Diesel exhaust can trigger heart attack, stroke

Diesel exhaust, a common air pollutant, causes premature deaths worldwide. Some of these deaths, in this report by Sade Oguntola, are traceable to heart attack and stroke.

Inhaling diesel exhaust fumes causes changes in the body that may make people more prone to heart attack or stroke, researchers have said.

The World Health Organisation estimated that air pollution causes 800,000 premature deaths worldwide and a recent US study suggested long-term exposure to traffic fumes increases the risk of death from heart disease and stroke by 76 per cent.

European scientists found that blood clots are more likely to form in otherwise healthy people who are exposed to relatively high amounts of diesel engine exhaust for a short time. This could cause a blocked vessel, heart attack or stroke.

The results of the study are closely tied to previous observational and epidemiological studies showing that shortly after exposure to traffic air pollution, individuals are more likely to suffer a heart attack. 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.

The group similarly in September reported in the New England Journal of Medicine that exposure to diesel fumes could put heart disease patients at risk from reduced blood supply to the heart and clots because they were far more likely to be starved of oxygen when exercising while breathing in such fumes than when exercising in clear air. The results showed that while they were inhaling diesel fumes the men experienced a three-fold increase in stress on the heart.

Lead author, Dr Nicholas Mills of Edinburgh University’s Centre for Cardiovascular Sciences said in a prepared statement that the study provided an explanation on why patients with heart disease are more likely to be admitted to hospital on days in which air pollution levels are increased.”

Though the British and Swedish scientists were not sure if the findings from the small study would be the same with exhaust from gasoline-powered engines since diesel engines spew many times more fine pollutant particles than gasoline engines, they however, supported the recommendation that people with heart and artery disease exercise away from traffic congestion to avoid the effects of this pollution.

The study involved 20 healthy men between the age of 21 and d 44. They breathed filtered air and also diluted diesel exhaust at a level approximating curbside exposure on a busy road.

Compared to breathing filtered air, breathing air with the diesel exhaust increased clot formation roughly 20 per cent to 25 per cent in the hours after exposure. The researchers also found an increase in platelet activation in the blood. Platelets play a main role in clotting.

Researchers performed the exposures in a specially built diesel exposure chamber. At two hours and at six hours after exposure, researchers allowed a small amount of participants’ blood to flow through a perfusion chamber. They measured clot formation, coagulation, platelet activation and inflammatory markers after each exposure.

To measure clot formation, researchers used low and high shear rates, recreating flow conditions inside the body’s blood vessels. Compared to filtered air, breathing air with diluted diesel exhaust increased clot formation in the low shear chamber by 24.2 per cent and the high shear chamber by 19.1 per cent. This was seen at both two and six hours after diesel exposure.

The researchers also found an increase in platelet activation, assessed by measuring the number of platelets associated with white blood cells. Platelets play a central role in blood clotting, and when they are activated, they associate with white blood cells such as neutrophils and monocytes. Diluted diesel exhaust inhalation increased platelet-neutrophil aggregates from 6.5 per cent to 9.2 per cent and platelet-monocyte aggregates from 21 per cent to 25 per cent at two hours after exposure. At six hours, researchers found a trend toward platelet activation, but it was not statistically significant.

After exposure to diesel exhaust, the participants had increased levels of activated platelets that became attached to white blood cells. When activated, the platelets can stick together and form a clot.

Dr. Mills said though most people tend to think of air pollution as having effects on the lungs but, as this study shows, it can also have a major impact on how our heart functions and as a result point to the need for pollution filters to be fitted to diesel cars. Diesel engines generated 10 to 100 times more pollutant particles than petrol engines and the number of diesel-powered cars was increasing.

Dr. Andrew Lucking of Britain’s University of Edinburgh, one of the researchers in the study that was presented at a meeting of the American Heart Association in Orlando said: "High levels of traffic pollution are known to increase the risk of heart attack in the immediate hours or days after exposure." According to him, the study showed a “potential mechanism that could link exposure to traffic-derived air pollution with acute heart attack.”

“Exposure to air pollution clearly is detrimental and we must look at ways to reduce pollution in the environment,” said Lucking.

Medical Director of the British Heart Foundation, Professor Peter Weissberg, said: “There is already evidence that air pollution can make existing heart conditions worse. This research is helping us work out why. It shows that in patients with coronary heart disease, diesel exhaust can reduce the amount of oxygen available to the heart during exercise, which may increase the risk of a heart attack.”

However, he did not recommend that people should stop exercising because of fear of what air pollution might do their heart. The benefits outweigh the risks, especially if you avoid exercising near traffic during the rush hour.

“Because of the overwhelming benefits of exercise on heart health, we would still encourage heart patients to exercise regularly, but preferably not when there is a lot of local traffic around. Heart patients can look out for pollution levels on their local weather forecasts,” explained Weissberg.

Dr. Ranti Familoni, a cardiologist at Olabisi Onabanjo Teaching Hospital, Sagamu said that “if diesel fumes will give any problem, it will start with in the lungs,” adding, “we know that in an individual that has had chronic exposure to any smoke, the fumes with time will damage the lungs and afterward lead to heart problems which arise from a fatty heart.”

However, Dr. Abiodun Moshood Adeoye, a consultant cardiologist with University College Hospital (UCH) stated that it is not actually the diesel that is the culprit, but its fumes. He declared that this is more of a pollution problem, which affects the heart, and if the person had artrial disease, a condition that affects the blood arteries, it can lead to coronary heart disease.

“This is the same in an individual that also smokes, who because of this can develop heart disease or who with a background heart problem may have his health problem worsen as a result of the smoke inhaled by him

However, the research is yet another data point suggesting that it’s time for European cities to enforce the EU directive on emissions. Cities can actually restrict traffic in some way. Some cities in Germany (e.g. Stuttgart) are looking to accelerate the process by banning high polluters (old diesels and old gasoline cars without catalytic converters) from entering the city centre on days with low air quality, starting in 2008.