Aorta to Pulmonary Artery Shunts:  Pulmonary Vascular Changes in Newborn Calves and Their Resolution Following Shunt Closure

The risk of surgery for congenital heart disease parallels the severity of associated pulmonary vascular disease. Therefore, many experimental studies on changes in pulmonary vasculature after the creation of systemic artery to pulmonary artery shunts have been reported. Most of these studies have been carried out in adult animals with a mature pulmonary vasculature.^1,2 The muscular pulmonary arterioles normally seen in the new-born human, calf, and dog thin out rapidly during the first year of life and the small pulmonary arterioles develop larger lumina and thinner walls. Some studies have been carried out in puppies^3-5 and in new-born calves⁶ with an immature pulmonary vascular bed. The latter studies are conflicting, and it was felt that the newborn calf would be a better experimental model than the newborn pup. Consequently, the purpose of this study was to create and to interrupt a large left to right shunt in