An ultrastructural morphometric comparison of the peripheral with the hilar air‐blood barrier of dog lung

Excised and isolated perfused lungs are frequently used as models for studies of fluid flow and membrane transport. Regional variations of the air and blood vascular compartments of the lung have been recognized to result from gravitational effects. This ultrastructural morphometric study considered the components of the air‐blood barriers of the peripheral and hilar regions of excised dog lungs. The lungs of three mongrel dogs were fixed by endotracheal instillation of glutaraldehyde and immersion in fixative. Stratified random sampling, point counting volumetry, and line intercept counts were used to determine the thicknesses of the air‐blood barrier and the epithelial, interstitial, and endothelial compartments. Point counting volumetry also established the volume density of the alveolar spaces. The morphometric values for structures within the periphery were statistically compared to those within the hilar region by Student's t‐test. Endotracheal and immersion fixation as used in this study, combined with stratified random sampling, equalized regional differences in the alveolar lumen volume and airblood barrier thickness. With these conditions no significant differences in the volume densities of the epithelial and endothelial cells and the interstitium of the air‐blood barrier were identified when those of the hilum were compared to those of the periphery.