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 hyster etic behavior. Strips were suspended in an organ bath filled with Kreb s solution (37 degrees C, pH 7.4) continuously bubbled with 95% O-2-5% 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 und er baseline conditions at different levels of stress (sigma = 10-26 g/ cm). Porcine pancreatic elastase (0.05 IU . mg tissue(-1) . ml Krebs s olution(-1)) was then added to the bath, and tension and length were m easured continuously for 15 min at sigma = 15 g/cm. After washout, mea surements were repeated at sigma = 10-26 g/cm. Elastance (E) and resis tance (R) were calculated using the equation of motion. Hysteresivity (eta), the structural damping coefficient, was obtained using the foll owing equation: eta = (R/E)pi 2f, where f is frequency. At baseline, w e 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 parameter s were compared at the same sigma before and after treatment. Again, e ta did not change. The constancy of eta after elastase suggests that d isruption of the elastin-collagen network does not alter the coupling between elastic and dissipative processes in lung tissue.