In patients with pre-existing heart or lung disease, being exposed to high levels of traffic-related air pollutants is associated with reduced heart rate variability (HRV) — a risk factor for sudden cardiac death, reports a study in the July Journal of Occupational and Environmental Medicine, official publication of the American College of Occupational and Environmental Medicine (ACOEM), according to a press release.

Using portable monitors to measure personal exposure to air pollution allowed the authors to show associations missed by previous studies based on ambient levels of air pollution, according to the study by Helen H. Suh, ScD, and Antonella Zanobetti, PhD, of Harvard School of Public Health.

The study included 30 Atlanta-area residents with lung disease (chronic obstructive pulmonary disease) or heart disease (previous myocardial infarction). Relationships between pollution exposure and HRV — which reflects weakened control of the heart by the autonomic nervous system — were assessed.

Ambient levels of air pollutants in the areas where the patients lived were unrelated to HRV. However, when the patients wore 24-hour monitoring devices, their personal exposure (levels of traffic-related air pollutants – specifically, elemental carbon and nitrogen dioxide) were significantly related to reduced HRV.

This suggests that personal-level exposure data may be necessary to show the relationship between pollution levels and changes in HRV. A previous study in Boston found that HRV was related to ambient pollutant levels, but the participants in those studies lived close to the pollution-monitoring stations.

In contrast, the Atlanta patients were spread out over a larger area, with differing population densities, distances from major roads, etc. The results add to recent evidence that short-term, personal exposure to traffic-related pollution is linked to decreased HRV and increased cardiac risk.

The link effects of traffic-related pollutants and HRV may also help to explain previous studies showing an increased risk of heart attack in the hour immediately after periods stuck in traffic, the researchers suggest. However, other factors would have to be taken into account — including the high stress levels from being stuck in traffic.