the growth and development of the pulmonary circulation, judging this by reduction in size and multiplication of intra-acinar arteries and an increase in muscularity of both pre and intra-acinar arteries and veins. In these patients elevation of pulmonary vascular resistance was associated with failure of the intra-acinar pulmonary circulation to develop normally and not with obliterative pulmonary vascular disease. Recent studies indicate that growth and development of the peripheral pulmonary circulation can be quantitated in lung biopsies taken from infants and young children with congenital heart disease. It should therefore be possibe to correlate structure and function at a critical period of lung development, before the changes of obliterative pulmonary vascular disease are established.