A comparison of respiratory oscillometry and spirometry in idiopathic pulmonary fibrosis: performance time, symptom burden and test-retest reliability

Study question In large multinational patient surveys, spirometry (which requires repeated, reproducible maximal efforts) can be associated with cough, breathlessness and tiredness, particularly in those with idiopathic pulmonary fibrosis (IPF). Oscillometry is an effort-independent test of airways resistance and reactance. We hypothesised that oscillometry would take less time to perform and would be associated with reduced symptom burden than spirometry. Patients and methods Spirometry and oscillometry were performed in 66 participants with IPF and repeated 2 weeks later. We compared time taken to perform tests, symptom burden and test-retest reliability with Bland-Altman plots and intraclass correlation coefficients (ICCs). Results Oscillometry took significantly less time to perform than spirometry (mean - 4.5 (99% CI - 6.0 to - 3.0) min) and was associated with lower symptom burden scores for cough (-1.3, 99% CI - 1.7 to - 0.8), breathlessness (-1.0, 99% CI - 1.4 to - 0.5), and tiredness (-0.5, 99% CI - 0.9 to - 0.2). On Bland- Altman analysis, all measures showed good agreement, with narrow limits of agreement and the mean bias lying close to 0 in all cases. The ICCs for forced expiratory volume in 1 s and forced vital capacity were 0.94 and 0.89, respectively, and ranged between 0.70 and 0.90 for oscillometry measures. Conclusion Oscillometry is quicker to perform and provokes less symptoms than spirometry in patients with IPF.