29.12A: Asthma

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Asthma is a common chronic inflammatory disease of the airways characterized by reversible airflow obstruction and bronchospasm.

Learning Objectives

Identify the triggers that cause asthma (reversible blockage of bronchi) attacks

Key Points

Symptoms of asthma include wheezing, coughing, chest tightness, and shortness of breath.
Asthma may also be classified as atopic (extrinsic) or non-atopic (intrinsic) and is thought to be caused by a combination of genetic and environmental factors.
Treatment of acute symptoms is usually with an inhaled short-acting beta-2 agonist (such as salbutamol).

Key Terms

asthma: A long-term respiratory condition, in which the airways may unexpectedly and suddenly narrow, often in response to an allergen, cold air, exercise, or emotional stress. Symptoms include wheezing, shortness of breath, chest tightness, and coughing.
beta-2 agonist: β2-adrenergic agonists, also known as β2-adrenergic receptor agonists, are a class of drugs used to treat asthma and other pulmonary disease states.
wheezing: A wheeze (formally called “sibilant rhonchi” in medical terminology) is a continuous, coarse, whistling sound produced in the respiratory airways during breathing. For wheezes to occur, some part of the respiratory tree must be narrowed or obstructed, or airflow velocity within the respiratory tree must be heightened.

Asthma is a common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath. The prevalence of asthma has been rising steadily since the early 1980s. Asthma is clinically classified according to the frequency of symptoms, forced expiratory volume over one second (FEV1), and peak expiratory flow rate. The latter can be measured with a peak flow meter. Asthma may also be classified as atopic (extrinsic) or non-atopic (intrinsic). It is thought to be caused by a combination of genetic and environmental factors. Treatment of acute symptoms is usually with an inhaled short-acting beta-2 agonist (such as salbutamol). Symptoms can be prevented by avoiding triggers such as allergens and irritants and by inhaling corticosteroids. Leukotriene antagonists are less effective than corticosteroids and thus less preferred. Its diagnosis is usually made based on the pattern of symptoms and/or response to therapy over time.

Two peak flow meters.: Peak flow meters are used to measure peak expiratory flow rate.

Although asthma is a chronic obstructive condition, it is not considered as a part of chronic obstructive pulmonary disease as this term refers specifically to irreversible combinations of disease such as bronchiectasis, chronic bronchitis, and emphysema. Unlike these diseases, the airway obstruction in asthma is usually reversible; however, if left untreated, the chronic inflammation from asthma can lead the lungs to become irreversibly obstructed due to airway remodeling. In contrast to emphysema, asthma affects the bronchi, not the alveoli.

Asthma Attacks

An acute asthma exacerbation is commonly referred to as an asthma attack. The classic symptoms are shortness of breath, wheezing, and chest tightness. While these are the primary symptoms of asthma, in severe cases air motion may be significantly impaired such that no wheezing is heard. Signs that occur during an asthma attack include the use of accessory muscles of respiration (sternocleidomastoid and scalene muscles of the neck); there may be a paradoxical pulse (a pulse that is weaker during inhalation and stronger during exhalation) and over-inflation of the chest. A blue color of the skin and nails may occur from lack of oxygen.

Alveolar Effects of Asthma: During an asthma episode, inflamed airways react to environmental triggers such as smoke, dust, or pollen. The airways narrow and produce excess mucus, making it difficult to breathe.

Causes

Asthma is caused by environmental and genetic factors. These factors influence how severe asthma is and how well it responds to medication. For example, increased exposure to indoor allergens in infancy and early childhood has been analyzed as a primary cause of the rise in asthma. Primary prevention studies aimed at the aggressive reduction of airborne allergens in a home with infants have shown mixed findings. Strict reduction of dust mite allergens, for example, reduces the risk of allergic sensitization to dust mites, and modestly reduces the risk of developing asthma up until the age of 8 years old. However, studies also showed that the effects of exposure to cat and dog allergens worked in the converse fashion; exposure during the first year of life was found to reduce the risk of allergic sensitization and of developing asthma later in life. Similarly, many environmental risk factors have been associated with asthma development and morbidity in children. For example, recent studies show a direct relationship between increased exposure to air pollutants and incidence of childhood asthma. Lastly, viral respiratory infections (e.g., rhinovirus, Chlamydia pneumoniae) are both a leading trigger of asthma exacerbation and may increase the risk of developing asthma, especially in young children.

Diagnosis

There is currently no precise physiologic, immunologic, or histologic test for diagnosing asthma. The diagnosis is usually made based on the pattern of symptoms (airways obstruction and hyperresponsiveness) and/or response to therapy (partial or complete reversibility) over time. The U.S. National Asthma Education and Prevention Program (NAEPP) uses a ‘symptom patterns’ approach. Their guidelines for the diagnosis and management of asthma state that a diagnosis of asthma begins by assessing for the presence of multiple key indicators such as wheezing, coughing, or viral infections which will increases the probability of a diagnosis of asthma. Spirometry is needed to establish a diagnosis of asthma.

Treatment

Upon diagnosis, bronchodilators are recommended for short-term relief of symptoms. In those with occasional attacks, no other medication is needed. If mild persistent disease is present (more than two attacks a week), low-dose inhaled glucocorticoids or alternatively, an oral leukotriene antagonist or a mast cell stabilizer is recommended. For those who suffer daily attacks, a higher dose of inhaled glucocorticoid is used. In a severe asthma exacerbation, oral glucocorticoids are added to these treatments. Avoidance of triggers is a key component of improving control and preventing attacks. The most common triggers include allergens, smoke (tobacco and other), air pollution, non selective beta-blockers, and sulfite-containing foods. Cigarette smoking and second-hand smoke (passive smoke) may reduce the effectiveness of management medications such as steroid/corticosteroid therapies.