Clinical Applications of Pediatric Pulmonary Function Testing—Introduction to the Series

Pulmonary function tests are key components of the evaluation and management of children with chronic lung diseases such as asthma, bronchopulmonary dysplasia (BPD), cystic fibrosis, and restrictive chest wall disorders. The well-known maxim that “children are not just little adults” certainly extends to the pediatric pulmonary function laboratory, where infants are sedated with chloral hydrate for a test that would take 10 min in a cooperative adolescent, toddlers watch “Sponge Bob” videos while performing tidal breathing maneuvers, and preschool children may be seen blowing party favors to learn forced expiratory maneuvers. The choice of the optimal test for a specific patient depends not only on developmental abilities, but also on the underlying pathophysiology of the disease process being evaluated. Does the patient have obstructive disease or restrictive disease? How is bronchodilator responsiveness best evaluated in a 2-year-old? How can lung volumes be assessed in a patient too young to cooperate with plethysmography? Understandably, the busy practicing pediatrician or pediatric pulmonologist may feel bewildered by the plethora of lung function tests available and unclear how best to utilize these tests in clinical practice.

This series on “Clinical Application of Pediatric Pulmonary Function Testing” provides practical, concise, state-of-the-art reviews of lung function tests for the clinical care of pediatric patients with pulmonary conditions, written by international experts in the field. The goal of each article is to review the available tests and the results of relevant research and discuss the applicability and utility of these tests in different age groups and disease states.

The first article in the series reviews pediatric spirometry reference equations. ¹ The comparison of an individual's lung function to that of a healthy reference population is important both in distinguishing health from disease and in monitoring lung function over time, particularly in a growing child. A wide range of reference equations exist, and no one equation is ideal for all situations. The article covers how reference equations are created, how to use them to interpret lung function measurements, and how to choose appropriate reference equations, highlights current limitations, and suggests areas for future research and collaboration.

The second article by Debley and coworkers discusses lung function measures in pediatric patients with recurrent wheezing and asthma. ² Recurrent wheezing affects almost one-third of infants and toddlers, yet resolves in the majority by school age. ³ Differentiating transient wheezing from persistent asthma in the early years is critical and lung function testing could play an important role. After reviewing the underlying pathophysiology of reversible airway obstruction, a wide range of lung function tests is discussed using an age-based approach, including spirometry, lung volume measurements, airway resistance measurements, and measures of airway inflammation. The clinical implications of recent research are reviewed, with an emphasis on distinguishing transient wheezers from those who will develop persistent asthma.

Lung function testing in children with BPD may be especially challenging because of development or motor impairments related to prematurity. Clinical follow-up of former preterm infants tends to concentrate on neurological outcomes, whereas children with BPD have been clearly demonstrated to have long-term pulmonary function deficits and are at increased risk of developing chronic obstructive pulmonary disease as adults.^4,5 Thus, it is important to monitor longitudinal lung function in these patients. In the third article in the series, Lum et al. provide a practical review of lung function testing in infants, preschool, and school-aged children with BPD, including the evaluation of coexisting asthma, exercise-induced bronchospasm, tracheomalacia, exercise intolerance, and fitness to fly. ⁶

Redding and colleagues review the utility of pediatric lung function testing in restrictive lung diseases, including those leading to respiratory muscle weakness such as Duchenne muscular dystrophy and spinal muscular atrophy, and primary chest wall disorders such as scoliosis. ⁷ The underlying pathophysiology of different disease processes is clearly elucidated. Lung function tests are reviewed in a practical manner, including those measured in the pulmonary function lab, the office setting, and the sleep center. Insights into disease processes gained through systematic evaluation of lung function and imaging are also discussed. This timely review will be of interest to pediatric orthopedists and rehabilitation specialists as well as pediatricians and pediatric pulmonologists.

Future articles in this series will include reviews of pulmonary function testing in children with cystic fibrosis and sickle cell disease, as well as an approach to the pediatric patient with exercise intolerance. Together, this series should help the busy practicing pediatrician or pulmonologist decide which lung function tests will be of greatest utility in the diagnosis and monitoring of individual patients from infancy through adolescence.