Normal spirometry equates to normal impulse oscillometry in healthy subjects.

Moreover small airways dysfunction as R5-R20 and AX is related to type 2 inflammation in asthma [[4]]. Impulse oscillometry (IOS) is an effort independent test performed with tidal breathing which can ascertain the presence of small airways dysfunction by measuring the heterogeneity of resistance between 5 and 20 Hz (R5-R20) or the area under the reactance curve (AX). We would also like to point out that in persistent asthma patients with preserved spirometry who have FEV1 > 80% predicted, the presence of raised values for R5-R20 was associated with a greater likelihood of long term poor disease control [[3]]. [Extracted from the article]