ALLERGIC RHINITIS AND ASTHMA - HOW IMPORTANT IS THE LINK

Dysfunction of the upper and lower airways frequently coexist, and the y appear to share key elements of pathogenesis. Data from epidemiologi c studies indicate that nasal symptoms are experienced by as many as 7 8% of patients with asthma and that asthma is experienced by as many a s 38% of patients with allergic rhinitis. Studies also have identified a temporal relation between the onset of rhinitis and asthma, with rh initis frequently preceding the development of asthma. Patients with a llergic rhinitis and no clinical evidence of asthma commonly exhibit n onspecific bronchial hyperresponsiveness. The observation that managem ent of allergic rhinitis also relieves symptoms of asthma has heighten ed interest in the link between these diseases. Intranasal corticoster oids can prevent increases in nonspecific bronchial reactivity and ast hma symptoms associated with seasonal pollen exposure. Similarly, amon g patients with perennial rhinitis, daily asthma symptoms, exercise-in duced bronchospasm, and bronchial responsiveness to methacholine are r educed after administration of intranasal corticosteroids. Antihistami nes, with or without decongestants, reduce seasonal rhinitis symptoms, asthma symptoms, and objective measurements of pulmonary function amo ng patients with rhinitis and asthma. The mechanisms that connect uppe r and lower airway dysfunction are under investigation. They include a nasal-bronchial reflex, mouth breathing caused by nasal obstruction, and pulmonary aspiration of nasal contents. Nasal allergen challenge r esults in increases in lower airway reactivity with 30 minutes, sugges ting a neural reflex. Improvements in asthma associated with increased nasal breathing may be the result of superior humidification, warming of inspired air, and decreased inhalation of airborne allergens. Post nasal drainage of inflammatory cells during sleep also may affect lowe r airway responsiveness. A link between allergic rhinitis and asthma i s evident from epidemiologic, pathophysiologic, and clinical studies. Future research, however, is needed to determine whether nasal therapy can alter the natural history of asthma.