Obesity is a modifier of autonomic cardiac responses to fine metal particulates.

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 microm), 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.