DIHEDRAL ANGLES OF SEPTAL BEND STRUCTURES IN LUNG PARENCHYMA

Alveolar parenchyma comprises two interacting tensile systems: the cab le system (a network of linear condensations of connective tissue) and the membrane system (a network of quasiplanar alveolar septa). infere nces can be drawn about the mechanics of this structure from its confi guration. We reported earlier (E. H. Oldmixon, J. P. Butler, and F. G. Hoppin, Jr. J. Appl. Physiol. 64:299-307, 1988) that the angles betwe en alveolar septa at the common three-way junctions (J) are nearly uni form, indicating that septal tensions are also nearly uniform. We now report on the interseptal angles at the next most common class of sept al junction (B), a structure where two septa meet along a segment of t he cable system. We find, first, that the distributions of interseptal angles at B junctions have means >120 degrees, are narrow and have fe w, if any, angles <120 degrees. The findings of uniform 120 degrees an gles at J junctions and a cutoff below 120 degrees at B junctions are also characteristic of soap films supported on a frame, which follows the physical principle of surface area minimization. We suggest that t his principle may be operative in parenchymal development and remodeli ng.