[h=3]Exercise-induced bronchoconstriction[/h] More generally termed
exercise-induced asthma, the preferred and more accurate term
exercise-induced bronchoconstriction better reflects underlying
pathophysiology. It is also preferred due to the former term giving the false impression that asthma is caused by exercise.
In a patient with EIB, exercise initially follows the normal patterns of bronchodilation. However, by three minutes, the constriction sets in, which peaks at around 10-15 minutes, and usually resolves itself by an hour. During an episode of this type of bronchorestriction, the levels of inflammatory mediators, particularly
leukotrienes,
histamine, and
interleukin, increase. TH2-type
lymphocytes are activated, with an increase in
T cells expressing CD25 (IL-2R), and
B cells expressing CD 23, causing increased production of
IgE. After exercise, the conditions will fade within one to three minutes. In most sufferers of EIB, this is followed by a
refractory period, of generally less than four hours, during which if exercise is repeated, the bronchorestriction is less emphasised. This is probably caused by the release of
prostaglandins.
The underlying cause of this type of bronchoconstriction appear to be the large volume of cool, dry air inhaled during strenuous exercise. The condition appears to improve when the air inhaled is more fully humidified and closer to body temperature.
This specific condition, in the general population, can vary between 7 and 20 percent. This increases to around 80 percent in those with symptomatic asthma.
In many cases, however, the constriction, even during or after strenuous exercise, is not clinically significant except in cases of severe to moderate emphysema.