Person:

Cavallari, Jennifer M

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.

Background: Increasing evidence suggests that obesity may impart greater susceptibility to adverse effects of air pollution. Particulate matter, especially PM({2.5}) (particulate matter with aero-dynamic diameter ≤2.5 μm), is associated with increased cardiac events and reduction of heart rate variability (HRV).Objectives Our goal was to investigate whether particle-mediated autonomic modulation is aggravated in obese individuals.Methods We examined PM({2.5})-mediated acute effects on HRV and heart rate (HR) using 10 24-hr and 13 48-hr ambulatory electrocardiogram recordings collected from 18 boilermakers (39.5 ± 9.1 years of age) exposed to high levels of metal particulates. Average HR and 5-min HRV [SDNN: standard deviation of normal-to-normal intervals (NN); rMSSD: square-root of mean squared-differences of successive NN intervals; HF: high-frequency power 0.15–0.4 Hz] and personal PM({2.5}) exposures were continuously monitored. Subjects with body mass index ≥ 30 kg/m(^2) were classified as obese. Mixed-effect models were used for statistical analyses. Results: Half (50%) of the study subjects were obese. After adjustment for confounders, each 1-mg/m(^3) increase in 4-hr moving average PM({2.5}) was associated with HR increase of 5.9 bpm [95% confidence interval (CI), 4.2 to 7.7] and with 5-min HRV reduction by 6.5% (95% CI, 1.9 to 11.3%) for SDNN, 1.7% (95% CI, –4.9 to 8.4%) for rMSSD, and 8.8% (95% CI, –3.8 to 21.3%) for HF. Obese individuals had greater PM({2.5})-mediated HRV reductions (2- to 3-fold differences) than nonobese individuals, and had more PM({2.5})-mediated HR increases (9-bpm vs. 4-bpm increase in HR for each 1-mg/m(^3) increase in PM(_{2.5}); p < 0.001). Conclusions: Our study revealed greater autonomic cardiac responses to metal particulates in obese workers, supporting the hypothesis that obesity may impart greater susceptibility to acute cardiovascular effects of fine particles.