Respiratory oscillometry is associated with respiratory symptoms and functional outcomes at 6-months post-COVID-19

BACKGROUND The long-term pulmonary sequelae of COVID-19 are incompletely characterized. Early studies using conventional pulmonary function tests (PFT) identified a predominant restrictive defect that improved over time despite persistent respiratory symptoms. Respiratory oscillometry is a different PFT modality that provides highly sensitive information regarding lung mechanics to complement spirometry. This cross-sectional study aims to characterize spirometry and oscillometry at 6 months post-COVID-19 in patients with mild-moderate acute infections, and assess their associations with respiratory symptoms and functional status using the 6-min walk test (6MWT).METHODS Patients in the Canadian COVID-19 Longitudinal Cohort Study were enrolled between Aug 2020-Mar 2022 for further evaluation with oscillometry and spirometry. Complete data, including 6MWT and Borg Dyspnea scale assessment, at 6 months post-COVID-19 infection were available in 213 of 549 patients for analysis. Patients admitted to the intensive care unit were excluded from analysis.RESULTS The cohort (61.0% women, median age; 44.9 years) comprised of 83.1% outpatients and 16.9% hospitalized ward patients. The overall prevalence of respiratory symptoms was high (54.3%) and similar in the 2 groups. Overall, 42.7% of all patients had abnormal oscillometry while only 16.6% had abnormal spirometry. Notably, 29.8% of patients with normal spirometry had abnormal oscillometry. Oscillometry was associated with the 6MWT, total respiratory symptoms and the change in the Borg dyspnea score pre- and post-6MWT(ΔBorg-dyspnea) in contrast to spirometry where little association was found.CONCLUSIONS Oscillometry detected abnormal lung mechanics that were associated with functional impairment and respiratory symptoms but indiscernible by spirometry.