One recent study concluded that an interaction between the fine particles found in diesel exhaust and the fatty acids in LDL ("bad") cholesterol activates the genes that can cause inflammation in blood vessels, speeding up the process of atherosclerosis. Left unchecked, atherosclerosis can lead to blockage of the blood vessels.
The current study looked at 20 men, all of whom had suffered a heart attack in the past but whose heart disease was stable. All participants were exposed to diluted diesel exhaust or filtered air for one hour both while resting and while riding an exercise bike.
Heart rates increased similarly in both the filtered air and diesel exhaust sessions. But those in the diesel exhaust group had lowered blood flow to the heart. The diesel exhaust also reduced the release of endothelial tissue plasminogen activator, a "clot buster."
"We have for the first time identified ischaemic and thrombotic mechanisms to explain why there are more admissions to hospitals with angina and heart attacks on days in which the levels of air pollution are increased. No previous studies have assessed the direct effect of air pollution on blood vessel and heart function in patients with coronary heart disease," Mills said.
In the real world, the effects may even be worse.
"In real life, you have diesel fuel exposure with a background of regular air pollution, the complicating ambient air pollution," Horovitz said.
Exactly how diesel exhaust creates this change in blood flow is unclear. It's also unclear which component of diesel fuel is responsible.
"It will be important to determine the components of diesel exhaust responsible for the adverse effects on the hea
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