Figure 5: The theoretical load that impedes ASM shortening during narrowing of the airway lumen. The load is expressed in gram per cm of airway length. In this example, the normal (black) and asthmatic (grey) loads were calculated for an airway of the 10th generation within a lung inflated to functional residual capacity (transpulmonary pressure of 5 cm H2O). The loads take into account the transpulmonary pressure, the passive elastic elements of the airway wall, the distortion of the parenchyma surrounding the airway during ASM shortening, and the cross-sectional geometry of the airway wall constituents and of the lumen [95]. The load is decreased in asthmatics because the thickening of the adventitia geometrically attenuates the coupling of the airway wall to the surrounding parenchyma [95].
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