Ambient Air Pollution Concentration Drives Chronic Respiratory Disease

Joel D. Kaufman, MD, MPH

A new US-based cohort analysis found a significant association between ambient air pollution and increased rates of emphysema.

The study adds to the concern surrounding increasing long-term air pollution exposure rates and its influence on chronic lower respiratory disease—already the third leading cause of death worldwide.

A team of investigators—led by Joel D. Kaufman, MD, MPH, of the School of Public Health at University of Washington, and R. Graham Barr, MD, DrPH, of the Department of Medicine at Columbia University Medical Center—sought to better understand the association between ambient air pollution exposure and respiratory morbidity and mortality. They noted previous efforts have mostly focused on short-term effects, with less emphasis on disease progression.

“No longitudinal studies of air pollution and emphysema progression on CT scan, to our knowledge, have been reported,” they wrote.

The team conducted their retrospective cohort using data from the Multi-Ethnic Study of Atherosclerosis (MESA), a clinical cardiovascular disease study which recruited patients aged 45-84 years old from 6 US metropolitan areas from 2000-2002—as well as the MESA Air Pollution Study, which recruited similarly aged patients from 2005-2017.

All MESA participants with valid air pollutant exposure estimates, outcomes, and covariates were included for the analysis. In total, 7071 adults were recruited.

Investigators assessed for residence-specific concentration estimates of air pollutant, including O₃, PM_2.5, NO_x, and black carbon. Their main outcome was percent emphysema, as defined by the percent of lung pixels less than -950 Hounsfield units.

Patients were assessed for percent emphysema up to 5 times via cardia CT scan from 2000-2007, and equivalent regions on lung CT scans from 2010-2018. Patients were given up to 3 spirometry tests from 2004-2018.

The mean patient age was 60 years at the time of recruitment, and 47.1% (n= 3330) were men. In the year of their baseline examinations, 5780 were assigned outdoor residential air pollution concentrations, and during the follow-up period had at least 1 follow-up CT scan. Just 2772 had at least 1 follow-up spirometric assessment over a period of 10 years.

Investigators found that median percent emphysema was 3% at baseline, then increased a mean 0.58 percentage points per 10 years. Mean ambient concentrations of PM_2.5 and NO_x decreased substantially during follow-up. Concentrations of each of the observed ambient pollutant estimates were significantly associated with increases in percent emphysema per 10 years.

Ambient O₃ concentrations were significantly associated with greater patient decline in forced expiratory volume in 1 second (FEV₁) per 10 years at both baseline and follow-up.

Though all 4 observed air pollutants have been associated throughout previous trials to respiratory events, few studies have found a longitudinal association between O₃, PM_2.5, and NO_x and lung function decline in older adults.

“To our knowledge, this is the first longitudinal study to assess the association between long-term exposure to air pollutants and progression of percent emphysema on CT in a large, community-based multiethnic cohort,” they wrote.

That said, Kaufman, Barr and colleagues observed several limitations—the first being that outdoor air pollution concentrations may not fully reflect the air pollution exposure and dose in each individual and their microenvironments.

“Outdoor concentrations do not explain all variation in indoor concentrations, and most individuals spend the majority of their time indoors,” they noted.

But becomes percent emphysema has been related to respiratory symptoms, hospitalizations, and mortality among individuals who may or may not suffer from airflow obstruction, these community-based findings are nonetheless novel indications that air pollution is associated with worsened lung health.

The study, “Association Between Long-term Exposure to Ambient Air Pollution and Change in Quantitatively Assessed Emphysema and Lung Function,” was published online in JAMA.