Exercise-induced asthma (EIA), or more accurately, exercise-induced bronchoconstriction, is a narrowing of the airways of the lungs triggered by vigorous physical activity. EIA constitutes a form of respiratory difficulty in which the airways become hypersensitive and inflamed. The muscles of these airways then contract or spasm; this reaction manifests as the symptoms of asthma.
Who is at risk?
According to the American Academy of Allergy, Asthma and Immunology, EIA affects 12 to 15% of the population. Most people who suffer from chronic asthma also experience symptoms when exercising. EIA often begins in childhood and typically occurs in athletes who participate in sports with an aerobic component, such as running, soccer, and rowing. Athletes who play winter sports, particularly hockey or skiing, are also more susceptible to EIA due to the effects of exercising in a cold environment. Many professional and Olympic athletes, including former British footballer (soccer player) David Beckham and women’s marathon world-record holder Paula Radcliffe, have been known to suffer from EIA.
The respiratory tract
The upper respiratory tract, including the nose, nasal passages, sinuses, mouth, and pharynx (throat), is primarily involved in taking in air to breathe, then warming, moistening, and filtering it. The lower respiratory tract begins just below the vocal cords with the trachea (windpipe) which, as it descends toward the lungs, branches off into 2 main bronchi (bronchus, singular) or airway tubes. Within the lobes of the lungs, the bronchi branch into smaller airways, called bronchioles, which divide into ever-narrower branches. These terminate in the alveoli or tiny membranous air sacs rich in capillaries (small blood vessels) where the actual exchange of carbon dioxide for oxygen takes place (Fig).
The walls of the bronchi are made up of 3 layers. The outer layer consists of hyaline (bluish or transparent) cartilage rings. The lumen or inner space of the airway’s tube is covered with smooth or involuntary muscle which is, in turn, lined with respiratory epithelial or membranous tissue. Microscopic hairs on the surface of this tissue called cilia filter out dust and other inhaled particles. Moreover, the connective tissue of the smooth muscle harbors various immune cells, such as mast cells and basophils, which release histamines (chemical compounds that cause smooth muscle to contract and capillaries to dilate); it also contains goblet cells that produce mucus. A thin, protective layer of mucus covers the epithelial tissue, helping to purify the inhaled air. During an asthma attack, mast cells and basophils release histamine and the smooth muscle of the bronchi contract or spasm, making it difficult to breathe.
What causes exercise-induced asthma?
During strenuous exercise, the body demands more oxygen and breathes faster. However, when someone with EIA exercises vigorously, a bio- and neurochemical pathway is triggered resulting in bronchospasms. While the precise mechanism governing these spasms remains unknown, 2 theories predominate; both are based on the notion that consistent and repetitive air movement can alter conditions in the bronchial tubes causing airway muscles to react. The first theory assumes that the movement of the air through the airways causes dryness that the body then combats by channeling a lot more blood into the region. This results in airway edema (swelling) and bronchospasm. The second theory assumes that the air movement decreases the temperature within the bronchi; this triggers excess blood flow in an attempt to heat the airways. As many people breathe through their mouth when they exercise, the air they inhale is cooler than when they breathe through their nose, and this could trigger bronchospasms and an attack of EIA. Some researchers believe that a combination of these 2 theories explains an attack. There are also many other asthma triggers, including food, airborne allergens, smoke, pollution, and upper respiratory infections. Evidence, however, suggests that the cascade of events that lead to bronchospasms in people with EIA do not follow the same inflammatory pathways that lead to such spasms in people with allergic asthma.
The best way to treat EIA is to prevent the onset of symptoms. Patients who are prone to attacks of EIA should therefore take the time to warm up adequately before vigorous activity. If the weather is cold, a mask or scarf can be used over the mouth to reduce the effect of breathing in cold air. Alternatively, sufferers who typically breathe through their mouth while exercising should try to breathe through the nose instead so that the air is warmer. Furthermore, those with EIA should avoid outdoor activity if the pollen count or pollution level is high.
When an EIA attack occurs, proper management of symptoms is key. While over the counter drugs are available, these are not long-lasting and should not be used by patients who also suffer from hypertension (high blood pressure), diabetes, thyroid, or heart disease. Doctors typically prescribe medications known as beta 2 adrenergic receptor agonists or bronchodilators. These drugs cause smooth muscle to relax and the bronchial passages to dilate; some also work to stabilize the cells that release histamine. They can be short-acting or long-acting and are usually dispensed through an inhaler. Albuterol is an example of a short-acting beta agonist. It can be taken either as pretreatment 10 minutes before exercising or for quick relief during or directly after exercising. Most asthma medications, however, need to be taken up to 60 minutes before vigorous activity in order to be effective. For best results, a long-acting bronchodilator should be taken every day. Asthma medication is now also available in pill or liquid form. Some liquid medications can be used in a nebulizer or vaporizing machine that transforms the medicine into a fine mist. Strong anti-inflammatory drugs known as corticosteroids are also sometimes prescribed for EIA sufferers.
Athletes and other EIA sufferers should not avoid exercise or sports. By planning ahead, doing warm up exercises, using medications as prescribed, taking extra precautions in cold weather, and avoiding allergens and pollutants, they can stay active.
Author: Meagan Dunn, MS, LAT, ATC, and BreAnna Hankins, LAT, ATC
Reprinted with permission from the Hughston Health Alert, Volume 29, Number 1,Winter 2017.