Development of the pulmonary circulation in ventricular septal defect: a quantitative structural study.

The application of quantitative morphometric techniques to evaluation of the lungs of nine children who died with a ventricular septal defect between the ages of 3 months and 4 years showed that the presence of pulmonary hypertension interferes with the growth and development of the pulmonary circulation. In all cases the preacinar arteries were of normal size and not dilated, and arterial size and number within the acinus were reduced and similar to those seen in the normal child at birth. Arterial and venous muscularity was increased as judged by an increase in wall thickness and by the presence of muscle in smaller and more peripheral arteries than is normal. Elevation of resistance was associated with failure of the intraacinar pulmonary circulation to develop normally rather than to obliterative pulmonary vascular disease. In view of the rapidity with which impairment of growth and elevation of resistance can develop, closure of a large defect is recommended before age 2 years.