Fetal lung growth and structural development occurs in stages, the researchers explained, thus timing of exposure may have differential effects on postnatal disease risk. They assessed the windows of susceptibility to particulate air pollution exposure during pregnancy on childhood asthma onset in a prospective urban birth cohort.

The study included 430 full-term (≥37 weeks gestation at birth) children followed to age 7 years and their mothers. Daily exposure to air pollution from sources including traffic, power plants, and other industrial sources consisting of fine particles in the prenatal period was estimated based on where these mothers lived. These fine particles, which are more likely to be inhaled deep into the lungs, have been linked to the greatest health risk and previous studies have suggested that effects on pregnant women can be transferred to the growing baby.

Children’s physician-diagnosed asthma was ascertained by maternal reports up to age 7 years. The team examined associations between weekly averaged prenatal PM_2.5 levels and children’s asthma using distributed lag models. This modeling framework describes delayed effects between predictors and an outcome and estimates associations at each week while adjusting for exposures at other weeks, assuming that the associations varying smoothly over time during gestation. Effect modification by gender and maternal pre-pregnancy obesity (body mass index [weight divided by height squared] ≥30 kg/m²) was also examined.

The researchers found that exposure to higher levels of fine particles in the second trimester was most strongly associated with increased asthma onset among the children, particularly for those born to non-obese mothers. The effect of maternal obesity, another known risk factor of childhood asthma onset, may be so strong that it was difficult to determine additional effects of air pollution among children born to obese mothers in this setting, the researchers noted.

While we should continue to improve air quality and minimize exposure to pregnant women throughout the entire pregnancy for a host of health reasons, pinpointing the gestational period during which air pollution has the greatest effects on the developing lung may add to our understanding of the mechanisms underlying this relationship.

—Dr. Rosalind Wright, MD MPH, senior investigator from the Department of Pediatrics at Icahn School of Medicine at Mount Sinai

Separately, a study in the American Journal of Respiratory and Critical Care Medicine reported that exposure to high levels of traffic-related air pollution is associated with changes in the right ventricle of the heart that may contribute to the known connection between air pollution exposure and heart disease.

Although the link between traffic-related air pollution and left ventricular hypertrophy, heart failure, and cardiovascular death is established, the effects of traffic-related air pollution on the right ventricle have not been well studied. Using exposure to nitrogen dioxide as a surrogate for exposure to traffic-related air pollution, we were able to demonstrate for the first time that higher levels of exposure were associated with greater right ventricular mass and larger right ventricular end-diastolic volume. Greater right ventricular mass is also associated with increased risk for heart failure and cardiovascular death.

—lead author Peter Leary, MD, MS, of the University of Washington Medical Center in Seattle

The study involved 3,896 participants in the Multi-Ethnic Study of Atherosclerosis who were free of clinical cardiovascular disease and who underwent cardiac magnetic resonance imaging (MRI). Using estimated exposure to outdoor oxides of nitrogen at the homes of participants over the year preceding MRI, the authors found that increased exposure to nitrogen dioxide was associated with an approximately 1.0 g (5%) increase in right ventricular mass and a 4.1 mL (3%) increase in right ventricular end-diastolic volume.

These relationships remained after accounting for differences among participants in cardiovascular risk factors, left ventricular mass and volume, markers of inflammation, lung disease and socioeconomic status.

The morphologic changes in the right ventricle of the heart that we found with increased exposure to nitrogen dioxide add to the body of evidence supporting a connection between traffic-related air pollution and cardiovascular disease. The many adverse effects of air pollution on human health support continued efforts to reduce this burden.

—Dr. Leary

Resources

• Y.-H.M. Chiu, B.A. Coull, I. Kloog, J. Schwartz, H.-H.L. Hsu, R.O. Wright, R.J. Wright (2014) “Identifying Prenatal Windows Of Susceptibility To Particulate Air Pollution On Childhood Asthma Onset In A Prospective Urban Birth Cohort,” B15. Air Pollution In Women, Children, And Elderly: Risk Susceptibility And Reduction. A2441-A2441

• Peter J. Leary, Joel D. Kaufman, R. Graham Barr, David A. Bluemke, Cynthia L. Curl, Catherine L. Hough, Joao A. Lima, Adam A. Szpiro, Victor C. Van Hee, Steven M. Kawut (2014) “Traffic-related Air Pollution and the Right Ventricle. The Multi-ethnic Study of Atherosclerosis,” American Journal of Respiratory and Critical Care Medicine Vol. 189: 1093-1100, doi: 10.1164/rccm.201312-2298OC