DOES THE ANATOMIC MAKEUP OF PARENCHYMAL LUNG STRIPS AFFECT OSCILLATORY MECHANICS DURING INDUCED CONSTRICTION

Parenchymal tissue strips have been used to investigate the mechanical behavior of the lung parenchyma. We questioned whether the relative a mounts of alveolar, blood vessel, and bronchial walls would be importa nt when the contractile response of parenchymal strips from Sprague-Da wley rats was studied. One group of strips was cut from the subpleural edge and another from between 1 and 3 mm proximal to the pleura. Stri ps were suspended in an organ bath filled with Krebs solution (37 degr ees C, pH 7.4) bubbled with 95% O-2-5% CO2. Resting tension (T) was se t at 1.1 g, and sinusoidal oscillations of 2.5% resting length at a fr equency of 1 Hz were applied. Measurements of length and T were record ed during baseline conditions and after acetylcholine (10(-3) M) was a dded to the bath. Elastance, resistance, and hysteresivity (the ratio of the energy dissipated to that conserved) were calculated. Strips we re fixed in Formalin at a T of 1 g, histological sections were prepare d, and the fractional areas of alveolar, blood vessel, and bronchial w alls were measured by using point counting. Significant differences we re found between the two groups of strips in the acetylcholine respons e and anatomic makeup. The magnitude of the changes of all the mechani cal parameters were correlated with the volume proportions of the diff erent anatomic constituents when all the strips were plotted together but not when the subpleural strips were considered alone. We conclude that subpleural parenchymal strips are a sound model of parenchymal lu ng behavior. When more proximal strips are studied, the amount of bron chial wall may play an important role in determining the hysteretic re sponse.