How the left lung is perfused after ligating the left pulmonary artery in the pig at birth: clinical implications for the hypoperfused lung.

The left pulmonary artery and ductus arteriosus were ligated in 14 pigs at birth. Animals were sacrificed at intervals from 2 to 24 weeks of age. In the right lung the pulmonary artery and in the left, either the distal pulmonary artery, bronchial arteries or both were injected. The fixed lung specimens were studied by arteriography, dissection and microscopic examination of serial and random sections of lung tissue. The bronchial arterial circulation to, and within the right lung appeared normal and was similar to that described in the human lung. In the left lung, the bronchial arterial circulation hypertrophied rapidly during the first 2 weeks, and large anastomoses between pulmonary and systemic circulations were found at the same sites as in the normal pig lung. The position and structural characteristics of the anastomosing arteries is described in the different types of broncho-pulmonary connection. In most animals aged 16 weeks or more, peripheral bronchial arteries immediately proximal to the anastomotic sites, developed intimal and medial proliferation. The left lung continued to grow although in all animals it was small. The axial pulmonary artery and its branches became smaller with age. These findings help explain how the lung is perfused and grows in children with congenital heart disease and an acquired collateral pulmonary arterial circulation.