Pulmonary artery occlusion and reperfusion causes microvascular constriction in the rabbit lung

Reperfusion injury of the lung after ischemia is associated with altered alveolar blood flow and ventilation-perfusion mismatch, which is a significant cause of morbidity and mortality after lung transplantation. We examined the effect of ischemia and reperfusion on the tone of individual subpleural arterioles in the pulmonary circulation by using video microscopy with polarized epiillumination.

In 11 open-chested rabbits anesthetized with pentobarbital (2.3 to 2.5 kg), we ventilated the lungs through the lower trachea (air or 50% oxygen) and examined the response of subpleural arterioles (diameter 75 +/- 13 microm) to ischemia (76 +/- 32 min) of the right lung caused by occluding the right main pulmonary artery. Observations were made during baseline, occlusion, and during early (20 to 32 min) and late (48 to 63 min) reperfusion using a long working distance lens (550x) with a dipping cone held at the pleural surface while the lungs were statically inflated (10 cm H2O) with oxygen for brief periods. Data are expressed as mean +/- standard deviation.

Arteriolar diameter was decreased 57% +/- 19% during early reperfusion. There was a decrease in blood flow and alveolar walls were pale, indicating reduced capillary perfusion. During late reperfusion, arteriolar diameter was diminished (19% +/- 26%); flow was still reduced. Overall pulmonary vascular resistance increased during early reperfusion but returned to baseline level during late reperfusion. Arterial partial pressure of oxygen averaged 200 mm Hg during ischemia and reperfusion.

Constriction of small arterioles by ischemia and reperfusion can have a significant effect on the early phase of ventilation-perfusion mismatch and pulmonary dysfunction by altering alveolar perfusion. This response does not appear to be mediated by hypoxia because it was not prevented by ventilation with oxygen.