Effects of collagenase and elastase on the mechanical properties of lung tissue strips

The dynamic stiffness (H), damping coefficient (G), and harmonic distortion (k(a)) characterizing tissue nonlinearity of lung parenchymal strips from guinea pigs were assessed before and after treatment with elastase or colla genase between 0.1 and 3.74 Hz. After digestion, data were obtained both at the same mean length and at the same mean force of the strip as before dig estion. At the same mean length, G and H decreased by similar to 33% after elastase and by similar to 47% after collagenase treatment. At the same mea n force, G and H increased by similar to 7% after elastase and by similar t o 25% after collagenase treatment. The k(d) increased more after collage-na se (40%) than after elastase (20%) treatment. These findings suggest that, after digestion, the fraction of intact fibers decreases, which, at the sam e mean length, leads to a decrease in moduli. At the same mean force, colla gen fibers operate at a higher portion of their stress-strain curve, which results in an increase in moduli. Also, G and H were coupled so that hyster esivity (G/H) did not change after treatments. However, k(a) was decoupled from elasticity and was sensitive to stretching of collagen, which may be o f value in detecting structural alterations in the connective tissue of the lung.