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The single breath nitrogen test and mortality - A 38 years follow up

Journal article
Authors Jan Olofson
Björn Bake
Bengt Bergman
K. Svardsudd
Published in Respiratory Medicine
Volume 112
Pages 75-80
ISSN 0954-6111
Publication year 2016
Published at Institute of Medicine
Pages 75-80
Language en
Keywords Mortality, Single breath nitrogen test, Spirometry, Smoking, Small airways function, Epidemiology, lung-function, pulmonary-function, small airways, respiratory symptoms, alveolar plateau, closing volume, population, disease, smoking, asthma, Cardiovascular System & Cardiology, Respiratory System
Subject categories Clinical Medicine


Background: Spirometry data predict mortality, but are less sensitive to detect dysfunction in small airways as compared to the slope of phase III (the N-2 slope) of the single breath nitrogen test. The association between the N-2 slope and mortality has been studied with conflicting results. In the present study the prognostic importance of the N-2 slope was tested taking spirometry variables into account. Methods: A systematic general population sample of 595 middle-aged men had a baseline investigation with lung function tests including spirometry and the N-2 slope. Age, smoking, and anthropometry variables were registered. The cohort was followed up regarding survival for 38 years. Results: The sample was subdivided by tertiles of the N-2 slope. A proportional hazards regression analysis was performed for each group of covariates: anthropometric, smoking variables, and spirometry variables, after accounting for age. Covariates with significant impact on mortality and the highest chi-square levels were smoking habit score and forced expired volume in 1 s corrected for height. These variables, in addition to age and the N-2 tertiles were entered into a final proportional hazards regression analysis. In this multivariate model, mortality was significantly related to age (p < .0001), smoking habit score (p < .0001) and the N-2 tertiles (p = .0004), but not to FEV1 when N-2 slope was allowed for in the model. Conclusions: Dysfunction in small airways as measured by the N-2 slope is significantly associated with overall mortality in middle-aged men, and outrivals spirometry as a predictor in multivariate analysis.

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