Clinical implications of concentration of alveolar nitric oxide in asthmatic and non-asthmatic subacute cough

Background and objective: Asthma is one of the important causes of subacute cough. Concentration of alveolar nitric oxide (CANO) is a sensitive inflammatory indicator of peripheral airways, which has received much less attention than fraction of exhaled nitric oxide (FeNO50). The main objective of this study was to explore the correlation between CANO and clinical parameters in asthmatic and non-asthmatic subacute cough, which might promote understanding the clinical utility of CANO in these special patient population. Materials and methods: 155 patients with subacute cough were included consecutively, of which 25 were diagnosed as asthma. Data for demographic characteristics, FeNO50, CANO, baseline spirometry, bronchial provocation test (or bronchodilation test) and response dose ratio (RDR) was collected. Differences between asthmatic and non-asthmatic group were analyzed. Spearman’s correlation coefficient (rho) was used to evaluate the correlation between FeNO50, CANO and other clinical parameters. Results: In patients with subacute cough, baseline CANO values did not differ between asthmatic and non-asthmatic patients (4.4(1.3, 11.4) versus 4.0(2.1, 6.8) ppb, P>0.05). Besides, CANO exhibited stronger association with pulmonary function parameters when compared with FeNO50. For asthmatic subacute cough, CANO was inversely correlated with FEV1/FVC (rho=-0.69, P<0.01) and small airway parameters including MEF25 (rho=-0.47, P<0.05) and MMEF (rho=-0.45, P<0.05). For non-asthmatic subacute cough, CANO was inversely correlated with MEF25 (rho=-0.19, P<0.05) and RDR (rho=-0.21, P<0.05). Conclusion: In subacute cough, asthmatic and non-asthmatic patients had similar values of baseline CANO. In both asthmatic and non-asthmatic subacute cough, CANO exhibited stronger association with pulmonary function parameters when compared with FeNO50. A low CANO value in non-asthmatic subacute cough corresponded to a higher value of RDR, which implied stronger tendency towards airway responsiveness.