Effect of lung injuries on [14C]urea permeability-surface area product in dogs

To determine whether [14C]urea permeability-surface area product (PS) is a reliable indicator of changes in permeability in various injuries and its relationship to indicator-dilution and gravimetric lung water contents, we studied six groups of anesthetized, paralyzed, and mechanically ventilated dogs (5 animals each). The groups consisted of control dogs, those injured by intravenous alloxan, oleic acid, or glass beads, and those exposed to acute hypoxia or increased left atrial pressure from volume loading (Pla). Interanimal variation of PS was large (3.0-15.0 ml/s), but successive hourly values in individual animals were stable for 2 h in experimental groups and for 4 h in controls. The PS increased after alloxan, elevated Pla, and 2 h of hypoxia; PS decreased after oleic acid and microemboli. The gravimetric lung water increased after alloxan, oleic acid, and microemboli, and indicator-dilution lung water increased only after alloxan. We conclude 1) that intersubject variability requires normalization to enable detection of significant deviation from base line, and 2) that decreased PS after oleic acid and microvascular injury occurred because vascular obstruction, which decreased surface area, masked probable coexisting increases in capillary permeability.