Control of airway function during and after exercise in asthmatics

In asthmatics, airway function can be quite variable during exercise depending on the level of exercise intensity, the duration of exercise, and whether the exercise is at constant load or variable in intensity. Airway diameter can be affected by activity of parasympathetic and sympathetic nerves, by systemic mediators such as catecholamines, and by local mediators such as histamine or leukoutrienes. Asthmatic airways are populated with more inflammatory cells than normal airways, and bronchoconstrictor mediator release from these cells is probably caused by drying of the mucosa during and after periods of increased ventilation. There are a few bronchodilating mediators present in bath asthmatic and normal airways that could protect against this bronchoconstriction, including prostaglandin PGE, and nitric oxide. Although it is clear that many of the inflammatory mediators play a role in causing bronchoconstriction after exercise, the role of either bronchoconstrictor or bronchodilator mediators in controlling airway function during exercise has yet to be resolved. In addition, the mechanical interaction between lung parenchyma and airways may provide a bronchodilating influence. In conclusion, the variability in airway function during exercise in asthmatics could be caused by balance among various bronchodilator and bronchoconstrictor mediators, but ii may also reflect a mechanical effect of varying levels of ventilation.