Elastic moduli of excised constricted rat lungs

Abstract

When airways constrict, the surrounding parenchyma undergoes stretch and distortion. Because of the mechanical interdependence between airways and parenchyma, the material properties of the parenchyma are important factors that modulate the degree of bronchoconstriction. The purpose of this study was to investigate the effect of changes in transpulmonary pressure (Ptp) and induced constriction on parenchymal bulk ( k) and shear (μ) moduli. In excised rat lungs, pressure was measured at the airway opening, and pressure-volume curves were obtained by imposing step decreases in volume with a calibrated syringe from total lung inflation. Calculation was made of k during small-volume oscillations (1 Hz). Absolute lung volume at 0 cmH2O Ptp was obtained by saline displacement. To calculate μ, a lung-indentation test was performed. The lung surface was deformed with a cylindrical punch (diameter = 0.45 cm) in 0.25-mm increments, and the force required to effect this displacement was measured by a weight balance. Measurements of k and μ were obtained at 4 and 10 cmH2O Ptp, and again at 4 cmH2O Ptp, after delivery of methacholine aerosol (100 mg/ml) into the trachea. Values of k and μ in rat lungs were similar to those reported in other species. In addition, k and μ were dependent on Ptp. After induced constriction, k and μ increased significantly. That k and μ can increase after induced constriction has important implications vis a vis the factors modulating airway narrowing.