The value of concentration of alveolar nitric oxide in diagnosing small airway dysfunction in patients with stable asthma

BACKGROUND: Exhaled nitric oxide (FeNO) is a simple, noninvasive, and reproducible test, and FeNO (50 ml/s) is often used to reflect airway inflammation. The peripheral small airway/alveolar nitric oxide (NO) concentration is derived from the output of NO at multiple flow rates. Concentration of alveolar NO (CANO), which has been reported to reflect peripheral small airway inflammation, may be related to parameters that reflect abnormal small airway function. AIM: This study aims to investigate the relationship among CANO levels, clinical features, and small airway function‐related indicators in patients with stable asthma and to provide a simple method for monitoring small airway function in asthma. DESIGN AND METHODS: We recruited 144 patients with well‐controlled, stable asthma, including 69 patients with normal small airway function (normal group) and 75 patients with small airway dysfunction (abnormal group). CANO and pulmonary function were measured. RESULTS: CANO was significantly higher in the abnormal group ([7.28 ± 3.25] ppb) than the normal group CANO ([2.87 ± 1.50] ppb). FEF25–75%pred ([55.0 ± 16.5]%), FEF50%pred ([46.4 ± 13.2]%), and FEF75%pred ([41.9 ± 13.1]%) in abnormal group were significantly lower compared with normal group ([89.9 ± 7.5]%), ([80.9 ± 6.8]%), and ([73.8 ± 5.0]%). CANO was negatively correlated and FEF25–75%pred, FEF50%pred, and FEF75%pred (r = −0.87, P < 0.001; r = −0.82, P < 0.001; r = −0.78, P < 0.001). CANO was positively correlated with age (r = 0.27, P = 0.001). The area under the ROC curve was 0.875 for CANO. The optimal cutoff point of 5.3 ppb had sensitivity and specificity values of 72% and 92% in diagnosing small airway dysfunction. CONCLUSION: CANO has diagnostic value for small airway dysfunction, and the optimal cutoff value is 5.3 ppb. However, the diagnostic evidence is still insufficient, so it still needs further exploration for its value in detecting small airway dysfunction.