The exhaled nitric oxide (eNO) signal is a marker of inflammation, and can be partitioned into proximal [J'awNO (nl/s), maximum airway flux] and distal contributions [CANO (ppb), distal airway/alveolar NO concentration]. We hypothesized that J'awNO and CANO are selectively elevated in asthmatics, permitting identification of four inflammatory categories with distinct clinical features.

The small airways comprise generations 8 to 23 of the bronchial tree, consist of airways with an internal diameter <2mm, and are classically difficult to assess and treat in persistent asthma. Small airways dysfunction (SAD) is integral to the asthma management paradigm as it is associated with poorer symptom control, greater levels of type 2 inflammation, and has been proposed as a potential treatable asthma trait. Although identification of SAD by oscillometry has been found to be clinically useful in managing asthma, very few physicians, including specialists, use this technique as part of standard or adjunct evaluation of lung function to diagnose asthma, grade severity of airway obstruction, ascertain disease control or the risk for future exacerbations or to make management decisions. To rectify the unrecognized value of oscillometry in the asthma community, a consortium of authors who are investigators with knowledge and experience of oscillometry wished to address the most important clinical questions raised by our colleagues who are considering using this technique, including its clinical utility. In this article, we discuss integral concepts including applicability of oscillometry as a predictive tool for asthma exacerbations and disease control; adequacy of spirometry and oscillometry in assessing SAD; potential limitations of oscillometry; as well as treatment options for SAD.

To present three clinically important developments related to the utilization of pulmonary function to objectively assess the asthmatic child. 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. 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.