Stimulus and mechanisms of exercise-induced bronchoconstriction

The stimulus for exercise-induced bronchoconstriction (EIB) is the loss of water by humidifying large volumes of air during exercise. The mechanism for EIB relates to the thermal and osmotic effects of water loss. The thermal theory proposes that EIB is a vascular event comprising vasoconstriction during exercise followed by rapid rewarming and a reactive hyperaemia at the end of exercise. The osmotic theory proposes that water loss induces an increase in osmolarity in the airways, which causes the release of mediators that cause bronchial smooth muscle to contract. Increased vascular permeability and leakage are common to both theories.