Pulmonary vasculature of piglets after correction of aorta-pulmonary shunts

In a previous article we described the functional and structural changes produced in the pulmonary arterial circulation of the growing pig by an aorta-pulmonary shunt. The present work describes the hemodynamic and morphologic adaptation that follows correction of the shunt. In four piglets, aged 5 weeks, an anastomosis was made between the thoracic descending aorta and the pulmonary trunk and left patent for 5 weeks. At the end of that time the mean pulmonary artery pressure (PAP) was 20 ± 3.8 mm Hg (mean ± SD), compared with 9 ± 2.1 mm Hg in a group of four age-matched sham-operated control piglets. The shunt was then surgically closed. After 10 weeks' recovery, the PAP was similar and normal in the two groups. We have already shown that pulmonary hypertension of similar degree and duration to that at the end of the patent shunt period produces the following structural changes, assessed by quantitative techniques: (1) preacinar arteries of normal external diameter but with a thicker medial coat than normal and (2) intra-acinar arteries in normal concentration, or smaller external diameter than normal, but with a medial coat appropriate to the external diameter: Smooth muscle is found in more peripheral arteries than is normal. In the present study, at the end of the recovery period, the shunt animals were compared with the sham-operated animals and had thicker medial coats in preacinar and intra-acinar arteries, muscle in more peripheral arteries than is normal, and an increased arterial and alveolar concentration for unit lung area. These results indicate that, in the growing porcine lung, 'recovery' from an aorta-pulmonary shunt that was associated with moderate pulmonary hypertension restores external arterial diameter to normal but leaves a thicker medial coat at the preacinar and intra-acinar levels and muscle more peripheral in the arterial bed. In addition, after shunt correction, multiplication of alveoli and arteries proceeds at a faster rate than normal, at least during the first 10 weeks of recovery.