Abstract and Introduction
Abstract
Purpose of review: To present three clinically important developments related to the utilization of pulmonary function to objectively assess the asthmatic child.
Recent findings: The new asthma guidelines (2007) have added the forced expiratory volume in 1 s/forced vital capacity (FEV1/FVC) ratio to the FEV1 as spirometric criteria for classifying asthma. Although a better indicator of airway obstruction, it has not clearly been shown to correlate with clinical criteria. The normal cut point for the ratio used in the guidelines of 85% for children may be too high, and compared to the lower limits of normal of 80%, could result in unnecessary treatment in some children. The bronchodilator response (BDR) phenotype reflects airway lability and has been associated with biomarkers of inflammation and responsiveness to inhaled corticosteroids as well as predicting long-term outcomes. Several studies have shown improved spirometric techniques in preschoolers as well as defining normal values in this age group. Impulse oscillometry (IOS), which is less demanding than spirometry, has been shown to identify asthmatic preschoolers in some cases better than spirometry and possibly identifying obstruction in the peripheral airways. It may also be a more useful test than spirometry in evaluating long-term drug studies.
Summary: In addition to the FEV1/FVC ratio to detect airway obstruction, the BDR phenotype would appear to give important additional information regarding airway lability and inflammation, and should be included as routine spirometry. IOS is a promising test to identify asthmatic preschoolers, but more studies are needed to determine exactly what it measures and what constitutes normal values.
Introduction
Useful objective measures for diagnosis and treatment strategies for childhood asthma remain elusive. The National Asthma Education and Prevention Program (NAEPP) Guidelines 2007 recommend prebronchodilator and postbronchodilator spirometry in children 5 years of age or older for diagnosis, severity classification, and assessing asthma control. This is particularly important because physicians are generally unable to determine the degree of airflow obstruction or whether it is reversible clinically. Furthermore, self or parent reported history are not usually reliable for determining the degree of airflow obstruction or excluding other diagnosis. In spite of these limitations of clinical assessment, a national survey of primary care providers reported that only 20% used spirometry in asymptomatic patients, and 59% of pediatricians never used spirometry. One reason may be that specific guideline-defined spirometric measures used to classify asthma severity and control, the forced expiratory volume in 1 s (FEV1) and the FEV1/forced vital capacity (FEV1/FVC) ratio generally correlate poorly with symptom-based severity in children. This is in contrast to the relationship seen in adults. In this review we will look at the evidence of whether the use of the current FEV1 and the FEV1/FVC ratio spirometric measures help the clinician with assessing asthma severity and control.
Recently there has been an appreciation that asthma phenotypes can be helpful in understanding pathobiological mechanisms and in the approach to pharmacotherapy. In this regard, the bronchodilator response (BDR) phenotype has been shown to be associated with biomarkers of inflammation and responsiveness to inhaled corticosteroids (ICS), as well as predicting long-term outcomes. In this review we will elaborate on the BDR phenotype and how it may be a useful adjunct to baseline spirometry in making therapeutic decisions.
Finally, new enthusiasm has been noted in assessing pulmonary function in the preschool child. A fresh approach to spirometry has been successfully demonstrated in children as young as 2–3 years of age. Furthermore, an alternative approach, impulse oscillometry (IOS), which requires only quiet tidal breathing, has been shown to be potentially more useful in identifying asthmatic preschoolers than traditional spirometry. There is also a suggestion that IOS may reflect airflow obstruction in the peripheral airways. In addition, a recent study showed that IOS may be particularly useful in detecting long-term therapeutic responses to controller medication. We will cover pertinent literature expanding these concepts in a population of children who traditionally has seldom been evaluated by pulmonary function particularly in the office setting.