Short-term exposure to high concentrations of tiny airborne particles does not hurt heart function, according to new research.

In earlier studies, people’s blood pressure spiked after even brief exposures to concentrated particulate air pollution. Taken together, the new work and previous studies suggest that the size and chemical makeup of the particles are more important indicators of health risk than the overall concentration in the air.

Scottish scientists tested 12 middle-aged men who had previously experienced a heart attack or undergone heart surgery and 12 age-matched, healthy men. Participants from each group were randomly assigned to sit for two hours in a chamber and breathe either filtered ambient air from Edinburgh or similar air with much higher concentrations of particles.

The team then measured heart rate, blood pressure and markers of inflammation in all the men. Those inhaling high concentrations of fine particles had similar markers of heart function as those breathing filtered air, the team reported in the June Environmental Health Perspectives.

Past studies have shown that similar exposure to high concentrations of particles from diesel exhaust raises blood pressure and constricts blood vessels, says Robert Brook, a cardiologist at the University of Michigan in Ann Arbor who was not involved in the study. “This suggests that particulate matter source, composition or chemistry may play an important role in determining the cardiovascular health implications of exposure,” he says.

Edinburgh sits on the edge of the North Sea, and strong winds carry most pollutants away from the city. So sea salt formed the bulk of airborne particles in this study, says Nicholas Mills a physician at the Edinburgh University Center for Cardiovascular Science and the lead author of the new paper. And sea salt may be more innocuous than particulates formed by combustion, such as diesel particles, he says.

One factor may be particle size and shape, Mills notes. Diesel specks measure 20 to 100 nanometers in diameter. In contrast, particles in the study were often 20 times larger. Tiny specks can penetrate deeper into the lungs and lead to higher levels of toxins in the blood.

The chemical makeup of carbon-rich fuel exhaust may also be inherently more toxic for humans, Mills say. While the study was well done, it only a tested a small number of people, Brook says. It also tested people in only one urban setting. Future work should be conducted in two separate cities, he says.

Currently air pollution is regulated only by the absolute concentration of particles suspended in the air, Mills says. Air testing might more effectively protect public health if it also tracked particles by size — specifically the amount of tiny, diesel-sized particles in the air, he says.

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