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

To determine the correlation between ultrastructural and physiological chan ges 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 g roup) to 80.3 Torr for 3.8 min and then determined the capillary filtration (K-fc) and osmotic reflection (sigma (d)) coefficients at a Ptm of 19.1 To rr 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 w ere compared with those obtained in six lobes in which Ptm was not transien tly elevated before K-fc, sigma (d), and ultrastructural evaluation. K-fc w as higher [0.249 +/- 0.042 (SE) vs. 0.054 +/- 0.009 g.min(-1).Torr(-1).100 g(-1); P < 0.01] and <sigma>(d) was lower (0.52 +/- 0.07 vs. 0.85 +/- 0.08; P < 0.01) in the high-pressure group. In contrast, although endothelial an d epithelial breaks were occasionally observed in some experiments, their i ncidence was not increased in the high-pressure group. These data suggest t hat the increased transvascular water and protein flux occurred through pat hways of a size not resolvable by electron microscopy after vascular perfus ion-fixation at a Ptm of 20.5 Torr.