SATURDAY, July 17 (HealthDay News) -- Exposure to high levels of traffic air pollution among people with heart or lung disease is associated with reduced heart rate variability (HRV), a risk factor for sudden cardiac death, finds a new study.

The study included 30 Atlanta-area residents with lung disease (chronic obstructive pulmonary disease) or heart disease (previous heart attack).

The Harvard School of Public Health researchers found no link between reduced heart rate variability and ambient levels of air pollutants in the areas where the participants lived. However, 24-hour portable monitoring devices worn by the patients showed a significant association between reduced HRV and personal exposure to traffic-related air pollutants, including elemental carbon and nitrogen dioxide.

A drop in heart rate variability -- a measure of the heart's ability to adapt to changes in the environment -- indicates weakened control of the heart by the autonomic nervous system.

The findings add to recent evidence of a link between short-term, personal exposure to traffic-related pollution and reduced HRV. They may also help to explain why some previous studies have found that people have an increased risk of heart attack in the hour immediately after being stuck in traffic, the Harvard researchers said in a university news release.

The study appears in the July issue of the Journal of Occupational and Environmental Medicine.

More information

The American Heart Association has more about sudden cardiac death.