Why do preterm infants wheeze? Clues from epidemiology

In this chapter, we discuss respiratory outcomes of preterm infants and the impact later in life of bronchopulmonary dysplasia (BPD). After the neonatal period, the major respiratory problems of preterm-born infants (with or without BPD) that require hospitalization are respiratory exacerbations caused by infections, particularly viral infections. In older children who were born prematurely, the most common symptoms are coughing, wheezing, and/or other asthma-like symptoms. Overall, in comparison to full-term born children, the risk of preterm-born children developing asthma or a wheezing disorder during childhood is almost twice as high. Patients are, however, often labeled asthmatic even though the underlying mechanisms are likely to be very different. There is no evidence of the widespread use of bronchodilators or inhaled corticosteroids, although a component of variable airflow obstruction may be present. To achieve optimal treatment, additional evidence is required. In order to prevent either over- or undertreatment, it is important to characterize diseases of the airways in the survivors of preterm birth. This is done in terms of the extent and nature of airflow obstruction, the pattern of any inflammation, and the presence of airway reactivity. Symptoms become milder as children grow older. Nevertheless, a group of adolescents and adults remains, who still present with chronic airway obstruction defined by recurrent episodes of wheezing and decreased lung function tests, that is, decreased forced expiratory volume. The risk of wheezing disorders increases as the degree of prematurity increases. Putative mechanisms for wheezing may include early lung injury or maldevelopment during infancy, respiratory infections during the first year of life, and structural changes of the lung parenchyma.