Dynamic properties of lung parenchyma: mechanical contributions of fiber network and interstitial cells

Yuan, Huichin, Edward P. Ingenito, and Béla Suki.Dynamic properties of lung parenchyma: mechanical contributions offiber network and interstitial cells. J. Appl.Physiol. 83(5): 1420-1431, 1997.We investigatedthe contributions of the connective tissue fiber network andinterstitial cells to parenchymal mechanics in a surfactant-freesystem. In eight strips of uniform dimension from guinea pig lung, weassessed the storage (G) and loss (G") moduli by usingpseudorandom length oscillations containing a specially designed set ofseven frequencies from 0.07 to 2.4 Hz at baseline, during methacholine(MCh) challenge, and after death of the interstitial cells.Measurements were made at mean forces of 0.5 and 1 g and strainamplitudes of 5, 10, and 15% and were repeated 12 h later in the same,but nonviable samples. The results were interpreted using a linearviscoelastic model incorporating both tissue damping (G) and stiffness(H). The G and G" increased linearly with the logarithmof frequency, and both G and H showed negative strain amplitude andpositive mean force dependence. After MCh challenge, the G andG" spectra were elevated uniformly, and G and H increased by<15%. Tissue stiffness, strain amplitude, and mean force dependencewere virtually identical in the viable and nonviable samples. The G andhence energy dissipation were ~10% smaller in the nonviable samplesdue to absence of actin-myosin cross-bridge cycling. We conclude thatthe connective tissue network may also dominate parenchymal mechanicsin the intact lung, which can be influenced by the tone or contractionof interstitial cells.