Air Pollution Constricts Healthy Blood Vessels
By Cat Lazaroff
ANN ARBOR, Michigan, March 12, 2002 (ENS) - For the first time, researchers have shown that air pollution can harm the blood vessels of healthy humans. The study provides further evidence that everyone - not just people with heart disease or other health problems - may be at risk from breathing polluted air.
A study published in Monday's issue of "Circulation: Journal of the American Heart Association" found that blood vessels in healthy lungs became constricted after exposure to polluted air. In the study, 25 healthy people inhaled elevated concentrations of fine particles plus ozone for two hours.
"We have a wealth of epidemiological data saying that air pollution is associated with adverse respiratory and cardiovascular outcomes, but there is still a lack of understanding as to how the association occurs physiologically," said Dr. Robert Brook, study coauthor and assistant professor of internal medicine in the division of hypertension and vascular medicine program at the University of Michigan in Ann Arbor.
"These findings suggest a possible reason why the rate of heart attacks and other cardiovascular events increases with exposure to air pollution for people with known heart and blood vessel disease," added Brook.
The researchers focused on ozone and fine particulate matter. Fine particles - those with a diameter of less than 2.5 micrometers - are emitted from burning fossil fuels, such as in car engine exhaust, power generation and many industrial processes.
Ozone and additional particulate materials are created when sunlight interacts with these emissions.
"In other research, exposure to fine particles has been implicated in coronary events such as heart attacks," Brook explained. "In contrast to larger particles, which are trapped in the upper airways when inhaled, the fine particles travel down to the alveoli, tiny air sacs at the base of the lungs, where they can affect the rest of the cardiovascular system by adversely impacting circulating blood. It is possible that the particles may even directly enter the blood."
The University of Toronto has one of only a few facilities in the world now using human volunteers that is capable of concentrating outdoor urban air particles to a desired pollution level, then piping them into a special air chamber for experiments such as this one, Brook said.
The researchers used ultrasound to measure the diameter of the volunteers' brachial artery - which runs from the shoulder to the elbow - before and after two hours of exposure to a concentrated mixture of ozone and fine particles. The level of concentration - 150 micrograms per cubic meter - was about twice the level suggested by the U.S. Environmental Protection Agency (EPA) as safe for 24 hours of exposure.
Brook described that exposure as similar to those found in urban areas during peak air pollution times such as rush hour traffic.
At least two days before or after the pollutant exposure, subjects underwent the same measurements after being exposed to air that was filtered to remove the pollutants. The volunteers' arteries showed no change in response to breathing filtered air, but constricted in response to the polluted air.
"Although the degree of constriction in and of itself is unlikely to produce significant problems in healthy individuals, such a constriction could conceivably trigger cardiac events in those individuals who have or are at risk for heart disease," said Brook.
"Our results are a clear demonstration that environmentally relevant concentrations of common air pollutants that can occur in urban settings adversely affect the blood vessels of healthy people," Brook said, adding that more research is needed to understand why air pollution has negative effects on blood vessels and to clarify the public health implications of these initial studies.
In the United States, the Environmental Protection Agency estimates that air pollution contributed to 60,000 heart related deaths in 1996, according to figures in the federal register.
"There have been some suggestions in previous studies that people with atherosclerosis tend to respond with greater than normal constriction, or narrowing of blood vessels, in response to certain hormones in the body," Brook said. "Could it be that their blood vessels also have enhanced constriction in response to air pollution? Future studies will be needed to answer that question."