The prevalence of asthma and allergic rhinitis is increasing, and nurse practitioners are poised to play a definitive role in improving care and outcomes. Asthma incidence has almost doubled in the last 20 years, with more than 20 million U.S. residents now affected.^1,2 Meanwhile, allergic rhinitis is a common condition affecting almost 20% of the population.³

A research-based ranking by the Asthma and Allergy Foundation of America determined that asthma has a significant impact on major U.S. cities in economic as well as health terms.⁴ Expenditures associated with asthma totaled $16.1 billion in 2004.² Meanwhile, expenditures associated with allergic rhinitis total around $5.3 billion per year.³ Although millions of people are directly or indirectly affected by asthma, most are not aware of its most common form: allergic asthma.

Between 60% and 78% of patients with asthma have coexisting allergic rhinitis.⁵ One in three people with allergic rhinitis eventually develops asthma.⁶ This is due to the propensity for an allergic response to spread from the nose to the bronchial mucosa.⁶

Our understanding of asthma and allergic rhinitis has evolved to a new level of recognition. Historically, these allergen-induced disease conditions were viewed as separate entities. Now, we know that the relationship between asthma and allergic rhinitis is better described as a single continuum of inflammation involving one common airway.

Nature vs. Nurture
The scientific debate about the cause of asthma is ongoing: Is it genetics or the environment? Which has a greater impact? The previous general consensus was that asthma was always environmentally linked. Experts believed that a person developed asthma based on air quality and the presence of environmental triggers - not because of a genetic predisposition. Nurse practitioners need to be aware of the emergence of new data in this debate. The American Academy of Allergy, Asthma and Immunology (AAAAI) states that a person's genetic predisposition to allergies is the most important predictor of his or her risk for developing asthma. Put more specifically, a child has a 30% chance of developing asthma if one parent has asthma and a 70% chance of developing asthma if both parents have asthma.⁷

Immunoglobulin E (IgE) plays a key role in mediating the allergic response in asthma.⁸ IgE is an immune cell that can recognize foreign substances, and it enables the body to react quickly when it encounters them. Scientists discovered in 1921 that the susceptibility to allergies could be transferred from one person to another by a blood transfusion. When the allergen was applied to a person who previously did not experience allergies, he developed signs of an allergic reaction. Subsequent research concluded that the IgE antibody causes most allergic reactions - and that IgE was responsible for the transfer of allergic response. This latter discovery was paramount in the quest to better understand the body's allergic response and how it developed.

For almost 25 years, the medical community has recognized that IgE is responsible for allergic responses and that most patients with asthma have elevated serum IgE levels.⁹ This explains the connection between asthma and allergies. Serum IgE levels are a marker of the immune response to allergens that results in the development of airway hyperresponsiveness.¹⁰ There is continued debate, however, about the level of IgE needed to cause asthma and whether it can predict the severity of the disease. Emerging data demonstrate that the association of total IgE level with asthma severity may reflect an influential role for specific IgE-mediated allergic reactions.¹¹

Serum IgE levels are age related, with peak levels occurring during childhood (usually between 8 and 12 years) and typically decreasing thereafter.¹² Applying what we now know about the relationship between asthma and allergies, it makes sense that in 2004, the prevalence of asthma was greater (85.1 per 1,000) in children birth to 17 years than in adults 18 years and older (63.9 per 1,000).² Similarly, for the past 8 years, the rate of asthma attacks in 5- to 17-year-olds was higher than in any other age group.²

Allergic Asthma
Allergic asthma, also referred to as extrinsic asthma, is a chronic inflammatory disorder of the airways. The symptoms of allergic and nonallergic asthma are the same, but the triggers are not. Allergic asthma is triggered by exposure to allergens, which are often inhaled. The most common inhaled allergens include dust mites, pet dander, pollens, mold, grass and ragweed. Through a complex set of reactions, these allergens cause the respiratory passageways to become inflamed and swollen.

Nonallergic asthma triggers generally don't cause inflammation, but they can provoke "twitchy" airways, especially in airways that are already inflamed. Nonallergic triggers include smoke, exercise, cold air, strong smells (chemicals, perfume), air pollutants and intense emotions.

The allergic cascade of asthma begins when an allergen is inhaled by someone who is sensitive to that allergen. A macrophage, part of the first line of defense in the immune system, engulfs and breaks down the allergen in an attempt to eliminate it from the body. This initiates a series of reactions among cells within the immune system, and the reactions lead to the production of plasma cells. Plasma cells are an important factor in allergic asthma because they produce IgE and release it into the blood. Patients who have allergies continue to make IgE as long as they breathe in allergens they are sensitive to. Ultimately, IgE attaches to mast cells. These cells are in the lungs, airways and nasal cavities and have IgE receptors on the outside surface.

As mast cells encounter allergens a second time (reexposure), the allergen binds to the IgE on the cell surface. This causes the mast cells to open and release their mediators (histamine, prostaglandins and leukotrienes), which contribute to airway inflammation, bronchoconstriction and the allergic response in asthma patients. The consequence of the inflammation and bronchoconstriction is an asthma exacerbation that varies in degree.