Intra-Breath Oscillometry Reveals Phase-Dependent Resistive Abnormalities in Respiratory Mechanics After Severe Covid-19

Post-COVID syndrome is often associated with persistent respiratory symptoms despite largely unremarkable conventional pulmonary function tests, suggesting the presence of subtle alterations in respiratory mechanics. We hypothesized that phase-resolved analysis of respiratory impedance would reveal dynamic abnormalities not captured by standard endpoint-based measures. In this prospective observational study, survivors of severe COVID-19 requiring veno-venous extracorporeal membrane oxygenation (V-V ECMO) (n = 9) were evaluated two years after recovery and compared with matched healthy controls (n = 9). Respiratory system impedance was assessed using intra-breath oscillometry at 5 Hz. Phase-dependent mechanical behavior was characterized by inspiratory-expiratory differences in phase-averaged resistance and reactance (ΔR av , ΔX av ), end-tidal differences (ΔR end , ΔX end ), and resistance and reactance loop areas (R loop , X loop ). Post-COVID patients exhibited significantly elevated end-expiratory resistance (p = 0.02), whereas end-inspiratory resistance did not differ significantly between groups. ΔR av (p = 0.01) and R loop (p = 0.03) were reduced compared with controls, while ΔR end , ΔX av , ΔX end and X loop did not differ significantly. These findings indicate altered phase-dependent mechanics in post-COVID patients, characterized by elevated end-expiratory resistance and attenuated within-breath resistance modulation. Intra-breath analysis of respiratory impedance thus provides complementary information on time-varying respiratory mechanics beyond conventional whole-breath oscillometry and may enable more sensitive characterization of subtle mechanical dysfunction.