Regression of the systemic vasculature to the lung after removal of pulmonary artery obstruction

Rationale: Pulmonary artery occlusion stimulates angiogenesis in the systemic circulation of the ipsilateral lung and increases systemic-to-pulmonary blood flow. Whether this systemic neovascularization decreases after lung revascularization is unknown. Objectives: To assess the influence of lung revascularization on anatomy and flow of bronchial vessels supplying a chronically ischemic lung in piglets. Methods: Piglets were studied before (control) and 5 wk after left pulmonary artery ligation and 5 wk after left pulmonary artery reimplantation into the pulmonary artery trunk. The systemic blood flow to the right and left lungs was measured using colored microspheres, and the bronchial vasculature was assessed using light-microscopic morphometry. Renal and total blood flow, systemic blood pressure, and pulmonary blood pressure were measured in each experimental condition. Measurements and Main Results: Systemic blood flow to the left lung increased from 0.4 +/- 0.1 to 11.5 +/- 3.8 ml/min/g (p < 0.05) after left pulmonary artery ligation and returned toward the control value (1.2 +/- 0.6 ml/min/g) after revascularization, whereas it remained unchanged in the right lung. The number of bronchial vessels increased twofold in the ligated lung (p = 0.01), and did not decrease after reperfusion; however, vessel diameters decreased markedly. Renal and total blood flows, as well as mean pulmonary and systemic arterial pressures, were similar in the three experimental conditions. Conclusion: Revascularization after a period of left pulmonary artery occlusion normalizes the systemic blood flow to the left lung and induces partial loss of collateral vessels.