Control of airway function during and after exercise in asthmatics

In asthmatics, airway function can be quite variable during exercise depend ing on the level of exercise intensity, the duration of exercise, and wheth er the exercise is at constant load or variable in intensity. Airway diamet er can be affected by activity of parasympathetic and sympathetic nerves, b y systemic mediators such as catecholamines, and by local mediators such as histamine or leukoutrienes. Asthmatic airways are populated with more infl ammatory cells than normal airways, and bronchoconstrictor mediator release from these cells is probably caused by drying of the mucosa during and aft er periods of increased ventilation. There are a few bronchodilating mediat ors present in bath asthmatic and normal airways that could protect against this bronchoconstriction, including prostaglandin PGE, and nitric oxide. A lthough it is clear that many of the inflammatory mediators play a role in causing bronchoconstriction after exercise, the role of either bronchoconst rictor or bronchodilator mediators in controlling airway function during ex ercise has yet to be resolved. In addition, the mechanical interaction betw een lung parenchyma and airways may provide a bronchodilating influence. In conclusion, the variability in airway function during exercise in asthmati cs could be caused by balance among various bronchodilator and bronchoconst rictor mediators, but ii may also reflect a mechanical effect of varying le vels of ventilation.