DYNAMIC PROPERTIES OF LUNG PARENCHYMA - MECHANICAL CONTRIBUTIONS OF FIBER NETWORK AND INTERSTITIAL-CELLS

We investigated the contributions of the connective tissue fiber netwo rk and interstitial cells to parenchymal mechanics in a surfactant-fre e system. In eight strips of uniform dimension from guinea pig lung, w e assessed the storage (G') and loss (G '') moduli by using pseudorand om length oscillations containing a specially designed set of seven fr equencies from 0.07 to 2.4 Hz at baseline, during methacholine (MCh) c hallenge, and after death of the interstitial cells. Measurements were made at mean forces of 0.5 and 1 g and strain amplitudes of 5, 10, an d 15% and were repeated 12 h later in the same, but nonviable samples. The results were interpreted using a linear viscoelastic model incorp orating both tissue damping (G) and stiffness (H). The G' and G '' inc reased linearly with the logarithm of frequency, and both G and H show ed negative strain amplitude and positive mean force dependence. After MCh challenge, the G' and G '' spectra were elevated uniformly, and G and H increased by <15%. Tissue stiffness, strain amplitude, and mean force dependence were virtually identical in the viable and nonviable samples. The G and hence energy dissipation were similar to 10% small er in the nonviable samples due to absence of actin-myosin cross-bridg e cycling. We conclude that the connective tissue network may also dom inate parenchymal mechanics in the intact lung, which can be influence d by the tone or contraction of interstitial cells.