Alveolar nitric oxide concentration reflects peripheral airway obstruction in stable asthma

BACKGROUND AND OBJECTIVE: Increased fraction of exhaled nitric oxide (FeNO) has been shown to reflect airway inflammation in asthma. Central airway NO flux (J'awNO; nL/s) and peripheral airway/alveolar NO concentration (CANO; ppb) can be calculated separately. CANO has been reported to reflect small airway inflammation. The aim of the present study is to correlate CANO levels with clinical and physiological parameters in patients with stable asthma. METHODS: Seventy-three well-controlled asthmatics (mean age 61) were enrolled. Measurement of FeNO (at 50, 100, 150 and 200 mL/s) and pulmonary function test were performed. J'awNO(TMAD) and CANO(TMAD) were calculated and corrected by the trumpet shape of the airway tree and axial back-diffusion (TMAD). RESULTS: CANO(TMAD) was significantly correlated with forced expiratory flow between 25-75% of the forced vital capacity (FVC) (FEF(25 -75)), FEF(25 -75) percentage of the predicted value (%pred), forced expiratory flow at 50% of the FVC (FEF(50)) and FEF(50) %pred (R = -0.39 P = 0.002, R = -0.29 P = 0.02, R = -0.39 P = 0.001, R = -0.29 P = 0.02, respectively). CANO(TMAD) was positively correlated with age (R = -0.45 P = 0.0002) and weakly correlated with duration of asthma (R = -0.27 P = 0.03). Forced expiratory volume in 1 s/FVC was negatively correlated with CANO(TMAD), J'awNO(TMAD) and FeNO 50 mL/s. Among these, correlation between forced expiratory volume in 1 s/FVC and FeNO 50 mL/s was the strongest (R = -0.34 P = 0.004). CONCLUSIONS: CANO(TMAD) may be a more specific marker of peripheral airway obstruction than FeNO and J'awNO(TMAD) in stable asthma.