Prenatal Exposure to [Formula: see text] and Cardiac Vagal Tone during Infancy: Findings from a Multiethnic Birth Cohort

BACKGROUND: The autonomic nervous system plays a key role in maintaining homeostasis and responding to external stimuli. In adults, exposure to fine particulate matter ([Formula: see text]) has been associated with reduced heart rate variability (HRV), an indicator of cardiac autonomic control. OBJECTIVES: Our goal was to investigate the associations of exposure to fine particulate matter ([Formula: see text]) with HRV as an indicator of cardiac autonomic control during early development. METHODS: We studied 237 maternal–infant pairs in a Boston-based birth cohort. We estimated daily residential [Formula: see text] using satellite data in combination with land-use regression predictors. In infants at 6 months of age, we measured parasympathetic nervous system (PNS) activity using continuous electrocardiogram monitoring during the Repeated Still-Face Paradigm, an experimental protocol designed to elicit autonomic reactivity in response to maternal interaction and disengagement. We used multivariable linear regression to examine average [Formula: see text] exposure across pregnancy in relation to PNS withdrawal and activation, indexed by changes in respiration-corrected respiratory sinus arrhythmia ([Formula: see text])—an established metric of HRV that reflects cardiac vagal tone. We examined interactions with infant sex using cross-product terms. RESULTS: In adjusted models we found that a 1-unit increase in [Formula: see text] (in micrograms per cubic meter) was associated with a 3.53% decrease in baseline [Formula: see text] (95% CI: [Formula: see text] , 0.02). In models examining [Formula: see text] change between episodes, higher [Formula: see text] was generally associated with reduced PNS withdrawal during stress and reduced PNS activation during recovery; however, these associations were not statistically significant. We did not observe a significant interaction between [Formula: see text] and sex. DISCUSSION: Prenatal exposure to [Formula: see text] may disrupt cardiac vagal tone during infancy. Future research is needed to replicate these preliminary findings. https://doi.org/10.1289/EHP4434