Healthy Men Face Heart Risk from Diesel Fumes

A joint study by UK and Swedish researchers suggests that diesel fumes from vehicle exhausts can cause heart problems not just in people with existing conditions but also healthy ones. The researchers found that fumes increase blood clots and platelets.

The study is not the first one to link exposure to traffic pollution and heart risk. Observational and epidemiological studies earlier have already shown that traffic pollution can lead to increased risk of heart attacks.

The new, comparatively smaller study was carried out by Dr. Andrew Lucking of the University of Edinburgh in Scotland and colleagues. They conducted a double blind, randomized cross-over study involving 20 healthy male volunteers aged 21 to 44 years.

A specially designed exposure chamber was set-up for the study. The men were first exposed to filtered air for the control part and then to 300 mg per cubic metre (mcg/m3) of diesel exhaust fumes. This is roughly the same concentration of diesel present in the air on a busy road.

Each participant was attached to a perfusion chamber and a small amount of his blood passed through it to measure clot formation, blood coagulation, platelet activity and other markers of inflammation. This was done twice – 2 hours and 6 hours after exposure respectively.

The number of platelets associated with white blood cells was measured for each participant to get an idea about platelet activation. When activated, platelets stick to white blood cells like neutrophils and monocytes and form clumps, an important part of blood clot formation.

For clot formation assessment, the researchers passed blood through a special shear chamber that stimulates the types of pressure blood would be under in blood vessels. Blood was tested at both high shear and low shear.

They found that breathing diesel fumes increased clot formation in the low shear chamber by 24.2% in comparison to breathing filtered air. Similarly, clot formation in the high shear chamber was found to be 19.1%. Both effects were present 2 hours and 6 hours after exposure to the diesel fumes.

Additionally, the diesel fumes were also found to increase platelet-neutrophil aggregates from 6.5% to 9.2% within 2 hours of exposure. The platelet-monocyte aggregates also went up from 21% to 25% in this period. However, 6 hours after exposure, these aggregates were not found to be statistically significant.

“This study shows that when a person is exposed to relatively high levels of diesel exhaust for a short time, the blood is more likely to clot. This could lead to a blocked vessel resulting in heart attack or stroke,” said Dr. Lucking while presenting their findings at a meeting of the American Heart Association’s Scientific Sessions 2007 in Orlando held last week.

“High levels of traffic pollution are known to increase the risk of heart attack in the immediate hours or days after exposure,” he added. In his opinion, this study shows a “potential mechanism that could link exposure to traffic-derived air pollution with acute heart attack.”

While the findings apply to diesel engine fumes, the researchers are not clear if exposure to gasoline fumes would produce the same effects. This is because the concentration of very fine particles is much higher in diesel fumes compared to gasoline fumes.

Diesel engines are on the rise because they offer superior fuel economy, but, as Dr. Lucking explained, “While diesel engines burn more efficiently, they also put more fine particulate matter into the air.”

The researchers now plan on taking their study to the next level by testing the effectiveness of the particle traps that are fitted to diesel engines to reduce exhaust particles. “Exposure to air pollution clearly is detrimental and we must look at ways to reduce pollution in the environment,” Dr. Lucking said.

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