Asthma | The Canadian Encyclopedia



Asthma is a chronic inflammatory disease of the lungs that is marked by recurring episodes of airway obstruction. It is one of the most prevalent chronic conditions affecting Canadians. Asthma often begins in childhood, but initial onset can occur at any age.


Asthma is a chronic inflammatory disease of the lungs that is marked by recurring episodes of airway obstruction. It is one of the most prevalent chronic conditions affecting Canadians. Asthma often begins in childhood, but initial onset can occur at any age.

Lung Function
In healthy lung function, air is inhaled through the nose and mouth, passes through the trachea, and then moves into the 2 bronchi (large airways), which branch off from the trachea and lead into the lungs. These 2 bronchi divide into the smaller bronchi of the 3 lobes of the right lung and 2 lobes of the left lung. The smaller bronchi branch out much like the branches on a tree, and end in small sacs called alveoli, which is where oxygen is passed to the blood and carbon dioxide is removed from it.

In asthmatic lungs, the flow of air in and out of the lungs is obstructed because the lining of the airways is inflamed and produces mucous, and/or the muscles around the airways have become sensitive and twitch and tighten, narrowing the airways (bronchospasm or bronchoconstriction). Asthmatic lungs always have some level of inflammation; this constriction is most likely to occur when the inflammation is left untreated. The asthmatic person experiences a range of symptoms, including tightness in the chest, shortness of breath, coughing, and wheezing. Symptoms range from mild to severe, vary from one person to the next and from one episode to the next, and may subside for long periods or flare up from time to time.

Disease Characteristics

The cause of the disease is unknown, but risk factors are recognized. They include a family history of asthma and/or allergies, exposure of susceptible children to high levels of antigen, exposure to tobacco smoke or chemical irritants, low birth weight and respiratory distress syndrome, and frequent respiratory infections during childhood. Longitudinal studies suggest that the susceptibility to asthma during childhood may be determined during fetal development and in the first 5 years of life.

There are several triggers that instigate an asthma attack, including allergens such as mold, animal dander, pollen, and dust mites and cockroaches (specifically, their feces). Non- allergic triggers include chemicals and fumes, strenuous exercise, cold air, tobacco smoke and smog, viral respiratory infections, intense emotions, and certain drugs, such as ASA and beta blockers. Urbanization appears to play a role in an increase in asthma. However, the nature of the risk has not been identified adequately because studies have not taken into account indoor allergens, even though they have been identified as risk factors.


Since the mid-1980s, the prevalence of asthma has increased. According to the World Health Organization, asthma has become a serious global public-health problem, affecting nearly 150 million people worldwide. In Canada, approximately 3 million people have asthma. It is the leading cause of hospitalization of children and of absenteeism from school, and the third-leading cause of work loss. Asthma costs the Canadian economy in excess of $600 million per year in care costs alone.

Diagnosis and Treatment

Canadian asthma experts have developed guidelines to diagnose and establish treatment plans for patients with asthma and other allergic diseases. The Canadian Asthma Consensus Guidelines were developed first in 1996, and revised in 1998 and 2001. The guidelines state that the goal of asthma management is reduction of airway inflammation through environmental control and medication, rather than through conducting intermittent therapy focused on short-term relief of symptoms.

Diagnosis is made by taking the patient's history and performing a thorough physical examination. A spirometer measures inhalation and exhalation and determines the level of airway obstruction. An allergy skin test determines substances that trigger the airway inflammation that can lead to asthma attacks.

If allergies are found to be triggers, immunotherapy may be a treatment option. Medication therapies minimize airway inflammation and treat airway narrowing. People with moderate to severe asthma take long-term medication such as anti-inflammatory drugs daily to control inflammation and prevent attacks. When symptoms occur, short- term medications (inhaled, short-acting beta2-agonists) are taken to relieve them. Because asthma is a chronic condition, it generally requires continuous medical care.

Besides medication, environmental control measures are also important to avoid or eliminate factors that trigger asthma flare-ups. Such measures include removing carpets or draperies that hold dust, eliminating exposure to second-hand smoke, and living in pet- free homes. Failure to comply with treatment, along with a lack of awareness of the severity of the condition, can lead to death. The mortality rate from asthma in Canada has been decreasing since 1990, but there are still approximately 10 asthma-related deaths per week.

Due to the increased number of diagnoses since the mid-1980s, researchers from the Ottawa Health Research Institute, with the assistance of scientists from the Canadian Institutes for Health Research, have investigated the prevalence of the condition. According to their study completed in late 2008, asthma may be over-diagnosed, possibly by as much as 30 percent. This suggests that doctors may be missing more serious problems. At issue is testing: the clinical diagnostic guidelines might not be easy to follow because of limited access to testing equipment. Although current clinical guidelines recommend that doctors use a spirometer to test for asthma, it appears that many family doctors diagnose asthma based on reported symptoms. According to the Asthma Society of Canada, less than 50 per-cent of people with asthma have ever had spirometry testing. Patients who have been diagnosed with asthma should not stop taking their medication without consulting with their physicians.

Further Reading