Effect of Pleural Membrane on the Propagation of Rayleigh-Type Surface Waves in Inflated Lungs

We model the lung parenchyma as an elastic half-space and the pleura as a taut elastic membrane in smooth or in welded contact with the half-space. In each instance we deduce that the presence of a sufficiently high surface tension T in the pleural membrane will lead to the existence of a cutoff frequency f₀ for the Rayleigh-type surface waves, and we derive an equation which gives T in terms of f₀ and parameters that characterize the layered medium. We performed experiments on four inflated horse lungs at transpulmonary pressures of 5, 10, and 15 cmH₂O. A comparison of the experimental results and the theoretical predictions provides an empirical test to the validity of the modeling.