14 DAY TRIAL // 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 The University of Edinburgh.
Researchers 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.
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.
"Cigarette smoke is an important indoor air pollutant," lead researcher Dr Nicholas 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.