MEAD, JERE, TAMOTSU TAKISHIMA, AND DAVID LEITH. Stress distribution in lungs: a model of pulmonary elasticity. J. Appl. Physiol. 28 (5): 596-608. 1970. Although lungs are exposed to transpulmonary pressure, the air spaces within are distended solely by forces applied from surrounding tissues. By relating these forces to the areas on which they operate, we derive the effective pressure distending air spaces. In uniformly expanded lungs this pressure probably approximates transpulmonary pressure. In nonuniformly expanded lungs the effective distending pressure differs from transpulmonary pressure, and in the appropriate sign to reduce the nonuniformity. This interdependence of air-space distention bears on a number of aspects of pulmonary function, including the size of air spaces which may be expanded from the gas-free state, the static and dynamic stability of air spaces, the dryness of air spaces, the forces distending airways and blood vessels within lungs, and the distribution of pulmonary edema. The principal function of the mechanical interdependence would appear to be to support uniform expansion of air spaces. The principal functional risk that it entails is increase in capillary transmural pressure in regions which become subjected to abnormally high outward-acting stress. lung elasticity; static recoil of lungs; atelectasis; alveolar stability; pleural pressure

MOST ESTIMATES of the rncchanical properties of lungs depend on measurement of transpulmonary pressure-ie, the pressure difference between the airway opening and the pleural surface. Implicit is the assumption that all parts of the lung, including those at a distance from the pleural surface, are exposed at their outside walls to pleural pressure; but within the lung the outside wall of one air space is the inside wall of its neighbor. Since, statically, gas pressure in all interconnected airways and air spaces is the same, there are no pressure differences across walls, and all forces distending airways and air spaces must arise from tissue attachments. In this paper we develop a model which relates these forces to transpulmonary pressure.