Obstruction from conditions in the wall of the lumen. An asthma episode may range in severity from mild to life threatening, depending on the degree of airway obstruction. With intense narrowing of the bronchi, severe hypoxemia may result. Non-allergic (intrinsic) asthma is precipitated by exercise, stress, and exposure to pulmonary irritants, but no specific allergen can be identified. Drugs such as aspirin and exposure to occupational allergens have also been identified as etiologic agents. Allergic (extrinsic) asthma is mediated by ige, which is produced in response to specific antigens. The ige binds to mast cells and causes them to release inflammatory chemicals in response to antigen. Skin testing may be helpful in identifying suspected allergens. Prevention of asthma attacks is an important part of therapy. Avoidance of precipitating factors and prophylactic drug therapy are recommended. Bronchodilators, corticosteroids, and oxygen therapy are mainstays of treatment for an acute attack. Acute bronchitis results from temporary inflammation of the tracheobronchial tree.