Effect of high transcapillary pressures on capillary ultrastructure and permeability coefficients in dog lung

Abstract

To determine the correlation between ultrastructural and physiological changes in blood-gas barrier function in lungs transiently exposed to very high vascular pressures, we increased capillary transmural pressure (Ptm) of 6 canine isolated perfused left lower lung lobe preparations (high-pressure group) to 80.3 Torr for 3.8 min and then determined the capillary filtration ( K fc) and osmotic reflection (ςd) coefficients at a Ptm of 19.1 Torr in the ventilated lung lobes. This was followed by perfusion fixation of the lobes at a Ptm of 20.5 Torr for ultrastructural analysis. These data were compared with those obtained in six lobes in which Ptm was not transiently elevated before K fc, ςd, and ultrastructural evaluation. K fc was higher [0.249 ± 0.042 (SE) vs. 0.054 ± 0.009 g · min−1 · Torr−1 · 100 g−1; P < 0.01] and ςd was lower (0.52 ± 0.07 vs. 0.85 ± 0.08; P < 0.01) in the high-pressure group. In contrast, although endothelial and epithelial breaks were occasionally observed in some experiments, their incidence was not increased in the high-pressure group. These data suggest that the increased transvascular water and protein flux occurred through pathways of a size not resolvable by electron microscopy after vascular perfusion-fixation at a Ptm of 20.5 Torr.