| Asthma is a chronic inflammatory disorder of the airways in which airflow in and out of the lungs may be blocked by bronchial muscle constriction (bronchospasm), swelling of airway tissue, and excess mucus. Asthma is characterized by acute episodes of obstructed breathing that occur with the narrowing of breathing passages, making it difficult to inhale but even more difficult to exhale. With mild asthma, the airways are relatively normal between attacks. In more severe asthma, there is some degree of constant airway constriction, with additional narrowing that occurs during an acute attack. Typical symptoms include wheezing, shortness of breath, chest tightness, and coughing.
Many types of cells and cellular elements are responsible for the stimulation of smooth muscle and the chronic inflammatory changes in the airway that are characteristic of asthma, including mast cells, eosinophils, T lymphocytes, macrophages, and neutrophils. Production of these cells by the immune system of individuals with asthma is an exaggerated (hyper-reactive) response triggered by various stimuli in the environment; individuals who do not have asthma are not affected in the same way. Individuals with asthma may have recurrent episodes of inflamed, narrowed airways when exposed to certain environmental triggers. Asthma attacks can be associated with varying degrees of airflow obstruction. Acute or chronic inflammation may also result in increasing bronchial responsiveness to triggers. The degree of hyper-responsiveness usually correlates directly with the severity of asthma.
Asthma symptoms can be triggered by allergens or irritants, upper respiratory tract infections (URI), stomach acid flowing back up the esophagus (gastroesophageal reflux disease [GERD]), certain medications or foods, anxiety, and exercise (exercise-induced asthma [EIA] or exercise-induced bronchospasm [EIB]). Individuals with allergic rhinitis (hay fever) are more likely to develop allergic asthma. Symptoms of asthma and allergic rhinitis can be triggered by seasonal or year-round allergens, which can include airborne pollens and molds, animal dander (dead skin flakes), house dust mite and cockroach droppings, and indoor molds.
Occupational asthma is generally defined as a respiratory disorder directly related to inhalation of fumes, gases, dust, enzymes, metals, animal proteins, fungi, pollens, pharmaceutical agents, or other potentially harmful substances while on the job. With occupational asthma, symptoms of asthma may develop for the first time in a previously healthy worker, or pre-existing asthma may be aggravated by exposure within the workplace. Occupational asthma has become the most prevalent work-related lung disease in developed countries.Risk: Susceptibility to allergic asthma appears to be an inherited trait; genetic factors significantly influence predisposition for developing any type of asthma, but environmental factors have a greater direct influence on the onset of the disease (Morris). Although asthma can begin at any age, most cases begin before the age of 25. Premature birth increases the risk of developing asthma. More boys have asthma than girls (male to female ratio 2:1) until puberty, when the prevalence becomes equal; in adulthood, more women have asthma than men. Asthma occurs in all races; blacks have more asthma attacks and are more likely than whites to be hospitalized for asthma attacks and to die from asthma ("Asthma"). Allergic rhinitis (hay fever) increases the risk of developing allergic asthma.
Smoking decreases the effectiveness of medications and worsens the overall asthmatic condition. Risk factors for asthma deaths include being older than 40, increased levels of blood eosinophils, cigarette smoking (more than 20 packs a year), and having a forced expiratory volume (FEV) of 40% to 69% (Morris). Incidence and Prevalence: The incidence of asthma is highest among the very young and very old; most cases are diagnosed before age 18. About 22 million people in the US have asthma; about 6 million of them are children under age 18 (Morris). Approximately 1.8 million emergency room visits annually involve asthma episodes, with 500,000 hospitalizations and 5,000 deaths (Morris).
Internationally, asthma prevalence in industrialized countries ranges from 2% to 10% (Morris); rates vary from 0.7% in Tokyo to a high of 6.3% in the United Kingdom, with an average of 5%; rates in nonindustrialized countries are lower (Canaday). Severe asthma affects about 300 million people worldwide (Morris). Both the prevalence and severity of disease appear to be increasing, particularly in children under age 6. This has been attributed to urbanization, air pollution, passive smoking, and increased exposure to environmental allergens. |