Institute for Clinical and Translational Science

Background

Previous reports suggest that peripheral airways are associated with asthma control. Patient history, although subjective is used largely to assess asthma control in children because spirometry is many times normal. Impulse oscillometry (IOS) is an objective non-invasive measurement of lung function, which has the potential to examine independently both small and large airway obstruction.

To determine the utility of IOS in assessing asthma control in children.

Asthmatic and healthy children (6–17 yrs) were enrolled in the study. Spirometry and IOS (resistance at 5 and 20 Hz, R5 and R20, respectively, reactance at 5 Hz, X5, resonant frequency, Fres, and area under the reactance curve between 5 Hz and Fres, AX) were collected in triplicate before and after a bronchodilator was administered. The physicians were blinded to the IOS measurements and assessed asthma control using ATS guidelines.

Small airway IOS measurements, including R5-20, X5, Fres and AX, of children with uncontrolled asthma (n=44) were significantly different from those of controlled asthmatic (n=57) and healthy (n=14) children, especially prior to the administration of a bronchodilator. However, there was no difference in large airway IOS (R20). No differences were found between controlled asthmatic and healthy children in any of the endpoints. ROC analysis showed cut-points for baseline R5-20 (1.5 cmH₂O·L⁻¹·s) and AX (9.5 cmH₂O·L⁻¹) that effectively discriminated controlled versus uncontrolled asthma (AUC=0.86 and 0.84), and correctly classified more than 80% of the population.

Uncontrolled asthma is associated with small airways dysfunction, and IOS may be a reliable non-invasive method to assess asthma control in children.