Background: Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive lung parenchymal disease associated with lung stiffening and reduced compliance. Current clinical practice relies on spirometry, primarily forced vital capacity (FVC), for monitoring and prognostication; however some individuals with IPF are unable to provide technically acceptable or reproducible results due to symptom burden associated with the need to perform repeated maximal forced manoeuvres. Impulse oscillometry (iOS) is a non-volitional lung function test that provides information on airways resistance and lung reactance, and may be a plausible alternative pr adjunct to spirometry. However limited data exist around the value of iOS in IPF.

Aims: To evaluate the symptom burden, time taken to perform, inter-occasion reliability, validity, minimal important difference (MID), and prognostic ability of iOS measurements in IPF.

Methods and results: Oscillometry took less time to perform and was associated with lower symptom burden scores than spirometry. Measures of iOS had good test-retest reliability in a cohort of 66 stable patients with IPF, when measured two weeks apart, and there were moderate strength correlations with conventional lung function measures at a single timepoint (n=78). Longitudinal change in iOS did not correlate with change in FVC, exercise capacity or health related quality of life. Distribution-based methods were used to identify MIDs of oscillometry measures over 6 and 12 months (n=132). Insufficient adverse events occurred over the 12 month follow-up period to provide robust evidence with regards to the prognostic value of iOS.

Conclusion: In patients with IPF, iOS is a quicker to perform than spirometry, and is associated with a lower symptom burden. It has good test-retest reliability, with moderate strength correlations with conventional lung function tests at a single timepoint. However, the value of this test as a longitudinal marker of lung function and prognosis requires further investigation.