Ambient air pollution alters heart rate regulation in aged mice

Abstract

Context: Heart rate alterations associated with exposure to particulate matter (PM) and gaseous pollutants have been observed in epidemiological studies and animal experiments. Nevertheless, the time-lag of these associations is still unclear.

Objective: Determine the association at different time-lags between the complex mixture of ambient concentrations of PM, carbon monoxide (CO), and nitrogen dioxide (NO₂), and markers of cardiac function in a model of aged mice.

Materials and methods: AKR/J inbred mice were exposed to ambient air, 6 h daily for 40 weekdays. During this period, the animals’ electrocardiogram (ECG), deep body temperature (Tdb), and body weight (BW) were registered, and concentrations of PM, CO, NO₂, as well as air temperature and relative humidity (RH) were measured. Data analysis included random effects models with lagged covariate methods.

Results: CO was significantly associated with declines in heart rate (HR) and heart rate variability (HRV), PM was significantly associated with declines in HRV and BW, and NO₂ was significantly associated with declines in HR. Some significant associations occurred in the same day (PM and HRV, PM and BW, CO and HR), whereas others were delayed by 1 to 3 days (CO and HR, CO and HRV, NO₂ and HR, PM and HRV).

Discussion and conclusion: Finding significant declines in heart function in aged mice associated with the combined effects of air pollutants at ambient concentrations and at different time-lags is of great importance to public health. These results further implicate the potential short term and delayed effects of air pollution on HR alterations.

Keywords::

• Particulate matter
• gaseous pollutants
• heart rate variability
• longitudinal data analysis
• aging

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Acknowledgements

The authors would like to thank Sushant Kapoor, Vikas Misra, Eric Abston, Jana Mihalic, Julie Richman, Richard Rabold, Vikram Nichani, Alexis Bierman, and Mathew Beatty for their contributions to this project.

Declaration of interest

This work was supported by the National Institute of Aging (AG-21057), the National Institute of Environmental Health Sciences (NIEHS) (PO1 ES 009606) (P50 ES 015903), US Environmental Protection Agency (R-32139), and the Johns Hopkins NIEHS Center in Urban Environmental Health (P30 ES 03819). Although the research described in this article has been funded wholly or in part by the United States Environmental Protection Agency through grant/cooperative agreement RD-83241701 to Dr. Jonathan Samet, it has not been subjected to the Agency’s required peer and policy review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred.