Role of alveolar nitric oxide in gastroesophageal reflux-associated cough: prospective observational study.

BACKGROUND

Fractional exhaled nitric oxide (FeNO) measured at multiple exhalation flow rates can be used as a biomarker to differentiate central and peripheral airway inflammation. However, the role of alveolar nitric oxide (CaNO) indicating peripheral airway inflammation remains unclear in gastroesophageal reflux-associated cough (GERC).

OBJECTIVES

We aimed to characterize the changes in alveolar nitric oxide (CaNO) and determine its clinical implication in GERC.

DESIGN

This is a single-center prospective observational study.

METHODS

FeNOs at exhalation flow rates of 50 and 200 ml/s were measured in 102 patients with GERC and 134 patients with other causes of chronic cough (non-GERC). CaNO was calculated based on a two-compartment model and the factors associated with CaNO were analyzed. The effect of anti-reflux therapy on CaNO was examined in 26 GERC patients with elevated CaNO.

RESULTS

CaNO was significantly elevated in GERC compared with that in non-GERC (4.6 ± 4.4 ppb 2.8 ± 2.3 ppb,  < 0.001). GERC patients with high CaNO (>5 ppb) had more proximal reflux events (24 ± 15 9 ± 9 episodes,  = 0.001) and a higher level of pepsin (984.8 ± 492.5 634.5 ± 626.4 pg/ml,  = 0.002) in sputum supernatant than those with normal CaNO. More GERC patients with high CaNO required intensified anti-reflux therapy (χ = 3.963,  = 0.046), as predicted by a sensitivity of 41.7% and specificity of 83.3%. Cough relief paralleled a significant improvement in CaNO (8.3 ± 3.0 4.8 ± 2.6 ppb,  < 0.001).

CONCLUSION

Peripheral airway inflammation can be assessed by CaNO measurement in GERC. High CaNO indicates potential micro-aspiration and may predict a necessity for intensified anti-reflux therapy.