Asthma Health Article

ASTHMA

Asthma is a common chronic lung disease characterized by a narrowing of the airways, resulting in obstruction of the flow of air and difficulty in breathing. The airflow obstruction is partially or completely reversible in most patients. Different designations of asthma include bronchial asthma, exercise-induced asthma, drug-induced asthma, occupational asthma, and cardiac asthma (airway narrowing in the setting of congestive heart failure). This discussion focuses primarily on bronchial asthma, a chronic inflammatory disorder of the airways (both the larger "bronchi" and the smaller "bronchioles"), resulting in airflow obstruction and increased sensitivity (responsiveness) of the airways to a variety of stimuli ("bronchial hyperreactivity").

About 15 million Americans, a third of whom are children, suffer from asthma, and more than 5,000 people die from it each year. The condition accounts for an estimated 100 million days of restricted activity and 470,000 hospitalizations annually in the United States. Over the last three to four decades both the prevalence and the death rate from asthma in the United States and many other developed countries have increased. In the United States, the increases in death rates have been higher in women than in men and higher in blacks than in whites.

The most important risk factor to develop bronchial asthma is atopy, an inherited predisposition to have allergies. An acute attack of asthma may occur if an atopic individual inhales allergy-provoking substances (allergens) such as ragweed, cat dander, or house dust. A variety of cells are involved in the asthmatic inflammatory reaction in the airway walls, including neutrophils, eosinophils, lymphocytes, mast cells, and macrophages. These cells release mediators (chemicals such as "cytokines") that provoke the inflammatory process. Asthma also occurs in people without allergies.

During an acute episode of asthma, bronchial narrowing ("bronchoconstriction") results from the buildup of plugs of mucus and cellular debris in the lumen, contraction of smooth-muscle cells ringing the airways, and inflammation and edema of the mucosa. Permanent changes in the airway, including enlargement of the submucosal mucous glands, proliferation of mucus-secreting cells and smooth-muscle cells, and deposition of fibrous tissue in the mucosa, may occur in chronic asthma, a process known as "airway remodeling."

The degree of airflow limitation in patients with asthma is measured by performing breathing tests (pulmonary function tests) such as spirometry and the recording of peak expiratory flow rates (PEFRs). This requires the patient to take in as deep a breath as possible and blow it out with maximum effort into a recording instrument. Obstructive dysfunction is detected if airflow rates are significantly less than predicted values. Partial or complete reversibility of the obstructive dysfunction is possible in most cases after the inhalation of a medication (e.g., albuterol) that dilates the airways. Between episodes of asthma, airflow rates may be normal. However, a patient who has had asthma for many years may display persistent and irreversible obstructive dysfunction as a result of airway remodeling. Spirometry is also employed in bronchial-provocation testing to determine if an individual with suspected asthma has bronchial hyperreactivity (an unusual degree of airway sensitivity to challenges such as exercise or the inhalation of dilute solutions of chemicals such as methacholine).

Patients with asthma suffer from shortness of breath, wheezing, chest tightness, and cough. These symptoms, which may be episodic or chronic, are often worse early in the morning and may disrupt sleep. Asthma often develops in childhood, but it may appear at any age. Episodes of asthma may be spontaneous, but more commonly they are "triggered" by various stimuli, such as inhaling allergens or nonspecific airway irritants (e.g., dusts, smoke, fumes, cold air), upper or lower respiratory tract infections, exercise, certain medications, and exposure to chemicals and other substances in the workplace. The frequency and severity of symptoms vary greatly from patient to patient and tend to be less episodic and more persistent with increasing age.

The diagnosis of bronchial asthma depends upon a medical history of one or more asthma symptoms, evidence of airflow limitation on physical examination or pulmonary function testing, and demonstration of some degree of reversibility of airflow obstruction. Other conditions that mimic asthma must be excluded. These include acute or chronic bronchitis, emphysema, bronchiectasis, cystic fibrosis, upper airway obstruction from various causes, abnormal function of the vocal cords, aspiration, lung cancer, congestive heart failure, pulmonary thromboembolism (blood clots in the pulmonary artery), and even certain psychiatric disorders.

Asthma is classified according to the severity and frequency of its symptoms and the results of pulmonary function tests. Mild intermittent asthma is managed by treating the occasional symptoms with inhaled bronchodilators, called beta₂-agonists. Persistent asthma is treated with daily anti-inflammatory drugs, especially inhaled corticosteroids, often in combination with one or more inhaled or oral bronchodilator drugs. A newer class of drugs called leukotriene modifiers is employed to manage some patients with persistent asthma. Severe persistent asthma requires the daily use of several medications, including oral corticosteroids such as prednisone. Acute, severe asthma may require the patient to be hospitalized to manage acute respiratory failure with supplemental oxygen and even respiratory support on a mechanical ventilator.

Patient education, environmental control, smoking cessation, and avoidance of factors known to provoke attacks are the mainstays of prevention. The importance of stopping smoking cannot be overemphasized. Patients with asthma must reduce exposure to allergens (such as house dust mites and animal danders), eliminate certain medications (such as beta-blocker drugs and aspirin), and avoid exposure to indoor and outdoor air pollutants. A diagnosis of occupational asthma requires that steps be taken to curtail workplace exposure to offending agents. Annual vaccination against influenza virus infection is recommended for patients with persistent asthma.

Fortunately, most patients with asthma respond well to appropriate medical management. Anti-inflammatory therapy for persistent asthma and immediate treatment for acute, severe attacks are essential steps to reduce morbidity and mortality from the disease. Death from bronchial asthma is considered to be preventable.

JOHN L. STAUFFER

(SEE ALSO: Chronic Respiratory Diseases; Emphysema; Pulmonary Function)