ULTRASTRUCTURAL STUDIES OF APERTURES IN THE INTERALVEOLAR SEPTUM OF THE ADULT HUMAN-LUNG

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Abstract
Lobes or lungs obtained at surgery or autopsy from 16 men were prepared for scanning electron microscopy [SEM] and transmission electron microscopy [TEM] under conditions of controlled pressures, using either airway or vascular perfusion fixation. Grossly normal areas of lung tissue, remote from the pathology for which it was removed, were examined. In lungs fixed by perfusing the airways, SEM disclosed mean alveolar diameters larger than those seen in vascular-perfused lungs: 226 vs. 178 .mu.m, respectively (P < 0.005). The average number of interalveolar apertures per exposed alveolar surface was greater in airway-perfused lungs than vascular-perfused lungs: 9 vs. 2, respectively (P < 0.005). By TEM in airway-perfused lungs, alveolar walls were interrupted by multiple gaps or pores 5.3 .mu.m in mean diameter and were essentially devoid of the alveolar surface lining layer. On TEM of vascular-perfused lungs, 84% of the gaps or pores in alveolar walls were bridged by an alveolar surface lining that contained material with the ultrastructural characteristics of lung surfactant. These closed pores averaged 2.6 .mu.m in diameter; they were significantly smaller than pores in lungs fixed via airway perfusion (P < 0.005). On SEM, apertures in alveoli < 250 .mu.m in diameter were smaller than those in alveoli .gtoreq. 250 .mu.m, in both airway-perfused lungs and vascular-perfused lungs (mean diameters, 7 and 10 .mu.m, respectively; P < 0.005). Most small interalveolar septal apertures or pores of normal human lungs are possibly bridged by and filled with extracellular material consistent with the alveolar surface lining, containing elements with the ultrastructural characteristics of lung surfactant. Lung fixation by the vascular route allows identification of this surface layer; fixation via the airways does not. Apertures greater than 10-20 .mu. in diameter probably are abnormal apertures and not pores of Kohn.

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