March 20, 2000 (Eugene, Ore.) -- Ozone and fine particles of matter in the air appear to lower the human heart's ability to vary its speed, resulting in increased heart attacks and heart-related deaths, according to researchers from Harvard Medical School in Boston.
"The heart's ability to vary its speed is valuable because it lets us respond quickly to changing requirements," says Ronald White, assistant vice president for national policy of the American Lung Association. "People intuitively understand that air pollution can affect the lungs, but now we're finding that it also affects other organs, especially the heart."
Many studies have previously found an association between episodes of air pollution and increases in both heart attacks and deaths due to heart-related causes. "The unanswered question has been, what is the mechanism behind this association?" says Diane Gold, MD, MPH, co-author of the study. Gold is an assistant professor of medicine at Harvard Medical School's Brigham and Women's Hospital in Boston.
Michael Lauer, MD, says, "It's not easy to measure exactly how much air pollution any particular person gets, because the exposure is diluted. Cigarette smoking in comparison is a direct exposure, like being hit with a jackhammer; air pollution is similar to being surrounded by a fishing net." Lauer is director of the exercise laboratory and staff cardiologist at the Cleveland Clinic Foundation.
The Harvard researchers asked 21 people to come in for a series of half-hour observation periods. They wore a device permitting continuous monitoring of their heart rate and other key measures while going through five minutes of rest, then standing, exercise, and slow breathing. This allowed researchers to see how quickly their hearts responded to changes in activities.
Researchers found that on days with high levels of fine particles and ozone, the subjects had reduced heart rate variability. Other pollutants such as carbon dioxide were not associated with declines in heart rate variability.
The fine particles that seem to be one source of the problem are extremely small, less than 2.5 microns in diameter. (For comparison, a human hair is about 75 microns in diameter.) According to White, the major sources of these particles are diesel trucks and buses, off-road equipment such as construction equipment, and smokestack gases that may travel from hundreds of miles away.
"This is one of a series of studies looking at heart rate variability, and probably the most comprehensive one that's been published to date," says Daniel Greenbaum, president of the Health Effects Institute in Boston. "One key question this study doesn't fully answer is whether this should concern those who do not have preexisting heart or lung disease." The Health Effects Institute is a nonprofit organization partially funded by the Environmental Protection Agency (EPA). Greenbaum is a member of the National Research Council's Committee on Research Priorities for Airborne Particulate Matter.
Additional studies are now under way to explore these issues using a range of methods, with results expected within two years, Greenbaum says. "The EPA has already set a standard for fine particle reduction. It is scheduled to review and possibly change that standard by 2002. After that we will see many efforts to actually reduce air pollution, so at that point, data on what parts of the particle mix are most toxic would be very useful."
Consumers should recognize that pollution control is not merely a matter of economics, Lauer says. "This research provides additional evidence that air pollution is dangerous. People should be concerned about it as a public health issue."
- Harvard researchers report everyday air pollution may impair the heart's ability to change the speed at which it beats, or its heart rate variability. This loss of heart rate variability could lead to more heart problems and heart-related deaths.
- Other studies have demonstrated the link between air pollution and rises in heart attacks and heart-related deaths. But the scientists in this study say this is the first time a team has shown that air pollution hinders the heart's ability to adjust to the pumping demands the body puts on it.
- A major culprit in air pollution seems to be the fine particles in diesel waste from buses, trucks, and heavy equipment. Doctors still don't know whether those who already have a heart problem are at greater risk.