Albumin clearance from alveoli: tissue permeation vs. airway displacement

In anesthetized, ventilated dogs, clearance of 2 +/- 0.2 ml alveolar-instilled 1% isosmolar [125I]albumin ([125I]RISA) was separated into bulk airway displacement and transalveolar tissue permeation by the use of collimated external detectors and by sampling of blood and lymph. The detectors were positioned perpendicular to the plane of bronchial drainage, and collimator resolution was characterized by a 50% decrease in count rate for a 5-mm lateral (transbronchial) instillate shift. Detector signals demonstrated no airway shift in 10 dogs studied, the signal decay equaling [125I]RISA absorption determined by lung homogenates. The mean rate constants of [125I]RISA lung clearance and epithelial permeation were 4.08 X 10(-4)-min-1 and 5.48 X 10(-4)-min-1, respectively. The diffusional permeability coefficient of alveolar epithelium for albumin was 4.06 X 10(-9) CM-S-1. Absorbed [125I]RISA was separated into blood and lymph components by collecting lymph from the right lymphatic duct (RLD) and thoracic duct. Mean blood/lymph removal ratio was 6.3/1, and correlated with plasma/RLD lymph steady-state albumin concentration ratios in individual animals. Over a mean observation period of 5.4 h, an average of 12.3% [125I]RISA was cleared from the instilled region. The data suggest that this amount was cleared by permeation; there was little evidence of airway clearance.