PULMONARY STRESS INJURY WITHIN PHYSIOLOGICAL RANGES OF AIRWAY AND VASCULAR PRESSURES

Purpose: The aim of this study was to assess the respective role of a small elevation in pulmonary capillary pressure, airway pressure, or b oth on alveolar capillary barrier permeability in an isolated perfused rat lung model. Materials and Methods: Four groups were studied with low or high airway pressure (LA: 10 mL/kg (tidal volume); HA: 20 mL/kg ), low or high pulmonary artery pressure (LP: 9 mm Hg; HP: 12 mm Hg): LALP, HALF, LAMP, and HAHP. The lungs were ventilated and perfused ex vivo for 30 minutes. Quantification of fluorescein isothiocyanate-labe led (FITC) dextran in bronchoalveolar lavage (BAL) fluid and radiolabe led tracers assessed alveolar capillary barrier permeability. Results: BALF FITC-dextran was similar in the three groups with either one or two low-pressure parameters (LALP, LAHP, HALP), but high amounts were found in the HAHP group (375.2 x 10(-6) mg/mL v, respectively, 21.4, 2 6.2, and 30 x 10(-6) mg/mL, P = .0001). These results were consistent with the albumin space and extravascular lung water: higher values onl y in the HAHP group statistically different from the other groups (P < .002). Interalveolar pore examined with scanning electron microscopy s howed an increase in diameters between LALP and HAHP (P < .0001). Conc lusions: We can conclude that elevation of either the pulmonary artery pressure from 8 to 11 mm Hg or the alveolar pressure from 10 to 15 mm Hg alone does not change the permeability of the alveolar capillary m embrane; however, there is an additive effect of these pressures, Copy right (C) 1998 by W.B. Saunders Company.