Guiding therapy by fractional exhaled nitric oxide & impulse oscillometry parameters in non-asthmatic individuals with chronic cough

Background & objectives Chronic airway inflammation and airway hyperresponsiveness are typical pathophysiological features of cough variant asthma. However, the characteristics of airway inflammation and airflow restriction in individuals with non-asthmatic chronic cough and their guiding value of clinical treatment remain to be determined. This study explored the characteristics and correlations between fractional exhaled nitric oxide (FeNO) and impulse oscillometry (IOS) in non-asthmatic individuals with chronic cough. It also investigated the possibility of chronic cough developing into asthma. Methods In total, 65 study participants with negative bronchial provocation test (BPT) were included in this retrospective study. Data were extracted from chronic cough patients' electronic medical records, including the demographics, FeNO, IOS and spirometric parameters before and after BPT. Study participants were divided into high-FeNO group (FeNO≥25 ppb) and low-FeNO group (FeNO< 25 ppb) based on FeNO levels. The correlation between the markers was investigated using the Spearman rank correlation test. Results We observed that individuals with non-asthmatic chronic cough exhibited significant increases in Z5, Fres, R5 and R5-R20 after BPT compared to before BPT. In addition, the IOS values of Z5, Fres, R5, and Rc were higher in the low-FeNO group than in the high-FeNO group, but a decrease in FEV1. Correlation analysis: IOS parameters showed a negative correlation with FeNO. However, there were positive correlations of FeNO with FEV1 and PEF. Interpretation & conclusions Our findings showed that individuals with non-asthmatic chronic cough may have varying levels of small airway resistance and inflammation severity. A combined use of FeNO and IOS measurements is conducive to the early clinical treatment of individuals with non-asthmatic chronic cough.