COPD patients with peripheral airway obstruction reversibility identified by exhaled nitric oxide.

Rationale: Besides its role as an inflammatory marker in asthma, fractional exhaled nitric oxide (FNO) provides information on the extent of the airway obstruction process through evaluating its change after bronchodilation.

Objective: To investigate whether FNO change after bronchodilation can identify different sites of airway obstruction in COPD patients.

Methods: FNO, FEV and the slopes (S) of the alveolar plateau of the single breath washout test (SBWT) were measured in 61 stable COPD patients (FEV 34.5% predicted) before and after the inhalation of 400 μg salbutamol. SBWT used Helium (He), and sulfur-hexafluoride (SF). Obstruction relief occurring in pre-acinar and intra-acinar small airways is expected to decrease S and S, respectively. Indices changes (Δ) after bronchodilation were expressed as a percentage of pre-bronchodilation values.

Results: FNO stability (∣ΔFNO∣ ≤ 11%) was observed in 19 patients [-2.7(6.7)%] [mean (SD)] (NO = group); ΔFNO > 11% [+37.4(27.7)%] in 20 patients (NO+ group) and ΔFNO < -11% in 22 patients [-31.2(9.8)%] (NO- group). A similar ΔFEV (p = 0.583; [+9.4(9.6)%]) was found in the three groups. In NO = and NO+ groups, neither S nor S changed; in NO- both S [-12.4(27.5)%, p = 0.007] and S [-20.2(20.4)%, p < 0.001] significantly decreased.

Conclusion: Different patterns of FNO response to β -agonists were observed in COPD most likely depending on the extent of the dilation process. A profile of airway obstruction with an extensive β -agonist response down to lung periphery is identified by FNO reduction after acute bronchodilation in 30% of COPD patients. The clinical relevance of this profile requires further investigation.