Effect of elastase on oscillation mechanics of lung parenchymal strips

Using isolated parenchymal strips from degassed rat lungs, we studied the contribution of the collagen-elastin network to lung tissue hysteretic behavior. Strips were suspended in an organ bath filled with Krebs solution (37 degrees C, pH 7.4) continuously bubbled with 95% O2-5% CO2. One end of the strip was attached to a force transducer and the other to a servo-controlled lever arm. Sinusoidal oscillations of 2.5% of resting length were applied at 1 Hz. Measurements were sampled under baseline conditions at different levels of stress (sigma = 10-26 g/cm). Porcine pancreatic elastase (0.05 IU.mg tissue-1.ml Krebs solution-1) was then added to the bath, and tension and length were measured continuously for 15 min at sigma = 15 g/cm. After washout, measurements were repeated at sigma = 10-26 g/cm. Elastance (E) and resistance (R) were calculated using the equation of motion. Hysteresivity (eta), the structural damping coefficient, was obtained using the following equation: eta = (R/E) pi 2f, where f is frequency. At baseline, we found that E and R were significantly dependent on sigma (P < 0.01), whereas eta was unchanged. During enzymatic digestion with elastase, there were significant decreases of tension, E, and R and no change in eta. Significant increases in E and R were found when these parameters were compared at the same sigma before and after treatment. Again, eta did not change. The constancy of eta after elastase suggests that disruption of the elastin-collagen network does not alter the coupling between elastic and dissipative processes in lung tissue.