Ambient Air Pollution Significantly Associated With Increases in Emphysema

Long-term ambient air pollutant exposure was significantly associated with increases in percent emphysema, according to a study published in the Journal of American Medical Association.

Researchers evaluated the relationship between long-term exposure to air pollutants and changes in lung images obtained via computed tomography (CT), lung function, and percent emphysema in a cohort of multi-ethnic adults living in US metropolitan areas enrolled in the Multi-Ethnic Study of Atherosclerosis (MESA) Air and Lung Studies. Percent emphysema was defined as the percent of lung pixels < -950 Hounsfield units. Full-lung and cardiac CT images used to calculate percent emphysema were performed at baseline and at follow-up. Spirometry and measurements of forced expiratory volume in 1 second (FEV₁) and forced vital capacity (FVC) were performed to assess lung function at baseline and at follow-up.

Air pollutants of interest were ambient ozone (O₃), fine particulate matter (PM_2.5), oxides of nitrogen, and black carbon. Long-term outdoor air pollution concentration was estimated based on the participant’s home address. Validated spatiotemporal exposure models were developed for each region using the US Environmental Protection Agency Air Quality System. The US metropolitan areas included Winston-Salem, North Carolina; New York, New York; Baltimore, Maryland; St. Paul, Minnesota; Chicago, Illinois; and Los Angeles, California.

Of the 6860 patients who performed baseline CT measurements, 84% completed ≥1 follow-up CT scan, and of the 3636 participants who performed baseline spirometry, 76% performed ≥1 follow-up spirometric lung function assessment (median follow-up time frame of 10 years). At baseline, 46% of participants were lifelong nonsmokers, 38% were white, 47.1% were men, and the mean age was 60 years old. Overall, the baseline measurement for percent emphysema was 3% and had a mean rate of change of 0.58 percentage points (95% CI, 0.38-0.78) over 10 years. Of the 826 participants with airflow obstructions at baseline, the mean decline in FEV₁ was 309 mL (95% CI, 299-319 mL), and in FVC was 331 mL (95% CI, 317-345 mL) over 10 years.

Annual mean concentrations of PM_2.5 and oxides of nitrogen declined during the course of the study, while O₃remained unchanged. Based on CT images, all air pollutants were significantly associated with increases in percent emphysema, O₃ 0.13 per 3 parts per billion (ppb; 95%CI, 0.03-0.24 ppb), PM_2.5 0.11 per 2 μg/m³ (95% CI, 0.03-0.19 μg/m³), oxides of nitrogen 0.06 per 10 ppb (95% CI, 0.01-0.12 ppb), and black carbon 0.10 per 0.2 μg/m³ (95%CI, 0.01-0.18 μg/m³).

Long-term O₃ exposure was significantly associated with an increase of 0.18 percentage points in percent emphysema (95% CI, 0.08-0.28), and oxides of nitrogen were significantly associated with a faster progression of percent emphysema (increase, 0.12 percentage points per 10 ppb; 95% CI, 0.04-0.19). In participants with airflow limitations at baseline, progression of emphysema due to O₃ was greater than in those without airflow limitations (increase of 0.35 percentage points; 95% CI, 0.18-0.51).

With regard to lung function, long-term exposure to O₃ was significantly associated with an 18.15 mL greater decline in FEV₁ (95% CI, 1.59-34.71 mL) and a 40.19 mL greater decline in FVC (95% CI, 17.88-62.49 mL), and a greater decline was associated with participants who smoked or had baseline airflow limitations.

Study limitations study included the inability to assess microenvironments of air pollution, only using the lower two-thirds of lungs to measure percent emphysema, advancements in CT technologies during the course of the study, and the lack of volume correction completed on CT data.

The researchers concluded, “Long-term exposure to ambient air pollutants, especially O₃, was significantly associated with increasing emphysema assessed quantitatively using CT imaging and with worsening lung function.”

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.

Reference

Wang M, Aaron CP, Madrigano J, et al. Association between long-term exposure to ambient air pollution and change in quantitatively assessed emphysema and lung function. JAMA. 2019;322(6):546-556.