Key Points
Definitions
ÎÎBronchial hyperresponsiveness (BHR) is an increase in sensitivity to an
agent and is expressed as the dose or concentration of a substance that
produces a specific decrease in forced expiratory volume in one second
(FEV1) (eg, provocation dose or provocative concentration causing a
decrease of 20% [PD20 or PC20, respectively]).
ÎÎExercise-induced bronchoconstriction (EIB) is defined as the transient
narrowing of the lower airways that occurs after vigorous exercise. It may
appear with or without asthma. The term exercise-induced asthma (EIA)
should not be used because exercise does not induce asthma but rather is a
trigger of bronchoconstriction. (D)
Prevalence
ÎÎEIB is reported in most asthmatic patients. (A)
ÎÎPatients with more severe or less well-controlled asthma are more likely to
manifest EIB than patients with less severe or better controlled disease. (A)
ÎÎThe true prevalence of EIB in the general population is poorly defined
because epidemiologic studies of EIB have not differentiated asthmatic
from nonasthmatic populations. In addition, there is no consensus for the
end point indicative of a positive response, and the conditions under which
exercise is performed frequently differ. (B)
ÎÎThe prevalence of EIB in elite athletes appears to be higher than in the
general population and depends on the type of sport, the maximum exercise
level, and environmental conditions. (B)
ÎÎThe prevalence of EIB varies with history, type of challenge, and conditions
under which the challenge is performed. (A)
ÎÎThe prevalence of EIB with and without asthma may be influenced by age,
sex, and ethnicity. (C)
Pathophysiology of Exercise-Induced Bronchoconstriction
ÎÎExercise-induced bronchoconstriction occurs in response to heating and
humidifying large volumes of air during a short period. The most important
determinants of expression of EIB response and severity are the water
content of the inspired air and/or the level of ventilation achieved and
sustained during exercise. (B)
ÎÎRespiratory water loss at high ventilation is associated with airway cooling
and dehydration and an increase in osmolarity of the airway surface. (B)
The predominant theory of EIB is the osmotic theory, although the thermal
theory may also play a role. (C)
