Surface forces in lungs. III. Alveolar surface tension and elastic properties of lung parenchyma

forces in lungs. III. Alveolar surface tension and elastic properties of lungparenchyma. J. Appl. Physiol. 60(4): 1358-1362,1986.-The bulk modulus and the shear modulus describe the capacity of material to resist a change in volume and a change of shape, respectively. The values of these elastic coefficients for air-filled lung parenchyma suggest that there is a qualitative dif-ference between the mechanisms by which the parenchyma resists expansion and shear deformation; the bulk modulus changes roughly exponentially with the transpulmonary pres-sure, whereas the shear modulus is nearly a constant fraction of the transpulmonary pressure for a wide range of volumes. The bulk modulus is ~6.5 times as large as the shear modulus. In recent microstructural modeling of lung parenchyma, these mechanisms have been pictured as being similar to the mech-anisms by which an open cell liquid foam resists deformations