Properties, function, and origin of the alveolar lining layer

Abstract

The properties of foam and bubbles arising in the lung have been studied, and evidence has been obtained as to the nature of the alveolar lining. In acute lung oedema, whether accompanied by respiratory movement or not, foam is found in the trachea; it is unaffected by chemical anti-foams, which rapidly destroy the foam formed by shaking oedema fluid with air. A method for obtaining similar foam from excised lung is described. In air-saturated water, bubbles 40 µ in diameter, obtained from the lung, may be stable for hours, while ordinary bubbles of this size contract and disappear in a few minutes under the influence of surface tension. From observations of these and also from measurements of sessile bubbles, it is shown that their surface tension may be less than 0.06 dyn/cm. The 'stability ratio’ of such bubbles is defined. They are stabilized by a layer of insoluble protein about 50 Å thick, and it is shown that this can only have had its origin as the original lining of the alveoli of the lungs. If the sharply curved alveolar surface had a surface tension as great as that of blood serum, there would be produced a negative pressure which would draw a transudate from the blood into the alveoli. The lining layer prevents this by reducing the surface tension to nearly zero. From observations on bubbles obtained from the lung under various conditions, it is shown that the lining layer is produced by surface adsorption from a substance (the lung lining substance) present as a jolly or slime lining the small air spaces. In the guinea-pig it develops only late in foetal life. Its peculiar surface properties are not present in blood or in tracheal mucus; it is therefore a specialized secretion and not a transudate from the blood. Methods for preparing atelectatic lung in vitro and for obtaining a solution of the lung lining substance are described. From gastric mucin, which has properties somewhat similar to those of the lung lining substance, a foam highly resistant to anti-foams has been prepared. The possible origin and pathological significance of the lung lining are discussed.

Hydrostatic Pressurization of Lung Surfactant Microbubbles: Observation of a Strain-Rate Dependent Elasticity

“…Similar wrinkling/smoothing behavior was observed for SURVANTA microbubbles at all pressurization rates. This behavior is reminiscent of the “clicking” behavior observed by Pattle on liberated lung bubbles and by Schurch et al on the captive bubble surfactometer as well as the “jerks” observed on Langmuir films of model LS. The wrinkling of SURVANTA shells suggested that the surface was rigid enough to deform out-of-plane as a mechanism to sustain the increasing surface stress.…”

Bio-Inspired Elastic Liquid-Infused Material for On-Demand Underwater Manipulation of Air Bubbles

“…At such length scale, the broad size distribution on the alveolus results in a huge difference on Laplace pressure of the encapsulated air bubbles. To enable simultaneous and uniform inhalation and exhalation of all alveoli, a layer of mucous surfactant lines out of each alveolus, lowering and balancing the surface tension of alveoli and enabling smooth gas flow in the lung (Figure a) . Meanwhile, the lining layer protects the alveoli tissue from direct contact of dust and other airborne contaminants. − The synergy of these features enables the robust gas exchange and adaptive function of the human pulmonary system in diverse climates.…”

Transepithelial transport by pulmonary alveolar type II cells in primary culture.

“…When lungs are fixed for electron microscopy by vascular perfusion, the only areas that appear to contain fluid are the corners ofthe alveoli, where the radius ofcurvature is short (2). At the corners, the net force of surface tension, which is a function of the radius ofcurvature and the actual surface tension, is directed to draw fluid into the alveolus (3)(4)(5)(6)(7). How this force is counterbalanced is not known.…”