Even exposure to low levels nitrogen dioxide (NO2), an indicator of residential outdoor air pollution, is associated with reduced lung diffusing capacity (DLco) in an Australian population, new research shows.
The study, comprising a subpopulation of more than 1,200 middle-aged adults from the Tasmanian Longitudinal Health Study cohort, extends previous spirometric findings of lung function and the impact of traffic related air pollution.
The researchers found exposure to NO2 was associated with reduced DLco in an exposure-response manner and independent of the participants’ smoking history (p <0.001).
More modest but still significant associations were seen between NO2 concentrations and decreased total lung capacity (TLC) and functional residual capacity (FRC) (p = 0.032 and p = 0.022 respectively).
The study, published in AJRCCM, also found living closer to a main road was associated with lower post-bronchodilator FEV1/FVC levels but only for smokers with less than a 10-pack-year history.
Conversely, distance from main road (DMR)-related reductions in TLC and FRC were seen only for never smokers.
“While the NO2-related increase in RV [residual volume] suggested an obstructive effect with air trapping in heavier smokers, the static lung volumes for nonsmokers residing within 200m of a major road support the co-presence of a restrictive lung process that might potentially influence the FEV1/FVC ratio,” the study said.
The research also noted that the adverse exposure-response influence of NO2 on lung diffusing capacity was at ambient levels well below the National Environment Protection Measure of 30ppb.
“This finding, combined with other features of a mixed obstructive/restrictive lung function pattern, supports the possibility of lung parenchymal damage from interstitial inflammatory, fibrotic and/or emphysematous processes.”
Lead researcher Dr Jennifer Perret, from the Allergy and Lung Health Unit at the University of Melbourne, said in a statement that the associations were complex.
“Specifically, we have uncovered a link between higher concentrations of nitrogen dioxide and lower ability of the lungs to transfer carbon monoxide gas regardless of smoking history; documented airflow obstruction to be unexpectedly more pronounced in smokers without an extensive history; and, discovered modestly lower lung volumes for never-smokers who lived within 200m of a major road.”
“These novel findings are consistent with the presence of both airway and lung tissue processes and were detected in the relatively low concentrations of air pollutants of Australia.”
“While the observed lung function impairments were insufficient to cause COPD on their own and may be partly reversible with lesser exposure, our findings add weight to measures to reduce traffic-related air pollution as much as possible.”