Influence of lung inflation on the elastic properties of intra-and extrapulmonary airways in man.

In excised human lungs, the proximal intrapulmonary airways and distal extrapulmonary airways were isolated in situ, by means of the technique of Takishima el al. (1975), and submitted to varying transmural pressures at constant lung inflation. Both intra-and extrapulmonary airways became stiffer, i.e. showed a decreased collapsibility, at higher levels of lung inflation. The altered mechanical behavior of the intrapulmonary airways with lung inflation, observed also by Hughes et al. (1974) and Takishima et al. (1975), has been attributed to a tethering action of the lung parenchyma on these airways. The same mechanism may be operating on the distal extrapulmonary airways, to the extent that the pleura and hilar structures transmit the stresses of the lung parenchyma. Alternatively, the elongation of the bronchi occurring during lung inflation might be responsible for their increasing resistance to collapse with lung volume. A separate study showed, indeed, that stretching of the bronchi reduces their collapsibility.