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- Describe the pathophysiology of bronchiolitis and list signs and symptoms
- Describe the treatment of a patient with bronchiolitis
- Describe the pathophysiology of asthma and list signs and symptoms
- Describe the treatment of a patient with asthma
- Describe the similarities and differences between the pathophysiology of bronchiolitis and asthma
- Discuss the epidemiological characteristics of bronchiolitis and asthma
A wheeze is a high-pitched, musical, continuous sound that originates from oscillations in narrowed airways. Wheezing is most often the result of bronchiolitis in infants and asthma in older children. This article will discuss the similarities and differences between these two childhood diseases, along with management of the infant or child with wheezing.
In children under 1 year of age, the respiratory syncytial virus (RSV) is estimated to be responsible for up to 70% of cases in previously healthy children.1 RSV is a virus of the family Paramyxoviridae, which includes many common respiratory viruses, such as those that cause measles and mumps. The name RSV derives from the fact that it A) is a virus that causes respiratory tract infections, and B) combines with nearby viruses to form a syncytia, or virus mass. The virus is so ubiquitous that nearly all children will have had an RSV infection by their second birthday. After first-time exposure to RSV, 25%-40% of infants and children will exhibit signs or symptoms of bronchiolitis, and 0.5%-2% will require hospitalization. Most children hospitalized for RSV infection are under 6 months of age.2 Bronchiolitis attributable to RSV was the leading cause of hospitalization among the general population of infants in the United States between 1997-2000, accounting for an estimated 96,000 hospitalizations during that time.3
Mortality associated with bronchiolitis has decreased in past decades, although young infants can still die from bronchiolitis. Those tend to be the sick ones who then develop bronchiolitis.3,4 The mortality rate is less than 1%, with fewer than 500 deaths a year attributed to RSV in the United States. Increased morbidity and mortality occurs in high-risk patients,3,5,6 including those younger than 6 weeks old, and those with a history of premature birth, hypoxia, congenital heart disease, chronic lung disease or immune deficiency.7,8,9 Bronchiolitis is more common in males, infants living in crowded conditions, and infants who have not been breast-fed.10,11,12
Bronchiolitis is predominantly a viral disease, with no evidence supporting bacterial etiologies. In addition to RSV, other infectious agents include parainfluenza, adenovirus, rhinovirus, mycoplasma and metapneumovirus. Viruses are spread from person to person by direct contact with nasal and oral secretions, airborne droplets produced with sneezing and coughing, and fomites. A fomite is any inanimate object, such as a bedsheet or clothing, capable of carrying and transferring an infectious agent.
After inoculation, viral replication begins in the epithelial cells of the upper airway, then spreads to the mucosal surfaces of the lower respiratory tract, including the bronchioles. Infection of the epithelial cells results in their destruction via normal cell lysis, courtesy of the immune system, or via apoptosis, genetically preprogrammed cell death. Necrotic cells slough off and release inflammatory mediators, leading to airway inflammation and edema. In addition, mucus production is increased. This combination of cellular debris, edema and increased mucus production results in narrowing and obstruction of the bronchioles, increased resistance to air flow, decreased ventilation and air trapping.