A glimpse in post-COVID pathophysiology: the role of exhaled breath condensate pH as an early marker of residual alveolar inflammation.

Background: Residual alveolar inflammation seems to be paramount in post-COVID pathophysiology. Currently, we still lack a reliable marker to detect and track alveolar phlogosis in these patients. Exhaled Breath Condensate (EBC) pH has robust evidences highlighting its correlation with lung phlogosis in various diseases. We aim to define the reliability of alveolar and bronchial EBC pH in the assessment and in the follow up of post-COVID-related inflammation.

Research design and methods: We enrolled 10 patients previously hospitalized due to COVID-19 pneumonia. We performed a complete follow-up after 3 months and 6 months from discharge. Each visit included routine blood tests, arterial blood gas analysis, 6-minute walking test, spirometry, diffusing capacity and body plethysmography. Finally, bronchial and alveolar EBC were collected at the end of each visit.

Results: Alveolar EBC pH was significantly lower than bronchial EBC pH at T1, alveolar EBC pH tended to be more acid after 3 months from hospital discharge compared to the same sample 6 months later. Serum inflammatory biomarkers showed no significant differences from T1 to T2. Alveolar EBC pH was positively correlated with neutrophil-lymphocyte ratio.

Conclusions: Collecting EBC pH could help to understand pathophysiologic mechanism as well as monitoring alveolar inflammation in the post-COVID syndrome.