Assessment of lung function variability documents airflow limitation in many patients with long covid.

BACKGROUND: It is estimated that 65 million people worldwide suffer from long covid (LC). Many LC symptoms are also reported by patients with airflow limitation, used to confirm asthma. The primary aim was to detect airflow limitation in LC patients by a methacholine bronchial provocation test (BPT) and if negative, by evaluation of diurnal variability in forced expiratory flow in 1 second (FEV1 ) over a two-weeks' period. The second aim was to assess responsiveness to asthma treatment on diurnal FEV1 variability and LC symptoms.

METHODS: Patients with LC for at least six months were recruited in this open diagnostic study. Burden of LC symptoms were reported on a 10-point Likert scale (0 = not troubled, 10 = extremely troubled) at inclusion and after three weeks' asthma treatment. A positive methacholine BPT was defined by an accumulated provocation dose (PD20 )<8 μmol causing 20% fall in FEV1 . App-based spirometer was used for diurnal FEV1 variability, deemed positive by diurnalvariability in FEV1 ≥12%.

RESULTS: Airflow limitation was documented by positive methacholine BPT in 8/30 (27%), or by excessive diurnal variability in FEV1 in 21/22 (95%) of the BPT negative LC patients. One patient dropped out due to personal issues. Three weeks' asthma treatment normalised mean diurnal FEV1 variability from 18.0% to 7.3%, p < 0.001. Significant reductions were observed for fatigue and dyspnoea, from 8.3 to 6.1, p < 0.001, and 3.0 to 0, p < 0.001, respectively.

CONCLUSION: This study indicate that airflow limitation may be detected in many LC patients if evaluation of diurnal variability in FEV1 is included in the diagnostics.