Issues in exercise-induced asthma.

It is concluded that challenge by exercise and ISH induces asthma by the same mechanism, the protective effect of water vapor is evidence that the events that lead to bronchial smooth muscle contraction begin in the airway lumen, it is the loss of water rather than the loss of heat from the airways that is the primary stimulus to EIA and HIA, the mechanism by which water loss induces asthma is by increasing the osmolarity of the epithelial fluid, in some subjects with asthma, cooling of the airways enhances the response to water loss, the increase in osmolarity stimulates the production and release of bronchoactive substances from mast cells and epithelial cells, vagal afferent pathways are activated by changes in osmolarity and by the released mediators, and vagal efferent activity may be modified by alpha-adrenoceptor antagonists and SCG.