Tidal breathing affects airway responsiveness to methacholine.

Asthma is characterized by increased airway responsiveness and airway inflammation. Airway hyperresponsiveness may be caused by increased airway smooth muscle contractility or by a decrease in the mechanical load that opposes airway smooth muscle contraction. Under static conditions, the equilibrium between contractility and load will determine the final airway smooth muscle length and therefore airway caliber. Because of tidal breathing, however, lungs normally function under dynamic conditions where both airway contractility and opposing load are affected. The capability of tidal breathing to appropriately modulate airway function might be the mechanism that differentiates airways of asthmatics from those of normal subjects.