Childhood Asthma and Wheezing Disorders

Abstract

Pulmonary function tests, mainly spirometry (FEV1), are generally considered the standard tools for objective evaluation and re-evaluation in childhood asthma. However, since most asthmatic children have FEV1 values in the normal range, independent of disease severity, the value of commonly used pulmonary function tests in short- and long-term evaluations of childhood asthma remains controversial. Other parameters may be more valuable for this purpose.Wheezing disorders in infancy are common and their prevalence has increased in the last decade. Clinically, it is often difficult to distinguish whether an obstructive episode is a transient ‘viral wheeze’ or the beginning of allergic asthma, which tends to persist in adulthood.There is an increased availability of techniques and commercial equipment for pulmonary function tests for this age group. Infant pulmonary function tests have been helpful in distinguishing between wheezy and healthy children and may have some predictive value, however for the time being, they are mainly research tools. The pathophysiology of asthma as it is currently understood consists of variable airway obstruction, as first described by Salter more than hundred years ago, bronchial hyperresponsiveness, as described in 1960, chronic airway inflammation, recognized over the last few decades to be the key mechanism of asthma, and airway remodelling, a number of structural changes considered over the last few years to be a primary key factor. Based on our understanding of the pathophysiology, combined assessment of the degree of airway obstruction, bronchial responsiveness, airway inflammation and airway remodelling would appear to be the best approach to diagnose and monitor asthma. In spite of this, diagnosis and monitoring of asthma in clinical praxis are still mainly based on symptom evaluation. The impact of airway remodelling on the natural course of the disease is still little understood. Assessment of airway inflammation has so far mostly been proven to be too invasive, too expensive, not sensitive or specific enough, and not insufficiently validated and standardized to be used in clinical practice and hence, at the moment, still mainly remains a research tool. In addition, despite there being some indications that the assessment of bronchial responsiveness is helpful not only in diagnosing but also in monitoring the disease, these techniques are rarely used in clinical practice. Therefore, although asthma is now recognized as a chronic inflammatory disease of the airways, reversible airway obstruction is still the main objective outcome measure recommended by most guidelines for the diagnosis and monitoring of asthma in childhood. However, some of the lung function parameters used, such as peak expiratory flow (PEF) and forced expiratory volume in 1 s (FEV1), have been lately shown not to be as helpful in the care of children with asthma. Whereas asthma is a well-defined disorder in children over 5 years of age, the diagnosis of asthma in younger children remains a challenge. Children presenting with wheeze at an early age belong to a heterogeneous group, and little is understood about the pathophysiology of wheeze in young children; hence, the diagnosis and monitoring of wheezy disorders in young children are difficult. The tools available for the assessment of airway inflammation and/or reversible airway constriction and bronchial responsiveness in this young age group are not yet available for clinical practice, but remain mainly available for research purposes. This chapter will cover the use of lung function tests in the initial evaluation and follow-up of both asthma in children older than 5 years and wheezy disorders in children younger than 5 years.