From the Journals

Nitrogen test predicts lung function decline



The slope of the alveolar plateau on the single-breath nitrogen test (SBN2) was a significant predictor of lung function decline and of chronic obstructive pulmonary disease (COPD), based on data from 907 adults.

In recent years, interest in small airways disease (SAD) has renewed, with research suggesting a link between SAD pathology and COPD progression, wrote Francesco Pistelli, MD, of the University of Pisa (Italy) and colleagues.

The SBN2 has been used to detect early SAD, but few studies have examined the relationship between SBN2 measures and lung function decline over time, they said.

In a study published in Pulmonology , the researchers reviewed data from adults aged 20 years and older who were enrolled in the Po River Delta prospective study in Italy. The study population included 907 individuals, with a mean age of 37.4 years; 56% were male.

The primary outcome was a change in lung function and incidence of COPD during an 8-year follow-up period.

COPD was defined using either the Global Initiative for Chronic Obstructive Lung Disease (GOLD) or ATS European Respiratory Society (ATS-ERS) criteria.

In a multinomial regression model, one SBN2 index, the slope of alveolar plateau (N2-slope) was significantly associated with rates of forced expiratory volume in 1 second (FEV1) decline, with a decrease of 7.93 mL/year for each one-unit change in N2-slope.

The N2-slope also was significantly associated with an increased risk of COPD, with a relative risk of 1.81 for mild obstruction and 2.78 for severe obstruction based on GOLD criteria. The association was similar for COPD based on the ATS-ERS criteria, with a relative risk of 1.62 for mild obstruction and 3.40 for moderate to severe obstruction.

Age was associated with an increased COPD risk using the GOLD criteria, but not the ATS-ERS criteria; neither sex nor current or former smoking were associated with increased COPD risk for either measure.

The results are consistent with some previous longitudinal studies, but not others, possibly because of differences in sampling procedures, test techniques, or statistical approaches, the researchers wrote in their discussion.

The study findings were limited by several factors including incomplete data on closing capacity and vital capacity, and by the lack of bronchodilator for performing baseline spirometry, since bronchodilator testing was not recommended at the time of the study, the researchers noted.

However, the results support the role of SAD as a contributor to COPD, and the potential value of the SBN2 test, they said. “Large prospective studies are needed to evaluate whether new proposed functional or imaging tests that measure small airways impairment may be useful in the early detection of COPD,” they noted. In the meantime, “pulmonologists could rediscover an ‘old’ test, which could provide important information on their patients at risk for developing COPD,” they concluded.

The study was supported in part by the National Research Council, Targeted Project and the Italian Electric Power Authority (ENEL). The researchers had no financial conflicts to disclose.

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