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Wheezing is a high-pitched whistling sound heard during expiration. It occurs when air flows through narrowed or partially obstructed airways, mostly the bronchioles. It can also be heard because of narrowing of larger airways.

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Wheezing is common in infants and children. An estimated 10–15% of all infants younger than 1 year have an episode of wheezing. Up to 25% of children younger than 5 years present at least once to medical attention for evaluation of wheezing.1 Recurrent wheezing over the age of 1 year usually indicates a diagnosis of asthma.

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The differential diagnosis for wheeze is broad.2 An initial episode of wheezing typically suggests viral respiratory tract infection. Since wheezing is often associated with viral respiratory infections in infants, it is difficult to distinguish an initial episode of asthma triggered by a viral respiratory tract infection from acute viral bronchiolitis. The causes of recurrent or persistent wheezing are more diverse. Common causes of recurrent wheezing include serial viral respiratory infections, poorly controlled asthma, and gastroesopheal reflux with pulmonary aspiration. Less commonly, recurrent wheezing is caused by congenital abnormalities of the lung, diaphragm, or branches of the aorta or pulmonary vessels. Vascular rings, aberrant right subclavian artery, innominate arterial compression, aberrant left pulmonary artery (pulmonary sling), and absence of the pulmonary valve may all present with abnormal respiratory sounds and distress in infants.3,4 Cystic fibrosis or immunologic defects may also manifest first with wheezing. In addition, wheezing may not be the reason why a caregiver brings a child to medical attention. Thus, children with wheeze can present in a variety of ways. These variable paths also provide clues to the etiology. Table 15–1 provides the most common presentations and associated signs and symptoms. Figure 15–1 provides anatomic locations of causes of wheezing.

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Table Graphic Jump Location
Table 15–1. Diagnostic Tests and Expected Results in Children with Less Common Causes of Wheezing

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