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Night Heart Rate Variability and Particulate Exposures among Boilermaker Construction Workers
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Details:
  • Description:
    Background

    Although studies have documented the association between heart rate variability (HRV) and ambient particulate exposures, the association between HRV, especially at night, and metal-rich, occupational particulate exposures remains unclear.

    Objective

    Our goal in this study was to investigate the association between long-duration HRV, including nighttime HRV, and occupational PM2.5 exposures.

    Methods

    We used 24-hr ambulatory electrocardiograms (ECGs) to monitor 36 male boilermaker welders (mean age of 41 years) over a workday and nonworkday. ECGs were analyzed for HRV in the time domain; rMSSD (square root of the mean squared differences of successive intervals), SDNN (SD of normal-to-normal intervals over entire recording), and SDNNi (SDNN for all 5-min segments) were summarized over 24-hr, day (0730–2130 hours), and night (0000–0700 hours) periods. PM2.5 (particulate matter with an aerodynamic diameter ≤ 2.5 μm) exposures were monitored over the workday, and 8-hr time-weighted average concentrations were calculated. We used linear regression to assess the associations between HRV and workday particulate exposures. Matched measurements from a nonworkday were used to control for individual cardiac risk factors.

    Results

    Mean (± SD) PM2.5 exposure was 0.73 ± 0.50 mg/m3 and ranged from 0.04 to 2.70 mg/m3. We observed a consistent inverse exposure–response relationship, with a decrease in all HRV measures with increased PM2.5 exposure. However, the decrease was most pronounced at night, where a 1-mg/m3 increase in PM2.5 was associated with a change of −8.32 [95% confidence interval (CI), −16.29 to −0.35] msec nighttime rMSSD, −14.77 (95% CI, −31.52 to 1.97) msec nighttime SDNN, and −8.37 (95% CI, −17.93 to 1.20) msec nighttime SDNNi, after adjusting for nonworking nighttime HRV, age, and smoking.

    Conclusion

    Metal-rich particulate exposures were associated with decreased long-duration HRV, especially at night. Further research is needed to elucidate which particulate metal constituent is responsible for decreased HRV.

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  • Funding:
    ES00002/ES/NIEHS NIH HHS/United States
    ES009860/ES/NIEHS NIH HHS/United States
    T42 OH008416/OH/NIOSH CDC HHS/United States
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