Figure 1: From . (a) Lumen pressure fluctuations in isolated bronchial segments (porcine) during tidal volume oscillation before and after a maximal dose of acetylcholine (ACh). Tidal volume oscillations produced a trough-to-peak pressure cycle from 5 to 10 cmH2O in relaxed airways. Contraction to ACh is seen by the elevation in trough pressure in a closed system. The increase in the amplitude of pressure cycles indicates stiffening of the airway wall to ACh. (b) Sigmoidal dose-response behaviour of ACh-induced increase in airway stiffness. Values are means ± SE ().