Asthma, Exercise-Induced

Pulmonary Function Criteria

A 15% decline in FEV1 with exercise is the generally accepted value for diagnosis of EIB. For people with a known history of asthma, a 20% decline in FEV1 with exercise is sometimes used as the criterion. The maximal decrease in FEV1 usually occurs after about 5 to 8 minutes of vigorous exercise, and pulmonary function tests (PFTs) usually return to baseline 60 minutes after exercise.

Epidemiology

Approximately 12% of the total population experiences symptoms of EIB. EIB can be detected in about 41% of those people with a history of allergic rhinitis, and 70% to 90% of asthmatics have EIB. There is equal distribution between the sexes, and it can occur at any age.

Risk Factors

A history of asthma is the biggest risk factor, followed by a family history of asthma, allergic rhinitis, recent infections (especially bronchitis), and chest symptoms such as cough and congestion.

Mechanism

The current understanding of EIB starts with the idea that hyperventilation during exercise causes drying of the airways and the epithelial cells, increasing intracellular osmolarity. This results in the release of mediators including histamine, leukotrienes, and others. These mediators then cause a transient bronchoconstriction or spasm. At the same time, another mechanism of EIB is taking place: The heat loss during exercise and the rapid rewarming of the airways after exercise cause reactive hyperemia of the microvasculature and edema of the airways, which sets up an osmotic gradient. This osmotic gradient results in the release of inflammatory mediators, causing bronchospasm.

Triggers

EIB can be triggered by cold air, dry air, or pollution or allergens in the air. Mouth breathing is more likely to cause symptoms because unlike nasal breathing, which warms the air, mouth breathing does not and is more likely to cause cooling of the airways and trigger EIB. Intense exercise is also more likely to trigger EIB, so sports such as cross-country skiing, basketball, long-distance running, soccer, and hockey are more likely to trigger EIB symptoms. Chemicals such as chlorine in pools, and insecticides, pesticides, herbicides, and fertilizers used in fields can also trigger symptoms.

Diagnosis and Testing