Small Airway Function in Children With Mild to Moderate Asthma

Subtle but significant differences in the proposed small airway impulse oscillometry (IOS), spirometry, and fractional exhaled nitric oxide (FE_NO) indices between children with recurrent wheezing and healthy controls have been reported in a study published in Annals of Allergy, Asthma & Immunology.                   

These findings suggest that early disease changes in the distal airways might be present in young children with mild asthmatic symptoms that is limited mainly to recurrent wheezing. The study was conducted in children who were referred to a tertiary unit between April 2016 and May 2017 because of symptoms indicative of possible asthma.

Investigators sought to evaluate small airway properties in children with mild to moderate asthmatic symptoms by using various indicators of small airway involvement (IOS, spirometry, multiple-breath nitrogen washout [MBNW] test, and extended FE_NO measurement). The secondary aim of the study was to evaluate the association of small airway function with asthma control and exercise-induced bronchoconstriction (EIB).

Children 5 to 10 years of age with either recurrent wheezing (n=42) or persistent, troublesome cough (n=16), and healthy controls (n=19) were enrolled in the study. All participants performed IOS, spirometry, and an MBNW test. Exhaled NO was measured at multiple flow rates, in order to determine alveolar NO concentration (CALV). Asthma control was assessed with the Childhood Asthma Control Test (C-ACT), short-acting beta₂-agonist (SABA) use within the past month, and asthma exacerbations during the last year.

Spirometry, IOS, and exhaled NO indices — all of which are related to small airway function — differed between children who had recurrent wheezing and healthy controls. In contrast, only forced expiratory flow at 25% to 75% of the forced vital capacity was associated with persistent cough. Based on the use of MBNW indices, no differences between the groups were observed.

In children who were symptomatic, small conducting airways ventilation inhomogeneity (Scond) and CALV were both significantly associated with exacerbations of asthma (P =.028 and P =.002, respectively). Lung clearance index and CALV were also significantly associated with EIB (P =.044 and P =.004, respectively) in symptomatic children. None of the proposed small airway indices were related to patients’ C-ACT scores or SABA use.

The investigators concluded that in children with recurrent wheezing, subtle changes were observed in the proposed small airway indices of IOS, spirometry, and exhaled NO. Moreover, small airway dysfunction, which was expressed as Scond and CALV, was also linked to asthma exacerbations and EIB.

Additional studies are warranted to clarify whether children who present with abnormalities in the proposed small airway indices might benefit from novel therapies aimed at targeting the small airways, and which of the available measures are ideal for identifying and following these individuals.

Reference

Knihtilä H, Kotaniemi-Syrjänen A, Pelkonen AS, Mäkelä MJ, Malmberg LP. Small airway function in children with mild-to-moderate asthmatic symptoms and healthy controls [published online July 27, 2018]. Ann Allergy Asthma Immunol. doi:10.1016/j.anai.2018.07.026