Surface forces and geometry of peripheral air spaces

In order to determine the effect of alveolar surface forces on the morphology of peripheral air spaces, excised but continuously perfused rabbit lungs were analyzed by morphometry. The lungs were inflated with air, with saline, or with air after the lungs had been rinsed with a detergent (0.01% Triton X 100) and fixed by vascular perfusion of osmium tetroxide at different points on the deflation limb of the pressure volume curve. The quantitative analyses showed that the alveolar surface area to volume ratio is quite different, being highest in saline filled and lowest in detergent rinsed lungs; that widespread alveolar collapses occurred in detergent rinsed lungs, in particular at low lung volumes (40% of TLC), where most air is contained in overextended ducts; that within a range of 40-80% TLC the power function relating alveolar surface to volume (S=K.V(b)) differed widely between the 3 experimental conditions, suggesting a complex inflation pattern of peripheral airspaces. These observations seem to be in accordance with the conclusion that alterations of normal surface forces at the tissue air interface of the alveoli disturb the normal arrangement of peripheral airspaces, and that the interdependence within the spatial network of alveolar septa is not sufficient enough to warrant their stability.