Infections of the Air Passages
Acute tracheobronchitis commonly complicates a severe upper respiratory tract infection, particularly Haemophilus influenzae infection of the larynx in young children and influenza in adults and children (see Chapter 32: The Ear, Nose, Pharynx, & Larynx). Viral tracheobronchitis may also be complicated by secondary bacterial infection, most commonly with Staphylococcus aureus.
Acute bronchiolitis is a common, often epidemic, infection of the small airways that occurs mainly in children under the age of 2 years. Most cases are mild, but 1–2% require hospitalization, and about 1% of these children die. Most cases are caused by respiratory syncytial virus; more rarely, parainfluenza virus and adenoviruses are responsible. The bronchioles show acute epithelial damage and lymphocytic infiltration of the walls. Their lumens are filled with mucus plugs, which cause distal alveolar air trapping. In patients who recover, the bronchiolar epithelium regenerates within 2 weeks. Patients present with acute-onset tachypnea and wheezing; fever is low-grade and may be absent. Cases caused by adenoviruses tend to have greater degrees of necrosis and a higher mortality rate.
Whooping Cough (Pertussis)
Caused by Bordetella pertussis, whooping cough is an extremely serious acute respiratory tract infection of the young. Prior to immunization (the “P” of diphtheria-pertussis-tetanus [Vaccine] (DPT)), it accounted for 40% of all deaths in the first 6 months of life. Clinically, it is an acute tracheobronchitis, characterized by paroxysmal coughing and an inspiratory whoop (most often seen in older children). Otitis media, bronchitis, and bronchiectasis are serious complications. Tetracycline is effective in therapy.
Bronchial asthma is a disease in which there is increased responsiveness of the tracheobronchial tree to a variety of stimuli. Exposure to these stimuli leads to bronchiolar smooth muscle contraction (bronchospasm). The cause of the increased responsiveness of the air passages is unknown but is believed to be related to bronchial inflammation. Bronchospasm causes obstruction to air flow—maximal in expiration—and a high-pitched wheeze. Expiration is prolonged because of airflow obstruction. Attacks of asthma are usually of short duration and reverse completely. Rarely, they may be severe and prolonged (status asthmaticus), and may lead to acute ventilatory failure and even death.
Etiology & Classification
Extrinsic Allergic Asthma
Extrinsic allergic asthma is a reagin-mediated type I hypersensitivity (atopic) reaction. It is common in childhood and has a familial tendency. Many different antigens may be involved (Table 35-1). Serum IgE is increased, and skin tests against the offending antigens are positive.
Table 35–1. Factors Involved in Asthma.