Interdependence between airways and the lung parenchyma is thought to be a major mechanism preventing excessive airway narrowing during bronchoconstriction. Because the elastance of the lung increases during bronchoconstriction, the lung's tethering force could also increase, further attenuating bronchoconstriction. We hypothesized that the bulk () and shear moduli (µ) of the lung increase similarly during bronchoconstriction. To test this hypothesis, we excised rabbit lungs and measured the lung volume, pulmonary elastance, , and µ at transpulmonary pressures of 4, 6, 8, 12, and 16 cmH₂O using pressure-volume curves, slow oscillations of the lung, and an indentation test. Bronchoconstriction was induced by nebulizing carbachol by using small tidal-volume ventilation to prevent hyperinflation. The measurement of  and µ was repeated after carbachol treatment. After carbachol treatment, the increase in  was significantly greater than that in µ. The estimated value for µ was ~0.5 × transpulmonary pressure both before and after carbachol treatment. These data suggest that the tethering effect of the lung parenchyma, which serves to attenuate bronchoconstriction, is not significantly increased during carbachol administration unless there is hyperinflation.

lung parenchymal interdependence; bulk modulus; shear modulus

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