Differential Clinical Significance of FENO₂₀₀ and CANO in Asthma, Chronic Obstructive Pulmonary Disease (COPD), and Asthma-COPD Overlap (ACO)

Purpose: To investigate the differential clinical significance of fractional concentration of exhaled nitric oxide measured at a flow rate of 200 mL/s (FENO₂₀₀) and concentration of nitric oxide in alveolar (CANO) in asthma, chronic obstructive pulmonary disease (COPD) or asthma-COPD Overlap (ACO).

Methods: A total of 178 patients were included, with 82 patients in asthma group, 47 patients in COPD group and 49 patients in ACO group. Data for demographic data, spirometry and exhaled nitric oxide were collected for comparative analysis, correlation analysis and discriminant canonical analysis.

Results: The values of FENO₂₀₀ in asthma, COPD and ACO groups were 11.0(7.0-22.3), 8.0(6.0-11.0) and 9.0(6.5-19.5) ppb, respectively. In the asthma group, FENO₂₀₀ exhibited negative correlations with FEV₁/FVC, MMEF and MEF50. No significant correlation was observed between CANO and pulmonary function parameters. In the COPD group, both FENO₂₀₀ and CANO showed negative correlation with pulmonary function parameters including FVC, FEV₁, PEF, MMEF, MEF75, MEF50. In the ACO group, FENO₂₀₀ demonstrated no significant correlation with pulmonary function parameters, while CANO was correlated with FEV₁, PEF, MMEF and MEF50. In COPD group, ΔFEV₁ in the bronchodilator test was correlated with FENO₂₀₀. As for the ACO group, ΔFEV₁ was correlated with CANO. In the discriminant canonical analysis, four parameters including gender, age, MEF75 and FENO₅₀ discriminated between the three groups of asthma, COPD and ACO.

Conclusion: In asthma, COPD and ACO, FENO₂₀₀ has demonstrated a robust correlation with CANO. Elevated FENO₂₀₀ levels are predominantly indicative of pulmonary function impairment in asthma and COPD, whereas elevated CANO levels are mainly correlated with pulmonary function impairment in COPD and ACO. Compared with FENO₂₀₀ and CANO, FENO₅₀ may have a better discriminatory ability in distinguishing asthma, COPD and ACO.