Usefulness of impulse oscillometry for the assessment of airway hyperresponsiveness in mild-to-moderate adult asthma

Background
Impulse oscillometry (IOS) is a novel method of assessing airway resistance. IOS is rarely used in assessing airway resistance after bronchoprovocation in adult asthma.
Objective
To ascertain the degree of change in IOS measurements seen in patients with asthma undergoing bronchial challenge testing.
Methods
Patients 18 to 65 years old with mild to moderate asthma, forced expiratory volume in 1 second (FEV₁) greater than 80% predicted, and diurnal FEV₁ variation less than 30% and taking inhaled corticosteroid (≤1,000 μg/day of beclomethasone dipropionate equivalent dose) were recruited. Sequential spirometry and IOS results were measured during bronchial challenge testing to inhaled methacholine and histamine.
Results
The magnitude of percentage of change demonstrated in total airway resistance at 5 Hz was greater than that observed for FEV₁ in the 2 bronchial challenge tests. For example, at a methacholine provocation concentration that caused a decrease in FEV₁ of 20%, a 43.5% change (95% confidence interval 29.4–57.5) was seen in total airway resistance at 5 Hz as measured by IOS compared with a 23.3% change (95% confidence interval 18.7–27.9) in FEV₁. The magnitude of change seen with other IOS outcomes, including peripheral airway resistance, area under the curve, and resonant frequency, also was greater compared with spirometry.
Conclusion
The potential application of IOS in the assessment of airway hyperresponsiveness in adult asthma has been demonstrated. Further population studies are required.