October 30, 2019
3 min read

Prenatal air pollution exposure affects cardiac vagal tone

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Whitney J. Cowell
Rosalind J. Wright

Infants exposed to airborne fine particulate matter appeared to have a disruption in cardiac vagal tone, researchers reported.

Exposed infants experienced changes in the parasympathetic nervous system as indexed by respiration-corrected respiratory sinus arrhythmia, a measure of heart rate variability, according to the researchers.

According to findings published in Environmental Health Perspectives, a 1-unit increase in exposure to particulate matter (in micrograms per cubic meter) during pregnancy was associated with a 3.53% decrease in baseline respiration-corrected respiratory sinus arrhythmia in infants 6 months of age (95% CI, −6.96 to 0.02).

Pollution and heart rate

“In addition to adult lifestyle factors, such as obesity and smoking, there is growing evidence that certain environmental factors interacting with an individual’s underlying genetic predisposition before birth may be just as important in ‘programming’ future heart health over one’s lifetime,” Whitney J. Cowell, MPH, PhD, postdoctoral fellow in environmental pediatrics and Rosalind J. Wright, MD, MPH, Horace W. Goldsmith Professor of Children’s Health Research in the Institute for Exposomic Research at Icahn School of Medicine at Mount Sinai, told Healio. “Our study provides new data showing that the developing autonomic nervous system may be sensitive to the mother’s particulate air pollution exposure during pregnancy. In the urban environment, the major source of particulate air pollution is from traffic and related exhaust. We found that when mothers were exposed to higher levels of particulate air pollution during pregnancy, their infants were more likely to have lower heart rate variability at rest and a blunted cardiac response when facing a stress challenge.”

Researchers observed that elevated exposure to particulate matter was associated with reduced parasympathetic nervous system withdrawal during stress and reduced activation during recovery, but determined the associations were not statistically significant.

“While we cannot interpret the magnitude of change that we observed in relation to air pollution exposure in terms of disease development, the observed pattern of heart rate response in these 6-month-old infants is a harbinger of future disorders such as high blood pressure and other cardiovascular disorders if persistent as the child continues to develop,” Cowell and Wright said in an interview. “Limiting exposure to particulate air pollution, to the extent it is feasible, and engaging in healthy, potentially buffering behaviors, such as consuming a healthy diet high in antioxidants, are important factors for pregnant mothers to be aware of.”

Moreover, prior studies have found little evidence that particulate matter passes through the placental barrier, suggesting that other mechanisms including altered placental gene expression, increased oxidative stress and changes to maternal immune system status could play a significant role in prenatal exposure, according to the researchers.

In addition, researchers did not observe any significant associations between particulate matter effects and infant sex.

‘Like double jeopardy’

“Overlapping research shows that a developing fetus is particularly vulnerable to air pollutants like particulate matter because their organ systems and related processes, including processes controlling the heart rate response to stress, are developing rapidly,” Cowell said in an interview. “Also, their ability to protect themselves from chemicals and pollutants has not had time to mature so they cannot detoxify these chemical exposures like adults can. Thus, it is like double jeopardy during this early window of development and we need to better understand mechanisms so that we can protect the baby by minimizing exposure in the mother.”

Researchers analyzed 237 maternal–infant pairs in a Boston-based birth cohort with infants aged 6 months, using continuous ECG monitoring during the Repeated Still-Face Paradigm. According to the study, this experimental protocol was designed to elicit autonomic reactivity in response to maternal interaction and disengagement.

“The levels of air pollution we observed in relation to the changes in infant heart rate variability are typical of U.S. urban environments and below U.S. EPA allowable levels. We do not consider these levels to be heavy, but rather expect the levels to which our study participants were exposed to reflect exposure of much of the U.S. population,” Cowell told Healio. “Clinicians and public health providers can advise pregnant women to check the Air Quality Index in their area and avoid being outside when it is high. While clinicians should encourage exercise in pregnant women, there are some things that can be advised in this regard as well. Women can be instructed to avoid exercising outside when the Air Quality Index is high and to never exercise near major roadways and where traffic tends to be more dense.” – by Scott Buzby

Disclosures: The authors report no relevant financial disclosures.