Impulse Oscillometry Findings and Their Associations With Lung Ultrasound Signs in COVID-19 Survivors

BACKGROUND: Because impulse oscillometry (IOS) can detect changes in the small airways and is safer to perform during the COVID-19 pandemic than other pulmonary function tests, it may have value in investigating pulmonary sequelae in COVID-19 survivors. This study evaluated the performance of IOS in detecting lung abnormalities in COVID-19 survivors and investigated the associations of the findings with those of lung ultrasound (LUS) and spirometry.

METHODS: In this cross-sectional study, 117 subjects underwent IOS at a frequency range of 4–20 Hz 2 months after COVID-19 diagnosis. They also underwent spirometry and LUS, and their aeration scores were calculated.

RESULTS: On IOS, the resonance frequency was > 12 Hz, and the area under the reactance curve was > 3.60 cm H₂O/L/s in 70 (59.8%) and 55 (47.0%) subjects, respectively. A heterogeneity of resistance between R4 and R20 (R4-R20) > 20% was observed in 60 (51.3%) participants. Based on their abnormalities in resistive and reactive parameters, 76 (65.0%) participants had abnormal IOS. Spirometry abnormalities were detected in 40 (34.2%) cases. LUS was abnormal in 51 (43.6%) participants, and the median aeration score was 0 (0–8) points. Abnormal IOS was associated with abnormal LUS (P < .001) and abnormal spirometry (P = .002). Abnormal spirometry had a significant but weaker association with abnormal LUS (P = .031). In participants who reported hospitalization, abnormal IOS was associated with both abnormal LUS (P = .001) and abnormal spirometry (P = .006). In participants who did not report hospitalization, abnormal IOS was associated with abnormal LUS (P < .001) but not abnormal spirometry (P = .063).

CONCLUSIONS: In COVID-19 survivors, IOS detected changes even when spirometry was normal. In these individuals, IOS parameters were more strongly associated with abnormalities on LUS than with abnormalities on spirometry.