This is transient constriction of the lower airways induced by vigorous exercise, and may or may not be associated by asthma. It is no longer referred to as ‘exercise-induced asthma’. It is caused by dehydration of the respiratory mucosa, due to the high ventilation in high-intensity aerobic exercise, which triggers mast cell activation with mediator release and bronchoconstriction. For obvious reasons, it tends to be worse in dry environments.
Treatment should be with prn use of short-acting bronchodilators, used either when needed or pre-exercise, but not more than two to four times weekly – more frequent use can cause tolerance and tachyphylaxis.
If bronchodilators are needed more often than this, add either a daily inhaled corticosteroid (if the patient is known to have asthma as well) or a LRTA. LRTAs aren’t effective for existing episodes of bronchoconstriction in the same way as SABAs are, but can be used pre-exercise for prevention; they need to be taken two hours before exercise and are effective for up to 24 hours, although there is wide inter-individual variation in effectiveness.
(BMJ 2016; 352:h6951)