Diesel disruption

Inhaling diesel exhaust at levels typically found in large cities may disrupt normal blood vessel and clotting activity, according to a first-of-its-kind study carried out by

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The report, published in Circulation: Journal of the American Heart Association, may explain the link between air pollution and heart disease, said lead researcher Dr Nicholas Mills, of the Centre for Cardiovascular Science at the University of Edinburgh.

In the study, researchers from Edinburgh and Sweden found that exposure to diesel exhaust for one hour during exercise caused a significant decrease in blood vessels’ natural ability to expand (dilate). Exposure to air pollution also decreased levels of an enzyme that helps prevent clots from forming.

Increases in air pollution are linked to death and illness involving the heart and blood vessels. The link between air pollution and heart disease is strongest for very small dust particles, of which the combustion of diesel and petrol in road transportation is the major source. But the underlying factors responsible for these effects of small particles on the heart and blood vessels have remained largely unknown.

In previous work, the group has reported abnormal blood vessel function in cigarette smokers, and this provided a clue. “Cigarette smoke is an important indoor air pollutant,” Mills said. “We hypothesized that the particles in diesel exhaust are likely to be just as harmful as particles derived from burning tobacco.”

The researchers tested their theory in 30 healthy, nonsmoking men 20 to 38 years old. The study participants underwent two separate one-hour evaluations, two weeks apart. Researchers conducted the test in a specially built diesel exposure chamber, where the men were exposed to either filtered air or diesel exhaust while riding a stationary bicycle and resting at 15-minute intervals.

Two and six hours after being in the exposure chamber, the men received infusions of vasodilating drugs - substances that cause blood vessels to relax and expand - in one arm. Researchers measured blood flow in the infused and non-infused arms. They found that forearm blood flow decreased significantly two hours after diesel exposure, and the reduced response to the vasodilators persisted at six hours. Such changes in the blood vessels are a risk factor for heart attacks.

“Whether these findings apply to gasoline-powered engines is unclear,” said Mills.

Diesel fuel and gasoline are burnt differently during engine operation. Researchers also found that a ‘clot-busting enzyme’, usually present in the blood, was reduced.

The researchers were particularly interested in diesel engines because they generate 100 times more pollutant particles than comparable-sized gasoline engines. The number of diesel-powered automobiles is increasing in Europe and other parts of the world.

“Diesel exhaust consists of a complex mixture of particles and gases. Before we can advocate the widespread use of particle traps in diesel engines, we need to verify that combustion derived particles are the responsible component,” Mills said. “If we do that, then it is likely that particle traps on exhaust pipes and cleaner fuels, currently under development, will greatly benefit public health.”

The study was funded by the British Heart Foundation.