Stop-flow studies of distribution of filtration in rat lungs

Lin, W., E. Jacobs, R. M. Schapira, K. Presberg, andR. M. Effros. Stop-flow studies of distribution offiltration in rat lungs. J. Appl.Physiol. 84(1): 47-52, 1998.The stop-flow approach was used to investigate where filtration occurs in the pulmonary vasculature after elevation of left atrial pressure andaspiration of HCl. Rat lungs were perfused for 11 min at zero leftatrial pressures, and then flow was stopped for 10 min and left atrialpressures were increased to 20 cmH₂O. Thereafter, ³HOH was instilled into the airspaces, and the pulmonary vasculature was flushed by perfusing it fromthe pulmonary artery to left atrium (anterograde flush) or in theopposite direction (retrograde flush). Increases in fluoresceinisothiocyanate (FITC)-dextran (molecular weight 2,000,000) indicatedfiltration, and these preceded increases in³HOH after anterograde but notretrograde flushes. This suggests that some filtration occurred throughvessels that were relatively venous compared with those through which³HOH exchange had occurred.Filtration increased fivefold after instillation of 0.1 N HCl inisotonic saline into the air spaces before perfusion. Increases inEvans blue-labeled albumin concentrations were <40% those ofFITC-dextran, indicating loss from the vasculature, but increases inunlabeled albumin and FITC-albumin were comparable.