ABSTRACT
Background: Airway inflammation post COVID-19 is a possible cause for persistent breathlessness. Aim(s): We sought to evaluate the role of fractional exhaled nitric oxide (FeNO) measurements in this cohort. Methodology: We report FeNO results in patients undergoing lung function testing as part of the PHENOTYPE study (NCT 04459351). Result(s): 83 patients had FeNO performed between January and Nov 2021. Of the patients admitted to hospital (n=78), the median time to testing from discharge was 96 days (IQR 90-115). Median FeNO results for the whole cohort was 20 ppb (16-29). 24/83 (29%) had a FeNO in the intermediate range [median 33 (IQR 28-45)], and 5/83 (6%), FeNO >50 ppb. Chi squared testing revealed no relationship between patient-reported breathlessness (p=0.12) or cough (p=0.45) and FeNO >=25ppb. 52 patients underwent repeat lung function and FeNO testing at a median of 363 (355-370) days post discharge. 26/52 (50%) of individuals had a FeNO>=25 ppb, with a median 35 (28-42): 10/52 (19%) deteriorated from normal to intermediate range and 2/52 from intermediate to high range as compared to initial values. 7/52 (13%) of FeNO results that were abnormal at the first visit, normalized with no additional treatment. Again, no association was found between breathlessness (p=0.48) or cough (p=0.73) at the second visit and a FeNO result >=25ppb. None of the patients with a FeNO >= 25 had a prior diagnosis of asthma. Conclusion(s): The clinical relevance of an intermediate or high FeNO in this cohort is unclear. However, this preliminary work highlights that in a significant proportion of patients, the FeNO is not normal even at 1 year post discharge. The trajectory of these changes and in particular, development of small airways disease are important to study.