Association Between Long-term Exposure to Ambient Air Pollution and Change in Quantitatively Assessed Emphysema and Lung Function

Importance

While air pollutants at historical levels have been associated with cardiovascular and respiratory diseases, it is not known whether exposure to contemporary air pollutant concentrations is associated with progression of emphysema.

Objective

To assess the longitudinal association of ambient ozone (O₃), fine particulate matter (PM_2.5), oxides of nitrogen (NO_x), and black carbon exposure with change in percent emphysema assessed via computed tomographic (CT) imaging and lung function.

Design, Setting, and Participants

This cohort study included participants from the Multi-Ethnic Study of Atherosclerosis (MESA) Air and Lung Studies conducted in 6 metropolitan regions of the United States, which included 6814 adults aged 45 to 84 years recruited between July 2000 and August 2002, and an additional 257 participants recruited from February 2005 to May 2007, with follow-up through November 2018.

Exposures

Residence-specific air pollutant concentrations (O₃, PM_2.5, NO_x, and black carbon) were estimated by validated spatiotemporal models incorporating cohort-specific monitoring, determined from 1999 through the end of follow-up.

Main Outcomes and Measures

Percent emphysema, defined as the percent of lung pixels less than −950 Hounsfield units, was assessed up to 5 times per participant via cardiac CT scan (2000-2007) and equivalent regions on lung CT scans (2010-2018). Spirometry was performed up to 3 times per participant (2004-2018).

Results

Among 7071 study participants (mean [range] age at recruitment, 60 [45-84] years; 3330 [47.1%] were men), 5780 were assigned outdoor residential air pollution concentrations in the year of their baseline examination and during the follow-up period and had at least 1 follow-up CT scan, and 2772 had at least 1 follow-up spirometric assessment, over a median of 10 years. Median percent emphysema was 3% at baseline and increased a mean of 0.58 percentage points per 10 years. Mean ambient concentrations of PM_2.5and NO_x, but not O₃, decreased substantially during follow-up. Ambient concentrations of O₃, PM_2.5, NO_x, and black carbon at study baseline were significantly associated with greater increases in percent emphysema per 10 years (O₃: 0.13 per 3 parts per billion [95% CI, 0.03-0.24]; PM_2.5: 0.11 per 2 μg/m³[95% CI, 0.03-0.19]; NO_x: 0.06 per 10 parts per billion [95% CI, 0.01-0.12]; black carbon: 0.10 per 0.2 μg/m³[95% CI, 0.01-0.18]). Ambient O₃and NO_xconcentrations, but not PM_2.5concentrations, during follow-up were also significantly associated with greater increases in percent emphysema. Ambient O₃concentrations, but not other pollutants, at baseline and during follow-up were significantly associated with a greater decline in forced expiratory volume in 1 second per 10 years (baseline: 13.41 mL per 3 parts per billion [95% CI, 0.7-26.1]; follow-up: 18.15 mL per 3 parts per billion [95% CI, 1.59-34.71]).

Conclusions and Relevance

In this cohort study conducted between 2000 and 2018 in 6 US metropolitan regions, long-term exposure to ambient air pollutants was significantly associated with increasing emphysema assessed quantitatively using CT imaging and lung function.