Effect of particulate matter (PM) and ozone (O 3 ) exposure on heart rate regulation in DBA/2J mice

We aimed to determine the effects PM and O 3 had on heart rate (HR) and heart rate variability (HRV) in DBA/2J (D2) mice. At 12 months of age, mice with implanted ECG telemeters were exposed to Baltimore PM by aspiration and then O 3 by inhalation. In a 3‐wk period, mice received weekly aliquots (50 μl) of PM suspended in PBS at incremental concentrations (2, 5, and 10 μg/μl), and then were exposed to O 3 (~500 ppb) for 3 hrs after each aspiration. Control mice were repeatedly treated with PBS and exposed to room air. A 3‐min ECG was recorded every 15 min for 4 hrs following the exposure sequence. There was a significant (p < 0.05) decline in HR in mice exposed to 2 μg/μl of PM and O 3 relative to controls. This same decline in HR was accompanied by significant increases in HRV (SDNN and rMSSD). The changes in HR and HRV were most significant in the 2 μg/μl concentration. Correlation analysis showed that a lower HR occurred at a given level of rMSSD in PM‐ and O 3 ‐exposed mice compared with controls. These data suggest that exposures to Baltimore PM followed by O 3 in D2 mice leads to significant declines in HR accompanied by increases in HRV. (Support: AG‐21057 and RD‐83241701)