Pulmonary artery occlusion and reperfusion causes arteriolar constriction and increases vascular resistance during early reperfusion in the intact rabbit lung

Ischemia-reperfusion of the lung leads to abnormal vascular responsiveness and progressive microvascular injury. We did experiments to determine effects of pulmonary artery occlusion and reperfusion on pulmonary arteriolar tone and vascular resistance. In 5 pentobarbital-anesthetized male rabbits with open chest, the lungs were ventilated through the lower trachea. Subpleural arterioles in the right lung, whose resting diameter averaged 71±18μm (mean±SD) were observed during brief periods when the lungs were statically inflated (10cmH₂0) with oxygen. The right pulmonary artery was occluded for 1-2 hrs and the occlusion was removed (reperfusion). Arterioles constricted by 36±20%, overall pulmonary vascular resistance increased by 44±23% and overall pulmonary blood flow decreased by 24±16% after 3-18 min of reperfusion (P<0.05), but were not significantly different from control after 50-69 min. Constriction was not prevented by ventilation with oxygen. With the same protocol, in 4 of 5 rabbits, myeloperoxidase content (a measure of neutrophil sequestration) in the right lung was not elevated above the left. Constriction of small arterioles by ischemia/reperfusion contributes to decreased blood flow and may have a significant role in the early phase of pulmonary dysfunction during reperfusion injury.