What is the role of impulse oscillometry (IOS) in the evaluation of asthma symptoms?

Updated: Nov 20, 2020
  • Author: Michael J Morris, MD, FACP, FCCP; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
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Impulse oscillometry (IOS) is gaining attention for the evaluation of obstructive lung disease, including asthma. IOS uses a speaker to produce pressure oscillations within the airway, resulting in measurement of pressure changes and flows with calculation of resistance, reactance, and resonance. Different frequencies are used to assess large and small airways, which is helpful to determine where the primary obstruction is occurring. For example, a patient with asthma would demonstrate increased resistance at 5 Hz (R5, distal airways) with a normal resistance at 20 Hz (R20, central airways). The primary benefit of IOS is the effort-independent nature of the test, such that small children and frail adults can easily perform the test. Therefore, in patients unable to perform spirometry or with normal spirometry but symptoms suggestive of asthma, IOS could be used to determine if there is increased airway resistance or a bronchodilator response compatible with bronchial hyperreactivity. IOS is also very quickly obtained, but provides no information on lung volumes or oxygen diffusion capacity. Currently, routine use of IOS is limited by a lack of universally accepted reference values across all patient populations.

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