the Basic Aspects of Asthma

What are the Basic Aspects of Asthma? (Hillel Koren - ORD)

There are almost 15 million asthmatics in the United States, resulting in 15.5 million outpatient visits and 415,000 hospitalizations per year. Approximately 5,000 people in the United States die each year from an asthma attack. Asthma also causes a significant economic impact, not only from the direct health care costs associated with treatment but also substantial indirect costs, such as absenteeism from work and lost productivity. The incidence and severity of asthma is increasing worldwide, despite the fact that ambient air pollution levels have dropped over the past ten years. This increase has occurred disproportionately among African Americans and other minorities in the United States. Poverty has been suggested as the reason for this; however, asthma is relatively lower in Africa, where poverty is quite high. It has also been considered that the answer lies in lifestyle changes, where changing to a less “traditional,” more Western lifestyle marks an increase in asthma incidence. In Australia, however, higher rates of asthma are found in the rural, rather than the urban, parts of the country. These examples illustrate the complexity of the asthma issue.

Asthma is a complex, multi-factorial disease characterized by reversible airway obstruction, non-specific airway hyperresponsiveness, and mucus hypersecretion; it is a chronic airway inflammatory disease with episodes of acute exacerbation. A complex network of immune cells, effector cells, cytokines, and other mediators interact to produce the asthmatic response. Asthma can vary widely in severity, both between and within individuals, but common symptoms include wheezing, shortness of breath, cough, chest tightness, and mucus production. Typical features of asthma include an increased level of immunoglobulin E, a positive reaction to inhaled allergens, and exaggerated bronchoconstriction in response to airway cooling or drying, exercise, and chemical or pharmacologic bronchoconstrictors (e.g., histamine or methacholine). The disease can be divided into two general categories, e.g., extrinsic and intrinsic. Extrinsic allergic asthma involves hereditary factors and allergens and is detected by the presence of serum IgE. Most childhood asthma falls into this category. Intrinsic asthma, which is more common in adults, does not involve these factors but results in similar pathobiology and treatment as extrinsic asthma.

Asthma is triggered by many factors in the environment, including house dust, pet dander, fungi, and cold air. Food allergens and stress can also trigger the condition. Genetic risk factors play a significant role in determining which people show signs of asthma, given similar exposure scenarios. The presence of atopy is a risk factor for developing overt asthma. If one parent is atopic, half of the children will have atopy. If both parents are atopic, 75 percent of the children will have atopy. If neither parent is atopic, there is a 15 percent chance of having an atopic child, which means that the potential for asthma exists. While there is certainly genetic control of asthma, there is no single gene responsible for its expression. The interaction between the environmental and genetic risk factors results in clinical asthma and the pathologic abnormalities of asthma, including bronchospasms, mucosal edema, airway inflammation, increased mucosal secretion, and a thickening of the basement membrane. While a normal airway has a well-organized epithelium, an asthmatic airway has a disrupted epithelium, is constricted, has a mucus hypersecretion plug, enlarged smooth muscle cells, and an inflamed basement membrane.

During the first hour after asthma attack, there is an initial drop in lung function and then an oscillation in function which decreases in a few days. Repeated episodes of airway inflammation can cause long-term structural damage and weakness, making the airways more prone to damage during the next attack. For this reason, it is important to control asthma so that the condition does not worsen.

Airways hyperresponsiveness alone is not necessarily diagnostic of asthma. Airway inflammatory cells in asthmatics characteristically include eosinophils, other polymorphonuclear granulocytes, and lymphocytes. Injury of the airway epithelium is present to varying extents, even in individuals with mild asthma. Evaluation of a patient with suspected asthma includes family, exposure, and social history. Tests for IgE antibody, pulmonary function, and allergy skin tests are conducted. The severity of asthma is different for any asthmatic and can range from mild, moderate, to severe persistent asthma, depending on the degree of exacerbation, activity levels, and compromise of pulmonary function (peak air flow).

The management and treatment of asthma involves working with the patient to develop treatment goals and an action strategy. Goals might be to prevent chronic and troublesome symptoms, prevent acute attacks, and continue all activities. The patient is provided with written, individualized instructions, a daily plan for management, and the long-term benefits of following the plan are discussed. The patient is taught how and when to use the peak lung flow meter, which can predict some asthma attacks. Medications are also helpful for control and include a regime of beta-agonist inhalers and steroids.

Poor disease management, lack of accessibility to medical services, inadequate advanced planning, and lack of outdoor exercise may contribute to the increased incidence and severity of asthma. In addition, it is possible that the decreased prevalence of infectious diseases has had an affect on the immune system, enhancing the response to allergens. ETS and other indoor air quality issues may also play a role. In summary, asthma appears to be a disease of modern, industrialized, affluent societies.

the Basic Aspects of Asthma