Lung water is increased in regions of higher neutrophil retention after acute bead embolization

Previous reports have shown that neutrophils are retained in the lung after acute embolization and that these neutrophils play an important role in the subsequent formation of permeability pulmonary edema. The present study was designed to test the hypothesis that acute embolic injury results in microvascular damage in lung regions with the greater retention of neutrophils. Seventeen pigs (20 +/- 2 kg) were embolized by injecting polystyrene beads (250 microns; labeled with 131I) into the right atrium over 5 min. Five pigs, which received no embolic beads, served as controls. Neutrophils (89 +/- 5% pure), isolated on Ficoll-Histopaque gradient, were radiolabeled with 111In-oxine. Twenty minutes after embolization, the radiolabeled neutrophils were injected into the right atrium along with 85Sr-labeled microspheres to mark the initial neutrophil distribution within the lung as well as the regional pulmonary blood flow at the time of their delivery. The animals were killed 50 min after embolization, and the lungs were removed, frozen over liquid nitrogen, and cut into 60 samples. The data show that after embolization regional neutrophil retention was inversely related to the regional blood flow but was not affected by the embolic load in the same region. Regional extravascular lung water was increased in regions of higher neutrophil retention, but the regions with increased edema did not receive a greater embolic load. These results show that microvascular injury occurs in the lung regions with the greatest neutrophil retention and that this increased retention of neutrophils is unrelated to the extent of embolization.