Single breath nitrogen test as predictor of lung function decline and COPD over an 8-year follow-up.

ABSTRACT

BACKGROUND: The single breath nitrogen (SBN2) test was proposed for early detection of "small airways disease" in the seventies. Few longitudinal studies have subsequently evaluated the relationships between SBN2 test measurements and lung function decline or COPD incidence. AIM: This study evaluates whether SBN2 test abnormalities may be significant predictors of lung function decline and COPD incidence over an 8-year follow-up. STUDY DESIGN AND METHODS: In this longitudinal study, 907 adults (20+ years old; 56% males) from the prospective Po River Delta epidemiological study underwent SBN2 test at baseline and spirometry testing at both baseline and follow-up 8-year apart. Multinomial and multiple regression models were used to assess associations of SBN2 indexes and rates of FEV1 decline or risk of COPD incidence over time, after adjusting for sex, height and baseline age, FEV1 and smoking status. COPD was defined according to either GOLD or ATS-ERS criteria. RESULTS: Among SBN2 indexes, only the slope of alveolar plateau (N2-slope) was significantly associated with rates of FEV1 decline (7.93 mL/year for a one-unit change in N2-slope, p<0.0001), and with an increased risk of developing COPD as defined by GOLD (RR 1.81, 95%CI 1.29-2.52, mild; RR 2.78, 95%CI 1.70-4.53, moderate or severe obstruction) and ATS-ERS criteria (RR 1.62, 95%CI 1.14-2.29, mild; RR 3.40, 95%CI 1.72-6.73, moderate or severe obstruction). CONCLUSION: In this population-based study, N2-slope from SBN2 test is a significant predictor of lung function decline and COPD incidence over an 8-year follow-up, confirming the role of the "small airways disease" in the natural history of COPD.